Gynodioecism in Cucumbers.

HE standard cultivars of cucumbers, Cucumis sativus L., are monoecious. These monoecious plants are male early in development and female later. The standard races exhibit marked differences in the expression of monoecism, ranging from weak to strong male tendency. Available information suggests that these racial differences reflect genetic variations governing rate of sex conversion during plant development ( SHIFRISS 1961 ) . There exists in cucumbers a rare gene which is often associated with complete femaleness ( TKACHENKO 1935), i.e., developmentally persistent gynoecism. Evidence provided by SHIFRISS and GALUN (1956) indicates that this gene does not control gynoecism per se but rather accelerates the rate of sex conversion. This gene was designated Acr ( SHIFRISS 1961 ) . It was postulated that two different gynodioecious races might be synthesized in this species by incorporating Acr into diverse genetic backgrounds. In a race of weak male background the females would be heterogametic, Acr acr females and acr acr monoecious, and in a race of strong male background the monoecious would be heterogametic, Acr Acr females and Acr acr monoecious. In this paper we report on the synthesis and behavior of such races.