Showing papers in "Crop & Pasture Science in 1978"

Drought resistance in spring wheat cultivars, 1. Grain yield responses.

Abstract: With a view to understanding the basis of cultivar differences in yield under drought, a wide range of cereal cultivars representing durum wheats (Triticum turgidum L.), triticales (X Tritosecale Wittmack), barleys (Hordeum vulgare), and especially tall and dwarf bread wheats (T. aestivum L.) were studied in field experiments in north-western Mexico over three seasons. Drought was created in this rain-free environment by permanently terminating irrigation at various stages before anthesis. Control treatments were well watered throughout the growing period. Detailed measurements of plant water status, leaf area and dry matter production, anthesis date, yield components and grain yield were made. This paper presents primarily the grain yield data. Drought levels were such that the mean yield of all cultivars under drought ranged from 37 to 86% of control yield, corresponding to irrigation cut-offs varying from 69 days before mean anthesis date to only 10 days before. In each experiment the grain yield under drought showed highly significant cultivar differences, which appeared consistent between years. Yields were adjusted for drought escape by using a correction factor which ranged from 2.9 to 8.5 g/m2 per day advance in flowering, being greater in experiments with less severe drought. The demonstration of linear relationships between cultivar yield and drought intensity, as indicated by the mean yield of some or all cultivars, prompted the consideration of cultivar yield under drought as the function of yield potential (Yp, yield without drought), drought susceptibility index (S), and intensity of drought. The cultivar groups showing lowest S values (most droughtresistant) were tall bread wheats and barleys; dwarf bread wheats were intermediate, and durum wheats and triticales were the most susceptible. However, because dwarf wheats have a higher yield potential (Yp) than tall bread wheats, it is suggested that, as a group, tall bread wheats would outyield dwarf wheats only under very severe drought. Also there was considerable within-group variability of S and Yp. Cultivar S values were consistent across experiments. Yield responses of tall and dwarf bread wheat groups obtained in these experiments agreed with those seen in extensive international trials under dryland conditions.

The effect of temperature on kernel development in cereals

Abstract: A study has been made of the effect of temperature on kernel development and mature kernel weight of three contrasting cereals: wheat, rice and sorghum. Wheat and sorghum showed clear and well-separated optimum temperatures for individual kernel dry weights of 15/10° and 27/22°C respectively, while rice showed a relatively small change in weight over temperatures ranging from 21/16° to 30/25°. Rice kernel development was less affected by temperature extremes than sorghum, but was more sensitive to low temperature than wheat. At the lower temperatures (21/16°) the rate of development of individual kernels was greater in wheat than in the other species, while in sorghum, which had a more marked temperature response, the rate of kernel development was greater than in the other cereals at the higher temperatures (30/25°). A preliminary analysis of barley suggests that kernel development in this cereal responds to temperature in a similar way to wheat. Measurements of net photosynthesis of the flag leaf blade and ear of each cereal, at intervals after anthesis, suggested that at the completion of kernel development a source of carbohydrate was still available for continued development at all temperatures. A preliminary examination was carried out on the role of respiration and of translocation in limiting kernel development at high temperatures.

Resistance to Boophilus microplus (Canestrini) in different breeds of cattle

Abstract: Resistance to the cattle tick Boophilus microplus was assessed in heifer herds of various breeds of beef and dairy cattle in spring and summer in Queensland. All cattle had had tick experience before assessment. Resistance levels were determined as the percentage of larval ticks that failed to survive to maturity following infestations with c. 20,000 larvae. Bos indicus Brahman beef cattle were the most resistant (99%), followed by B. indicus × B. taurus (95–97%) and B. taurus British cattle (85%). In the dairy breeds, B. taurus Jersey cattle (98%) were more resistant than Guernsey (93%), Australian Illawarra Shorthorn (89%), and Friesian (85%), but not significantly different from B. indicus × B. taurus Australian Milking Zebu (96%). Cattle were classified as having high (> 98%), moderate (95–98%), low (90–95%), or very low (< 90%) resistance. The frequency distributions of resistance in B. indicus × B. taurus cattle showed that 80% had moderate to high resistance and that culling of 20% of the cattle would about halve the mean tick population. Of B. taurus cattle, 80% had low to very low resistance. Supplementary information on sibling bull herds showed that their resistance levels and frequency distributions of resistance were similar to those of the heifer herds.

The influence of level of feed intake on sperm-producing capacity of testicular tissue in the ram

Abstract: The experiment examined the effect of supplementing a roughage diet with lupin grain on the capacity of testicular tissue to produce spermatozoa. Changes in testicle size were estimated by comparative palpation. At the end of the experiment the rams were castrated and the morphology of the testes and their capacity to produce sperm were studied. At the highest level of feed intake, liveweight increased by 32% and testicle volume by 67% during the feeding period of 9 weeks. Rams on a diet that reduced testicle size produced 18 x l06 sperm/g testis per day, and those on a diet that increased testicle size produced 26 x l06 sperm/g testis per day. Those rams whose testes were increasing in size at castration had significantly larger seminiferous tubules, which occupied a significantly greater proportion of the testicle volume, than rams fed on diets that reduced the size of their testes. The variation in rates of sperm production, together with the large differences in testicle weight, resulted in wide differences in total sperm production among rams fed on different diets.

