Genotypic variations in chlorophyll fluorescence and stomatal conductance of cocoa in relation to drought tolerance

Abstract

Cocoa plants are susceptible to environmental conditions, especially temperature and drought. The chlorophyll fluorescence and stomatal characteristics indicated the high adaptation of cocoa leaves to under-storey conditions. The present study was carried out to access the level of drought tolerance in newly introduced genotypes of cocoa. In general, the chlorophyll fluorescence indices and stomatal conductance were significantly decreased during stress period as compared to non-stress period. There were significant variations in these parameters among different genotypes. Similarly, the leaf water potential was also reduced and showed genotypic variations. The results based on cluster analysis indicated existence of 11 groups, based on Rescaled Value Distance (Euclidian distance 5). Among the cocoa clones, AMZ-10/A, AMZ-12 and AM-3/9 were most susceptible to drought. The most tolerant genotypes based on the difference in physiological variables and rank sums were in group 2, which included RIM-189, RIM-2, RB-49, RB-47 and JA-1/19. The results indicated genetic variability in cocoa in response to drought stress.