Abstract
Selection for leaf protoplasmic drought tolerance in Upland cotton was done using the release of inorganic phosphorous (P1) as a criterion of membrane damage and acid phosphatase activity increase. This screening methods can be used after either polyethylene glycol 600 (PEG) osmotic treatment, or heat treatment (50ºC) of leaf discs and it can be applied in a recurrent selection programme for drought resistance. Heritability of PED P1 release was 38% with a genetic gain of 12.5% for the second selection cycle and 11.9% for the third. Heritability of heat treatment P1 release was 30% with a genetic gain of 9.4 and 8.9% for the second and third cycles, respectively.
