Impacts of heat stress on the photosynthetic apparatus and polen viability in green pepper cultivars (Capsicum annuum L.)

The effect of high temperature stress on photosynthetic apparatus and polen viability between two commercial sweet green pepper cultivars, Stryama and Milkana F-1, was investigated. The first genotype is the father parent of the second, which was developed on the bases of male sterility. During the bud formation and flowering periods, the plants were treated with high temperatures of 40 and 45 degrees C for 2 and 1 h, respectively. Chlorophyll fluorescence, chlorophyll content, pollen germination, flower tube length, and correlation links between the studied parameters were measured. The applied stress increased the initial (Fo) fluorescence in dark-adapted leaves and decreased the maximum (Fm) and variable (Fv) fluorescence. The quantum yield (Fv/Fm) of the PS II also decreased in stressed plants under two temperature treatments, with the highest increase at 45 degrees C for 1 h. Results showed that the contents of chlorophyll in pepper leaves were significantly reduced when exposed to high temperature stress throughout the experiment. The photosynthetic efficiency of cultivar Milkana F-1 revealed a trend towards higher tolerance than cultivar Stryama. The cytological results of the pollen germination and the high percentage of viable pollen showed the presence of heterosis effect in Milkana F-1 1 cultivar in high temperature stress conditions.