Studies on the cytoplasmic-genic male sterility in acid citrus

This study was focused on the certification of genetic control of male sterility in ten-year-old acid citrus seedlings derived from various cross combinations and the early selection of male sterile hybrid seedlings with RAPD markers. The results of study carried out for three years were as follows. It was found that (1) the male sterility was controlled by independent three genes ms1, ms2 and ms3 that are recessive, (2)additive gene effect was recognized among three genes : ms1 and ms2 are complementary genes and ms3 is a dominant gene with epistasis effect for ms1 and ms2. (3)Amazingly, genotypes of citrus cultivars used in the present study were heterozygous for the ms genes. (4)Cytoplasm of Sudachi had a factor to restore the male sterility in the progenies. Precocious flowering in 3- to 5-month-old hybrid seedlings from crosses with Yuzu, Hanayu, Kabosu and Sudachi was observed. Monoembryonic and male sterile HY-16, which was derived from Hanayu x Yuzu, was produced precocious hybrid seedlings with high frequencies (6% for HY16 x Yuzu and 16% for HY16 x Foster Pink grapefruit). In these seedlings, male sterile and fertile seedlings segregated 5 : 3 for HY16 x Yuzu and 1: 1 for HY16 x Foster Pink grapefruit, suggesting the estimated male sterility genotypes for HY16 and Yuzu were correct. Based on these results, genotypes of 12 citrus cultivars were determined. Furthermore, RAPD markers linked to ms genes were studies with a bulk method and analyzed with about 100 random primers. One RAPD marker as to CMN-A10 primer was found to link to ms1 gene with a distance of 6.3 cM. The cytological observation of anther development in male sterile seedlings indicated that microsporogenesis were inhibited before and after meiosis.