Sex expression and breeding strategy in Commelina benghalensis L.

ABSTRACT

This paper describes the results of a series of experiments conducted to unravel the patterns of sex expression and reproductive output in a fascinating species with high variation in sexuality. Commelina benghalensis L., an andromonoecious rainy season weed, bears male and bisexual fl owers in axillary spathes of all the plants investigated. Bisexual fl owers are of two types; chasmogamous (CH) and cleistogamous (CL). The former are borne on subaerial and the latter on subterranean shoots, in addition to those on aerial spathes. Three populations of the species, designated JU1, JU2 and JU3, were scanned for three consecutive years from 1996 to 1998, and the number and distribution of male, CH and CL fl owers per plant were found to vary. The mere number of CH/CL fl owers per plant is by itself not an accurate measure of mixed mating. It is necessary to confi rm that CH fl owers actually outcross and, if they do so, to what extent. Comparison of the pollen/ovule (P/O) ratio and percentage pollen germination on the stigmas of the CH and CL fl owers have been used as indices of the pollination system. Confi rmation of this was sought from the fruit and seed sets obtained after manual pollination of emasculated fl owers with self- and cross-pollen. Results so obtained were compared with those of natural pollination. In the majority of CH fl owers, the male and female reproductive phases (i.e. anther dehiscence and stigma receptivity) overlap, providing for self-pollination. However, two exceptions to this general behaviour were found in some plants of all the three populations. In some CH fl owers, the female phase matures prior to anther dehiscence while in others, the anthers are sterile. Such plants, designated as variants 1 and 2, respectively, facilitate cross-pollination. While the CL fl owers contribute to the production of selfed progeny, the variants of CH ones permit formation of outcrossed progeny, indicating a mixed mating strategy in C. benghalensis.