SEARCHING FOR TOLERANCE TO WATER-STRESS IN COTTON GENOTYPES - PHOTOSYNTHESIS, STOMATAL CONDUCTANCE AND TRANSPIRATION

Net photosynthetic (PN) and transpiration (E) rates and stomatal conductance (g(s)) were determined in cotton genotypes under drought during the growth cycle. A decrease in P(N), E and g(s) was observed as soil water availability diminished. P(N) appeared closely related to stomatal aperture at low g(s) levels. However, intercellular CO2 concentration was not so much affected by stomatal closure. An important inter- and intra-genotypic variation in g(s) was found at the initial sampling dates. Inter-genotypic variation for P(N) increased with time, probably as a result of a higher capacity for water uptake in some genotypes.