Showing papers in "Crop & Pasture Science in 2004"

Effects of nutrition and management on the production and composition of milk fat and protein: a review

Abstract: The composition and functional properties of cow’s milk are of considerable importance to the dairy farmer, manufacturer, and consumer Broadly, there are 3 options for altering the composition and/or functional properties of milk: cow nutrition and management, cow genetics, and dairy manufacturing technologies This review considers the effects of nutrition and management on the composition and production of milk fat and protein, and the relevance of these effects to the feeding systems used in the Australian dairy industry Dairy cows on herbage-based diets derive fatty acids for milk fat synthesis from the diet/rumen microorganisms (400–450 g/kg), from adipose tissues (<100 g/kg), and from de novo synthesis in the mammary gland (about 500 g/kg) However, the relative contributions of these sources of fatty acids to milk fat production are highly dependent upon feed intake, diet composition, and stage of lactation Feed intake, the amount of starch relative to fibre, the amount and composition of long chain fatty acids in the diet, and energy balance are particularly important Significant differences in these factors exist between pasture-based dairy production systems and those based on total mixed ration, leading to differences in milk fat composition between the two High intakes of starch are associated with higher levels of de novo synthesis of fat in the mammary gland, resulting in milk fat with a higher concentration of saturated fatty acids In contrast, higher intakes of polyunsaturated fatty acids from pasture and/or lipid supplements result in higher concentrations of unsaturated fatty acids, particularly oleate, trans-vaccenate, and conjugated linoleic acid (CLA) in milk fat A decline in milk fat concentration associated with increased feeding with starch-based concentrates can be attributed to changes in the ratios of lipogenic to glucogenic volatile fatty acids produced in the rumen Milk fat depression, however, is likely the result of increased rates of production of long chain fatty acids containing a trans-10 double bond in the rumen, in particular trans-10 18 : 1 and trans-10-cis-12 18 : 2 in response to diets that contain a high concentration of polyunsaturated fatty acids and/or starch Low rumen fluid pH can also be a factor The concentration and composition of protein in milk are largely unresponsive to variation in nutrition and management Exceptions to this are the effects of very low intakes of metabolisable energy (ME) and/or metabolisable protein (MP) on the concentration of total protein in milk, and the effects of feeding with supplements that contain organic Se on the concentration of Se, as selenoprotein, in milk In general, the first limitation for the synthesis of milk protein in Australian dairy production systems is availability of ME since pasture usually provides an excess of MP However, low concentrations of protein in milk produced in Queensland and Western Australia, associated with seasonal variations in the nutritional value of herbage, may be a response to low intakes of both ME and MP Stage of lactation is important in determining milk protein concentration, but has little influence on protein composition The exception to this is in very late lactation where stage of lactation and low ME intake can interact to reduce the casein fraction and increase the whey fraction in milk and, consequently, reduce the yield of cheese per unit of milk Milk and dairy products could also provide significant amounts of Se, as selenoproteins, in human diets Feeding organic Se supplements to dairy cows grazing pastures that are low in Se may also benefit cow health Research into targetted feeding strategies that make use of feed supplements including oil seeds, vegetable and fish oils, and organic Se supplements would increase the management options available to dairy farmers for the production of milks that differ in their composition Given appropriate market signals, milk could be produced with lower concentrations of fat or higher levels of unsaturated fats, including CLA, and/or high concentrations of selenoproteins This has the potential to allow the farmer to find a higher value market for milk and improve the competitiveness of the dairy manufacturer by enabling better matching of the supply of dairy products to the demands of the market

Identity and pathogenicity of Fusarium spp. isolated from wheat fields in Queensland and northern New South Wales

Abstract: To establish the identity of Fusarium species associated with head blight (FHB) and crown rot (CR) of wheat, samples were collected from wheat paddocks with different cropping history in southern Queensland and northern New South Wales during 2001. CR was more widespread but FHB was only evident in northern NSW and often occurred with CR in the same paddock. Twenty different Fusarium spp. were identified from monoconidial isolates originating from different plant parts by using morphology and species-specific PCR assays. Fusarium pseudograminearum constituted 48% of all isolates and was more frequently obtained from the crown, whereas Fusarium graminearum made up 28% of all isolates and came mostly from the head. All 17 Fusarium species tested caused FHB and all 10 tested caused CR in plant infection assays, with significant (P < 0.001) difference in aggressiveness among species and among isolates within species for both diseases. Overall, isolates from stubble and crown were more aggressive for CR, whereas isolates from the flag leaf node were more aggressive for FHB. Isolates that were highly aggressive in causing CR were those originating from paddocks with wheat following wheat, whereas those from fields with wheat following maize or sorghum were highly aggressive for FHB. Although 20% of isolates caused severe to highly severe FHB and CR, there was no significant (P < 0.32) correlation between aggressiveness for FHB and CR. Given the ability of F. graminearum to colonise crowns in the field and to cause severe CR in bioassays, it is unclear why this pathogen is not more widely distributed in Australia.

Growth and physiological responses of six barley genotypes to waterlogging and subsequent recovery

Abstract: In this study, the growth response of 6 barley genotypes of different origin (3 from China, 2 from Australia, 1 from Japan) to waterlogging and subsequent recovery was evaluated in 2 different soil types, an artificial potting mix and a Vertosol. A range of physiological measurements was assessed, to develop a method to aid selection for waterlogging tolerance. Plants at the 3 or 4 expanded leaf stages were subjected to waterlogging for 3 weeks followed by 2 weeks of recovery. Both shoot and root growth was negatively affected by waterlogging. As waterlogging stress developed, chlorophyll content, CO2 assimilation rate, and maximal quantum efficiency of photosystem II (Fv/Fm) decreased significantly. The adverse effect of waterlogging was most severe for genotype Naso Nijo, intermediate for ZP, Gairdner, DYSYH, and Franklin, and least for TX9425 in both trials. Studies of the root anatomy suggested that such a contrasting behaviour may be partially due to a significant difference in the pattern of aerenchyma formation in barley roots. The adverse effects in stressed plants were alleviated after 2 weeks of drainage for all genotypes. In general, TX9425 continued to grow better than other varieties, whereas recovery of Naso Nijo was extremely slow. It is suggested that screening a small number of lines for waterlogging tolerance could be facilitated by selecting genotypes with least pronounced reduction of photosynthetic rate or total chlorophyll content, and for a larger number of lines, chlorophyll fluorescence is the most appropriate tool. Additional keywords: chlorophyll content, photosynthesis, chlorophyll fluorescence, aerenchyma.

