Genetic variation in populations of two Mediterranean annual pasture legumes (Biserrula pelecinus L. and Ornithopus compressus L.) and associated rhizobia

Genetic variation between and within populations of Biserrula pelecinus L. (biserrula) and Ornithopus compressus L. (yellow serradella) and associated rhizobia was studied using germplasm collected from sites in central-easte rn and south-eastern Sardinia (Italy). Pods and root-nodule bacteria were c ollected on diagonal transects at each site. Plants were characterised in n ursery rows and the rhizobia were isolated and tested for their effectivene ss. Thirteen morphological traits were recorded and the results were analys ed using cluster analysis. Genetic and phenotypic variation of rhizobia were assessed using DNA analys is (PCR, RAPDs) and effectiveness indices, respectively. Genetic variation based on morphological traits was found between and within sites for both s pecies. Pod characteristics and flowering time were the most important trai ts assisting in discriminating between accessions. Flowering time varied mo re in serradella than in biserrula, particularly at Cantoniera Cannas. Alth ough all rhizobial strains nodulated all accessions of biserrula, great var iability in capacity to fix nitrogen was evident between and within sites. Distinct PCR amplification profiles were generated for individual rhizobial strains, which confirmed the phenotypic variability (effectiveness indices ) of the strains. No relationship was found between host and rhizobia varia tion. The results are discussed in terms of (a) genetic differences for each spec ies within and between sites; (b) differences in behaviour in respect to ge netic variation between biserrula, serradella, and other Mediterranean annu al legumes; and (c) spatial variability and symbiotic effectiveness of rhiz obia.