Germplasm characterization of Sesbania accessions based on isozyme analyses

Twenty-two accessions belonging to seven species of Sesbania Scop. (S. emerus, S. exasperata, S. grandiflora, S. rostrata, S. sesban, S. tetrapteraand S. virgata), were evaluated in order to characterize the isozyme electrophoretic patterns and to estimate their genetic variability and outcrossing rates. Eight isozyme systems were used: acid phosphatase (ACP), isocitrate dehydrogenase (IDH), phosphoglucomutase (PGM), malate dehydrogenase (MDH), phosphoglucoisomerase (PGI), glutamate oxaloacetate transaminase (GOT), peroxidase (PRX) and catalase (CAT), with two gel/electrode buffers and distilled water as the extraction buffer. Cotyledons were chosen for enzyme extraction. The accessions were compared considering the presence/absence of bands for each system. A dendrogram was obtained using the Jaccard similarity index and the UPGMA clustering method, classifying the accessions into eight groups, evidencing both inter- and intraspecific variability. Annual species were classified in one major group separate from the perennials (S. grandiflora, S. sesban, S. virgata), which were allocated into two other main groups. S. virgata accessions (subgenus Daubentonia) were clearly separated from the other species. Isozyme banding patterns for the accessions are presented for each system. A high incidence of intraspecific monomorphism was observed. Interpretation in terms of loci and alleles was made for S. sesbanand S. virgataaccessions, which presented polymorphism for the systems PGI, GOT (S. sesban) and MDH (S. virgata). The average expected heterozygosity estimates varied from 0.0 to 0.231 for S. sesban and 0.0 to 0.20 for S. virgata. A mean number of 2.0 alleles per locus was observed for both species. Population multilocus outcrossing rate (t_m) of 0.62 was estimated for S. sesban, indicating a partial allogamy mode of reproduction. Individual families presented multilocus rates varying from 0.00 to 1.00, indicating both self-pollination and cross-pollination.