R. G. Sears

Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl92 (heat-susceptible), were crossed to produce F1, F2, and F3populations, and their grain-filling duration (GFD) at 30/25 °C 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F1 and F2 populations followed the normal model (χ2, p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritability of 80%, and realized heritability of 96%for GFD were determined from F2 and F3 populations. Products from 59primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 andXgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F2 population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F2population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars.

Genotypic differences in utilization of assimilate sources during maturation of wheat under chronic heat and heat shock stresses

Heat stress from chronic, prolonged exposure up to 32 °C or heat shock from brief exposure to 33 °C and above alters the source of assimilates for grain growth of wheat (Triticum asetivum L.). Our objectives were to identify genotypes that resist chronic heat stress and heat shock and to determine the relative contributions of photosynthesis and stem reserves to grain filling under both conditions. Twenty-eight genotypes were grown in controlled enviroments at 20/15 and 30/25 °C day/night in light and darkness during maturation in the first experiment, and six genotypes were grown in light at the same temperatures and at 40/35 °C followed by 20/15 or 30/25 °C in the second experimnet. Heat susceptibility indices (HSI) were calculated from grain yields of the genotypes in both experiments. The ratio of chlorophyll variable fluorescence to maximum fluorescence (Fv/Fm), a measure of the stability of photosynthesis, and carbohydrate reserves in the stems were measured in the second experiment. Photosynthesis provided 63 and 65% of assimilates in the grain at 20/15 and 30/25 °C, respectively, but both stable photosynthesis in some genotypes and high content of reserves in other genotypes were associated with low susceptibility to stress. The Fv/Fm ratio was decreased by heat shock and returned to normal values intolerant genotypes when the treatment was followed by 20/15 °C but not 30/25 °C. Grain yield was highly correlated among 20/15, 30/25, and 40/35 °C followed by 20/15 °C treatments, suggesting that similar plant traits were involved. We conclude that assimilates from either stable photosynthesis or high reserve levels provided for high grain yields during heat stress. Combining the two traits could improve heat tolerance of wheat but might not be feasible if other traits are impeded.

Transfer of Hessian fly resistance from ‘Chaupon’ rye to hexaploid wheat via a 2BS/2RL wheat-rye chromosome translocation

SummaryFour wheat-rye lines derived from a cross between hexaploid wheat ‘ND 7532’ and ‘Chaupon’ rye were homogeneous for resistance to biotype L of the Hessian fly,Mayetiola destructor. Because the wheat parent was susceptible and the rye parent was resistant to larval feeding, resistance was derived from rye. Resistance of ‘Chaupon’ and the wheat-rye lines was expressed as larval antibiosis. First-instar larvae died after feeding on plants. Chromosomal analyses using C- and N-banding techniques were performed on plants of each line to identify genomes and structural changes of chromosomes. Results showed that two of the resistant lines were chromosome addition lines carrying either the complete rye chromosome,2R, or only the long arm of2R. The other two resistant lines were identified as being2BS/ 2RL wheat-rye translocation lines. It was concluded, therefore, that the long arm of rye chromosome2R carries a gene or gene complex that conditions antibiosis to Hessian fly larvae and, in the2BS/2RL translocation lines, this rye chromatin is cytologically stable and can be used directly in wheat breeding programs.

Growth and senescence characteristics associated with tolerance of wheat-alien amphiploids to high temperature under controlled conditions

Tolerance of wheat (Triticum aestivumL.) to high temperature might be improved by introducing alien genes from amphiploids. Our objectives were to determine responses of synthetic hexaploid and octaploid amphiploid wheats to high temperature and evaluate their potential usefulness for developing improved cultivars. Thirty synthetic hexaploids from durum wheat (T. turgidum L.) × Aegilops tauschii Cos. Accessions and four octaploid amphiploids from Chinese Spring wheat × different grasses were grown at 20/15 and 30/25 °C day/night during maturation. Tolerance was ascertained by two measures of senescence, leaf chlorophyll content and grain filling duration, plus grain yield and its components. Leaf chlorophyll was measured after 10 and 15 days of treatment, and grain yield was determined at maturity to calculate the heat susceptibility index(HSI), a gauge of the reduction in yield at high temperature of each line relative to all other lines. Chlorophyll content, grain filling duration, yield, and kernel weight were highly negatively correlated with HIS of the hexaploid amphiploids at30/25 °C, but grain yield was positively correlated with HSI at20/15 °C. The hexaploid lines might be useful for improving wheat for regions where stress from high temperature occurs frequently. Chlorophyll content and grain filling duration also were highly negatively correlated with HSI of the octaploid lines, but they would be less directly useful for improving wheat because the kernel number was reduced greatly due to unbalanced meiotic chromosomal segregation.

