SOIL AND PLANT FACTORS ASSOCIATED WITH SUDDEN-DEATH SYNDROME OF SOYBEAN

Sudden death syndrome (SDS) of soybean (Glycine max [L.] Merr.) is a s oilborne disease of increasing importance in high-yield environments. This study was conducted to determine which combinations of soil ferti lity parameters and soybean cyst nematode (Heterodera glycines Ichinoe ) (SCN) second stage juvenile (J2) population levels were associated w ith SDS disease severity. Also, the effect of SDS disease severity on leaf nutrient content and on soybean yield and seed germination were d etermined. These studies were conducted at the Pine Tree Station, in C olt, on a Crowley silt loam (fine, montmorillonitic, thermic Typic Alb aqualfs) over 3 yr with the soybean cultivar Lee 74. Soil factors asso ciated with SDS were increased levels of soil available P, electrical conductivity (soluble salts), organic matter, and exchangeable Na, Ca, and Mg. Decreased levels of leaf N, Mg, Cu, and Mn and increased leve ls of leaf Ca were related to increased levels of SDS severity. Sudden death syndrome severity was negatively correlated with yield in 2 of 3 yr and with seed quality in 1 of 2 yr. Soybean cyst nematode second stage juvenile population density decreased as SDS severity increased in the study relating soil and leaf nutrient levels fo SDS. This may r eflect a decrease in the ability of a diseased root system to support nematode reproduction. In the yield studies, however, SCN was negative ly correlated to yield and positively correlated to SDS in 1 of 2 yr. Soybeans grown in high production environments of increased soil ferti lity and irrigation appear to be more susceptible to SDS. Sudden death syndrome affects yields by a reduction in seed size and number and ma y, under the proper environmental conditions, affect seed germination. The role of SCN in SDS is still unclear.