Showing papers by "International Maize and Wheat Improvement Center published in 2000"
TL;DR: Pathogenicity of Pgt-Ug99 was studied in seedling tests of available wheats containing Sr31, as well as other stem rust differential lines, and Virulence to the T. ventricosum-derived gene Sr38, which is linked to Lr37 and Yr17 and occurs in cultivars from Australia, the United Kingdom, and the United States, was not known previously.
Abstract: In much of the world, resistance to stem rust in wheat, caused by Puccinia graminis f. sp. tritici, is based at least in part on the gene Sr31. During February 1999, high levels of stem rust infection were observed on entries in wheat (Triticum aestivum) grown in a nursery at Kalengyere Research Station in Uganda. Because several of the rusted entries were known to carry the 1BL-1RS chromosome translocation containing the Sr31, Lr26, and Yr9 genes for rust resistance, virulence to Sr31 was suspected. Urediniospores, collected in bulk from rusted stems of seven entries containing Sr31, were suspended in light mineral oil and sprayed on primary leaves of 7-day-old seedlings of South African wheat cv. Gamtoos (=Veery #3, pedigree: Kvz/Buho‘S’//Kal/BB). Plants were kept overnight at 19 to 21°C in a dew chamber before placement in a greenhouse at 18 to 25°C. After ≈14 days, urediniospores were collected from large, susceptible-type stem rust pustules and subsequently increased on Gamtoos, which served as a sel...
618 citations
TL;DR: In this paper, evidence from Ghana suggests that gender-linked differences in the adoption of modern maize varieties and chemical fertilizer result from gender linked differences in access to complementary inputs, especially land, labor, and extension services.
290 citations
TL;DR: A significant positive correlation has been found between iron and zinc concentrations, suggesting that these two traits may be combined relatively easily during breeding, and the very high values seen in wild types and landraces need to be confirmed in trials in which all the best material is planted in the same location and year.
Abstract: In the search for genetic material with high iron and zinc concentration in wheat grain, a significant positive correlation has been found between iron and zinc concentrations, suggesting that these two traits may be combined relatively easily during breeding. In future research, the very high values of iron and zinc in the grain seen in wild types and landraces need to be confirmed in trials in which all the best material is planted in the same location and year. In addition, it is important to determine if these high levels of iron and zinc in the grain can be maintained in high-yielding material.The production of semi-dwarf wheat through the introduction of the rht genes has resulted in substantial yield increases. However, this is associated with a reduction in iron and zinc concentrations in some bread wheat genotypes, but not in durum wheat. The presence of the 1B/1R translocation in the wheat germplasm of the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) to increase leaf rust resist...
281 citations
TL;DR: Gene Yr18, known to be present in Opata, strongly reduced disease response in field trials and was tightly linked with leaf-rust resistance gene Lr34, which was associated with APR.
Abstract: Stripe (yellow) rust, caused by Puccinia striiformis West, is an important constraint to wheat production in cool environments With the purpose of identifying genes for resistance to the disease, a RFLP mapping population of recombinant inbred lines developed from a synthetic [Triticum turgidum L x Aegilops tauschii (Coss) Schmal] x T aestivum L cv 'Opata 85' cross was visually evaluated for seedling infection type in three greenhouse inoculation tests and for adult-plant disease severity in four field tests at Celaya and Toluca, Mexico A previously unidentified gene from Ae tauschii, designated as Yr28, was located on chromosome arm 4DS Although Yr28 strongly influenced seedling resistance, it showed a strong effect in adult plants at only the warmer of the two field sites A second gene showed high environmental sensitivity in seedling tests, with resistance associa0ted with Opata marker alleles near the adult-plant resistance (APR) gene Yr18 on chromosome arm 7DS Gene Yr18, known to be present in Opata, strongly reduced disease response in field trials and was tightly linked with leaf-rust resistance gene Lr34 Three other regions from Opata on chromosome arms 3BS, 3DS, and 5DS were also associated with APR
263 citations
TL;DR: After a very thorough evaluation of the genetic variability of iron and zinc potentially available in white-grained tropical maize germplasm, promising genetic variability was found in both improved maize germ plasm and landraces.
Abstract: The Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) maize-breeding programme has been focusing on identifying white-grained maize germplasm that has the potential to increase kernel i...