Modelling the growth and water uptake function of plant root systems: a review

Abstract: Crop models have been intensively used as a tool to analyse the performance of cropping systems under variable climate in terms of productivity, profitability, and off-site impact. The importance of modelling the function of plant roots in water and nutrient uptake from the soil is becoming increasing clear with the expanding application areas of crop models. This paper reviews the approaches and assumptions used in growth and uptake modelling of plant roots, and how the responses of plant root system to internal and external factors are captured in the widely used crop models. Most modelling approaches are based on one of the following assumptions: (i) that plant roots are uniformly distributed in homogenous soil layers and all roots have the same ability for uptake, or (ii) that plant root length is always sufficient for resource uptake in rooted soil layers. In structured soils, an overestimation of water uptake is likely to be expected. Further studies on root growth, distribution, and function in structured soils will require quantification of soil structures and root distribution patterns; and for non-uniformly distributed plant populations, spatial distribution of plant roots and non-uniform uptake need to be modelled. Root architecture modelling may help to address such issues. However, in order for the model to be useful at the field production level, simplified approaches that require easily measurable inputs need to be developed. Some examples are given. The oversimplification of root response to soil drying and hardness is likely to lead to overestimation of root growth and water uptake in dense soils. A soil strength factor needs to be incorporated so that the improved model can help evaluate the effect of subsoil compaction on production and resource use. Responses of root growth and uptake to soil salinity, boron toxicity, and extreme pH need to be further investigated if models are to be used for evaluation of crop performance in such environments. Effect of waterlogging also needs to be added for use of the model on heavy clay soils under irrigation or concentrated rainfall. There is an urgent need for joint efforts of crop physiologists, agronomists, breeders, and soil scientists to integrate interdisciplinary knowledge and to collect data that better describe the crop root system and its growth and uptake ability, to quantify plant process level responses, and for better soil quantification. Such knowledge and data are essential for improvement of model performance and successful applications.

Genotype by environment studies across Australia reveal the importance of phenology for chickpea (Cicer arietinum L.) improvement

Abstract: Chickpea (Cicer arietinum L.) genotypes comprising released cultivars, advanced breeding lines, and landraces of Australian, Mediterranean basin, Indian, and Ethiopian origin were evaluated at 5 representative sites (Merredin, WA; Minnipa, SA; Walpeup, Vic.; Tamworth, NSW; Warwick, Qld) over 2 years. Data on plant stand, early vigour, phenology, productivity, and yield components were collected at each site. Site yields ranged from 0.3 t/ha at Minnipa in 1999 to 3.5 t/ha at Warwick in 1999. Genotype by environment (G × E) interaction was highly significant. Principal components analysis revealed contrasting genotype interaction behaviour at dry, low-yielding sites (Minnipa 1999, Merredin 2000) and higher rainfall, longer growing-season environments (Tamworth 2000). Genotype clusters performing well under stress tended to yield well at all sites except Tamworth in 2000, and were characterised by early phenology and high harvest index, but were not different in terms of biomass or early vigour. Some of these traits were strongly influenced by germplasm origin. The material with earliest phenology came from Ethiopia, and southern and central India, with progressively later material from northern India and Australia, and finally the Mediterranean. There was a delay between the onset of flowering and podding at all sites, which was related to average temperatures immediately post-anthesis (r = –0.81), and therefore larger in early flowering material (>30 days at some sites). Harvest index was highest in Indian and Ethiopian germplasm, whereas crop height was greatest in Australian and Mediterranean accessions. Some consistently high yielding genotypes new to the Australian breeding program were identified (ICCV 10, BG 362), and the existing cultivar Lasseter was also confirmed to be very productive.

Livestock grazing management and biodiversity conservation in Australian temperate grassy landscapes

Abstract: There is an increasing interest in the development of livestock grazing management strategies that achieve environmental sustainability and maintain or improve the long-term production capacity of commercial grazing systems. In temperate Australia, these strategies are generally focussed on reducing perennial pasture decline, soil loss, acidity, and salinity. An additional challenge facing land managers and researchers is developing grazing strategies that also maintain and enhance local and regional biodiversity. However, few studies have assessed the compatibility of management practices for maintaining long-term productivity and biodiversity conservation. We still have only a very basic understanding of the effects of different grazing strategies and pasture management on biodiversity and this is a major impediment to the development of appropriate and compatible best management practice. We argue that although there is an increasing desire to find management strategies that protect and enhance biodiversity without hindering long-term agricultural production, in many cases this may not be possible. Current knowledge suggests that compatibility is most likely to be achieved using low-input systems in low productivity (fragile) landscapes, whereas in highly productive (robust) landscapes there is less opportunity for integration of productive land-use and biodiversity conservation. There is an urgent need for improved communication and collaboration between agronomic and ecological researchers and research agencies to ensure that future programs consider sustainability in terms of biodiversity as well as pasture and livestock productivity and soil and water health.

Maturation temperature and rainfall influence seed dormancy characteristics of annual ryegrass (Lolium rigidum)

Abstract: The role of temperature and rainfall during seed development in modulating subsequent seed dormancy status was studied for Lolium rigidum Gaud. (annual ryegrass). Climatic parameters relating to geographic origin were compared with annual ryegrass seed dormancy characteristics for seeds collected from 12 sites across the southern Western Australian cropping region. Seed germination was tested soon after collection and periodically during subsequent after-ripening. Temperature in the year of seed development and long-term rainfall patterns showed correlations with aspects of seed dormancy, particularly the proportion of seeds remaining dormant following 5 months of after-ripening. Consequently, for one population the temperature (warm/cool) and water supply (adequate/reduced) during seed development were manipulated to investigate the role of maternal environment in the quantity and dormancy characteristics of seeds produced. Seeds from plants grown at warm temperatures were fewer in number, weighed less, and were less dormant than those from plants grown at cool temperature. Seeds that developed under both cool temperature and reduced moisture conditions lost dormancy faster than seeds from well-watered plants. Seed maturation environment, particularly temperature, can have a significant effect on annual ryegrass seed numbers and seed dormancy characteristics.

