Effect of short-term heat stress prior to flowering and early grain set on the grain yield of wheat

Abstract

Short periods of heat stress in spring under Mediterranean climate can have large effects on crop yields. Most studies on heat stress have focused on crop responses to extended periods of high temperature under controlled environment conditions. There is limited information on the effects of short periods of heat stress on the yield of wheat. Therefore, field and controlled environment studies were undertaken to determine the effects of short-term heat stress on flag leaf senescence, as well as grain yield and its components. Wheat genotypes were exposed to heat stress for a single-day at two different stages: (H1) near flowering or green anther stage and (H2) early grain set or 7-10 days after anthesis (DAA) in 2009 and 2010. Heat treatment was applied in the field in a portable purpose-built heat chamber in which the temperature was steadily increased to a maximum of 35°C, which was maintained for 3h before being allowed to steadily decrease to the ambient temperature, like a typical spring heat event. Similar to the field studies, wheat genotypes were also exposed to a single-day heat event (35°C maximum) in the controlled environment (CE) study. This single-day heat stress event caused a significant reduction in grain yield and yield components in both years. Heat stress (H1 or H2) accelerated the rate of loss of flag leaf chlorophyll content. A higher rate of senescence in 2009, which was warmer and drier than 2010, was associated with greater yield loss. Reduction in grain yield among the genotypes was negatively correlated (r=-0.79; p<0.001) with the rate of flag leaf senescence. Heat stress reduced post-heading duration and grain yield across genotypes and heat stress treatments was strongly correlated (r=0.80; p<0.001 in 2009 and r=0.82; p<0.001 in 2010) with post-heading duration. There was also a significant (p<0.001) positive correlation between wheat grain yield and grain number m-2 (2009: r=0.79 and 2010: r=0.70) and wheat grain yield and individual grain mass (IGM) at harvest (r=0.70 in 2009 and r=0.82 in 2010). Standardized partial regression coefficient (b) showed that of the two yield components the contribution of grain number (b=0.786) to the grain yield was higher than IGM (b=0.435) in 2009. In contrast, IGM (b=0.665) appeared to be a stronger contributor to the grain yield than grain number (b=0.443) in 2010. Grain yield loss of different wheat genotypes was strongly correlated (r=0.91; p<0.001) between the field and CE. The results of these studies showed that under field and CE conditions, Janz was consistently the most sensitive genotype to heat stress. In contrast, CM9-6Y, CM9-4Y and Krichauff appeared to be most tolerant to heat stress. Averaged over the two growing seasons and heat stress treatments, the reduction in grain yield was greater in Janz (25%) than in CM9-6Y and CM9-4Y (13% each), followed by Krichauff (16%) and Excalibur (18%). It could be suggested that early headed wheat genotypes with slower rate of leaf senescence after heat exposure and longer post-heading duration could be more tolerant to heat stress. © 2014 Elsevier B.V.