223 citations
TL;DR: The objective of this research was to assess the relationship of 18 major ancestors of North American soybean germplasm with 87 plant introductions (PIs) that are potential new sources of genetic variation for soybean breeding programs.
Abstract: The genetic base of soybean [Glycine max (L.) Merr.] cultivars developed for North America is very narrow. This may threaten the ability of breeders to sustain improvement and increase vulnerability of the crop to pests. The objective of this research was to assess the relationship of 18 major ancestors of North American soybean germplasm with 87 plant introductions (PIs) that are potential new sources of genetic variation for soybean breeding programs. Genetic distances (GD) among the 105 genotypes analyzed were calculated from 109 polymorphic DNA fragments amplified with random oligonucleotide primers and simple sequence repeat (SSR) primer pairs. Two hierarchical clustering algorithms were combined with data resampling and multidimensional scaling (MDS) to evaluate relationships among the genotypes. Genetic distances ranged from 0.08 to 0.76, with a mean of 0.52. Genotypes were placed in 11 clusters on the basis of a consensus of the different methods utilized. Co-occurrence values calculated from the resampling iterations showed that the stability of clusters varied. The most stable grouping was among ancestors that corresponded with known relationships based on pedigree and maturity. Several groups of PIs are distinct from the majority of the ancestors. These genotypes may be useful to breeders wanting to utilize genetically diverse introductions in soybean improvement.
216 citations
TL;DR: Improved RUE will be partly a function of a genotype's ability to buffer itself against changes in its environment to match the demand imposed by its development, given a lack of specific knowledge on the genetic basis of RUE.
Abstract: source- and sink-strength is a complex genetic challenge since a crop will change between source and Radiation use efficiency (RUE) of a crop is a function sink limitation as conditions vary during the day, and of several interacting physiological phenomena, each with phenological stage. Improved RUE will be partly of which can be tackled independently from the a function of a genotype’s ability to buffer itself against point of view of genetic improvement. Although wheat changes in its environment to match the demand breeding has not raised RUE substantially, theoretical imposed by its development. Analysis of the physiocalculations suggest room for improvement. Selection logical basis of genotype by environment interactions for higher rates of leaf photosynthesis at saturating may indicate avenues for genetic improvement. The light intensities (A max ) has not resulted in improved genetic control of photosynthetic regulation may be RUE of crops, perhaps in part because most leaves in elucidated in the future through the application of a canopy are not light-saturated. However, higher A max genomics. However, given a lack of specific knowledge may be observed as a pleiotropic effect of other yield- on the genetic basis of RUE, empirical selection is enhancing genes (e.g. genes for reduced height). currently the most powerful tool for detecting favourGenetic transformation of Rubisco to double its speci- able genetic interactions resulting from crosses ficity for CO 2 would theoretically increase A max by between lines with superior photosynthetic traits and perhaps 20%, and some evidence suggests that photo- other high yielding characteristics. Selection for synthesis at sub-saturating light intensities would also superior segregants can be accelerated using rapidly be improved. However, photo-protection may be jeop- measured physiological selection traits, such as ardized if capacity for oxygenase activity is impaired. stomatal conductance or canopy temperature Photosynthetic rate of the whole canopy can be depression. enhanced by manipulation of leaf angle, which is under relatively simple genetic control, and possibly Key words: Radiation use efficiency, photosynthesis, by manipulating leaf-N distribution throughout the genetic modification, wheat breeding, yield potential. canopy. Genetic diversity for adaptation of lower canopy leaves (e.g. changes in chlorophyll a5b ratio) Introduction to reduced light intensity observed in some crops needs to be investigated in wheat. Improved RUE may Genetic yield potential of wheat has been increasing at be achieved by increasing sink demand (i.e. kernel an annual rate of approximately 0.9% over the last 30 number) if excess photosynthetic capacity exists years (Calderini et al., 1999). However, global demand is during grain filling, as suggested by a number of predicted to increase by 1.6% per year over the next 20 studies in which source‐sink balance was manip- years, from the current production of 550 million tonnes ulated. Some evidence suggests that improved sink (Rosengrant et al., 1995). Given the economic and strength may be achieved by lengthening the duration environmental constraints related to increased land use or intensification of agricultural inputs, genetic of the period for juvenile spike growth. Balancing
189 citations
TL;DR: In this article, the authors measured the net photosynthetic rate (An), stomatal conductance (gs), chlorophyll content and dark respiration rate on 16 wheat cultivars (Triticum aestivum L.), grown in replicated yield trials in a warm, irrigated, and low relative humidity environment in central Mexico.