Effect of environment and cultivar on source limitation to grain weight in wheat

Abstract: The relative increase in final kernel weight (SR, %) with an artificial reduction of about 80% in the number of grains per spike was assumed to estimate the degree of post-anthesis assimilate or source limitation to grain weight in wheat. This assumption was supported by comparisons with other treatments designed to alter the ratio of source to grain number. SR was determined in crops grown under irrigation and high fertility in north-west Mexico over a 5 year period, in order to examine the effect of environment (year, sowing date) and cultivar on source limitation. Some old tall cultivars and many modern short cultivars of wheat (Triticum aestivum L., T. turgidum L.) and triticale (X Tritosecale Wittmack) were studied. For modern cultivars, kernel weight always appeared to be limited by source, SR averaging 21% over all years for eight such cultivars. For a given cultivar, environmental effects were considerable, being partly explained by a positive relationship between SR and mean temperature after anthesis. Each year SR was significantly affected by cultivar and, despite cultivar by year interaction, showed some consistency between years. Old bread wheats and triticales usually showed low source limitation (SR <10%), whereas most modern cultivars, regardless of species, showed higher source limitation (SR up to 50%) and higher grain yields, probably because of higher grain numbers per sq metre. Within this latter group, there was no relationship between SR and grain yield. The kernel weight attained as a result of grain number reduction, defined here as potential kernel weight, was a stable cultivar trait useful in understanding yield variation.

Influence of Sward Characteristics on Grazing Behaviour and Growth of Hereford Steers Grazing Tropical Grass Pastures

Abstract: Relationships between sward characteristics, grazing behaviour and growth of Hereford steers were studied on nitrogen-fertilized (378 kg ha-1 yr-1) Setaria anceps cv. Nandi and Digitaria decumbens swards continuously stocked at 4.3, 6.2 and 8.0 beasts ha-1 during five periods over 2 years. Availability of herbage, as measured by bite size, and nitrogen content and in vitro digestibility of herbage in the top of the swards were the two most important factors influencing the performance of steers. The relative importance of these factors varied between seasons, between stocking rate treatments and to a lesser extent between pasture species. The highest growth rates were measured on the leniently stocked pastures because steers were able to harvest feed easily (a large bite size) and could more readily select the more nutritious plant parts from the top of the sward. The swards were highly heterogeneous, and numerical analysis of data showed that at the same herbage yield, spatial distribution of herbage (leaf bulk density and leaf to stem ratio) and the nutritive value (in vitro digestibility and nitrogen content) of herbage greatly influenced the growth of steers. Cattle were unable to satisfy their feed requirements on some high quality but low-yielding swards, despite increasing grazing time to compensate for the small bites prehended (up to 707 min in 24 hr in spring). Consequently nitrogen and digestibility contents of extrusa samples were at times poor indicators of performance.

Breeding Australian Illawarra Shorthorn cattle for resistance to Boophilus microplus. I. Factors affecting resistance

Abstract: Selection and breeding for tick resistance in an Australian Illawarra Shorthorn (AIS) herd was undertaken from 1966 to 1971. Mating of half the AIS herd with a Brahman bull in 1968–69 provided a comparison of tick resistance in selected Bos taurus and crossbred B. taurus x B. indicus cattle. Parent cows and their progeny were ranked for resistance to ticks, infestations of which were acquired as a result of grazing infested pastures, and from periodical artificial infestation with cohorts of c. 20,000 larvae of Boophilus microplus. Ranking and assessment of resistance levels were based on counts of semi-engorged female ticks on the right side. Parent cows selected for high resistance consistently carried fewer ticks than cows selected for low resistance. Mating of cattle selected for high resistance produced progeny that were significantly more resistant than the progeny of cattle selected for low resistance. However, the Brahman bull, which had slightly lower resistance than the AIS bull, produced progeny with higher resistance, even when mated with AIS COWS selected for low resistance. Pregnant cows were significantly less resistant than non-pregnant cows, and lactating cows were very much less resistant than non-lactating cows. Young cows were more resistant than older cows. Calves at foot carried fewer ticks than their dams when grazing infested pastures, but after weaning they were less resistant than their parents when resistance was determined from artificial infestations. Female calves carried fewer ticks than males on almost all occasions, but differences were not significant in winter. Significant seasonal changes in resistance were demonstrated in AIS and Brahman x AIS weaner and yearling cattle. All cattle were less resistant in winter. Changes were greatest in Brahman x AN females, on which the average numbers of female ticks that matured following artificial infestations in January 1970 (summer), July 1970 (winter) and January 1971 (summer) were 151, 1046 and 95 respectively.

Two Diseases in Stylosanthes spp. Caused by Colletotrichum gloeosporioides in Australia, and Pathogenic Specialization within One of the Causal Organisms

Abstract: Two anthracnose diseases caused by Colletotrichum gloeosporioides have been found in Stylosanthes spp. in northern Australia. The two diseases can be readily distinguished by their symptoms and their pure-culture characteristics. The disease classified as type A was widespread, but the other, type B, was found at only two localities. In spray-inoculation tests under controlled conditions, S. guianensis cv. Endeavour was highly susceptible to type B isolates, and some lines of S. fruticosa, S. humilis, S. scabra and S. viscosa were highly susceptible to the type A isolates. Two pathogenic races of type A were recognized from the reaction of S. viscosa 33941 towards them. The importance of these diseases is discussed, together with aspects of disease dissemination and future control strategies.

