Hybridity, polyploidy and change in breeding system in a Ruellia hybrid

Abstract

Ruellia tweediana and R. tuberosa are large flowered chasmogamous diploids (n=17) with normal meiosis and fertility. F 1 hybrids, successful in only one direction (R. tweediana x R. tuberosa), are vegetatively vigorous and possess 17 often heteromorphic bivalents with high degree of segregational irregularities. It is exclusively cleistogamous and completely pollen and seed sterile. Like F 1, the artificial amphidiploid (n=34) is also cleistogamous but shows preferential chromosome pairing with complete restoration of fertility. The parental chromosomes are sufficiently differentiated and cleistogamy is either genie or due to gene-cytoplasm interaction but sterility is entirely chromosomal. All floral parts excepting calyx are highly deformed. Such a deformity is associated with sterility in the F 1 but with fertility in the amphidiploid. This is perhaps the first case of origin by hybridization of a true breeding and fully fertile cleistogamous taxon from two chasmogamous species. It also shows the extent and nature of change in breeding system brought about by hybridization and/or polyploidy. The chromosome numbers in the six, out of 16, obligate cleistogamous taxa (Table 4) show that they are high polyploids. Perhaps their origin has been in the same manner as in the present case.