171 citations
TL;DR: Findings suggest complementary roles for professional breeders and Mexican farmers in enhancing mass selection methods to improve maize landraces on farms – if farmers themselves perceive benefits from the collaboration.
Abstract: Experimental results and farmer surveys from a Mexican community located in the buffer zone of a biosphere reserve indicate that farmers' seed selection practices protect the phenological integrity of their traditional maize varieties as they define them, despite numerous factors contributing to genetic instability. Analysis of morphological and genetic data suggests that when subjected to significant gene flow through cross-pollination, ear characteristics are maintained through farmers' selection even though other characteristics may continue to evolve. Because the effects of farmers' selection practices are confined largely to ear characteristics, their practices appear to offer only limited scope for variety improvement. Farmers' expectations of what they can achieve through seed selection are similarly limited. These findings suggest complementary roles for professional breeders and Mexican farmers in enhancing mass selection methods to improve maize landraces on farms – if farmers themselves perceive benefits from the collaboration.
160 citations
TL;DR: It is demonstrated that the genetic variation in the concentrations of zinc and iron in cultivated modern tetraploid and hexaploid wheats is extremely low when compared with the variation found in wild diploids and tetra ploids, which suggests that wild wheats can be considered a major source of genetic diversity for increasing zinc andIron density in the seeds of modern wheats.
Abstract: In the case of cultivated modern wheats, the variation in zinc and iron concentrations in seeds is relatively small. Moreover, environmental and management factors exert a greater effect on variation of micronutrient concentrations of modern cultivated wheats than genetic factors. Wild wheats might serve as an important source of new genetic material for increasing micronutrient concentrations in seeds. To investigate this, we studied the variation in zinc and iron concentrations in seeds of wild and primitive diploid wheats and wild tetraploid wheats. The variation was particularly large in the case of zinc. The highest concentrations of zinc were found in the seeds of ssp. boeoticum (178 mg/kg) and ssp. dicoccoides (159 mg/kg). The results demonstrate that the genetic variation in the concentrations of zinc and iron in cultivated modern tetraploid and hexaploid wheats is extremely low when compared with the variation found in wild diploid and tetraploid wheats. This suggests that wild wheats, particular...
160 citations
TL;DR: The sequence of breeding stages that led to the development of acceptable quality protein maize (QPM) germplasm at the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) are described.
Abstract: The paper describes the sequence of breeding stages that led to the development of acceptable quality protein maize (QPM) germplasm at the Centro Internacional de Mejoramiento de Maiz y Trigo (CIMM...
01 Jan 2000
TL;DR: The associations of molecular markers with qualitative and quantitative disease resistance loci will be a useful information for marker-assisted selection.
Abstract: Stripe rust, leaf rust, and Barley Yellow Dwarf Virus (BYDV) are important diseases of barley (Hordeum vulgare L). Using 94 doubled-haploid lines (DH) from the cross of Shyri x Galena, multiple disease phenotype datasets, and a 99-marker linkage map, we determined the number, genome location, and effects of genes conferring resistance to these diseases. We also mapped Resistance Gene Analog Polymorphism (RGAP) loci, based on degenerate motifs of cloned disease resistance genes, in the same population. Leaf rust resistance was determined by a single gene on chromosome 1 (7H). QTLs on chromosomes 2 (2H), 3 (3H), 5 (1H), and 6 (6H) were the principal determinants of resistance to stripe rust. Two- locus QTL interactions were significant determinants of resistance to this disease. Resistance to the MAV and PAV serotypes of BYDV was determined by coincident QTLs on chromosomes 1 (7H), 4 (4H), and 5 (1H). QTL interactions were not significant for BYDV resistance. The associations of molecular markers with qualitative and quantitative disease resistance loci will be a useful information for marker-assisted selection.
TL;DR: In most tillage-straw treatments, 21% of the difference in wheat grain yields was due to the N supply component at low N rates; at high N rates, 97% wasDue to N use efficiency.
