Interactive Effects of Soybean Cyst Nematode, Arbuscular-Mycorrhizal Fungi, and Soil pH on Chlorophyll Content and Plant Growth of Soybean

Nutritional deficiency chlorosis, especially iron-deficiency chlorosis, and the soybean cyst nematode (SCN) limit soybean yield. Arbuscular mycorrhizal fungi (MF) generally have beneficial effects on plant growth. The interactive effects of SCN, MF, and soil pH on leaf chlorophyll content (LCC) and growth of soybean were examined in a greenhouse experiment. The experiment was a randomized complete block design with three factors: SCN population densities, MF inoculation, and soil pH levels. SCN reduced LCC, and the effect increased with increasing time during 5 to 9 weeks after planting, especially in the high-pH (pH 8) soil. MF increased LCC in low-pH (pH 5.6) soil regardless of SCN population density and in the high-pH soil without SCN. However, MF reduced LCC if both pH and SCN population density were high. The high-SCN population density (inoculation with 10,000 eggs per 100 cm³ of soil) reduced soybean shoot weight in all soils regardless of MF. MF increased shoot weight at pH 6.9 and pH 8 but not at pH 5.6. When MF was present, shoot weight was generally highest at pH 6.9. At high SCN when MF was absent, plant growth was better in pH 5.6 than pH 6.9 and pH 8 soils. This study demonstrates that SCN causes greater damage to soybean when interacting with high pH, and MF had a beneficial effect on soybean growth regardless of SCN infection in all pH soils, in spite of the negative effect of MF on LCC at approximately 5 to 9 weeks after planting in high-pH soil at high SCN population density.