Affinity between Trifolium alexandrinum and T. apertum—Cytological Investigation in Embryo Rescued Hybrid

Abstract

Interspecific hybrid of Trifolium alexandrinum L. (Egyptian clover or berseem) with T. apertum Bobrov was developed through embryo rescue. Both the species are annual diploids (2n=16). Chromosomal pairing and fertility of F₁ and F₂ generation was studied with a view to understand the phylogenetic relationship of the two species and possibility of recombination between their respective genomes. The parental species showed regular bivalent formation followed by normal disjunction, pollen and seed fertility. Among six F₁ hybrids, Hybrid 19, 20 and A-15-P1 showed multivalent formations at diakinesis while the rest three showed near normal bivalent formation. Pollen fertility among first generation hybrids was substantially high (>90%) except in Hybrid 19, which showed 78.7% pollen fertility. Variation for pollen size was also observed in Hybrids 19 and 20. 88.75 to 98.25% chromosomes contributed in bivalent formation. Among F₂ plants, the meiotic behaviour was near normal and in most of the PMCs, eight bivalent formation was seen. F₂ plants B-26-P1 and B-34-P1, however, showed formation of 0.2 quadrivalent and 0.33 trivalent per PMC respectively. Among other F₂ plants infrequent formation of univalents was seen. In general, the plants showed more bivalents per PMC than that among F₁ plants and 95 to 100% chromosomes associated as bivalents. Pollen fertility among these plants was also more than 95% in majority cases. Fertile F₁ hybrids followed by fertile F₂ generation and absence of segregation for fertility is an indicator that the two species are not differentiated by sizeable differences in their chromosomal/genic constitution and possesses close affinity.