Abstract: Wheat (Triticum aestivum L.) in the Yaqui Valley, northwest Mexico, is planted as a winter crop using a raised-bed, furrow-irrigated system and high fertilizer N rates. Wheat residues are usually burned before planting maize (Zea mays L.) as a summer crop. The N use of wheat planted following conventional tillage using a raised-bed system (CTB) incorporating both wheat and maize residues was compared with wheat planted using permanent raised beds (PB) under four residue management treatments: all straw (wheat and maize) left as stubble, straw partly removed (maize residues removed; wheat residues retained), all straw removed, and all straw burned. Each wheat plot was split into seven N fertilizer (N t ) treatments: five applied at planting (0, 75, 150, 225, and 300 kg ha 1 ) and two at the 1st node stage (150 and 300 kg ha -1 ). Maize received a uniform N f application of 150 kg ha -1 . The N use efficiency of wheat with 150 kg N f ha -1 at the 1st node stage was superior to basal applications at the same rate. Permanent bed-all straw left as stubble and PB-all straw burned had the highest average wheat grain yields (5.57 and 5.52 Mg ha 1 , respectively), N use efficiency (28.2 and 29.1 kg grain kg -1 of N supply, respectively), and total N uptake (133 and 137 kg ha -1 , respectively). Total N uptake for 150 and 300 kg N f ha -1 at the 1st node stage was 14 and 8% greater, respectively than at planting. In most tillage-straw treatments, 21% of the difference in wheat grain yields was due to the N supply component at low N rates; at high N rates, 97% was due to N use efficiency.
TL;DR: Field experiments evaluated the impact of relay-intercropping two legume crops, cowpea and sunnhemp, into smallholder maize in Zimbabwe to quantify biomass and N yield and the response of a subsequent maize crop to legumes.
Abstract: The rising real prices of purchased inputs is driving smallholder maize (Zea mays L.) production towards lower levels of inorganic fertilizer. Legume intercrops are a source of plant N that can be produced locally and offer a practical complement to inorganic fertilizers. Field experiments conducted on a loamy sand (Typic Kandiustalf) soil evaluated the impact of relay-intercropping two legume crops, cowpea (Vigna unguiculata L.) and sunnhemp (Crotolaria juncea L.) into smallholder maize in Zimbabwe. The objectives were to quantify: (i) biomass and N yield of intercropped legumes, (ii) the impact of the legumes on companion maize yield and N uptake, and (iii) the response of a subsequent maize crop to legumes. Dry matter yield ranged from 0.6 to 4.6 Mg ha -1 for cowpea and 0.9 to 2.9 Mg ha -1 for sunnhemp, over two years. At the most, cowpea and sunnhemp produced 154 and 82 kg N ha -1 , respectively. Companion maize grain yields were not reduced when the legumes were relay-intercropped into maize fertilized at 0 to 60 kg N ha -1 . However, maize yields were reduced 18 to 31% when maize + legume intercrops were fertilized at 120 kg N ha -1 . In the subsequent year, maize grain yields were increased by 8 to 27% following maize + legume when no fertilizer N was applied, compared with maize following maize. Legumes reduced fertilizer needs of a subsequent maize crop by 36 kg N ha -1 . Intercropped annual legumes and small amounts of inorganic fertilizer offers a strategy to meet the N needs on smallholder farms.
TL;DR: In this paper, the validity of a bell-shaped curve describing the area of individual leaves as a function of leaf number was investigated, and a method was developed to directly estimate total leaf area when total leaf number and area of the largest leaf are known.
Abstract: Leaf area development of six tropical maize cultivars grown in 1995 and 1996 in several tropical environments in Mexico (both favourable and moisture-and N-limited) was observed and analysed. First, the validity of a bell-shaped curve describing the area of individual leaves as a function of leaf number was investigated. When individual cultivar-environment combinations were normalized for area of the largest leaf and for total leaf number, one parameter set described all combinations. It remained difficult, however, to estimate these parameters in advance, which limits predictive applications in crop growth models. Analytical application after flowering, when parameter values can be determined, is possible. Second, a method was developed to directly estimate total leaf area when total leaf number and area of the largest leaf are known. The method makes use of the facts that the area of the largest leaf relative to total plant leaf area is constant and that this constant is linearly related to total leaf number. This study has shown that approaches previously presented by others are applicable in modified form over a wide range of environmental conditions.
