Flowering in wheat (Triticum aestivum L.) is highly sensitive to heat stress. Eleven spring wheat genotypes were exposed to heat stress (34/16°C, day/night temperature) during flowering to investigate the impact on time of day of flowering, seed set, grain yield, and quality under controlled environment chambers. In general, all 11 wheat genotypes recorded peak flowering during cooler hours of the day (i.e. either early in the morning or late in the evening). The trend was more pronounced under heat stress, providing first evidence of an alternative mechanism (i.e. heat escape in wheat minimizing damage during flowering). On average, significant reduction in net CO2 assimilation (17%), starch (25%), and protein content in grain (21%), seed set (7–19%), kernel weight (11–15%), and grain yield (22–38%), but with 17% increase in flag leaves proline concentration, was recorded under heat stress over control. The negative impact of heat stress on seed set was greater among the primary spikes than for the main spike. This differential impact is mainly attributed to limited plasticity of early reproductive processes such as gametogenesis to escape heat stress, unlike heat escape phenomena observed at flowering. KSG1203 and KSG41 exhibited heat escape strategy, whereas KSG1194 emerged as a true heat‐tolerant line. Systematic characterization of time of day of flowering to introduce the heat escape trait and developing heat tolerance strategies for early reproductive stages in ongoing wheat breeding programs is an ideal strategy to minimize heat stress damage.

The predicted increase in global temperatures will increase the probability of exposing sorghum [Sorghum bicolor (L.) Moench] to heat stress during critical reproductive developmental stages, such as flowering and post‐flowering periods. Greenhouse and field studies were conducted to quantify the impact of heat stress on pollen germination and other post‐flowering physiological processes affecting grain yield. Pollen collected from 24 diverse sorghum genotypes grown under greenhouse conditions were tested for their tolerance to heat stress. Using the same set of genotypes, field‐based heat tents were used to impose heat stress from booting stage to maturity. Pollen grains from field experiments were tested under three different types of heat stress combinations to identify genotypes with pollen having true heat tolerance. Heat stress induced a significant reduction in grain yield (16–73%), pollen germination (2–95%), photosynthesis (0.5–50%), and photochemical efficiency of photosystem II (1–8%) and increased thylakoid membrane damage (2–27%) compared with control conditions. Reduced grain yield with heat stress exposure was not compensated by grain weight increase. In vitro pollen germination revealed SC155 to possess true heat‐tolerant pollen, even under severe stress exposure. Macia and BTx378 recorded higher relative grain yield and pollen germination, providing opportunities for mapping genomic regions responsible for heat tolerance using currently available biparental mapping populations in RTx430 and BTx623 backgrounds, respectively.

Using existing protocols, RNA extracted from seeds rich in starch often results in poor quality RNA, making it inappropriate for downstream applications. Though some methods are proposed for extracting RNA from plant tissue rich in starch and other polysaccharides, they invariably yield less and poor quality RNA. In order to obtain high yield and quality RNA from seeds and other plant tissues including roots a modified SDS-LiCl method was compared with existing methods, including TRIZOL kit (Invitrogen), Plant RNeasy mini kit (Qiagen), Furtado (2014) method, and CTAB-LiCl method. Modifications in the extraction buffer and solutions used for RNA precipitation resulted in a robust method for extracting RNA in seeds and roots, where extracting quality RNA is challenging. The modified SDS-LiCl method revealed intense RNA bands through gel electrophoresis and a nanodrop spectrophotometer detected ratios of ≥ 2 and 1.8 for A260/A230 and A260/A280, respectively. The absence of starch co-precipitation during RNA extraction resulted in enhanced yield and quality of RNA with RIN values of 7–9, quantified using a bioanalyzer. The high-quality RNA obtained was demonstrated to be suitable for downstream applications, such as cDNA synthesis, gene amplification, and RT-qPCR. The method was also effective in extracting RNA from seeds of other cereals including field-grown sorghum and corn. The modified SDS-LiCl method is a robust and highly reproducible RNA extraction method for plant tissues rich in starch and other secondary metabolites. The modified SDS-LiCl method successfully extracted high yield and quality RNA from mature, developing, and germinated seeds, leaves, and roots exposed to different abiotic stresses.

Drought affected rice areas are predicted to double by the end of this century, demanding greater tolerance in widely adapted mega-varieties. Progress on incorporating better drought tolerance has been slow due to lack of appropriate phenotyping protocols. Furthermore, existing protocols do not consider the effect of drought and heat interactions, especially during the critical flowering stage, which could lead to false conclusion about drought tolerance. Screening germplasm and mapping-populations to identify quantitative trait loci (QTL)/candidate genes for drought tolerance is usually conducted in hot dry seasons where water supply can be controlled. Hence, results from dry season drought screening in the field could be confounded by heat stress, either directly on heat sensitive processes such as pollination or indirectly by raising tissue temperature through reducing transpirational cooling under water deficit conditions. Drought-tolerant entries or drought-responsive candidate genes/QTL identified from germplasm highly susceptible to heat stress during anthesis/flowering have to be interpreted with caution. During drought screening, germplasm tolerant to water stress but highly susceptible to heat stress has to be excluded during dry and hot season screening. Responses to drought and heat stress in rice are compared and results from field and controlled environment experiments studying drought and heat tolerance and their interaction are discussed.

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.