Abstract
The inheritance of the crooked twig and thorn trait from Flying Dragon (Hiryu) trifoliate orange was studied by utilizing one-year-old seedlings obtained from selfings and crossings of trifoliate orange cultivars and strains, including the Flying Dragon and Citrus plants. The segregation patterns of crooked-type and straight-type seedlings were different in reciprocal crosses: crooked-type seedlings occurred only in progenies from seed parents with cytoplasm inherited from Flying Dragon but not in the progenies from seed parents without that cytoplasm. As straight-type seedlings segregated in the progeny in which crooked-type ones occurred, it was considered that the cytoplasmic and the nuclear genes would play roles in the inheritance of crookedness of twigs and thorns and that a crooked-type seedling occurs when both the cytoplasmic and the nuclear genes are of the crooked-type. The hypothesis regarding the nuclear gene, namely, that the expression of crookedness is controlled by three pairs of complementary genes, Cr1, Cr2 and Cr3, and that the genotype of the Flying Dragon is Cr1cr1Cr2cr2Cr3cr3, was consistent with the observed segregation ratios, except for that in one advanced population of Flying Dragon.