Variation between and within Species of Rapeseed (Brassica campestris and B. napus) in Response to Drought Stress. I Sensitivity at Different Stages of Development

Abstract: Drought imposed at different times on four spring cultivars of each of two oilseed rape species (Brassica campestris and B. napus) markedly influenced seed yield and its components and other characteristics of the mature plant. In general, drought reduced those plant and yield components associated with plant size, whereas other characters were variable, depending on the species and treatments. Seed yield was lowest in both species when drought was applied either from stem elongation or from the time of anthesis. However, considering grain yields in terms of the amount of water added in each treatment, B. napus cultivars were most sensitive at anthesis, with the exception of Masoweicki which was most sensitive at pod-filling. In B. campestris, Span was most sensitive when drought stress was first imposed at stem elongation, whilst other cultivars were sensitive at later reproductive stages. Principal component analyses reduced the complex interrelationships between all variables excluding yield to two major factors in each species and treatment. In general, the first factor, which explained most of the variation in the parameters measured, was composed of variables associated with plant size, whereas the second was composed of variables which were independent of plant size. The relative importance of these two factors as yield determinants varied substantially with the different species and treatments. In B. napus the first factor was the major determinant of yield ill the control and in the drought treatment imposed from stem elongation. In B. campestris the second factor was a significant determinant of yield in all treatments and the major factor influencing yield in the control and stem elongation treatments. Increased root weight was associated with increased yield in the drought treatments in both species, but this was primarily due to its association with plant size. When the influence of plant size was accounted for, it was observed that a smaller root weight relative to the above-ground plant weight and a greater tap-root weight relative to lateral root weight was associated with higher yield in both species in all drought treatments. As well as these latter characters, seed weight per pod, and harvest index were the most important group of characters contributing to yield in both species in all treatments when variation in plant size was accounted for.

Selection of pea lines for resistance to pathotypes of Ascochyta pinodes, A. pisi and Phoma medicaginis var. pinodella

Abstract: The pathogenicity of 45 isolates of Ascochyta pinodes, Ascochyta pisi and Phoma medicaginis var. pinodella collected in South Australia has been examined on selected pea lines. Twenty-six isolates of A. pinodes were differentiated into 15 pathotypes, 15 isolates of A. pisi were differentiated into 13 pathotypes, and four isolates of P. medicaginis var. pinodella into one pathotype. Adequate sources of resistance were identified against all the pathotypes excepting pathotypes 1 of A. pinodes and A. pisi. The necessity to breed for broadly based resistance to Ascochyta species is discussed.

Accumulation and Distribution of Mineral Elements in the Annual Lupins Lupinus albus L. and Lupinus angustifolius L.

Abstract: The mineral nutrition of L, albus and L. angustifolius was studied under nutrient-sufficient conditions in sand culture. Mineral accumulation by both species was closely synchronized with dry matter accumulation. Fruits acquired major proportions of the nitrogen, phosphorus, potassium, magnesium and zinc of both species. Leaflets were major sites of accumulation of calciun~, iron and manganese; stem and petioles accumulated substantial amounts of potassium, phosphorus, magnesium, copper and sodium. Intensities of intake of calcium, magnesium and iron by roots of L. angustifolius were higher than in L, albus. The situation was reversed for sodium. Cotyledon reserves of nitrogen, phosphorus, potassium and zinc were mobilized to seedling parts with 85-97 % efficiency, other elements much less effectively. During fruiting, vegetative parts of the shoot showed net losses of 60-80 % of their nitrogen, phosphorus and potassium, 20-50 % of their magnesium, iron, zinc, manganese and copper, and less than 15 % of their calcium and sodium. Mobilization from vegetative structures was generally more efficient in L. albus than in L. angustifolius. Leaflets showed higher mobilization efficiencies than stem and petioles. Post-anthesis mobilization furnished the equivalent of 23-59 % of the fruit's intake of nitrogen, phosphorus, potassium, magnesium and manganese, 10-25 % of the zinc, calcium, iron and copper, and 2 % or less of the sodium. Nitrogen, phosphorus and potassium attained higher concentrations in fruits than in mature, non-reproductive parts; less mobile elements (calcium, sodium, iron and manganese) showed the opposite effect. Concentrations of sodium and manganese were especially low in fruits of L. angustifolius compared with L. albus.

Senescence, digestibility and carbohydrate content of buffel grass and green panic leaves in swards

Abstract: Seasonal changes in the rate of production, senescence and change in dry matter digestibility (DMD), cell wall content (CWC) and non-structural carbohydrate content (TNC) of leaves of buffel grass and green panic were followed over a period of 2 years in grazed swards in a dry, subtropical environment in southern Queensland. The swards were buffel grass sown alone with (buffel plus-nitrogen) and without (buffel minus-nitrogen) nitrogen fertilizer, buffel grass/Siratro mixture and green paniclsiratro mixture. New, fully expanded leaves developed at the rate of c. one every 9–10 days in summer, 11 days in spring and 14–20 days in autumn. The overall rate of senescence of these leaves was fastest during the summer growing season and slowest during the cooler, drier conditions of autumn. Leaves in the buffel plus-nitrogen and buffel/Siratro swards senesced more rapidly than those on the buffel minus-nitrogen treatment. Leaf senescence was particularly accelerated by frost in the dry season and by intermittent periods of water stress during otherwise good moisture conditions in the growing season. The DMD of recently developed leaves was generally higher in spring than in summer and autumn, and CWC showed the reverse trend. The decline in DMD of leaves as they aged was considerably higher in spring and summer (c. 0.5 unit/day) than in autumn (0.1–0.3 unit/day); these changes were proportionately greater than expected from the increase in CWC. Frosts caused a precipitous decline in DMD. Leaves of buffel plus-nitrogen were 2–4 units higher in DMD than buffel minus-nitrogen leaves when young, but the former leaves declined in DMD more rapidly as they aged; the DMD of leaves from the buffel—Siratro swards was intermediate. The level of TNC was highest, up to c. 12%, in spring (largely due to an increase in starch) and lowest in late summer-autumn (c. 8%). Diurnal variation in TNC was small (2 percentage units from 0600 to 1800 hours) and did not affect the estimation of DMD.

