HORMONAL CONTROL OF SEX EXPRESSION IN BUFFALO GOURD (CUCURBITA FOETIDISSIMA HBK.).

Abstract

Seven field experiments and two in-vitro studies were performed to elucidate hormonal control of staminate flowering in gynoecious and monoecious buffalo gourd (Cucurbita foetidissima HBK.) sex types. Objectives included development of techniques effecting staminate induction on gynoecious phenotypes which normally produce abortive stamenless male buds. Natural and synthetic growth regulants shown to modify sex expression in other cucurbits were surveyed for their masculinizing potential. Several compounds exogenously-applied to apical meristems elicited changes in shoot morphology. However, only aminoethoxyvinylglycine (AVG, an ethylene synthesis inhibitor) effected staminate induction on gynoecious segregates. Growth rate, patterns of female flowering or ontogeny of stamenless buds differentiated prior to treatment were not influenced by AVG. AVG was applied at various dosages (0-500 ppm) and produced male buds on all replicates treated at levels of 125 ppm or higher. The mean number of staminate buds induced varied linearly with dosage and averaged from 0-7.5 male flowers/shoot. A control model for staminate induction mediated by endogenous ethylene was advanced and potential benefits of this phenomenon to breeding efforts and/or to hybrid seed production were discussed. Ethephon (an ethylene releasing compound) was applied at various dosages to monoecious plants in anticipation of simulating the gynoecious phenotype. Although morphological changes were evident (i.e. reduction in shoot growth rate and floral initiation, increase in floral bud abortion and tissue senescence), ethephon failed to reduce staminate flowering or increase differentiation of antherless buds as expected. Dosage levels employed and/or confounding environmental factors may have contributed to the lack of staminate inhibition. During in-vitro studies, indirect evidence for ethylene-mediated control of male flowering was obtained by staminate proliferation in buds of gynoecious explants treated with silver nitrate (an inhibitor of ethylene action) and by formation of stamenless buds on monoecious explants treated with ethephon. However, low levels of floral induction under culture conditions employed rendered these results inconclusive. An incidental study of segregation ratios among AVG-facilitated self- and cross-pollination progeny upheld the supposition for monogenic inheritance of gynoecy in buffalo gourd.