Conversion and determination of sex in Vitis vinifera L. (sylvestris)

Sex conversion in the male V. vinifera (sylvestris) clone 030-44 could not be attributed to germinal mutation of the major gene for sex. The differences in sex expression among male seedling vines can best be explained on the basis of an undetermined number of minor modifying genes able to shift a very sensitive threshold. The frequency of sex conversion within a given seedling vine was greatly influenced by environmental, both local and seasonal, conditions. The following facts were established in Vitis vinifera L. (sylvestris): (1) the male sex is heterogametic and is inherited as a simple Mendelian factor, maleness being completely dominant;(2) homozygous males are as viable as heterozygous males, they are phenotypically alike and can only be identified by breeding tests;(3) pure and hermaphroditic males are genetically alike as far as the major gene for sex is concerned;(4) sex chromosomes are not differentiated, either morphologically or physiologically.A pair of alleles, SuF and Sum, were used to explain the results obtained on selfing the hermaphroditic male clone 030-44. The gene SuF determines maleness and its allele Sum in homozygous condition determines femaleness. The gene SuF is completely dominant over its allele Sum. The genotypes of the homozygous and heterozygous males are SuF SuF and SuF Sum respectively, and that of the female is Sum Sum. The evolution of cultivated V. vinifera hermaphrodites in the light of present results is discussed