Exposure to temperatures ≥30°C during flowering and grain filling stages can negatively affect seed set and seed weight in spring wheat (Triticum aestivum L.). The screening of a large set of germplasm under hot wheat growing environments (Indo‐Gangetic Plain in India) led to the identification of promising heat‐tolerant genotypes. The selected set of 28 diverse spring wheat genotypes were exposed to heat stress (34/16°C day/night temperatures) for 10 d during flowering and for 30 d during grain filling to quantify genetic variability in pollen germination, photosynthesis, and yield parameters under controlled‐environment conditions. Pollen grains collected immediately at anthesis (between 0530 and 0630 h) were incubated on liquid in vitro pollen germination media. Averaged across wheat genotypes, a significant reduction in pollen germination (39.9%, P < 0.001) was recorded from plants exposed to heat stress. Heat stress for 10 d during flowering induced significant reduction in seed number (15.4 and 23.0%) and seed weight (32.3 and 34.6%) on main and primary spikes, respectively, compared with the control. Heat stress during grain filling had a more pronounced impact on seed weight (16 and 22%) than seed number (2.7 and 9.3%) in main and primary spikes, respectively. Genotypes KSG025 and KSG1214 with higher seed number, seed weight, and harvest index and appreciable pollen germination under heat stress were identified as candidate donors for simultaneously enhancing flowering and post‐flowering heat tolerance in spring wheat.

Most high-yielding, semidwarf wheat (Triticum aestivum L.) grown around the world contains either Rht1 or Rht2 genes. The success of these high-yielding cultivars is greatest in the most productive farming environments but provide marginal benefits in less favorable growing conditions such as shallow soils and low-precipitation dryland farming. Further, growing evidence suggests semidwarf genes not only affect early seedling growth but limit grain yield, especially under abiotic stress conditions. There are 23 other reduced-height mutants reported in wheat, most of which have not been functionally characterized. We evaluated these mutants along with their parents for several traits affecting seedling emergence, early seedling growth, and photosynthetic efficiency. Two-to seven-fold differences in coleoptile length, first leaf length, root length, and root angle were observed among the genotypes. Most of the mutations had a positive effect on root length, while the root angle narrowed. Coleoptile and first leaf lengths were strongly correlated with emergence. A specialized deep planting experiment identified Rht5, Rht6, Rht8, and Rht13 with significantly improved seedling emergence compared to the parent. Among the mutants, Rht4, Rht19, and Rht12 ranked highest for photosynthetic traits while Rht9, Rht16, and Rht15 performed best for early seedling growth parameters. Considering all traits collectively, Rht15 showed the most promise for utilization in marginal environments followed by Rht19 and Rht16. These wheat mutants may be useful for deciphering the underlying molecular mechanisms of understudied traits and breeding programs in arid and semiarid regions where deep planting is practiced. | INTRODUCTIONThe incorporation of height reducing genes in both rice (Oryza sativa L.) and wheat semidwarf high-yielding cultivars were instrumental to the "Green Revolution." These high-yielding, semidwarf wheat cultivars are resistant to lodging and have a high grain yield (due to increased productive tillers and biomass) in response to nitrogen fertilizer and water applications.Together, improved genetics and agronomic management greatly increased grain yields during the 1960s, enabling autonomous wheat production in several developing countries including those in Latin America and Asia (Casebow et al., 2016;Gale & Youssefian, 1985). High-yielding, semidwarf cultivars contain the mutant form of reduced-height (Rht) gene Rht1/Rht2 (Rht-B1b/Rht-D1b), incorporated from the Japanese dwarf wheat "Norin10." These genes were cloned and mapped to homoeologous group 4 (4BS/4DS) chromosomes and encodes a DELLA domain protein negatively regulating the gibberellin-based growth response in plants (Borojevic & Borojevic, 2005;Peng et al., 1999). Since their introduction into wheat, these genes have been extensively utilized in wheat breeding Amita Mohan and Nathan P. Grant equally contributed to this study.

Heat Shock Protein 101 (HSP101), the homolog of Caseinolytic Protease B (CLPB) proteins, has functional conservation across species to play roles in heat acclimation and plant development. In wheat, several TaHSP101/CLPB genes were identified, but have not been comprehensively characterized. Given the complexity of a polyploid genome with its phenomena of homoeologous expression bias, detailed analysis on the whole TaCLPB family members is important to understand the genetic basis of heat tolerance in hexaploid wheat. In this study, a genome-wide analysis revealed thirteen members of TaCLPB gene family and their expression patterns in various tissues, developmental stages, and stress conditions. Detailed characterization of TaCLPB gene and protein structures suggested potential variations of the sub-cellular localization and their functional regulations. We revealed homoeologous specific variations among TaCLPB gene copies that have not been reported earlier. A study of the Chromosome 1 TaCLPB in four wheat genotypes demonstrated unique patterns of the homoeologous gene expression under moderate and extreme heat treatments. The results give insight into the strategies to improve heat tolerance by targeting one or some of the TaCLPB genes in wheat.

Short-statured plants revolutionized agriculture during the 1960s due to their ability to resist lodging, increased their response to fertilizers, and improved partitioning of assimilates which led to yield gains. Of more than 21 reduced-height (Rht) genes reported in wheat, only three—Rht-B1b, Rht-D1b, and Rht8—were extensively used in wheat breeding programs. The remaining reduced height mutants have not been utilized in breeding programs due to the lack of characterization. In the present study, we determined the inheritance of Rht18 and developed a genetic linkage map of the region containing Rht18. The height distribution of the F2 population was skewed towards the mutant parent, indicating that the dwarf allele (Rht18) is semi-dominant over the tall allele (rht18). Rht18 was mapped on chromosome 6A between markers barc146 and cfd190 with a genetic distance of 26.2 and 17.3 cM, respectively. In addition to plant height, agronomically important traits, like awns and tiller numbers, were also studied in the bi-parental population. Although the average tiller number was very similar in both parents, the F2 population displayed a normal distribution for tiller number with the majority of plants having phenotype similar to the parents. Transgressive segregation was observed for plant height and tiller number in F2 population. This study enabled us to select a semi-dwarf line with superior agronomic characteristics that could be utilized in a breeding program. The identification of SSRs associated with Rht18 may improve breeders’ effectiveness in selecting desired semi-dwarf lines for developing new wheat cultivars.

The wheat reduced height genes (Rht) played an important role in "The Green Revolution" by reducing damage due to lodging and making wheat more responsive to fertilizer applications. The successful use of cultivars containing Rht-B1b and Rht-D1b around the world compelled the scientist to identify and generate height mutants through induced mutation in wheat. There are manyRht genes known in wheat, however genetic and molecular characterization of many Rht genes are lacking. The Rht3 gene was originally found in the cultivar, Tom Thumb, and resulted in 46% reduction in plant height compared to the wild type allele, rht3. The objectives of our investigation were to identify SSR markers linked to Rht3 and to develop a genetic linkage map of the region containing the Rht3 gene. The Rht3 gene was located on chromosome 4B using bulked segregant analysis. Genetic linkage mapping using an F2 population placed Rht3 between markers wmc125 and gwm149 with a genetic distance of 14.4 cM and 23.6 cM, respectively. Identification of SSR markers associated with Rht3 may help breeders to more efficient screen for reduced height genes in breeding programs with diverse environmental conditions.