TL;DR: Senescence was evaluated at different stages of the grain-filling period in eight durum wheat varieties using numerical image analysis (NIA), while the maximal rate of senescence, Vsmax, correlated to thousand-kernel weight.
Abstract: Senescence was evaluated at different stages of the grain-filling period in eight durum wheat varieties using numerical image analysis (NIA). The varieties were grown under early, severe drought conditions on the high plains of Setif in Algeria. After flowering, three different irrigation treatments were applied. Treatment effect was small, while a genotypic effect was noted for most of the senescence parameters. Senescence correlated to biomass, while the maximal rate of senescence, Vsmax, correlated to thousand-kernel weight. The potential of the method of numerical image analysis for monitoring flag leaf senescence, detecting genotypic variability and selecting genotypes with delayed senescence is discussed.
Zusammenfassung
Die Alterung des Fahnenblatts wurde wahrend der Kornfullungsphase in acht Durumweizenlinien mit Hilfe von numerischer Bildanalyse (NIA) untersucht. Die Sorten wurden in der Hochebene von Setif (Algerien) angebaut, wo sie fruhzeitiger und drastischer Trockenheit ausgesetzt waren. Nach dem Bluhstadium wurden drei verschiedene Bewasserungsstufen angewendet. Der Behandlungseffekt war gering, wahrend die genotypischen Effekte fur die meisten der Alterungsparameter signifikant war. Alterung korrelierte mit Biomasse, wahrend die maximale Rate der Alterung, Vsmax, mit dem Tausendkorngewicht korreliert war. Die verschiedenen Einsatzmoglichkeiten der numerischen Bildanalyse fur die Uberwachung der Fahnenblattalterung werden diskutiert, die es erlauben genotypische Unterschiede zu identifizieren und Genotypen mit verlangsamter Alterung zu selektieren.
TL;DR: Net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and chlorophyll concentration estimate all correlated with yield of inbred lines, and An and gs measured on individual F5 plants correlated genetically and phenotypically with An, gs, and yield of the inbreeding lines deriving from the same plants, in both environments where yield was evaluated.
TL;DR: At all three locations, N2 fixation was highly positively correlated with the dry matter production and total N yield of faba bean, highlighting the importance of rotation with fababean in the cereal-based cropping systems of Ethiopia.
Abstract: N2 fixation by leguminous crops is a relatively low-cost alternative to N fertilizer for small-holder farmers in developing countries. N2 fixation in faba bean (Vicia faba L.) as affected by P fertilization (0 and 20 kg P ha–1) and inoculation (uninoculated and inoculated) with Rhizobium leguminosarium biovar viciae (strain S-18) was studied using the 15N isotope dilution method in the southeastern Ethiopian highlands at three sites differing in soil conditions and length of growing period. Nodulation at the late flowering stage was significantly influenced by P and inoculation only at the location exhibiting the lowest soil P and pH levels. The percentage of N derived from the atmosphere ranged from 66 to 74%, 58 to 74% and 62 to 73% with a corresponding total amount of N2 fixed ranging from 169 to 210 kg N ha–1, 139 to 184 kg N ha–1 and 147 to 174 kg N ha–1 at Bekoji, Kulumsa and Asasa, respectively. The total N2 fixed was not significantly affected by P fertilizer or inoculation across all locations, and there was no interaction between the factors. However, at all three locations, N2 fixation was highly positively correlated with the dry matter production and total N yield of faba bean. Soil N balances after faba bean were positive (12–58 kg N ha–1) relative to the highly negative N balances (–9–44 kg N ha–1) following wheat (Triticum aestivum L.), highlighting the importance of rotation with faba bean in the cereal-based cropping systems of Ethiopia.
TL;DR: In this paper, a study was conducted to determine whether synthetic hexaploids also could contribute genetic diversity to enhance leaf photosynthetic rate and other physiological traits, and three different populations of BC 2 F 2, synthetic-derived lines were evaluated at the Agricultural Research ('enter for the Northwest (INIFAP) Experimental Station, near Ciudad Obregon, Sonora, Mexico.