Success stories: breeding for wheat disease resistance in Kansas.

the development, release, and adoption of wheat cultivars with resistance to important wheat diseases. As a result of the annual disease survey and estimation of losses, the impact that resistant cultivars had on disease losses could be quantified. This paper describes the use of genetic resistance in wheat for control of diseases and related yield effects in Kansas during the past 25 to 30

Wheat Genetics Resource Center: The First 25 Years

The Wheat Genetics Resource Center, a pioneering center without walls, has served the wheat genetics community for 25 years. The Wheat Genetics Resource Center (WGRC) assembled a working collection of over 11,000 wild wheat relatives and cytogenetic stocks for conservation and use in wheat genome analysis and crop improvement. Over 30,000 samples from the WGRC collection of wheat wild relatives, cytogenetic stocks, and improved germplasm have been distributed to scientists in 45 countries and 39 states in the United States. The WGRC and collaborators have developed standard karyotypes of 26 species of the Triticum / Aegilops complex, rye, and some perennial genera of the Triticeae. They have developed over 800 cytogenetic stocks including addition, substitution, and deletion lines. The anchor karyotypes, technical innovations, and associated cytogenetic stocks are a part of the basic tool kit of every wheat geneticist. They have cytogenetically characterized over six‐dozen wheat–alien introgression lines. The WGRC has released 47 improved germplasm lines incorporating over 50 novel genes against pathogens and pests; some genes have been deployed in agriculture. The WGRC hosted over three‐dozen scientists especially from developing countries for advanced training. The WGRC was engaged in international agriculture through several collaborating projects. Particularly noteworthy was the collaborative project with Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) on the production of synthetic wheats. It is estimated that “by the year 2003–2004, 26% of all new advanced lines made available through CIMMYT screening nurseries to cooperators for either irrigated or semi‐arid conditions were synthetic derivatives.” The WGRC is applying genomics tools to further expedite the use of exotic germplasm in wheat crop improvement.

Performance of wheat variety blends in Kansas

This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright 1980 Kansas State University Agricultural Experiment Station and Cooperative Extension Service.

Use of winter wheat x Triticum tauschii backcross populations for germplasm evaluation.

The wild diploid goatgrass, Triticum tauschii (Coss.) Schmal., is an important source of genes for resistance to both diseases and insects in common wheat (Triticum aestivum L.) We have evaluated grain yield, kernel weight, protein concentration, and kernel hardness of 641 BC2 F1-derived families from direct crosses involving four T. aestivum cultivars and 13 T. tauschii accessions over 2 years and at two Kansas, USA, locations. On average, T. tauschii germplasm depressed grain yield and increased protein concentration, whereas kernel weight was affected either positively or negatively, depending on the T. tauschii parent. Three T. tauschii parents produced a large proportion of families with very soft endosperm. Some variation among progeny of different T. tauschii parents resulted from the segregation of genes for resistance to leaf rust (caused by Puccinia recondita Rob. ex Desm.). This study confirmed that random BC2-derived families can be used to evaluate the effects of T. tauschii genes in the field. This methodology, although laborious, can provide useful information which is not obtainable by the screening of T. tauschii accessions themselves.

The Current Status of Chromosome Analysis in Wheat

The first definitive observations on the morphology (size and arm-ratio) of the chromosomes of common wheat (2n=67×=42) were made on monosomic laggard chromosomes at anaphase I or telophase II of meiosis of the 21 different monosomics (Morrison, 1953; Sears, 1954). These observations allowed the cytogenetic identifications of chromosomes 1B and 6B (satellited but with different arm ratios) and chromosome 5B, being highly heterobrachial with the longest long arm of the whole chromosome complement. The remaining chromosomes were not distinctive enough to be identified in somatic cells from the morphological data.

Heterotic effects of wheat-rye chromosomal translocations on agronomic traits of hybrid wheat (Triticum aestivum L.) under an adequate moisture regime

Translocated chromosomes T1BL⋅1RS and T1AL⋅1RS have been widely used in many wheat (Triticum aestivum L.) breeding programs to develop high yielding cultivars. The objective of this study was to evaluate the heterotic effects of T1BL⋅1RS + T1AL⋅1RS, T1BL⋅1RS, and T1AL⋅1RS on yield and yield components of hybrid wheat grown under adequate moisture regimes. Thirteen hybrid wheats and seven parents with different chromosome constitutions relative to T1AL⋅1RS and T1BL⋅1RS were evaluated in a randomized complete block design. Variable performance was observed among the hybrids tested. Two of the three hybrids with T1BL⋅1RS + T1AL⋅1RS, produced 25.26% and 44.64% more grain than the hybrids with only T1BL⋅1RS. This was due to increased biomass, harvest index (HI) and spike density. However, the combination of these two translocations resulted in reduced kernels/spike, spikelets/spike and spike length compared to the T1BL⋅1R Stranslocation alone. When comparing closely related parents, the parent with T1AL⋅1RS produced 23.51% more grain yield than the non-translocated parent. The presence of T1AL⋅1RS resulted in 10.37% heterotic advantage for yield due to increased biomass, KW, and spike density. When the two wheat-rye translocated chromosomes are present in the same hybrid, T1AL⋅1RS seems to have a positive effect on yield through spike density and HI, but masks the effects of T1BL⋅1RS for some agronomic traits.