Determination of spikelet number in wheat. III.* Effect of varying temperature on ear development

Abstract: The effects on rate of development and spikelet number per ear in eight wheat cultivars grown at various temperatures (16/9, 23/16, and 30/23°C for 8/16 hr) throughout or transferred from one temperature to another at floral initiation were studied under normal (12.5–14.0 hr) and 24 hr photoperiods. Under a 24 hr photoperiod, the durations of the vegetative, spikelet and elongation phases, and spikelet number per ear decreased as the temperature increased from 16/9 to 30/23°C in all cultivars. The rate of spikelet initiation increased as temperature increased from 16/9 to 23/16° in most cultivars, but further increase in temperature caused a variable response. Under a normal photoperiod, increasing the temperature from 16/9 to 23/16°C changed spikelet number little, but further increase in temperature decreased it in most cultivars. The rate of initiation increased, but the durations of the vegetative, spikelet and elongation phases, and the apex length at floral initiation decreased in all cultivars as the temperature increased from 16/9 to 23/16°; with further increase in temperature, the rate of initiation, apex length and duration of the elongation phase decreased in most cultivars, but the durations of the vegetative and spikelet phases either increased or changed little. Variation in the number of spikelets per ear in relation to variation in the factors considered to be its possible determinants is discussed with a view to understanding the control of spikelet number. ___________________ *Part II, Aust. J. Agric. Res., 28: 575 (1977).

Variation between and within species of rapeseed (Brassica campestris and B. napus) in response to drought stress. II.* Growth and development under natural drought stresses

Abstract: Two rapeseed species and cultivars within each of these species differed significantly with respect to the influence of variation in sowing date on growth, development and yield on two different soil types. Soil moisture stress, particularly after anthesis, was the major environmental factor affecting these processes. Grain yield declined markedly with later sowings in both species, and B. napus, despite its later maturity, was more tolerant of severe soil moisture deficits since its grain yield was consistently higher than B. campestris in the more stressed environments. The major distinguishing feature between species contributing most to this difference in yield was the pattern of dry matter accumulation. In B. campestris most of the dry weight of the plant was accumulated after anthesis when drought was most severe, whereas in B. napus dry weight accumulation occurred before anthesis. This resulted in a greater contribution of reserves accumulated by anthesis to grain-filling in B. napus. Most of the variation in seed yield resulted from differences in sowing dates and soil types. When these environmental effects were excluded, the main determinants of genotypic variation in yield were the numbers of pods and branches and harvest index in both species, growth rate in the post-anthesis phase in B. campestris, and plant weight and root/shoot ratio at anthesis in B. napus. Selection strategies for yield improvement in rapeseed growing in drought-stressed environments are discussed. _____________________ *Part I, Aust. J. Agric. Res., 29: 469 (1978).

Effect of defoliation on root growth of some arid zone perennial plants

Abstract: The effect of defoliation on the extension, longevity and branching of roots was studied with use of root observation boxes. Three perennial species commonly found in the southern portion of the Australian arid zone—wallaby grass (Danthonia caespitosa), old man saltbush (Atriplex nummularia) and bladder saltbush (A. vesicaria)&,dash;were investigated and compared with lucerne (Medicago sativa). The rate of root extension of theAtriplex spp. was about double that of M. sativa and D. caespitosa and for all species was proportionately reduced with the severity of defoliation. Root mortality increased and branching of roots decreased with increasing severity of defoliation. Time-lapse photography showed that extension of the roots of D. caespitosa began to slow down about an hour after complete defoliation whereas extension of the roots of A. nummularia and M. sativa did not begin to slow down until 12–24 hr after defoliation.

The effects of copper and nitrogen supply on the retranslocation of copper in four cultivars of wheat

Abstract: The retranslocation of copper and nitrogen was studied in four cultivars of wheat grown in pots of a copper-deficient sand from Lancelin, W.A. Plants were grown at two levels of nitrogen and three levels of copper, and harvested three times during growth and at maturity. Plants grown at low copper were severely copper-deficient and yielded no grain. At low nitrogen, plants at marginal copper gave similar grain yields to plants at high copper. Application of high nitrogen at marginal copper either had little effect or depressed grain yield. Application of high nitrogen at high copper gave a strong positive interaction producing maximal grain yield in each cultivar. Low copper supply delayed yellowing and the decline in copper and nitrogen content of the oldest leaf of each cultivar. Application of high nitrogen further delayed yellowing of the oldest leaf and loss of its copper and nitrogen. Probably the copper content of the oldest leaf does not decline until the leaf begins to senesce. Senesced leaves retain low concentrations of copper and nitrogen. It is suggested that at marginal copper, copper retention by senesced vegetation limits the retranslocation of copper from vegetation to grain. Susceptibility to copper deficiency differed markedly with stage of growth and with cultivar. At marginal copper and high nitrogen, copper deficiency almost eliminated the grain yield of Argentine IX, but had relatively small effects on Gamenya, Olympic, and Petit Rojo. The higher susceptibility of grain production in Argentine IX to copper deficiency was not related to its copper content in whole tops or to its grain protein concentration. The susceptibility may have resulted from the ability of this cultivar to form large numbers of tillers which competed with the developing grain for retranslocated copper.

