Inheritance of the An2 Gene and Epistatic Interactions in Petunia exserta × P. axillaris Hybrids

ADDITIONAL INDEX WORDS. flavonoids, flower color, anthocyanins ABSTRACT. A regulatory gene, An2, controls structural genes within the flavonoid biosynthetic pathway. The inheritance of An2 expression in crosses between P. axillaris (an2) and P. exserta (An2 + ) was studied. Floral pigmentation was quantitatively inherited and involved the expression of a single regulatory gene (An2) and three structural genes (Hf1, An6 and Fl). White flowers were produced in an2 - genotypes; while pigmented flowers were produced in An2 + genotypes. The intensity of pigmentation was determined by the interaction of An2 with An6, Hf1 and Fl, as well as substrate competition between the An6 and Fl encoded enzymes. magenta (Munsell 7.6RP 4.9/13.6) of the P. integrifolia parent. Mather and Edwardes (1943) concluded that there must be at least a two gene difference between P. axillaris and P. integrifolia; however, segregation ratios did not fit any known inheritance pattern. The authors suggested the distortion in segregation resulted from the action of polygenes. Another explanation for the distortion in the segregation ratios could be in the meiotic pairing between these species. If pairing is not normal, segregation ratios are distorted (Jackson, 1991). Several observations suggest this is occurring in P. axillaris x P. integrifolia hybrids. First, the hybrid can only be made with P. axillaris as the female parent (Mather, 1943). Second, meiotic abnormalities (univalents, laggards, unequal chromatid distribu- tion, etc.) can be seen in the F1 interspecific hybrid (Steere, 1932). This paper describes the inheritance of the An2 regulatory gene in crosses between P. axillaris and P. exserta Stehmann. Petunia exserta is a newly described species with red flowers that is closely related to P. axillaris (Stehmann, 1987). Both species are in the same taxonomic section of the genus; therefore, chromosome pairing is expected to be normal in the interspecific hybrids.

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