Effect of Phytophthora Rot on Yield and Chemical Composition of Soybean Seed1

Three cultivars of soybeans (Glycine max (L.) Merr.), ‘Hill,’ ‘Hood,’ and ‘Lee,’ susceptible to phytophthora rot caused by Phytophthora megasperma Drecks. var. sojae Hildeb. and a resistant near‐isogenic line of each cultivat were evaluated for 3 years at three locations in Arkansas. Near‐isogenic lines were derived by crossing each cultivar to ‘Arksoy,’ which is resistant to this disease, and making five backcrosses to the recurrent parent. Yields of these resistant lines did not differ significantly from those produced by susceptible cultivars at Stuttgart where damage from phytophthora rot was negligible. At locations where damage from this disease was moderately severe, yields of Hood and Lee generally were significantly lower than their resistant near‐isogenic lines with yields of Hood reduced more than Lee. Yields of Hill generally were reduced less than other cultivars. Cultivars damaged by phytophthora rot produced seed with lower protein and higher oil content than nearisogenic lines resistant to this disease. Protein and oil content of seed of susceptible cultivars and their resistant near‐isogenic lines did not differ significantly at the location where damage from this disease was negligible.