[Two complementary dominant genes controlling apomixis in genus Citrus and poncirus]

Apomixis is very common in Citrus genus and its related genus. Two monoembryonic tangerine varieties (C. reticulata Blanco) Clementine and Wilking were used as seed parents to cross with four polyembryonic orange varieties [C. sinensis (L.) Osbeck]. Both sexual and apomictic progenies were found in each F1 population with different segregation ratios. In a total of 74 Wilking progenies, 23 were monoembryonic and 51 polyembryonic and the ratio of sexual and apomictic progenies was about 1:2 tested either in each individual cross or in the whole Wilking cross combionations. In Clementine progenies, 84 were monoembryonic and 71 polyembryonic and the ratio was about 1:1 tested either in each individual cross or in the whole Clementine cross combionations. According to the results together with other data published, a possible apomixis controlling mechanism was proposed, which involves two complementary dominant genes named as A1 and A2 that control apomixis in genus Citrus and Poncirus. Trees of genotype A1-A2-, except for homozygous of dominant gene A1 (which is lethal), can produce apomixis seeds. And those of other genotypes will produce sexual seeds. The segregation and recombination of these two genes accorded with Mendel's genetic laws. The proposed mechanism could explain genotypes controlling polyembryony-monoembryony existing both in nature species and artificial hybridization progenies as well as most of the known hybridization results.