SEX DETERMINATION IN ACTINIDIA .1. SEX-LINKED MARKERS AND PROGENY SEX-RATIO IN DIPLOID A-CHINENSIS

First results from two strategies aimed at elucidating the genetics of sex in the dioecious genus Actinidia Lindl. (Actinidiaceae) support t he hypothesis that sex-determining genes are localized in a pair of ch romosomes which, although cytologically indistinguishable, function li ke an XX/XY system with male heterogamety. A. chinensis Planch., a clo se relative of the kiwifruit [A. deliciosa (A. Chev.) CF Liang et AR F erguson], has diploid and tetraploid races. Bulk segregant analysis to find sex-linked markers revealed two markers whose inheritance patter ns in three diploid families showed X and Y linkage and indicated that the male is the heterogametic sex. Some recombination between the mar kers and the sex-determining loci was also demonstrated. Sex ratios in 12 progenies from controlled crosses varied around 1:1, as expected f or an XX/XY system.