Field evaluation of maturity group IV late RoundUp Ready soybean cultivars to Cercospora leaf blight, frogeye leaf spot, Septoria brown spot, and target spot in west MS, 2016

摘要

A field evaluation of 36 maturity group IV late soybean cultivars to Cercospora leaf blight (CLB), frogeye leaf spot (FLS), Septoria brown spot (SBS), and target spot (TS) was performed at Charleston, MS. Soybean cultivars were planted in a Sharkey clay loam on 27 Apr. The previous crop was soybean. Plots consisted of four rows of soybean, spaced 19-in. apart, planted with 9 seed per foot of row and trimmed to a final length of 14.5 ft. The experimental design was a randomized complete block with three replications. Plots were not irrigated. Field evaluations for the presence of foliar disease were conducted at approximately R6 using a 0 to 9 scale whereby 0=no disease and 9=excessive disease symptoms. Leaf surface area affected was evaluated for FLS while CLB was rated based on the presence of disease on leaves (0 to 5), petioles (6), and on pods and stems (7 to 9) based on disease intensity as assessed by coloration of plant material (leaves with distinct purple coloration and petioles, pods andmain stems with purple to near black coloration). Septoria brown spot was rated in a similar fashion based on the presence of the disease within the plant canopy so that 0 to 3 indicated the presence in the lower canopy, 4 to 5 in the middle canopy, 6 to8 in the upper canopy, and 9 indicative of extensive defoliation throughout the entire plant canopy and the disease in the upper most canopy. Target spot was rated in a similar fashion to the Septoria brown spot assessments with disease being rated on awhole plot basis based on the presence of the disease within segments of the plant canopy using a 0 to 9 scale. Plots were harvested on 14 Sep by harvesting all three rows of soybean. Yield was calculated by standardizing moisture to 13%. Disease ratingand yield data were analyzed using the SAS GLM procedure (Version 9.3, SAS Institute, Cary, NC). Means separation was conducted using Fisher's protected least significant difference at P=0.05.