EFFECTS OF DROUGHT STRESS ON GROWTH RESPONSE IN CORN, SUDAN GRASS, AND BIG BLUESTEM TO GLOMUS ETUNICATUM.

The responses of mycorrhizal corn (Zea mays L.), sudan grass [Sorghum vulgare (Piper) Hitch.], and big bluestem (Andropogon gerardii Vitman) under drought stress were compared. Although growth of each of the plant species benefited from the mycorrhizal fungus under adequately watered conditions, inoculation had no effect on the growth of corn or sudan grass when cyclic drought stress was imposed on these plants. In contrast, growth of mycorrhizal big bluestem was significantly greater than non-mycorrhizal big bluestem, even under severe drought stress. Drought-stressed mycorrhizal plants without phosphorus amendment were not larger than drought-stressed, non-inoculated, fertilized (15 mg kg p) plants, suggesting no increased drought tolerance. The ability of Glomus etunicatum Becker & Hall to benefit plant growth under drought stress was apparently plant-mediated and possibly related to the dependency of the plant on this mycorrhizal fungus. Under adequately watered conditions, inoculated corn and sudan grass were respectively 1.23 and 1.13 times larger than non-inoculated plants, while inoculated big bluestem was 6.56-fold larger than non-inoculated control plants.