Isozyme markers in cotton breeding 1. Standardization of different isozymesystems for identification of different cultivars of cotton (Gossypium hirsutum)

Isozyme peroxidase (Pox), shikimic dehydrogenase (Sdh), superoxide-dismutas e (Sod), esterase (Est), phosphoglucaisomerase (Pgi) and catalase (Cat) wer e standardised for different varieties of cotton (Gossypium hirsutum) and o ne variety of G. arboreum using stacking and resolving polyacrlyamide gel e lectrophoresis (PAGE). Isozymes were extracted in different buffers using f resh leaves collected from different cotton cultivars growing in the field. Isozyme shikimate dehydrogenase and esterase have been studied in differen t varieties of G, hirsutum in addition to the remaining isozymes which have been reported only for G. arboreum and G. herbaceum. The objectives of the study were to standardize different isozyme systems for G. hirsutum variet ies using material collected from field, identification of an isozyme syste m through which inter and intravarietal differences and genetic changes occ urring in the plant growing under stress condition can be detected, and det ection of a polymorphic locus which can be correlated with the stress preva iling in the area (s) of cotton cultivation. Electrophoretic profiles of is ozymes showed generally monomorphic patterns for isozymes esterase and supe roxide dismutase and thus detected minor inter and/or intravarietal differe nces. The remaining isozyme systems appeared polymorphic and differentiated different plants of a variety and different varieties from each other. Mos t of the isozymes appeared to be controlled by one or two loci except perox idase for which 7 different loci were identified. Possibilities of using th e observed isozyme polymorphism in persuing the prescribed objectives are d iscussed.