Puroindoline genes and their effects on grain quality traits in southern Australian wheat cultivars

Abstract: Grain hardness is a major determinant of the classification and end-use of wheat. Two genes, Pina-D1 and Pinb-D1, have a major effect on this trait, so for wheat breeding programs it is important to identify the alleles of these genes present in elite germplasm. This study was conducted to identify the alleles present in southern Australian germplasm, and to determine if they affected quality characteristics other than grain hardness. Only 3 genotypes were identified. These were Pina-D1a/Pinb-D1a producing soft grain, Pina-D1a/Pinb-D1b producing moderately hard grain, and Pina-D1b/Pinb-D1a producing very hard grain. WW15 was the probable source of Pina-D1a/Pinb-D1b in most cultivars; however, Halberd represented another source. An important source of Pina-D1b/Pinb-D1a was the CIMMYT line Pavon, with sources from the old Australian cultivars Gabo and Falcon probably still present in modern germplasm. In an analysis of grain quality data from the Victorian Institute for Dryland Agriculture breeding program, the Pina-D1b/Pinb-D1a genotype had a significantly higher water absorption and significantly lower milling yield than the Pina-D1a/Pinb-D1b genotype, which indicates that these genes will impede the development of hard-grained cultivars that combine high water absorption and high milling yield.

Production risk of canola in the semi-arid subtropics of Australia

Abstract: The area of canola is expanding in the wheat-based farming systems of the summer-dominant rainfall zone of the Australian wheatbelt. Despite this, there is little information on yield and oil content expectations in relation to rainfall, location, and soil type and the reliability of the crop in a region characterised by high climatic variability. In this paper we assess variation in profitability of canola production in locations with different rainfall in the north-eastern wheatbelt by using long-term simulations at 4 locations spanning the climatic range of the region (Gunnedah, Moree, Walgett, Roma) with a validated model (APSIM-Canola). A new semi-mechanistic method for simulating oil content, accounting for temperature and water deficit effects during grain filling, is described and tested. Key agronomic determinants of reliable grain yield and oil content are identified. Long-term simulations showed strong effects of location, plant-available soil water at sowing (PAW), and in-crop rainfall on grain yield expectations. Yield was negatively related to sowing date, particularly in those situations of high water supply (PAW and in-crop rainfall). Grain yield was positively related to in-crop rainfall up to 300 mm, with water use efficiency in most seasons falling between 6 and 12 kg/ha.mm. Variation in oil content was most strongly affected by sowing date, followed by location, with PAW having a minor effect. Importantly, the price bonus cut-off for oil content of 42% was exceeded in 25, 40, 40, and 55% of seasons for Roma, Walgett, Moree, and Gunnedah, respectively. Negative and falling phases of the SOI in April–May were associated with lower grain yield and oil contents, whereas positive and rising phases with higher grain yield and oil content. This suggests that the choice to sow canola over other alternatives could be a tactical decision that depends upon the seasonal climate outlook. The approach used in this paper can be applied to the analysis of canola production risk (yield and oil content) and profitability in other prospective environments.

The impact of plant breeding on the grain yield and competitive ability of wheat in Australia

Abstract: Fourteen wheat (Triticum aestivum L) cultivars released to Australian growers over the last century were examined to determine the impact of crop breeding on competitive ability with weeds In 1999 and 2000 the weed used in the field study was annual ryegrass (Lolium rigidum Gaud) and in 2001 oats (Avena sativa cv Marloo) was the weedy competitor In 2 out of 3 years (1999 and 2001), when Puccinia recondita (leaf rust) infection was not a problem, there were consistent trends for improvement in yielding ability through breeding effort over time In these 2 seasons the yielding ability of wheat increased by around 15 kg/hayear as compared with a yield increase of only 47 kg/hayear in 2000 due to a heavy P recondita infection In 1999 and 2000, when annual ryegrass was used as the weedy competitor, there was no systematic trend for changes in crop yield loss with time (r = 047 in 1999; r = 008 in 2000, P > 005) However, in 2001, when oat was used as the weed, there was a significant positive linear relationship (r = 081, P < 001) between the year of cultivar release and crop yield loss, indicating inferior competitive ability of the modern cultivars Old cultivars such as Nabawa not only provided superior weed suppression, they were also more tolerant of weeds as indicated by the smaller yield loss Plant height appeared to be an important contributor to the superior competitiveness of the standard height, older cultivars Other morphological traits contributing to superior competitive ability included greater leaf length and width, light interception, and flag leaf length To improve the competitive ability of modern wheats without compromising their yielding ability, morphological traits that enhance early crop vigour (size of leaf 1 and 2) and light interception without affecting harvest index may need to be incorporated from carefully selected germplasm

Effect of previous crops on crown rot and yield of durum and bread wheat in northern NSW

Abstract: The effect of previous crops (oilseed, legume, and cereal) on the incidence and severity of crown rot (Fusarium pseudograminearum, Fp) and yield of wheat was investigated in 3 field studies in northern New South Wales. The experiments were designed to compare the effectiveness of the Brassica break crops canola (Brassica napus L.) and mustard (B. juncea L.) with chickpea (Cicer arietinum L.) on reduction of Fp in subsequent wheat crops. Responses to previous broadleaf and cereal crops were investigated in Fp-tolerant bread wheat (Triticum aestivum L.) and Fp-susceptible durum wheat [Triticum turgidum L. ssp. durum (Dest.)]. In all experiments, broadleaf break crops increased the yield of Fp-susceptible durum wheat compared with durum after cereals (by 0.24–0.89 t/ha). The same response was observed for the Fp-tolerant wheat at 2 of the 3 sites (0.71 and 0.78 t/ha), with a lower yield (0.13 t/ha) after break crops than after cereals at one site during a drought. The yield of the Fp-susceptible durum wheat was generally higher after brassicas than after chickpea (yield advantage 0.27–0.58 t/ha), whereas there was no such difference in the tolerant wheat variety. In most cases, these yield responses to the previous crops were closely related to the severity of Fp infection. Overall yield of susceptible durum wheat was reduced by 1% for each 1% increase in Fp severity at harvest. Residual water and nitrogen (N) did not explain responses to previous crops, although common root rot (Bipolaris sorokiniana) may have contributed to some of the responses at the sites. There was little evidence that the lower disease and higher yield following brassicas compared with chickpea was related to suppression of Fp by biofumigation. More plausible explanations are that residual cereal residues decomposed more rapidly under dense Brassica canopies thus reducing Fp inoculum, that Fp severity was increased following chickpea due to higher soil N status, or that brassicas resulted in soil/residue biology that was less conducive to Fp inoculum survival. Evidence for the latter was provided by consistently higher levels of Trichoderma spp. isolated from wheat following brassicas compared with chickpea or cereals. Irrespective of the mechanisms involved, the results demonstrate that Brassica oilseeds provide an effective break crop for crown rot in northern NSW. Furthermore, brassicas may provide an excellent alternative rotation crop to chickpea for high value durum wheat due to an apparent capacity to more effectively reduce the severity of crown rot infection in subsequent crops.

