Phosphorus efficient pastures: variation in mycorrhizal colonisation of subterranean clover

Trifolium subterraneum (subterranean clover) is an important annual pasture legume in southern Australia. Development of more phosphorus (P)-efficient cultivars could improve the P balance of pastures. Subterranean clover hosts arbuscular mycorrhizal fungi (AMF). In glasshouse studies, AMF can enhance P uptake by subterranean clover. To examine whether subterranean clover cultivars differ in their levels of colonisation by AMF, a core collection of subterranean clover (97 lines, representing ~80% of genetic diversity in the species), and 42 cultivars were grown in a glasshouse in a low-P sandy soil with indigenous AMF. The soil was free of root diseases. The percentage of root length colonised by AMF, specific root length, average root diameter, shoot P concentration and shoot dry mass were measured. Variation in colonisation within the core and among the cultivars was similar, ~12-68% of root length. However, 41% of the core lines had > 40% of root length colonised compared with 24% of the cultivars. There was a positive linear correlation between colonisation level and shoot P concentration (r2=0.36, P<0.0001), but not shoot dry mass. Relationships between colonisation level and specific root length or average root diameter were weak. We conclude that potential may exist to develop subterranean clover lines with higher or lower colonisation by AMF. However, the benefits of doing so must first be established under field conditions.