Abstract: Wild ancestors of common wheat (Triticum aestivum L.) have been reported to have higher maximum photosynthetic rates than modern wheat cultivars. Synthetic hexaploids, obtained by crossing tetraploid wheat and Aegilops tauschii Coss., have proven useful as a source of resistance or tolerance to biotic and abiotic stresses. This study was conducted to determine whether synthetic hexaploids also could contribute genetic diversity to enhance leaf photosynthetic rate and other physiological traits. Three different populations of BC 2 F 2 , synthetic-derived lines were evaluated at the Agricultural Research ('enter for the Northwest (INIFAP) Experimental Station, near Ciudad Obregon, Sonora, Mexico. Differences in maximum photosynthetic rate were detected among genotypes. Several synthetic-derived lines showed higher photosynthetic rates than their recurrent parent. Staygreen. determined as days between senescence and physiological maturity, of most synthetic-derived lines did not differ from the recurrent parents. Maximum photosynthetic rate was negatively associated with leaf area and positively associated with stomatal and mesophyll conductances, and leaf temperature depression. Mesophyll conductance accounted for 85% of the variation in maximum photosynthetic rate. These results suggest that synthetic-derived wheat can be also a source of genetic diversity for important physiological traits such as enhanced photosynthetic rate.
TL;DR: In this paper, the effects of burning crop residues on crop yields in the Yaqui Valley have not previously been documented, and alternative practices have not been proposed, and the authors conducted a 5-yr study at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico, to compare the effect of burning with other straw management strategies on wheat and maize yields.
Abstract: In the Yaqui Valley, northwest Mexico, the crop sequence that is becoming more common consists of planting wheat (Triticum aestivum L.) as a winter crop on a raised bed followed by maize (Zea mays L.) as a summer crop. In this area, straw of both winter and summer crops is commonly burned. The consequences of burning crop residues on crop yields in the Yaqui Valley have not previously been documented, and alternative practices have not been proposed. A 5-yr study was conducted at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico, to compare the effects of burning with other straw management strategies on wheat and maize yields. We tested two tillage systems (conventional-tilled bed, CTB, and permanent bed, PB), five straw management treatments (incorporated with CTB and straw as stubble, partly removed, removed, or burned with PB), and seven N treatments, five applied preplant (0, 75, 150, 225, and 300 kg N ha -1 ) and two at the 1st node stage (150 and 300 kg N ha -1 ) of wheat. Maize following wheat received a uniform application of 150 kg N ha -1 . The combination of PB and straw as stubble produced superior maize and wheat grain yields in high-yielding environments; in low-yielding environments, PB-straw burned produced greater wheat grain yields. Nitrogen fertilizer application of 150 and 300 kg N ha -1 at the 1st node stage of wheat increased grain yields compared with preplant N fertilizer applications. Permanent beds combined with retaining all crop residues in the soil as stubble have the potential to increase both wheat and maize yields in the Yaqui Valley.
TL;DR: In this article, four environments with contrasting potential for agricultural productivity and infrastructure development were identified in Guanajuato State, Mexico, to test hypotheses about the relacionship of maize biological diversity to the region's potential for agro-ecological and infrastructural development.
Abstract: Four environments with contrasting potential for agricultural productivity and infrastructure development were identified in Guanajuato State, Mexico, to test hypotheses about the relacionship of maize biological diversity to the region’s potential for agricultural productivity and infrastructure development. Samples of all types of maize grown by a random sample of farmers were collected from each environment. Landraces were the dominant maize class in all four environments; the use of improved varieties was negligible. Several diversity indices were calculated, and no statistically significant differences were apparent between the environments with the most contrasting agroecological and infrastructural conditions. Statistical differences in diversity are apparent when the development of infrastructure interacts with agroecological factors in an environment. Qualitative data suggest that the richness of maize populations may be associated with maize yield potential in a geographical area, whereas the evenness of maize populations may be associated with the presence of infrastructure. These findings suggest further hypotheses about regional patterns of maize diversity.
TL;DR: A theoretical model is developed and applied to the search for disease and pest resistance in ex situ collections of wheat genetic resources, employing actual data on frequency distributions, disease losses, and search costs.
Abstract: A theoretical model is developed and applied to the search for disease and pest resistance in ex situ collections of wheat genetic resources, employing actual data on frequency distributions, disease losses, and search costs. Experiments developed from case studies clarify several misperceptions about the value of gene banks and their utilization by breeders. The observation that wheat breeders “use” gene banks rarely does not imply that marginal accessions have low value. High costs of transferring genes with conventional breeding techniques mean that it may be efficient to store certain categories of genetic resources (such as landraces) “unused” for many years. Copyright 2000, Oxford University Press.