Availability to grazing sheep of gastrointestinal nematode infection arising from summer contamination of pastures

Abstract: In two successive years, separate phalaris-subterranean clover pasture plots near Canberra were contaminated with nematode eggs by grazing with naturally infected sheep in each of the summer months (December, January, February) and the first month of autumn (March). At intervals until mid- to late winter, the availability of infection on pasture was estimated by grazing with worm-free 'tracer' lambs which were subsequently slaughtered for worm counts. Summer rainfall in both years was above average. Tracer counts of Haemonchus contortus and Ostertagia, Trichostrongylus and Nematodirus spp. per l08 eggs per hectare remained high during summer, with evidence that migration of larvae to the herbage could continue for at least 2 months after contamination. Rates of decline in tracer worm counts over the autumn and winter did not differ between years, and from an assumed maximum 2 months after contamination in each of the summer months, were fastest from December and slowest from February contamination. These rates were similar for all genera on December-contaminated plots, but on January and February plots, Ostertagia spp. declined more slowly. H. contortus numbers fell sharply in early autumn to be low by the end of May. By mid July there would be few larvae of all genera available on pastures contaminated in December and January, but this is less certain on February-contaminated pastures, especially for Ostertagia spp. Implications for the control of nematode infections in sheep by anthelmintic treatment and grazing management are considered.

The nitrogen metabolism of sheep consuming Flinders grass (Iseilema spp.), Mitchell grass (Astrebla spp.) and mixed native pasture

Abstract: Some aspects of nitrogen metabolism of sheep given Mitchell grass (Astrebla spp.), Flinders grass (Iseilema spp.) and mixed native pasture were investigated. All diets were of low nutritive value as demonstrated by negative nitrogen and energy balances in sheep on these diets. Studies of urea metabolism demonstrated a significant relationship between plasma urea concentration, the rate of irreversible loss of urea from plasma and the rate of urea degradation in the digestive tract. On average, 81% of the urea synthesized in the body was transferred to the digestive tract and degraded to ammonia and carbon dioxide. The proportion of urea degradation occurring intraruminally was estimated during an intravenous infusion of 14C urea by measuring the rate of appearance of 14CO2 in ruminal fluid, the proportion degraded post-ruminally being obtained by difference. Urea degraded in the rumen accounted for 7–13% of the total quantity degraded in the digestive tract, and the rate of urea transfer (0.55 ± 0.13 g nitrogen/day) was not related to the rate of urea synthesis in the body. The lower digestive tract was the major site of urea degradation in sheep given these low protein diets, and the rate of urea transfer to this part of the digestive tract was linearly related to the rate of urea synthesis in the body. The implications of these findings are discussed in relation to nitrogen conservation in sheep given low quality diets.

Growth and flowering in salt-stressed avocado trees

Abstract: The effect of salinity (0, 5, 10 and 2 0 mM sodium chloride) on the growth, ion composition and flowering response of Fuerte scion grafted to rootstocks of Mexican, Guatemalan and Mexican × Guatemalan (Zutano) race is described. Scions on the Mexican and Zutano stocks were less tolerant of salinity than scions on the Guatemalan stock based on measurements of stem diameter and biomass. The less tolerant trees also contained higher concentrations of sodium and chloride in leaves. The entry of sodium into scions on the Mexican and Zutano stocks was associated with increased succulence of stems and leaves. This response altered the mineral composition of the leaves. Leaf potassium and nitrogen per unit of dry weight increased on the Mexican stock given 20 mM sodium chloride. By taking account of the changes in succulence, however, it could be demonstrated that potassium and nitrogen concentrations on a leaf water basis remained close to control values. Calcium ion failed to make the adjustment, and the already low calcium levels were further reduced by succulence. Succulence was responsible for a 25–37% dilution of sodium and chloride in the leaves of scions on Zutano and Mexican stocks, given 2 0 mM sodium chloride. Salt stress promoted the flowering of Fuerte scion. Low salinity (5mM sodium chloride) failed to stimulate flowering in trees on the Guatemalan stock. High salinity (20mM sodium chloride) was detrimental to flowering in scions on the Mexican stock and resulted in reduced numbers of floral buds, flowers per bud, inflorescences per bud and flowers per inflorescence. The experimental results are discussed in relation to the salinity situation in the irrigated horticultural areas along the River Murray.

Epidemiological factors influencing the success of roguing for the control of bunchy top disease of bananas in New South Wales.

