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-eastern and south-eastern Sardinia (Italy). Pods and root-nodule bacteria were collected on diagonal transects at each site. Plants were characterised in nursery rows and the rhizobia were isolated and tested for their effectiveness. Thirteen morphological traits were recorded and the results were analysed using cluster analysis. Genetic and phenotypic variation of rhizobia were assessed using DNA analysis (PCR, RAPDs) and effectiveness indices, respectively. Genetic variation based on morphological traits was found between and within sites for both species. Pod characteristics and flowering time were the most important traits assisting in discriminating between accessions. Flowering time varied more in serradella than in biserrula, particularly at Cantoniera Cannas. Although all rhizobial strains nodulated all accessions of biserrula, great variability 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 variation. The results are discussed in terms of (a) genetic differences for each species within and between sites; (b) differences in behaviour in respect to genetic variation between biserrula, serradella, and other Mediterranean annual legumes; and (c) spatial variability and symbiotic effectiveness of rhizobia

Hardseededness and the pattern of softening in Biserrula pelecinus L., Ornithopus compressus L., and Trifolium subterraneum L. seeds

Experiments measuring seed bank size, hardseededness, and seed softening of biserrula (Biserrula pelecinus L.) were conducted at Merredin and Perth in Western Australia. At Merredin, a mixture of 2 biserrula accessions was grazed, shallow cultivated, or left uncultivated and ungrazed. Seed bank size, seedling regeneration, and seed softening were measured over 2 years. At Perth, softening of biserrula, yellow serradella, and subterranean clover seeds grown at 2 sites (Binnu and Northam) was compared on the soil surface and after burial at 2 and 10 cm over a period of 2 years. Seed bank size of biserrula at Merredin ranged from 14 000 to 17 500 seeds/m 2. Regeneration was greater in the second year (800-1 700 seedlings/m 2) than in the first year (40-600 seedlings/m 2). In both years the shallow cultivated treatment recorded the highest number of seedlings. About 90% of biserrula and serradella seed remained hard after 2 years on the soil surface, compared with only about 10% of subterranean clover. Serradella softened more rapidly when buried 2 cm below the soil surface (8-12% hard) than it did on the soil surface (84-92% hard) (P <0.05). In contrast, the softening of subterranean clover decreased with increasing depth. Biserrula was intermediate, although it too softened most rapidly at 2 cm (78-95% hard compared with 82-97% on the surface) (P < 0.05). Rate of seed softening in all species decreased with increasing depth of burial below 2 cm. Of the 4 accessions of biserrula, an accession from Greece (83% hard after 2 years exposure) was significantly softer than the other accessions. The results indicate that biserrula is very hardseeded, although there is sufficient variation in hardseededness for the selection of somewhat softer lines. Its pattern of softening suggests that biserrula may be successful in the ley farming system (crop/pasture rotations) of southern Australia