Comparative salinity tolerance of symbiotically dependent and nitrogen-fed pigeonpea (Cajanus cajan) and its wild relative Atylosia platycarpa

Summary

Once symbiosis between the pigeonpea cultivar ICPL 227 and the Rhizobium sp. strain IC 3024 is established, it is efficient in fixing N₂ under saline conditions and can support growth comparable to N-fed plants in growth media with up to 6 dS m^-1 salinity. However, the early stages of establishment of the pigeonpea-IC 3024 symbiotic system have proved sensitive to salinity. The present study showed that the number of nodules was markedly reduced at 8 dS m^-1 salinity; however, nodule development and functioning were not affected by salinity in the pigeonpea-IC 3024 symbiosis. The symbiotic system of Atylosia platycarpa and Rhizobium sp. strain IC 3087 was established successfully even at 12 dS m^-1 and supported growth comparable to that of N-fed plants. P levels in leaves were increased under saline conditions in N-fed and N₂-fixing pigeonpea and A. platycarpa. There were no consistent differences in the leaf Na and chloride levels between N-fed and N₂-fixing plants of pigeonpea and A. platycarpa. The present study suggests that the rhizobial symbiosis may not be a necessary factor for initial screening of pigeonpea and related wild species for salinity tolerance.