Wheat (Triticum spp.) is a major staple food crop in many parts of the world in terms of cultivated area and food source. Abiotic stresses such as high temperature and drought are the major factor limiting wheat production worldwide. In major wheat growing areas, terminal drought stress occurs during the grain filling phase when soil moisture is very limited and spring air temperature increases; these factors negatively affect grain filling and might cause a substantial reduction in grain yield. Under such stress, the accumulation of water-soluble carbohydrates (WSC) in the stem and their remobilization to the grain is critical to ensure efficient grain filling and eventually optimal grain size. In this project, our main hypothesis is that wheat genotypes with high levels of WSC in the stem and/or peduncle around anthesis and high WSC remobilization to the developing grains show a corresponding higher tolerance to heat and drought stress during grain-filling stage.

A panel of 25 spring wheat genotypes was evaluated under four environments: dry, hot, irrigated, (Obregon, Mexico) and Mediterranean-rain-fed (Israel). The phenotypic evaluation concentrated on field-stem traits: [Internode diameter (ID), Internode wall width (IWW), solidness, peduncle length (PL) and stem-WSC (SWSC) content from heading to maturity; Yield traits: biomass (BM) at maturity, and thousand-grain weight (TGW); grain yield (GY) and harvest index (HI). Analysis of variance (ANOVA) highlighted both environmental and genotypic impact on stem traits, grain size and yield. Across all environments except heat, SWSC accumulation reached the peak 25 days after heading (DAH) with the highest values under drought and Mediterranean environments. Under heat, increased investment in ID resulted in a higher accumulation of SWSC at 25 DAH.