European Journal of Sustainable Agroecosystems

Background: Sequential heat stress is a major obstacle for barley (Hordeum vulgare L.) production under climate change. Unlike single heat events, repeated heat exposure causes cumulative damage, and, therefore, the development of rapid tools to identify thermotolerant genotypes is needed.
Methods: Three heat stress cycles were utilized on different cultivars and advanced barley cultivars to arrive at research findings through chlorophyll fluorescence imaging process of Fv/Fm, PSII, ETR and NPQ. Different physiological traits were evaluated through biochemical measures such as relative water content, antioxidant enzyme activities, etc.
Results: Genotypes G7 and G9 were able to maintain their photosynthetic efficiency (Fv/Fm > 0.78; ΦPSII > 0.55) during the sequential heat stress because of their high antioxidant activity and heat shock protein expression. On the contrary, better photosynthetic efficiency in the susceptible genotypes decreased progressively and Fv/Fm was less than 0.60 received after the third heat stress cycle. High Fv/Fm value continuously correlated positively with increased grain yield (r = 0.89–0.94; P < 0.001), thus can be used as an early indicator of thermotolerance.
Conclusions: Heat-tolerant varieties of barley maintain photosystem II functionality due to their improved photoprotection and antioxidant defense during frequent heat exposure. Chlorophyll fluorescence imaging is fast, non-invasive and can be used to characterize numerous genotypes rapidly, allowing for heat-resistant germplasm identification.