Effect of benomyl-mediated mycorrhizal association on the salinity tolerance of male and monoecious mulberry clones

Mulberry is an economically important crop for sericulture in China. Mulberry plantations are shifting inland, where they face high salinity. Arbuscular mycorrhizal fungi (AMF) reportedly enhance mulberry's tolerance to salinity. Here, we assessed if additional adaptive advantages against salinity are provided by sex differences beyond those provided by mycorrhizal symbiosis. In a pot experiment, male and monoecious plants were exposed to three salinity regimes (0, 50, and 200 mM NaCl) and two mycorrhiza-suppressed conditions (with or without benomyl application) for more than 16 months. We noticed that salinity alone significantly decreased the mycorrhizal colonization rate, salinity tolerance, K+ concentrations, and the ionic ratios of all plants. Mycorrhizal association mildly ameliorated the salt-induced detrimental effects, especially for monoecious plants, and sex-specific responses were observed. Meanwhile, both sexes had adopted different strategies to enhance their salinity resistance. Briefly, mycorrhizal monoecious plants exhibited a higher net photosynthetic rate and lower translocation of Na+ from root to shoot compared with mycorrhizal males under saline conditions. Their salt tolerance was probably due to the Ca2+/Na+ in roots. In comparison, male plants exhibited lower Na+ acquisition, more Na+ translocated from root to shoot, higher root biomass allocation, and higher N concentrations under harsh saline conditions, and their salt tolerance was mainly related to the K+/Na+ in their shoots. In conclusion, our results highlight that AMF could be a promising candidate for improving plant performance under highest salinity, especially for monoecious plants. Cultivators must be mindful of applying fungicides, such as benomyl, in saline areas.