Effect of Two Species of Arbuscular-Mycorrhizal Fungi on Vegetative Growth and Phosphorous Uptake of Mexican Lime Rootstock (Citrus aurantifolia) Under Drought Stress Conditions

Mycorrhizal fungi can preserve plant against environmental stresses, such as drought, by symbiosis with host plant. A greenhouse experiment was conducted as factorial in completely randomized design with four replications. The objectives of this experiment were evaluation of effect of two species of arbuscular-mycorrhiza (AM) fungi and three different levels of drought stress (Non-stress, mild stress and severe stress) on root colonization, plant growth parameters (leaf, shoot and root dry weight, plant height, basal stem diameter and leaf number per plant), mycorrhizal dependency, leaf chlorophyll content and leaf P concentration of Citrus aurantifolia rootstock in agriculture research station of Darab, Iran, in 2009-2010. Results showed that all measured parameters were negatively affected by drought stress. The negative effect of drought on plant root were greater than those of plant shoot. However, shoot and root dry weights of citrus plant colonized by two species of AM fungi were significantly higher than those of NM plants at all of moisture levels. A similar trend was observed for other plant growth parameters under drought conditions. Both species of AM fungi improved phosphorous (P) nutrition uptake of the host plant under drought stress. The observed decline in beneficial effects of mycorrhizal colonization with increasing drought stress was attributed to the significant decrease in root colonization. It was concluded that AM colonization, particularly G. mosseae, improved drought tolerance of citrus rootstock and compensated, in part, for the deleterious effect of drought stress.