Vesicular–arbuscular mycorrhizal (Glomus fasciculatum) influence on soybean drought tolerance in high phosphorus soil

Abstract

Vesicular-arbuscular mycorrhizal fungi (VAM) may enhance growth of nonirrigated soybean (Glycine max (L.) Merr.) by improving host drought tolerance. The purpose of this study was to determine growth and yield response of drought-stressed soybean to infection by the mycorrhizal endophyte Glomus fasciculatum. Plants were grown in the greenhouse in Kennebec silt loam soil (fine silty, mixed, mesic, Cumulic Hapludoll). The treatments included the presence or absence of both G. fasciculatum and drought stress, arranged in a 2 .times. 2 factorial design (12 replications). To create stress treatments, water was withheld for 9 d during the pod elongation stage, and half of the plants were harvested immediately after the stress period and half at physiological seed maturity. Plants harvested immediately after stress (51 d after emergence) had significant reduction in mycorrhizal infection and soybean nodulation. The root-to-shoot ratio of stressed plants inoculated with VAM decreased 24% compared with noninoculated plants, indicating enhanced host drought tolerance by G. fasciculatum. Total seed weight of stressed plants increased 10% when infected with VAM as a result of reduced pod abortion. Significant G. fasciculatum .times. drought stress interactions were found for total seed weight, pod number, seed number, and root-to-shoot ratio, showing that G. fasciculatum had a more positive effect on drought-stressed compared with control plants. Transpiration rates during the stress period were similar for infected and noninfected plants. Enhanced yield of infected plants may have been the result of improved P nutrition or more extensive soil water extraction. The results of this experiment show potential benefits of VAM colonization in soybean in arid and semiarid regions.