Chlorophyll <em>a</em> Fluorescence as an Indicator of Temperature Stress in Four Diverse Cotton Cultivars (<em>Gossypium hirsutum</em> L.)

Heat stress has a detrimental effect on cotton (Gossypium hirsutum L.) production worldwide. The reproductive stage is especially vulnerable to heat stress, which will result in significant yield losses. Chlorophyll a fluorescence (ChlF) induction kinetics was used to investigate the heat tolerance of four cotton cultivars. Cultivars Arkot 9704, VH260, DP393, and DP 210 B2RF were subjected to 30°C and 40°C heat treatments. Plants were grown for 46 days up to the pinhead square stage whereafter plants were subjected to the two temperature regimes for a period of 6 hours. Decreases in the maximum quantum yield of PSII (Fv/Fm) and the performance indexes (PIABS and PITOTAL) reflected the negative impact of elevated temperature on photosynthesis in all four cultivars. In cultivar DP393 the lowest drop in values for Fv/Fm, PIABS, and PITOTAL, showed the genetic capacity of this cultivar to cope with heat stress. Cultivars VH260, DP210 and to a lesser extent Arkot 9704 were adversely affected by heat stress. Chlorophyll a fluorescence measurements and the interpretation of the functions within the chlorophyll transient proved to be a fast and accurate method of identifying heat-tolerant cotton cultivars