LABILE SEX EXPRESSION IN ANDROMONOECIOUS SOLANUM-HIRTUM - FLORAL DEVELOPMENT AND SEX DETERMINATION

Sex expression (the proportions of hermaphrodite and staminate flowers produced) of the andromonoecious species Solanum hirtum is labile, and this lability of whole plant sex expression is due to labile sex expression of individual floral buds. In this paper I examine the developmental processes that underlie the differences in floral sex expression of hermaphrodite and staminate flowers of Solanum hirtum, focusing particularly on the processes responsible for the observed lability of floral sex expression. Differences in bud growth rate and relative growth of floral organs in these buds are evident at about the time of megasporocyte meiosis (11-12 days before anthesis). However, gynoecial sterility in staminate buds does not occur until just 6-7 days before anthesis. At this time, abnormalities in ovule development occur in staminate buds: the ovules begin to appear necrotic, the integumentary tapetum collapses, and the megagametophytes of many ovules cease normal development. These observations are consistent with the predictions of labile floral development.