TL;DR: Large, exploitable genotypic variation for tolerance to Zn deficiency in bread wheat is shown, and total amount of Zn per shoot, absolute shoot growth under ZN deficiency, and relative shoot growth can be used as reliable plant parameters for assessing genotypeic variation in tolerance toZn deficiency.
Abstract: A greenhouse experiment was carried out to study severity of the zinc (Zn) deficiency symptoms on leaves, shoot dry weight and shoot content and concentration of Zn in 164 winter type bread wheat genotypes (Triticunt aestivum L.) grown in a Zn‐deficient calcareous soil with (+Zn=10 mg Zn kg−1 soil) and without (‐Zn) Zn supply for 45 days. Tolerance of the genotypes to Zn deficiency was ranked based on the relative shoot growth (Zn efficiency ratio), calculated as the ratio of the shoot dry weight produced under Zn deficiency to that produced under adequate Zn supply. There was a substantial difference in genotypic tolerance to Zn deficiency. Among the 164 genotypes, 108 genotypes had severe visible symptoms of Zn deficiency (whitish‐brown necrotic patches) on leaves, while in 25 genotypes Zn deficiency symptoms were slight or absent, and the remaining genotypes (e.g., 31 genotypes) showed mild deficiency symptoms. Generally, the genotypes with higher tolerance to Zn deficiency originated from Bal...
TL;DR: In this article, the authors provide an overview of Kazakhstan's wheat system following independence and identify policies and constraints currently influencing the operation and development of the system, including current operating environment, intra-sectoral linkages, and overall macroeconomic conditions.
TL;DR: A highly significant correlation observed between the genetic and geographic distances among the populations, provided genetic support for dispersal of the fly from its presumed origin in West Asia to Morocco.
Abstract: The RAPD-PCR technique was used to study genetic variation within and among geographical populations of the Hessian fly, Mayetiola destructor (Say), from Morocco and Syria, associated with the fly's ability to overcome resistance in three wheat cultivars containing H5, H13 and H22 resistance genes. Variation was detected both for the level of susceptibility of the cultivars and RAPD profiles of M. destructor populations. By the use of RAPD-PCR, high genetic variability was detected among individuals and populations of M. destructor within and between areas separated geographically. The DNA fingerprints of populations of M. destructor were area-specific with Nei's measures of genetic distance ranging from 0.156 (between Abda and Beni Mellal, Morocco) to 1.977 (between Marchouch, Morocco and Lattakia, Syria). Cluster analysis of the genetic distances among the populations, identified the Syrian population as an outlier. A highly significant correlation (r = 0.81) observed between the genetic and geographic distances among the populations, provided genetic support for dispersal of the fly from its presumed origin in West Asia to Morocco.
TL;DR: It was hypothesized that, as the relevant resistance genes were successfully pyramided into the germplasm, the distinction between these two mega-environment types would disappear, and the results of the retrospective analyses support this hypothesis.
Abstract: CIMMYT (the International Maize and Wheat Improvement Center) has routinely conducted international wheat yield trials to study the adaptation of spring bread wheat. The first of these, the International Spring Wheat Yield Nursery (ISWYN), was conducted for 31 years from 1964 to 1994 inclusive (30 cycles were conducted as no nursery was distributed in 1993 because of Karnal Bunt). Recently, pattern analysis methods have been developed and a set of computer programs written, which enable retrospective analyses of such historical databases to appraise the relationships among test environments in a way that discriminates among genotypes. Such an analysis was conducted on the 30 years of yield data from ISWYN and the classification derived from these analyses was compared with an agroecological classification of spring wheat test environments derived by CIMMYT. The incidence of foliar diseases (stem rust, leaf rust, yellow rust, Septoria spp. and Fusarium spp.) was important in the distinction between the high-rainfall low-latitude (mega-environment 2) and the high-input-irrigated low-latitude (mega-environment 1) environment types. The accumulation of resistance genes for these diseases has been an objective of the CIMMYT wheat breeding program. It was hypothesized that, as the relevant resistance genes were successfully pyramided into the germplasm, the distinction between these two mega-environment types would disappear. The results of the retrospective analyses support this hypothesis.