AMF species improve yielding potential of Cd stressed pigeonpea plants by modulating sucrose-starch metabolism, nutrients acquisition and soil microbial enzymatic activities

Cadmium (Cd) is one of the most perilous soil contaminants, restricting growth and yielding potential of crop plants. Arbuscular mycorrhizal fungi (AMF) can impart Cd stress tolerance by establishing a mutualistic relationship with host plants. However, selection of the most competent AMF species is required in order to attain maximum benefits. Therefore, the current study was designed to assess the efficacy of four AMF species; Rhizoglomus intraradices (R. int), Claroideoglomus etunicatum (C. etu), Claroideoglomus claroideum (C. cla) and Funneliformis mosseae (F. mos) in imparting tolerance to pigeonpea [Cajanus cajan (L.) Millsp.] plants under Cd (0, 25, 50 mg/kg) stress. Cd accretion hampered growth, nutrients uptake, sugar-starch metabolism and productivity of stressed plants. Mycorrhizal supplementations enhanced growth and yield by reducing Cd uptake and improving carbohydrate synthesis of stressed plants with maximum gains provided by + R. int, closely followed by + F. mos and + C. etu, and least by + C. cla. This could be accredited to their differential colonization (MC) capability (R. int, F. mos, C. etu, and C. cla with 69.85, 60.92, 58.48 and 50.36% respectively, under Cd-50). Higher efficacy of R. int could be linked to maximum glomalin production as well as soil microbial enzyme activities [phosphatases-acidic, alkaline (PHAs), invertase (INV), glucosidase (BGA), protease (PRO)] which, boosted the bioavailability of nutrients (N, P, C) to the stressed plants. Thus, our study suggested that pigeonpea plants were responsive to all the four AMF species, with host-R. int symbiosis exhibiting the strongest potential in alleviating Cd stress.