RELATIONSHIP BETWEEN TOLERANCE TO PHYTOPHTHORA ROT AND SOYBEAN YIELD

Phytophthora rot is a major soybean disease in the Eastern US corn bel t. The objective of this experiment was to determine the genetic relat ionship between tolerance to phytophthora rot and agronomic traits mea sured in environments where the disease was not a factor. A set of 66 random lines from a broad-based population was evaluated for agronomic traits in seven field environments and for tolerance in greenhouse te sts. Pairs of resistant and susceptible isolines were used to determin e whether phytophthora rot was present in the field environments. The phenotypic correlation between tolerance and yield in five environment s where phytophthora was negligible was non-significant (r = -0.09). T here was a positive correlation between tolerance and seed weight (r = 0.31) and a negative correlation between tolerance and plant height ( r = -0.25). None of these correlations is large enough to hinder devel opment of agronomically acceptable, tolerant cultivars.