An in vitro study on the ability of polyethylene glycol to inhibit the effect of quebracho tannins and tannic acid on rumen fermentation in sheep, goats, cows, and deer

Abstract: . Batch cultures of rumen microorganisms, using rumen fluids from 4 ruminant species, sheep, goats, cows, and deer, were used to study the ability of polyethylene-glycol (PEG 6000) to inhibit the effect of 2 types of tannins, quebracho (QUE, a condensed tannin) and tannic acid (TA, a hydrolysable tannin) on several in vitro rumen fermentation characteristics. Both QUE and TA were able to impair ruminal fermentation (they reduced gas production, extent of degradation, ammonia-N, and volatile fatty acid concentrations, etc.; P < 0.05), with differences depending on the inoculum donor. The clearest effect of tannins was the reduction of the rates of fermentation, which was observed in all species (P < 0.05). The detrimental effects of tannins were removed by the presence of PEG in most cases, but there were important variations and noticeable exceptions. Thus, for instance, PEG failed to revert the negative effect of TA on the rate of fermentation and the extent of degradation (P < 0.05). The extent of the limited ability of PEG to completely inhibit the negative effects of tannins on in vitro ruminal fermentation seems to depend both on the type of tannin and the species of the rumen inoculum donor.

Screening rhizobacteria for improving the growth, yield, and oil content of canola (Brassica napus L.)

Abstract: One hundred rhizobacteria previously isolated from the rhizospheres of Brassica species were screened for their growth promoting activity in Brassica napus L. under gnotobiotic conditions. Results revealed that 58% of the rhizobacteria increased root length (up to 139%), 39% enhanced shoot length (up to 78%), and shoot weight (up to 72%) of Brassica napus L. Based upon growth promotion of B. napus seedlings under gnotobiotic conditions, 10 promising plant-growth-promoting rhizobacteria (PGPR) were selected and tested for their effectiveness in growth promotion, yield, and oil content of B. napus grown in pots. The pot trials revealed that inoculation with selected PGPR increased plant height, root length, number of branches per plant, stem diameter, number of pods per plant, 1000-grain weight, grain yield, and oil content over a range of 7–57% above the uninoculated control. These isolates were then assayed for their ability to produce auxins in vitro in the presence and absence of L-tryptophan. Regression analysis showed that in vitro auxin production by these bacteria was significantly related to the number of branches and oil content of B. napus. It is highly likely that improvement in growth and yield of the inoculated plants is due to an increase in the number of branches per plant, since there was a positive correlation of this growth parameter with the number of pods per plant, 1000-grain weight, grain yield, and seed oil content. Results indicated that simultaneous screening of rhizobacteria for growth promotion under gnotobiotic conditions and in vitro production of auxins could be a useful approach for selecting effective PGPR.

Impacts of Brassica break-crops on soil biology and yield of following wheat crops

Abstract: Biofumigation refers to the allelopathic effects of brassicas on non-desirable soil organisms in a rotation cropping system. These effects are additional to non-hosting of root diseases, responsible for much of the break-crop effect observed in a following cereal crop. We investigated the biofumigation impacts of canola on take-all disease and rhizosphere microorganisms of following wheat crops. The biofumigation potential of the canola was tested by comparing effects of Brassica and non-Brassica break-crops and by using canola varieties with differing levels of root glucosinolates, the precursors of isothiocyanates, which are thought to be the primary biofumigant molecules released by brassicas. There was no evidence that biofumigation was related to superior growth of wheat following brassicas compared with non-Brassica break-crops, nor among the wheat crops following canola varieties with differing root glucosinolate levels. However, the break-crop effect was evident in agronomic, take-all, and some rhizosphere microbial measurements of the wheat–wheat rotations compared with fallow–wheat or break-crop–wheat rotations. Thus the break-crop effect was the primary advantage conferred by the brassicas. Any additional biofumigation effect on yield or disease was not significant in our study and does not appear to be influenced by root glucosinolate content. For broad-acre cropping with current canola or mustard varieties, and adequate grass weed control, the agronomic characteristics of canola varieties chosen should take precedence over their biofumigation potential.

Current and potential uses of optical remote sensing in rice-based irrigation systems: a review

Abstract: For high water usage cropping systems such as irrigated rice, the positive outcomes of producing a staple food source and sustaining the economy often come at the cost of high resource use and environmental degradation. Advances in geospatial technology will play an increasingly important role in raising productivity and resource use efficiency and reducing environmental degradation, both worldwide and within Australia. This paper reviews the current use of one of these technologies, remote sensing, with the rice-growing region in Australia as a case study. Specifically, we review applications of remote sensing in crop identification, area measurement, regional yield forecasting, and on-farm productivity monitoring and management. Within this context, consideration is given to classification algorithms and accuracy assessment, hyperspectral remote sensing, positional and areal accuracy, linear mixture modelling, methane (CH4) emissions, yield forecasting techniques, and precision agriculture. We also discuss the potential for using remote sensing to assess crop water use, which has received little attention in rice-based irrigation systems, even though it is becoming increasingly important in land and water management planning for irrigation areas. Accordingly, special attention is given to the role of remote sensing with respect to the surface energy balance, the relationship between surface temperature and remotely sensed vegetation indices, and water use efficiency. A general discussion of other geospatial issues, namely geographic information systems and spatial interpolation, is provided because earth-science analysis using remote sensing is often intrinsically integrated with other spatially based technologies and aspects of geographical science.

