Effect of Plant Age, Maturity Group, and the Environment on Disease Progress of Sudden Death Syndrome of Soybean

摘要: Disease progress of sudden death syndrome (SDS) soybean, caused by Fusarium solani, was determined in a standard susceptible cultivar, Lee 74, planted uniformly throughout the test site and 42 soybean cultivars representing maturity groups (MG) IV-VIII, 1986-1989. severity assessed weekly from middle July through first October using visual rating scale percent leaf area exhibiting foliar symptoms SDS. The disease ratings were used to calculate absolute infection rate (dy/dt) for each cultivar at time under curve (AUDPC). In SDS progressed two phases: an initial rapid increase about 35% affected slower after that point. This two-phase fit segmented model exponential equations. fits these equations highly significant (P 1%/day or, if lower than 1%/day, highest dy/dt attained). DAP significantly < 0.0001) related AUDPC (R = −0.58 R 0.38, respectively). Cultivars race 6 cyst nematode (SCN), Heterodera glycines, predominate field, developed 10 days earlier had higher levels resistant SCN. earliest increases occurred between 71 77 1986, 69 74 1987, 75 83 1988 most MGs. Accumulated heat periods 910-942, 852-916, 857-963 degree-days 1988, respectively. three MG VII VIII large 52 608 degree-days. general, however, increased same across MGs, but no specific reproductive stage