Relative Effect of Vesicular-Arbuscular Mycorrhizal Fungi on the Growth and Yield of Soybeans†

The growth and yield response of greenhouse-grown soybean plants to colonization by 19 isolates (including 6 Glomus and 3 Gigaspora species) of vesicular-arbuscular mycorrhizal fungi is reported. Each isolate was evaluated in a high (169 kg/ha Bray-I P₂O₅) and a low (50 kg/ha Bray-I P₂O₅) fertility soil. Colonization by most Glomus isolates significantly increased plant top dry weight and seed yields, and of these isolates most produced larger increases in dry weight in the low fertility soil. Colonization by five of the Gigaspora isolates did not significantly affect top dry weight and seed yield in the high or Iow fertility soil. The value of comparative testing of species is discussed.