Determinants of oil concentration and seed yield in canola and Indian mustard in the lower rainfall areas of Western Australia

Abstract: Oil concentration and seed yield of canola (Brassica napus) are usually low and variable when grown in the lower rainfall areas of Western Australia This paper identifies determinants of oil concentration and seed yield in these areas Through a series of cultivar × sowing date experiments at 5 lower rainfall locations and one high rainfall location as comparison, we evaluated the impact of sowing date, cultivar, and location on these 2 key agronomic traits We also examined relationships between oil concentration, seed yield, and post-anthesis duration, post-anthesis temperature, and post-anthesis rainfall with a view to investigate the adaptive requirements of canola for the lower rainfall areas Cultivars differed in their capacities to produce oil and seed yield The ranking of cultivars for oil concentration, and seed yield to a lesser extent, remained constant across sowing dates and locations Both seed yield and oil concentration decreased with delayed sowing On average, oil concentration was reduced by 11 percentage points and seed yield by 309 kg/ha for every 2 weeks delay in sowing The magnitude of reduction in oil concentration from delayed sowing was far greater in a low rainfall site at Mullewa than in the high rainfall site at Mt Barker Later sowings shortened post-anthesis duration With a given sowing date, early flowering cultivars resulted in longer post-anthesis duration Oil concentration increased by 12 percentage points for a 10-day increase in post-anthesis duration Both oil concentration and seed yield increased with higher post-anthesis rainfall and lower post-anthesis temperature The rates of increase were 07 percentage points for oil and 116 kg/ha for seed yield for every 10-mm increase in post-anthesis rainfall The rates of reduction were 068 percentage points for oil and 289 kg/ha for seed yield for every 1°C increase in post-anthesis temperature These relationships suggest that a combination of an early date of sowing with an early flowering cultivar would be essential for the production of high yield and high oil canola in the lower rainfall areas Indian mustard (B juncea) showed tolerance to high temperature and water deficit, but the low yield potential makes it uneconomical with early sowing Further improvement in seed yield could be dependent on increased tolerance of canola to high temperature and water deficit during seed growth and development

Association between canopy reflectance indices and yield and physiological traits in bread wheat under drought and well-irrigated conditions

Abstract: Spectral reflectance (SR) indices (NDVI (R900 -R 680/R900 + R680); GNDVI (R780 -R 550/R780 + R550); and water index, WI (R900/R970)); and 6 chlorophyll indices (R740/R720, NDI = R750 − R705/R750 + R705, R780 − R710/R780 − R680 ,R 850 − R710/R850 − R680, mND = R750 -R 705/R750 + R705 -2 R445, and mSR = R750 - R445/R705 -R 445) were measured with a FieldSpec spectroradiometer (Analytical Spectral Devices, Boulder, CO) on bread wheat (Triticum aestivum L.) genotypes adapted to irrigated and drought conditions to establish their relationship with yield in field-grown plots. Bread wheat genotypes from the International Maize and Wheat Improvement Center (CIMMYT) were used for this study in 3 experiments: 8 genotypes in a trial representing historical progress in yield potential, and 3 pairs of near-isolines for Lr19, both of which were grown under well- watered conditions; and the third experiment included 20 drought tolerant advanced genotypes grown under moisture stress. These were grown during the 2000 and 2001 spring cycles in a temperate, high radiation environment in Obreg´ on, NW M´ exico. The 9 SR indices were determined during grain filling along with canopy temperature depression (CTD), flag leaf photosynthetic rate, and chlorophyll estimates using a SPAD meter. The relationship of SR indices with grain yield and biomass fitted best with a linear model. NDVI and GNDVI showed positive relationships with grain yield and biomass under well-irrigated conditions (r = 0.35-0.92), whereas NDVI showed a stronger association with yield under drought conditions (r = 0.54). The 6 chlorophyll indices showed significant association with yield and biomass of wheat genotypes grown under well-irrigated conditions (r = 0.39-0.90). The association between chlorophyll indices and chlorophyll estimates was correlated (r = 0.38-0.92), as was the case for photosynthetic rate (r = 0.36-0.75). WI showed a significant relationship with grain yield in wheat genotypes grown under drought stress conditions (r = 0.60) as well as with grain yield and biomass under well-irrigated conditions (r = 0.52-0.91). The relationship between WI and CTD was significant (P ≤ 0.05) in both environments (r = 0.44-0.84). In conclusion, the SR showed potential for identifying higher-yielding genotypes in a breeding program under dry or irrigated conditions, as well as for estimating some physiological parameters.

Cynara cardunculus L., a potential source of inulin in the Mediterranean environment: screening of genetic variability

Abstract: Cynara cardunculus L. is a diploid (2n = 34) outcrossing perennial species, native to the Mediterranean basin, comprising the globe artichoke, the cultivated cardoon, and the wild cardoon. These species have potential as biomass, sugar, and oilseed crops. This paper aimed to study the genetic variability for sugar production and sugar composition in the roots of different C. cardunculus L. genotypes, in order to select those suitable for this specific purpose in the Mediterranean environment. At harvest the total biomass and root production, averaged for all genotypes, were 20.4 and 9.8 t DM/ha; they were influenced by genotype, with a CV of 37.4 and 38.5%, respectively. On average for all of the genotypes, the roots showed a total sugar content of 367 g DM/kg, with a CV of 17.1%; the main compound was inulin (85.0% of total sugars). The wild cardoon 'SR1' showed the highest total sugar content (470 g/kg DM). On average for all of the genotypes, the total sugar and inulin yields were 3.6 ± 0.20 and 3.0 ± 0.16 t/ha, respectively. It was possible to obtain total sugar yields higher than 4 t/ha in 6 genotypes ('BH', 'VP', 'E438', 'L01', 'C2', 'P1') of the 15 studied. Additional keywords: C. cardunculus L., genotype screening, root yield, sugar characterisation, inulin yield.

Variation within and between two saltbush species in plant composition and subsequent selection by sheep

Abstract: This work examines nutritive value and preference by sheep of 2 saltbush species, river saltbush (Atriplex amnicola) and old man saltbush (Atriplex nummularia). Both species are woody perennials that are native to Australia and used in commercial grazing systems. The hypothesis for this study was that sheep will graze saltbushes with higher nutritive value and lower secondary compounds in preference to bushes with lower nutritive value and higher secondary compounds. This was expected to be found both within and between the old man and river saltbush species. To test the hypothesis, 10-month-old Merino ewes grazed a 10-ha plot containing a mixture of old man and river saltbush in approximately equal proportions. Within the plot, and prior to grazing, 20 bushes of each species were pegged for identification and samples of edible plant material collected for analysis. Each week during the grazing period the bushes were photographed for assessment of preference. Sheep preferred river saltbush to old man saltbush and also showed some preferences for specific bushes within each species. Differences in digestibility of dry matter and organic matter, crude protein, ash, oxalates, and nitrates were not clearly associated with differences in preference. Although the reasons for preferences were not demonstrated, the analysis of the plant material did indicate that the content of total ash and oxalates was at levels likely to depress voluntary feed intake.