Abstract: An infection chain was reconstructed from historical data of a typical outbreak of bunchy top disease of bananas to determine factors influencing the seasonal occurrence and eradication of disease under roguing. The results were described by a mathematical model involving four random variables (incubation period, relative infection rate, detection efficiency and eradication efficiency) and one fixed variable (inspection interval). The model successfully predicted the course of roguing in an independent disease outbreak. The incubation period of the disease depended on the time taken for two banana leaves to emerge after inoculation. At Alstonville, N.S.W., the incubation period varied from 19 days in summer to 125 days in winter. The relative infection rate varied on average from 0.027 to 0.001 new infections per old infection per day in summer and winter respectively. Efficiency of disease detection by experienced inspectors depended on the number of leaves displaying disease symptoms and, equally, on time of year. Under the normal 3-weekly inspection routine, detection efficiency varied from 0.94 in summer to 0.19 in winter, plants being found on average at the two-leaf stage of disease. The efficiency with which banana growers eradicated diseased plants following their detection was found to be a characteristic of the grower concerned but was, in general, poorest in late summer.

The effect of fallowing on the yield of wheat. I. The effect on soil water storage and nitrate supply

Abstract: The effect of fallowing before a wheat crop was studied in South Australia in an environment with suboptimal rainfall in the growing season. A 9–10 month pre-sowing fallow increased mean water storage (0–120 cm depth) at sowing by 28 mm, compared with a non-fallow soil preparation (2 month period of cultivation). Variation in additional storage ranged from nil to 125 mm. These amounts depended on soil type and season: in coarse-textured soils, fallowing conserved little additional water, but in fine-textured soils much additional water could be stored. Storage was not related to the summer rainfall (November-March) before sowing but was related to rainfall during July and August in the previous winter—just before or at the start of the fallow period. A combination of these two factors, fine-textured soil and good July–August rainfall, gave considerable storage. Fallowing also increased the nitrate nitrogen content in the surface 60 cm at sowing; the mean additional nitrogen amounted to 19 kg/ha in the coarse-textured soils and 30 kg/ha in the fine-textured soils. The largest increases due to fallowing were recorded in soils following medic leys and with ample rains on the fallow in spring. Comparison is made between these findings and those obtained with fallowing in other parts of Australia.

Relationships between flowering and honey production of red ironbark, Eucalyptus sideroxylon (A. Cunn.) Benth., and climate in the Bendigo district of Victoria

Abstract: Records of growth, flowering and honey production of red ironbark (Eucalyptus sideroxylon (A. Cunn.) Benth.) forests in the Bendigo district of Victoria are analysed. The sequence in which stems and flowers develop is described. Annual growth is bimodal and occurs during autumn and spring. Growth requires a threshold temperature of 16–17°C and a monthly rainfall of 45–60 mm. The rate at which flower buds develop in exposed umbels is related to the temperature and rainfall during the spring growing season. Flowering starts in January, reaches a maximum in July and ends in September. Honey production depends on flowering abundance, the number of hives at a site, the length of the harvesting time, and rainfall and temperature during and before harvest.

Selection for reproduction rate in Australian Merino sheep: direct responses

Abstract: Two groups of Australian Merinos have been under selection for low (O) and high (T) reproduction rate since 1954, and a third (B) for high rate since 1959. The O and T groups were founded on Peppin ewes from one flock which had borne singles (or twins) in two successive years, mated to single- (or twin-) born rams from the same flock. The B group was founded on two quintuplet rams and ewes born in multiple births (13 in one intake, 91 in a second), from a medium-wool non-Peppin flock belonging to the Seears Brothers, of 'Booroola', Cooma, which had been under selection for multiple births for 10–15 years. In 1959, the lambing percentage of the flock (lambs born to ewes joined) was stated to be 170-180. Selection for both sexes in the early years of the experiment was based on the presence (or absence) of multiple births in the record of the dam's first three lambings, or in that of the ewe herself, again during her first three lambings. In later years this was combined with a dam's ranking coefficient based on all available records, the coefficient being based on deviations from average performance at the ages of record, and the heritability of repeated records. The sex of her litter mates was found to have no effect on a ewe's lambing performance. The litter size in which she was born had no effect on her lambing performance when she belonged to the O or B group, but twin-born ewes in the T group were sometimes at a disadvantage compared with singles-for their lambings at 2–4 years if their dams were adult, and for those at 5–7 years if their dams were 2-year-olds. Selection response was analysed by examining T – O and B – O differences in performance for ewes born in successive calendar years, the two criteria of performance being the percentage of ewes with at least one multiple birth in their first three lambings, and ranking coefficients based on the same lambings (at 2–4 years). A regression of each difference on time is an estimate of the annual rate of genetic change due to selection; no attempt has been made to relate such changes to what might be predicted from parameters. Adjustments were made for the handicap suffered by twin-born T group ewes by adding 10.0 to the percentage showing at least one multiple birth for those whose dams were adult, 3.4 to the 2-4-year-old ranking coefficient of those ex adults, and 2.6 to the 5-7-year-old ranking coefficient of those ex 2-year-old dams. No unbiased correction for age of dam was possible; instead, T – O and B – O differences were calculated separately for progeny of adults and progeny of 2-year-olds, and a weighted mean difference computed. The groups ran at Deniliquin until 1964, and at Armidale from 1965. In spite of the change in environment, and a bad drought in 1965, regression lines could be fitted to all differences except the 2-4-year-old ranking coefficient in group T. Initial responses in percentage of ewes with at least one multiple birth in their fist three lambings were 35.2 and 40.1 for T – O and B – O respectively, and the linear regression coefficients, measuring continuing response, were 2.39 ± 0.58 and 5.52 ± 1.33. The initial responses account respectively for 68 and 62% of the average superiority of the high lines during the experiment. Initial responses for ranking coefficients at 2-4 years of age were 8.2 and 21.7 for T – O and B – O respectively, corresponding approximately to 0.26 and 0 + 72 lambs born/ewe/lambing. Continuing responses fluctuated more than for percentage of ewes with multiple births; regression coefficients of 0.67 ± 0.17 were fitted for T – O from 1954–56 to 1964, and 3.6 ± 1.2 for B – O from 1961 to 1968. The former is equivalent to 0.02, and the latter to 0.11 lambs born per ewe per year. Initial responses contributed 57–76% of the average superiority of the high line (T or B) over O, depending on the regression coefficient used. For the 1968 drop, the difference in ranking coefficient at 2–4 years was equivalent to 0.38 lambs born/ewe/lambing for T – O, and 1.04 lambs born/ewe/lambing for B – O. Ranking coefficients based on lambings at 5–7 years are the result of selection on the ewes themselves, in addition to genetic gains. The T – O and B – O differences in these coefficients showed approximately the same rate of annual change as those at 2–4 years. Corrections were made to some data from T ewes in estimating response, but in practice twin ewes might give a lower performance at their early lambings. However, the actual performance of the flocks shows that any such disadvantage was not serious. In 1972, ewes aged 2–7 years in the three groups bore respectively 1.11, 1.36 and 2.10 lambs per ewe joined. Clearly, the reproduction rate has responded to selection, the rate of response being far higher in the B group than the T. Clearly, also, initial selection of the base animals made a major contribution to the superiority of the high lines, though there has also been a continuing response.

