Heat stress in food legumes: evaluation of membrane thermostability methodology and use of infra-red thermometry

Heat tolerance in 45 chickpea, lentil, and faba bean genotypes was investigated during 2007/2008 and 2008/2009 at Alexandria Agriculture Research Station, Alexandria, Egypt, using screening methods employing the membrane thermostability technique. Threshold temperature to be used in screening for heat tolerance at germination was also investigated for each crop. Temperatures, responsible for 50% germination were 40, 33.5, and 29°C for chickpea, faba bean, and lentil, respectively. Germination percent under high temperature varied significantly (P ≤ 0.05) amongst genotypes. Germination percentage ranged from 4.8 to 71.6, 39.2 to 90.0, and 4.8 to 68.6, in chickpea, lentil, and faba bean, respectively. Differences were significant (P ≤ 0.05) among faba bean and chickpea genotypes. Membrane relative injury (RI%) showed significant (P ≤ 0.05) variability among the genotypes and ranged from 10.57 to 58, 5.2 to 61.7, and 15.7 to 52.7 in chickpea, lentil, and faba bean, respectively. Canopy temperature was measured to evaluate heat avoidance in tested genotypes. Infra-red thermometry was used to measure canopy temperature and the gradient of canopy to ambient air temperature (∆T_C-A) in moisture stressed and unstressed treatments. Canopy temperature, leaf water potential (LWP) and leaf water content were affected by the level of soil moisture. Genotypes were able to bring their canopy temperatures to levels lower than ambient air temperatures but the differences were not significant. A heat stress index (HSI) were computed relating the ∆T_C-A in moisture stressed to unstressed treatments. Regression of leaf water potential (LWP) and the heat stress index (HSI) was significant (P ≤ 0.05) in faba bean genotypes in the stressful environment. The results of the present investigation emphasize the efficiency of membrane thermostability technique in selection for heat tolerance in early stages of growth in food legumes.