Field evaluation of maturity group IV early RoundUp Ready soybean cultivars to Cercospora leaf blight, frogeye leaf spot, Septoria brown spot, target spot and green stem at Stoneville, MS (silt loam soil, irrigated), 2016

摘要

A field evaluation of 22 maturity group IV early RoundUp Ready soybean cultivars to Cercospora leaf blight (CLB), frogeye leaf spot (FLS), Septoria brown spot (SBS), target spot (TS), and green stem (GS) was performed in Stoneville, MS. Soybean cultivars were planted in a Bosket and Commerce very fine sandy loam soil on 5 May. The previous crop was cotton. Plots consisted of four rows of soybean, spaced 30-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 furrow irrigated as needed. 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 and main 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 to 8 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 a whole plot basis based on the presence of the disease within segments of the plant canopy using a 0 to 9 scale. Green stem was rated as a percentage of the plants within the entire plot that contained green stems and leaf material that had not reached physiological maturity as indicated by mature pods. Plots were harvested on 20 Sep by harvesting the middle two rows of soybean. Yield data were adjusted to 13% moisture. Disease rating and 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.