Cross-host compatibility of commercial rhizobial strains for new and existing pasture legume cultivars in south-eastern Australia

Abstract

Perennial legumes have potential to increase pasture productivity in the high rainfall zone (600–850 mm) of south-eastern Australia through their ability to use summer rainfall and fix nitrogen (N2). Various perennial legumes are being evaluated for this environment; however, little information exists on legume–rhizobia cross-host compatibility and its consequences for biological N2 fixation. This is especially important when legumes are sown into fields with a background of competitive rhizobia such as WSM1325 or sown as a pasture mix with different host–symbiont pairs. We studied the effectiveness and cross-host compatibility of five commercial rhizobial strains for a range of pasture legumes (nine species, 18 cultivars) under controlled environment conditions, and further evaluated nodule occupancy and competitiveness of a newly established pasture (13 species, 20 cultivars) in the field, by determining nodulation and production (biomass and N2 fixation). Three of the commercial inoculant strains formed root nodules with multiple legume species; commonly however, less N2 was fixed in cases where the inoculant was not the recommended strain for the legume species. Within a legume species, cultivars could differ in their ability to form effective root nodules with multiple rhizobial strains. White clover cvv. Trophy, Haifa and Storm, strawberry clover cv. Palestine, and Talish clover cv. Permatas formed effective nodules with both TA1 and WSM1325 rhizobial strains. White clover cultivars that could not form an effective symbiosis with the common background strain WSM1325 fixed less N2. The white clover × Caucasian clover hybrid formed effective symbiosis with strain TA1 but not with other commercial strains. Some species such as birdsfoot trefoil, Talish clover, sulfur clover and tetraploid Caucasian clover formed ineffective symbiosis in the field. Until resolved, this will likely inhibit their further development as pasture plants for similar permanent pasture environments.

Legume persistence for grasslands in tableland environments of south-eastern Australia

“…A detailed sampling of the Mandurama site in the first year was used to determine relative differences in N 2 fixation between species and is reported in Rigg et al . (2021).…”

“…The persistence of birdsfoot trefoil was poor at all sites, including those in Series 2, even though the breeding line evaluated was developed specifically for the types of environments commonly found across tableland regions in southern Australia (Real et al 2012). Sainfoin and sulfur clover were evaluated at only a small number of sites in the present study, owing to low availability of seed, and sainfoin was sown without rhizobial inoculation (Rigg et al 2021). Both species were previously identified as species of interest for Australian agriculture (Li et al 2008); however, the data in the present study were inadequate to draw firm conclusions.…”

“…In subsequent years, measures of aboveground biomass were generally taken at ~12-week intervals with sites either grazed by livestock following sampling or mown if livestock were not available. A detailed sampling of the Mandurama site in the first year was used to determine relative differences in N 2 fixation between species and is reported in Rigg et al (2021).…”

“…Persistence of Haifa is often reported as variable (Caradus and Woodfield 1997) but is improved with higher stolon densities, reduced stocking rate (or no grazing) and increased rainfall (Roberts 1987). In a sampling of the Mandurama site (Series 3) in the establishment year, Rigg et al (2021) demonstrated that many of the nodules in the perennial clovers were inhabited by Group C-like rhizobia rather than the Group B strain used to inoculate the seed. They further demonstrated that, under controlled environment conditions, Haifa white clover formed effective symbiosis with the Group C strain, in contrast to all other white clover cultivars, for which efficacy was reduced with the Group C strain relative to Group B.…”

Strawberry clover (Trifolium fragiferum): current status and future role in Australian agriculture

“…trifolii strain TA1 (Group B) (Drew et al 2012). In studies by Rigg et al (2021), strawberry clover cv. Palestine formed effective nodules with both TA1 and WSM1325 (Group C) rhizobial strains, but formed ineffective symbioses with rhizobial strains used for other perennial legumes.…”