Identity and pathogenicity of fungi associated with root and crown rot of soft red winter wheat grown on the upper coastal plain land resource area of Mississippi

Seedling stand, disease severity and fungal incidence were determined from untreated 'Wakefield' soft red winter wheat planted on a Leeper silty clay loam in field tests conducted at the Mississippi Agricultural and Forestry Experiment Station, Plant Science Research Center, Mississippi State Univer sity, Starkville, Mississippi during the 1996-97 and 1997-98 growing season s. Seedling stand was reduced by 40% each year in plots established with un treated seed. Cochliobolus sativus was the most frequently isolated fungus. Fusarium acuminatum, Fusarium eguiseti and Fusarium solani were the most p revalent Fusarium spp. Seven other Fusarium spp. and 23 species of other fu ngal genera were isolated. Pathogenicity tests with three isolates each of C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, F usarium compactum, Embellisia chlamydospora and Microdochium bolleyi were p erformed in test tube culture and two isolates each of C. sativus C. spicif er, F. acuminatum, E. chlamydospora and M. bolleyi under greenhouse conditi ons. In test tubes and in the greenhouse, seedlings infected with isolates of C. sativus developed seedling blight, discoloration and necrosis, primar ily in seminal roots and crowns. In the greenhouse, C. sativus induced lesi ons on the lower leaf sheath and reduced seedling height, seedling emergenc e, dry and fresh weight of roots and shoots. Isolates of F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora and M, bolleyi induced slight to moderate orange to light-brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer isolates had the most pre-emerg ence activity, inducing black root discoloration and root pruning of wheat seedlings and reducing seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, F. acuminatum reduced seedling height, seedling emergence and root and shoot dry weights. Microdochium bolleyi and E. chlam ydospora reduced fresh and dry weight of roots, plant emergence and shoot d ry weight. Fusarium acuminatum and C. spicier reduced the growth rate of wh eat seedlings. All fungi evaluated showed increased disease severity compar ed to the untreated control. The high frequency of isolation of C. sativus from crown and root tissues can be partially explained by the dry, warm con ditions during the early stages of wheat seedling development in the Upper Coastal Plain Land Resource Area of Mississippi.