Genetic analysis of coleoptile length and diameter in wheat

Abstract: Lack of moisture near the soil surface commonly delays sowing, reducing grain yields of Australian wheat (Triticum aestivum) crops. Deep sowing would allow growers to make use of soil moisture lying below the drying topsoil, but the short coleoptiles of semidwarf wheats reduce emergence when sowing at depths greater than 5 cm. Selection of longer, thicker coleoptiles would help in improving emergence in hard or crusted soils, or when deep sowing, yet little is known of genetic control of coleoptile size in wheat. A diallel mating design was generated from crosses between 12 Australian and overseas wheats, and assessed for coleoptile size at different temperatures (11, 15, 19, and 23°C). Repeatabilities for coleoptile diameter and length were moderate to high on an entry-mean basis (R2 = 0.48 and 0.77, respectively), reflecting large genotype and small genotype × temperature interaction variances. Genotypic variation among parents translated into large and significant (P < 0.01) differences among F1 progeny (94–142 mm and 1.56–1.84 mm for length and diameter, respectively). General (GCA) and specific combining ability (SCA), and reciprocal effects were significant (P < 0.01) for length and diameter. Baker’s GCA/SCA ratio was high (0.62–0.77) for coleoptile length but intermediate for diameter (0.38–0.64), indicating strong additive genetic control for length. Further, GCA effects and parental means were strongly correlated (r = 0.81–0.91, P < 0.01) indicating parent length to be a useful predictor of progeny performance. Coleoptile lengths for progeny derived from Rht8, Rht9, and Rht12 dwarfing gene donors were generally shorter (c. –7 to –13%) but were still an average 47% longer than coleoptiles of Rht-B1b and Rht-D1b controls. The genetic correlation for coleoptile length and diameter was small (rg = –0.25 ± 0.15n.s.) suggesting that the two traits are genetically independent. Development of wheats with longer, thicker coleoptiles should be readily achieved in selection among partially inbred families from crosses targetting improved establishment.

Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection

Abstract: Sources of variation in fibre diameter attributes of Australian alpacas and implications for fleece evaluation and animal selection were investigated using data collected in the years 1994-97, from 6 properties in southern Australia. Data were analysed using REML (multiple regression analysis) to determine the effect on mean fibre diameter (MFD) and coefficient of variation of MFD (CV(FD)) of age, origin (property), sex (entire male, female), breed (Huacaya, Suri), liveweight, fibre colour, individual, and interactions of these effects. The mean (n = 100) age (range) was 4.2 years (0.1-11.9), liveweight 72.0 kg (12.0-134 kg), MFD 29.1 µm (17.7-46.6 µm), CV(FD) 24.33% (15.0-36.7%). A number of variables affected MFD and CV(FD). MFD increased to 7.5 years of age, and correlations between MFD at 1.5 and 2 years of age with the MFD at older ages were much higher than correlations at younger ages. Fibre diameter 'blowout' (increase with age) was positively correlated with the actual MFD at ages 2 years and older. There were important effects of farm, and these effects differed with year and shearing age. Suris were coarser than Huacayas with the effect reducing with increased liveweight; there was no effect of sex. Fleeces of light shade were 1 µm finer than dark fleeces. CV(FD) declined rapidly between birth and 2 years of age, reaching a minimum at about 4 years of age and then increasing; however, CV(FD) measurements on young animals were very poor predictors of CV(FD) at older ages, and the response of CV(FD) to age differed with farm and year. Suris had a higher CV(FD) than Huacayas on most properties, and MFD, liveweight, and sex did not affect CV(FD). Fleeces of dark shade had higher CV(FD) than fleeces of light shade in 2 of the years. It is concluded that there are large opportunities to improve the MFD and CV(FD) of alpaca fibre through selection and breeding. The potential benefit is greatest from reducing the MFD and CV(FD) of fibre from older alpacas, through reducing the between-animal variation in MFD and CV(FD). Sampling alpacas at ages <2 years is likely to substantially decrease selection efficiency for lifetime fibre diameter attributes. AR B. A. M and t Varpaca a

Influence of chlorsulfuron on rhizobial growth, nodule formation, and nitrogen fixation with chickpea

Abstract: Sulfonylurea residues have been found to inhibit the growth of some legume crops and pastures in seasons following application. Negative effects of these herbicides on symbiotic nitrogen fixation by legume crops and pastures have been demonstrated. Reductions in nitrogen fixation may result from a direct effect of the herbicide on rhizobial growth and/or an indirect effect on plant growth. In this study the influence of chlorsulfuron on the growth of chickpea rhizobia [Mesorhizobium ciceri (CC1192)], the growth of chickpea plants, and the extent of nodulation and nitrogen fixation by the chickpea/rhizobia symbiosis were examined. In vitro studies (in yeast mannitol broth and a defined medium) showed that chlorsulfuron applied at double the recommended field application rate did not influence the growth of chickpea rhizobia. An experiment using 14C-labelled chlorsulfuron was conducted to determine if rhizobial cells exposed to chlorsulfuron could deliver the herbicide to the point of root infection and nodule formation. Approximately 1% of the herbicide present in the rhizobial growth medium remained with the cell/inoculum material after rinsing with 1/4 strength Ringer’s solution. This was considered unlikely to affect chickpea growth, nodulation, or nitrogen fixation. A pot experiment was used to define the influence of chlorsulfuron on the growth, nodulation, and nitrogen fixation of chickpeas. The presence of chlorsulfuron in the soil reduced the nodulation and nitrogen fixation of the chickpea plants. Pre-exposing rhizobia to chlorsulfuron before inoculating them into pots with germinating chickpea seeds, reduced the number of nodules formed by 51%. Exposure of chickpeas and chickpea rhizobia to chlorsulfuron can adversely affect the formation and activity of symbiotic nitrogen-fixing nodules, even when only the rhizobial inoculant is exposed briefly to the herbicide.