Studies of the environmental physiology of tropical merinos

Abstract: Rectal temperature measurements of tropical Merino sheep taken in the sun during summer indicated that there were high and low temperature groups. Animals of low temperature status (e.g. 39.4°C) also exhibited a low respiration rate (e.g. 110/min) in comparison with their less adapted counterparts (40.0° and 190/min). These differences were greatest when ambient temperatures were high. The repeatability of temperature status was 0.46 (P < 0.01). Animals of folds (p) phenotype had significantly higher rectal temperatures than folds (–) animals (P < 0.05). Shearing caused a marked but transient increase in rectal temperature. Compensatory mechanisms apparently involved an increase in cutaneous heat dissipation and/or a decrease in exogenous heat load. Evaporative water loss (80–115 ml/kg/day) greatly exceeded the non-evaporative water loss (40–65 ml/kg/day) of sheep in metabolism cages. Respiratory water loss could account for only 8–10% of the total daily evaporative water loss. Non-respiratory evaporative water loss (as measured by difference) was c. 75–100 ml/kg/day. There were no striking differences between high and low temperature status sheep in this regard. Measurements of respiratory (2 ml/kg/hr) and non-respiratory (5.5 ml/kg/hr) evaporative water loss made in hygrometric tents suggested that the greater non-respiratory water loss was partly due to a higher rate of loss and partly to a longer period of loss per day. This suggestion was supported by the diurnal patterns of rectal temperatures and respiration rates reported here, though no firm conclusions could be made as to the thermotaxic effect of non-respiratory water loss and thermoregulation of tropical Merinos with varying amounts of wool cover.

The Diagnosis of Sulphur Deficiency in Wheat

Abstract: In a glasshouse experiment with wheat (Triticum aestivum L.), changes in the concentrations of total sulphur, sulphate sulphur, amide nitrogen, and total nitrogen/total sulphur ratio with age, plant part, and nitrogen and sulphur supply, were studied. This was done so that more reliable methods can be devised for the assessment of the sulphur status of this species. Each of the indices studied was strongly related to the current and subsequent sulphur status of the wheat plant. Amide nitrogen provided the greatest relative change in values between sulphur-deficient and sulphur-adequate plants, and on that basis was the most sensitive index. However, each of these indices had shortcomings which could preclude its general acceptance as a useful indicator of sulphur status. The most promising index of sulphur status was shown to be the proportion of total sulphur held as sulphate. This criterion was unaffected by nitrogen supply or plant age. The data suggest that wheat plants containing more than one-tenth of their sulphur as sulphate are adequately supplied with sulphur.

The effect of fallowing on the yield of wheat. II. The effect on grain yield

Abstract: The effect of fallowing on wheat yields is reported for a South Australian environment where 62 % of the variation in yield is ascribed to water supply and where water use efiiciency in grain production ranges from 1 to 11 kg/ha/mm. The mean yield response from a fallow (initial tillage 9 months before sowing) compared with a non-fallow (tillage 2 months before sowing) in 28 seasonal, site and fertility situations was 335 kg/ha and the maximum 875 kg/ha. Each additional millimetre of water stored through fallowing gave on average 8 kg grain per ha. Only fine-textured soils stored considerable water through fallowing. The additional nitrate in fallow gave yield responses when the non-fallow soil contained less than 70 kg nitrate nitrogen per ha, but only when water use by the crop exceeded 230 mm. The results are related to responses to fallowing obtained in other wheat-growing districts in Australia.

