Molecular confirmation of unidirectional hybridization in Begonia x taipeiensis Peng (Begoniaceae) from Taiwan

Abstract

An unusual Begonia that sheds staminate flowers prematurely at bud stage was collected from several localities in northern Taiwan. Observations on morphology, pollen stainability, and seed set of this species initially suggested a hybrid origin. Morphological comparisons, distribution patterns, chromosome cytology, and experimental hybridization showed that such plants are F1 hybrids (2n = 41) between Begonia formosana (Hayata) Masamune (n = 30) and B. aptera Blume (n = 11), both of which are widespread in Taiwan and sympatric in most of their ranges. These hybrids were named Begonia x taipeiensis Peng. Experimental crosses between the putative parental species consistently resulted in germinable seeds and healthy F1 plants only when B. formosana was used as the female parent. Molecular data obtained from sequences of the atpB-rbcL spacer of chloroplast DNA confirmed that unidirectional hybridization between the putative parents in the wild resulted in the formation of B. x taipeiensis. No natural hybrid populations with a maternal origin from B. aptera have been detected. Abortion caused by a post-pollination barrier occurs when B. aptera was used as a maternal parent. Low pollen fertility of F1 hybrids indicates that the natural hybrid is maintained by recurrent hybridization between the parental species.