Host range of six diverse Scorpiurus muricatus microsymbionts

The host range of a diverse subset of S. muricatusnodulating Mesorhizobium was tested to determine if a potential inoculant may affect the yield of non-target legumes. No strains nodulated Bituminaria bituminosa, Cicer arietinum, Hedysarum coronarium and Lupin angustifolius, while generally ineffective symbioses were formed with Biserrula pelecinus, Lotus corniculatus, Lotus ornithopodioides and Ornithopus sativus. Therefore, there is the potential for an S. muricatus inoculant to negatively impact the yield of non-target legumes. Six diverse Mesorhizobium strains (WSM1386, WSM4809, WSM4814, WSM4841, WSM4850 and WSM4871) were selected based on their nodulation gene phylogeny, core gene phylogeny and origin of isolation to investigate S. muricatus microsymbiont host range (i.e., the breadth of legumes these organisms can nodulate). These strains were inoculated separately onto eight legumes grown in Australian farming systems (B. pelecinus, B. bituminosa, C. arietinum, H. coronarium, L. corniculatus, L. ornithopodioides, L. angustifolius and O. sativus) in N-depleted glasshouse conditions and assessed for nodulation. All six strains formed pink nodules (indicative of nitrogen fixation) on B. pelecinus and L. corniculatus, four formed pink nodules on L. ornithopodioides, and WSM4871 formed pink nodules whereas WSM1386 and WSM4809 formed white nodules on O. sativus. No strains formed nodules on B. bituminosa, C. arietinum, H. coronarium and L. angustifolius. Only two symbioses were effective, where the inoculated host produced significantly greater SDW than the N-starved control: WSM4809 on L. ornithopodioides and WSM4871 on L. corniculatus. These data suggest S. muricatus microsymbionts will not affect the yield of B. bituminosa, C. arietinum, H. coronarium and L. angustifolius, but may affect B. pelecinus, L. corniculatus, L. ornithopodioides and O. sativus. Therefore, if a highly effective S. muricatus strain is identified, understanding its host range is essential to determine whether it may impact non-target legumes.