Gas exchange-yield relationships of malting barley genotypes treated with fungicides and biostimulants

Abstract Optimization between photosynthetic carbon assimilation and stomatal water loss is the key in order to breed crops for future climate. We analyzed stomatal conductance (gs), CO 2 assimilation rate (Anet), fungal diseases, grain yield and yield components of seven European malting barley genotypes treated with fungicides alone or together with biostimulants in the field over three consecutive seasons. Stomatal conductance, net assimilation rate and grain yield were affected by genotype, treatment and year. We then examined which of these traits are most strongly correlated with yield. Grain yields ranged between 6000-8300 kg ha −1 in 2015 and 2017, but only 3500–6000 kg ha −1 in 2016 due to hotter and drier weather. The benefits of treatments with fungicides or fungicides together with biostimulants were greater in 2016, when the treatments increased yields by 20–21% on average, compared to 0–11% in 2015 and 2017. In 2016, gs and Anet were correlated with grain yield, indicating that in hotter and drier than average season maintaining higher transpiration and photosynthesis resulted in higher yield. In 2015 and 2017, average values of instantaneous gs and Anet were not significantly correlated with grain yield. Pooling all years, longer pre-heading period, higher grain numbers per ha and per ear, larger 1000-kernel weight and higher water use efficiency were associated with higher grain yield, whereas a negative correlation was detected between grain yield and the number of ears per area. Thus, developing fewer productive tillers per area, but more and heavier grains per ear led to higher grain yield. Major barley fungal pathogens had a negative effect on grain yield via shortening of grain filling period.