Variation between and within Species of Rapeseed (Brassica campestris and B. napus) in Response to Drought Stress. III* Physiological and Physicochemical Characters

Abstract: Genotypic variation in physiological and physicochemical parameters associated with drought resistance was observed between cultivars in Brassica napus and B. campestris. Significant variation in proline accumulation, chlorophyll stability, germination rate and percentage, relative turgidity, growth rates and water use efficiency were found in plants grown under simulated drought conditions in a glasshouse. No variation was detected between cultivars for leaf diffusive resistance or heat tolerance. A yield index for each cultivar was derived from yield performances in nine different field environments. Chlorophyll stability and proline accumulation in leaf tissue and germination percentage in solution equivalent to - 17.5 bars osmotic potential was clearly related to this yield index in B. napus and to a lesser extent in B. campestris. The winter cultivars of B, napus also possessed drought resistance characteristics, and they may be a valuable resource for the development of cultivars for droughted environments. Parameters were measured in a glasshouse, prior to anthesis, and therefore offer potential as ancillary selection criteria for drought resistance in oilseed rape growing in Western Australia.

Watermelon mosaic virus 1 and 2 in Queensland cucurbit crops

Abstract: Watermelon mosaic virus type 1 (WMV-1) has not previously been reported from Australia and has become prevalent in Queensland only since 1970. Watermelon mosaic virus type 2 (WMV-2) continues to reach a high incidence in marrow (Cucurbita pepo) and pumpkin (Cucurbita maxima and Cucurbita moschata) crops, WMV-2 is rarely isolated from watermelons (Citrullus vulgaris) in which epidemics of WMV-1 now cause serious reductions in yield. The Queensland Blue cultivar of C. maxima, the most important cucurbit crop, produces severely distorted fruit following infection by WMV-1, although it is little affected by WMV-2. Physical properties of these WMV isolates and electron microscopic examination of the virus particles and associated cellular inclusions showed them to be similar to those reported elsewhere, but there were some distinctive host reactions for the WMV-2 isolates. No resistance to either WMV-1 or WMV-2 was found in commercially available C. pepo, C. maxima or C. vulgaris. The resistance of Cucumis metuliferus to Australian WMV-1 isolates was confirmed, and a source of resistance to both WMV-1 and WMV-2 was found in Lagenaria siceravia. Methods of separation of WMV-1 and WMV-2 from mixed isolates and methods for the identification of each on differential hosts and by serology were shown to be effective.

Corrigendum - The effect of defoliation on inflorescence production, seed yield and hard-seededness in swards of subterranean clover

Abstract: Swards of three strains of subterranean clover (Seaton Park, Yarloop, Midland B) were subjected to a range of defoliation treatments. In all strains, cutting at weekly intervals at a height of 1.5–2 cm from 1 month after sowing until the onset of flowering led to a slight delay in flower initiation but the time of flowering was little affected. The rate of inflorescence production, however, was always increased, as was the total number of inflorescences produced by the end of flowering. In particular, seed yields were increased by at least 30% compared with uncut controls. This effect was attributable partly to increased inflorescence numbers and partly to increases in other yield components as a consequence of the burial of a large proportion of burrs. Cutting increased the initial level of hard-seededness in Seaton Park and Yarloop; in addition the rate of breakdown of hard-seededness in all strains was slower in seed from the defoliated swards. When cutting was continued until midway through flowering (with the cutting height progressively raised) the seed yield in Yarloop and especially in Midland B was much lower than that obtained when cutting was stopped at the beginning of flowering; but in Seaton Park there was no reduction. With further cutting-until the end of flowering-seed yields were less than when cutting was stopped midway through flowering. Extending cutting into the flowering period (compared with cutting only until the onset of flowering) resulted in a decline in the initial level of hard-seededness and an increase in the rate of breakdown of hard-seededness in Midland B but had little effect in Yarloop or Seaton Park.

Responses of a standard Australian and a Mexican wheat to temperature and water stress

Abstract: Single plants of Gabo, an Australian spring wheat, and Pitic 62, a Mexican semi-dwarf one, were grown at 20°C in a growth cabinet until anthesis. They were then transferred to glasshouses at 18/13, 21/16 and 24/19°C day/night temperatures and supplied with 20, 60 and 100% of their ad lib. water requirements. In terms of water use, dry matter production and grain yield, patterns of response to temperature and water stress were very similar for the two varieties. Highest yields were obtained at 21/16°C. Efficiencies of water use increased as water supply decreased; they were lower at 18/13°C than at higher temperatures. The amounts of dry matter produced after the treatments were imposed were taken as biological indexes of the nine environments. Over the entire range of those values, the grain yields of Pitic 62 were consistently higher than those of Gabo. Significant features of Pitic 62 that contributed to its higher yields were that: (1) by anthesis it had produced larger ears from a given weight of supporting shoot tissues; (2) after anthesis it mobilized a higher percentage and amount of stem and leaf material that apparently contributed to grain production. Two broad categories of shoots were distinguished. The first four shoots of both varieties were very tolerant of water stress, producing 50% of their potential grain yield on 20% of ad lib. water supplies. These shoots experienced water stress only after anthesis. Younger shoots experienced the stress treatments from an earlier stage of development; they were very sensitive to water stress and their grain yields were related linearly to water supply. Harvest index values varied with the category of shoot selected and with size of shoot or plant. Implications of relationships between grain weight and shoot weight for crop selection are discussed.