No abstract

Increasing temperatures can severely affect wheat (Triticum aestivum L.) production, particularly when it coincides with the grain-filling period. Heat stress induces rapid senescence resulting in early maturity and shortened grain-filling period. In this study, the applicability of in vivo chlorophyll fluorescence (Chl-F) and chlorophyll index to track rate of senescence in flag leaves and spikes exposed to heat stress were investigated. Seven winter wheat varieties were exposed to post-flowering heat stress using growth chambers [35/15 • C (heat stress) and 25/15 • C (control) day/night] and unique field-based heat tents (imposed +6 • C higher than ambient). Effective quantum yield of photosystem II (PSII) (QY) was recorded temporally in flag leaves and spikes, and compared with in vitro chlorophyll-a (Chl-a) concentration and non-invasive estimation of chlorophyll and flavonoids index. Time point indicating the start of senescence (changepoint, CP) for QY was advanced by 0-8 and 0-6 d in flag leaves and spikes, respectively, under heat stress. In the chamber experiment, sustained heat stress induced accelerated decline of QY, particularly in wheat cultivars Larry and WB4458. Stronger positive relationship between days to senescence in spikes and thousand kernel weight indicated an extended period of assimilate supply from sink compared to the source tissue, during grain filling. Capturing heat stressinduced changes in photosynthetic pigments and QY at high temporal frequency presents an effective phenotyping approach for testing genetic diversity in largescale field experiments involving different crops.

Summary Increasing populations and temperatures are expected to escalate food demands beyond production capacities, and the development of maize lines with better performance under heat stress is desirable. Here, we report that constitutive ectopic expression of a heterologous glutaredoxin S17 from Arabidopsis thaliana (AtGRXS17) can provide thermotolerance in maize through enhanced chaperone activity and modulation of heat stress‐associated gene expression. The thermotolerant maize lines had increased protection against protein damage and yielded a sixfold increase in grain production in comparison to the non‐transgenic counterparts under heat stress field conditions. The maize lines also displayed thermotolerance in the reproductive stages, resulting in improved pollen germination and the higher fidelity of fertilized ovules under heat stress conditions. Our results present a robust and simple strategy for meeting rising yield demands in maize and, possibly, other crop species in a warming global environment.

Despite the ability of sorghum [Sorghum bicolor (L.) Moench] to withstand harsh environmental conditions, it is susceptible to water-deficit stress during grain filling. To identify post-flowering drought tolerant sorghum genotypes, parents of nested association mapping populations were evaluated under controlled and water-deficit conditions in greenhouse and field conditions. In both experiments, water-deficit stress was imposed by withholding water during the grain-filling period.In field experiments, rootzone soil moisture was measured weekly using a neutron probe to quantify the plant available water under well-watered and water-deficit conditions. Investigations were focused on determining the variability in the grain-filling pattern across different positions within the panicles (intra-panicle) of 11 different sorghum genotypes. Water-deficit conditions characterized by low plant available water had a consistently negative association with grain number along different positions in the panicle. Our findings indicate that maintaining grain numbers per panicle under post-flowering water deficit is more important than increasing individual grain weight. Among the tested genotypes, SC35 and SC1103 were most tolerant to water-deficit conditions under greenhouse and field conditions, respectively. Currently available biparental populations, developed using these genotypes, provide an opportunity to enhance tolerance to post-flowering water-deficit stress in sorghum.