A differential capacity of arbuscular mycorrhizal fungal colonization under well-watered conditions and its relationship with drought stress mitigation in unimproved vs. improved soybean genotypes

Abstract

Modern breeding programs may cause a reduction in plant responsiveness to arbuscular mycorrhizal (AM) fungi. In this study, we tested the hypothesis that responses such as higher arbuscule formation and mycorrhizal dependency (MD) in unimproved soybean genotypes than in improved genotypes is related to drought stress tolerance caused by enhanced growth parameters and oxidative stress regulation. Firstly, four unimproved and four improved soybean genotypes were compared under well-watered conditions. After 20 days, all of the unimproved soybean genotypes showed increased arbuscule formation, as well as a positive and higher MD index in foliar mineral nutrient and growth parameters compared with the four improved genotypes. Secondly, tolerance to drought stress was evaluated in the two improved soybean genotypes and the two unimproved genotypes selected for the most contrasting response to arbuscule formation under well-watered conditions. After 20 days of 30% of field capacity, arbuscule formation was higher in the unimproved than improved genotypes. Mycorrhizal dependency evaluated as leaf area as well as shoot and root dry mass were highest in the unimproved AM genotypes. Moreover, levels of malondiadehide were lower and proline was higher in the unimproved rather than the improved genotypes. The potential capacity of arbuscule formation is discussed as a selection criterion to identify improved soybean genotypes with increased efficiency under well-watered conditions and an enhanced capacity to relieve drought stress.