Estimations of vapour pressure deficit and crop water demand in APSIM and their implications for prediction of crop yield, water use, and deep drainage

Abstract: Vapour pressure deficit (VPD) has a significant effect on the amount of water required by the crop to maintain optimal growth. Data required to calculate the mean VPD on a daily basis are rarely available, and most models use approximations to estimate it. In APSIM (Agricultural Production Systems Simulator), VPD is estimated from daily maximum and minimum temperatures with the assumption that the minimum temperature equals dew point, and there is little change in vapour pressure or dew point during any one day. The accuracy of such VPD estimations was assessed using data collected every 15 min near Wagga Wagga in New South Wales, Australia. Actual vapour pressure of the air ranged from 0.5 to 2.5 kPa. For more than 75% of the time its variation was less than 20%, and the maximum variation was up to 50%. Daytime mean VPD ranged from 0 to 5.3 kPa. Daily minimum temperature was found to be a poor estimate of dew point temperature, being higher than dew point in summer and lower in winter. Thus the prediction of vapour pressure was poor. Vapour pressure at 0900 hours was a better estimate of daily mean vapour pressure. Despite the poor estimation of vapour pressure, daytime mean VPD was predicted reasonably well using daily maximum and minimum temperatures. If the vapour pressure at 0900 hours from the SILO Patched Point Dataset was used as the actual daily mean vapour pressure, the accuracy of daytime VPD estimation was further improved. Simulations using historical weather data for 1957-2002 show that such improved accuracy in daytime VPD estimation slightly increased simulated crop yield and deep drainage, while slightly reducing crop water uptake. Comparison of the APSIM RUE/TE and CERES-Wheat approaches for modelling potential transpiration revealed differences in crop water demand estimated by the two approaches. Although the differences had a small effect on the probability distribution of simulated long-term wheat yield, water uptake, and deep drainage, this finding highlights the need for a scientific re-appraisal of the APSIM RUE/TE and energy balance approaches for the estimation of crop demand, which will have implications for modelling crop growth under water-limited conditions and calculation of water required to maintain maximum growth.

Over-expression of HMW glutenin subunit Glu-B1 7x in hexaploid wheat varieties (Triticum aestivum)

Abstract: In Canada in 1993, a special market class of wheat, Canada Western Extra Strong (CWES), was established to segregate wheat varieties known to produce very strong and extensible doughs. These exceptional dough properties enable CWES cultivars to be blended with wheats of lesser quality as well as being suited to the manufacture of frozen dough products. The high molecular weight (HMW) glutenin allele (Glu-B1al) that confers these properties, particularly dough strength, has now been identified. Typically, the presence of the Glu-B1al (7 + 8*) allele is associated with the overexpression of HMW-GS 1Bx 7. RP-HPLC was used to quantify the proportion (% area) of individual HMW-GS relative to total HMW-GS in wheat varieties of different origin. The B genome contributed the highest percentage of HMW-GS, with the exception of Glu-B1d (6 + 8*) where the D genome contributed the most. Cultivars that possessed the Glu-B1al allele contained a significantly higher (P < 0.001) proportion of HMW-GS (56.80 ± 3.25%) encoded by the B genome. This suggests that the proportion of Glu-B1 subunits, relative to the total amount of HMW-GS expressed, has a major effect on dough strength. We also identified germplasm, of different origin, that contains the Glu-B1al allele and overexpresses subunit 7, including the most likely source of this allele in bread wheat cultivars. The Glu-B1al allele in the varieties identified in this paper could be traced, at least through one parent, to the Argentinean bread wheat cultivar Klein Universal II. RP-HPLC elution and expression profiles of various common HMW-GS are also discussed. Additional keywords: quality, dough, protein, SDS-PAGE, RP-HPLC, Glu-1 allele, HMW-GS, Glu-B1al.

Yield of wheat and canola in the high rainfall zone of south-western Australia in years with and without a transient perched water table

Abstract: The yields of wheat and canola in 2 successive years with and without the development of a perched watertable were compared in the high rainfall zone of south-western Australia. In 2001, no perched watertable was observed and wheat and canola yields were close to their estimated potentials. In 2002, a perched watertable developed at less than 30 cm below the soil surface for more than 8 days and at less than 50 cm below the soil surface for at least 30 days at the tillering stage of wheat and at the rosette stage of canola. The air-filled porosity of the soil fell below the critical value of 10% at 10 and 30 cm depth for about 40 days. This reduced the maximum leaf area index of canola by 46% and of wheat by 30%, and reduced the shoot dry matter of wheat at flowering by 27% and by 40% at podding in canola compared with those in 2001. The growth of the wheat roots was constrained at depths from 50-90 cm from the soil surface in 2002 compared with 2001. However, the roots of canola and wheat were able to grow to at least 1.4 m in both 2001 and 2002. In both years, a much higher proportion (>10%) of roots was present in the clay subsoil compared with previous reports in south-western Australia and enabled the crops to utilise a greater amount of water from the clay subsoil. The wheat yield in 2002 was 37% lower than in 2001 and well below the potential, largely as a result of a reduced tiller number per plant and ears per unit area. Despite the greater reduction in dry matter in canola than in wheat in 2002, the seed yield of canola was 17% higher in 2002 than in 2001. Canola, an indeterminate crop, was able to respond to the late rain that occurred in 2002 compared with 2001 and produced a significantly higher seed number per unit area. In 2002, grain size in wheat was 25% larger than in 2001, but this increase was insufficient to compensate for the yield loss resulting from the fewer ears per unit area. It is concluded that early transient perched watertable induced subsurface waterlogging, and that the subsurface waterlogging can be a major constraint to crop growth in the high rainfall region of southwestern Australia, and that reducing waterlogging could be a key to achieving higher crop production.

Could Tetragonisca angustula latreille (Apinae, Meliponini) be effective as strawberry pollinator in greenhouses?

Abstract: We evaluated the contribution of the stingless bee Tetragonisca angustula as a strawberry pollinator using primary flowers of the ‘Oso Grande’ cultivar. We applied 4 pollination treatments: open-pollination in the field, T. angustula pollination inside a greenhouse, and spontaneous self-pollination in the field and greenhouse. In each treatment we determined berry weight, number of achenes, number of fertilised ovules, fertilisation rates, and the percentage of marketable fruit. The results showed that one colony of this species in a greenhouse with approximately 1350 strawberry plants was adequate to pollinate ‘Oso Grande’ primary flowers. The contribution of T. angustula to the weight and shape of primary berries demonstrated that this bee species is an effective strawberry pollinator and it can promote a significant increase in overall strawberry production.

