Hybridization in the genus Vigna savi

Rashid, Kamaludin A (1988) Hybridization in the genus Vigna savi. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The effect of using a large range of parental genotypes of Vigna radiata, V. mungo, V. umbellata and V. angularis in production of interspecific hybrids was investigated. Cross-compatibility between these four Vigna species was also investigated and identified. These four species can cross reciprocally even though several isolating mechanisms operate between them. Pollen tube studies showed that there were no pre-fertilization barriers operating between these species. However, the isolating mechanisms which seem to be operating between these species are zygote mortality and hybrid inviability which are due to abnormal embryo development (post-fertilization barriers). It was observed that reciprocal differences are found in most interspecific crosses for the relative success of pod set, embryo abortion, in vitro and in vivo embryo development and in seedling lethality. Cytoplasmic differentiation appears to be a major factor in speciation among these Asiatic Vigna species. Fertility of the interspecific hybrids, later generations, the amphidiploids and the triploid plants produced were investigated cytologically. Meiotic behaviour of the parents and the hybrids indicates the homology between these species. The amphidiploids obtained in the present investigation had increased pollen fertility. The increase of pollen stainability from 14.7% in F₁ to 87.5% in C₅ generation indicate a probable high level of homologous chromosome pairing in meiosis. A comparative study of early embryo development of these Vigna species was undertaken. It shows that embryo and endosperm development in each parental species are normal but in the crosses generally, the embryo does not develop normally and finally aborts. This was due to the disharmonious interaction between embryo, endosperm and maternal tissues. Growth regulators were applied to prevent early embryo abortion and to encourage pod development before any attempts were made to culture the embryo. Embryo culture techniques were useful in rescuing the embryos before they were aborted. The first successful triploid plants produced between V. radiata and V. umbellata in this investigation will open the way for hexaploid levels for those crosses which are otherwise incompatible at the diploid level.