Solute accumulation and osmotic adjustment in leaves of Brassica oilseeds in response to soil water deficit

Abstract: To establish methods for improving drought tolerance in Brassica oilseeds, we examined the influence of soil water deficit on solute accumulation in expanded and expanding leaves. We assessed the contribution of individual solutes to osmotic adjustment (OA) and determined the effect of homozygosity on the variation of the expression of OA. Juvenile plants of canola (Brassica napus cvv. Karoo and Monty) and Indian mustard (B. juncea line PI-81792) were grown under glasshouse conditions. The 3 genotypes expressed similar magnitudes of OA in response to drought, compared with a 2-fold higher OA in expanding leaves than in fully expanded leaves. Drought-induced changes in OA of expanded leaves of all genotypes were largely due to the accumulation of nitrate (42-47%), soluble sugars (31-38%), and proline (11-14%). In expanding leaves, K + accumulation was significant (23-27%) as was proline (17-22%), whereas nitrate and soluble sugars were less important than in expanded leaves. By comparison, ions of Na+, Cl-, and water-soluble Mg 2+ and Ca2+ did not contribute significantly to OA. Proline was hardly detected in well watered plants, but sharply increased in leaves of droughted plants in direct proportion to the magnitude of OA (80 ± 7 mmol/MPa, r2 = 0.94). A comparison between doubled haploid (DH) and commercial seed sources of 2 B. napus cultivars showed similar mean values in OA. The DH lines had a 33% lower coefficient of variation in OA than cv. Karoo and 48% lower than cv. Monty among replicate plants. Proline may be a suitable 'marker' for OA in juvenile Brassica plants because of all the solutes measured, its concentration was directly proportional to the magnitude of OA across cultivars and leaf types. The use of DH lines will improve the precision in selection of genotypes that have the capacity to osmotically adjust under soil water deficit.

Influence of ad libitum feeding of urea-treated wheat straw with or without corn steep liquor on intake, in situ digestion kinetics, nitrogen metabolism, and nutrient digestion in Nili-Ravi buffalo bulls

Abstract: Influence of different levels of corn steep liquor (CSL) on chemical composition of urea-treated wheat straw (UTWS), feed intake, ruminal characteristics, digestion kinetics, nitrogen (N) metabolism, and nutrient digestibility by ruminally cannulated buffalo bulls was studied using 4 × 4 Latin square design. Wheat straw was treated with 5% urea and ensiled with 0, 3, 6, and 9% CSL on a dry matter (DM) basis and was ensiled in laboratory silos for 5, 10, and 15 days. Neutral detergent fibre (NDF) contents of UTWS ensiled with 0, 3, 6, and 9% CSL were 74.01, 76.16, 77.34, and 78.93%, respectively. Acid detergent fibre (ADF), cellulose, and lignin were similar across treatments. The increase in NDF content was due to increased neutral detergent insoluble nitrogen (NDIN), as when NDF was calculated on crude protein (CP)-free basis (NDF - NDIN × 6.25), its concentration was same for UTWS ensiled with or without CSL. Four diets were formulated to contain 20% concentrate and 80% UTWS ensiled with or without CSL. Dry matter, digestible DM, organic matter (OM), CP, ADF, and NDF intakes were higher in bulls fed UTWS ensiled with CSL. Significant increases in both DM disappearance and rate of disappearance and a reduction in lag time of UTWS ensiled with CSL was noticed. There were significant differences in ruminal ammonia concentrations between diets containing UTWS ensiled with or without CSL at 3, 6, and 12 h postprandial. Higher digestibilities for DM, OM, CP, ADF, and NDF were noted with UTWS ensiled with CSL. Nitrogen balance was positive for all animals; however, the animals fed UTWS ensiled with CSL retained higher amount of N. These results indicated that CSL was very effective in enhancing the utilisation of ammoniated straw for buffaloes by minimising the nutrient loss at ruminal and cellular levels. AR M. N et al Nut ti a

Glyphosate resistance in Eleusine indica (L.) Gaertn. from different origins and polymerase chain reaction amplification of specific alleles

Abstract: Glyphosate-resistant populations of Eleusine indica (L.) Gaertn. were found in 4 areas in Malaysia that had received repeated applications of glyphosate for a period ranging from 5 to 15 years. The resistance ratios calculated from dose-response experiments were 2.9 (Chaah), 2.1 (Lenggeng), 3.3 (Bidor), and 2.8 (Temerloh). Two point mutations were detected in position 875 within the 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) gene resistant population, causing a C to T transition leading to Pro106 to Ser106 substitution in Bidor and Temerloh or C to A transversion leading to Pro106 to Thr106 substitution in Chaah. Sequence comparisons of the 3115 bp of the EPSPS gene revealed identical sequences in both the susceptible (S) and resistant (R) populations of Lenggeng. The identical sequences in both the Lenggeng populations, S and R, suggest that the resistance mechanism found in Lenggeng R may be different from Chaah R, Bidor R, and Temerloh R. The polymerase chain reaction (PCR) amplification of specific alleles (PASA) was developed to detect 2 distinct single-point mutations, probably conferring herbicide resistance in Chaah R, Bidor R, and Temerloh R. PASA profiles showed only one DNA fragment for the entire S population and 2 different additional fragments, each specific for one resistance allele, for the R population. AR C. H. Ng et al PCRi a ge

Identification of a major QTL for yellow leaf spot resistance in the wheat varieties Brookton and Cranbrook

Abstract: Yellow leaf spot (YLS) or tan spot, caused by Pyrenophora tritici-repentis, is a major foliar disease of wheat. A bioassay was used to identify YLS seedling resistance phenotypes of Krichauff/Brookton and Cranbrook/Halberd doubled-haploid (DH) populations. Bulked-segregant analysis was used to identify amplified fragment length polymorphism (AFLP) markers linked to a YLS resistance locus in the wheat cultivar Brookton. Three AFLPs were linked to YLS resistance and also to each other. One of these AFLPs was mapped to the interval Xbcd351–Xcdo400, which has been assigned to chromosome 5BL. Microsatellite markers in this region were selected from several maps and were genotyped on the Krichauff/Brookton population. Together with the bulked segregant analysis (BSA)-derived AFLPs, the microsatellite markers explained up to 39% of the total phenotypic variation (logarithm of odds ratio, LOD ≥ 7.32), confirming the chromosome 5BL assignment of a Brookton YLS resistance locus, at or near the previously identified Pyrenophora tritici-repentis toxin-insensitivity locus tsn1. The marker–trait linkage was validated in the Cranbrook/Halberd DH population, in which the same microsatellite markers explained up to 60% of the total trait variance for YLS. The markers identified can be used for the selection of the Brookton and Cranbrook YLS seedling resistance locus on chromosome 5B.