Field evaluation of maturity group IV conventional and LibertyLink soybean cultivars to Cercospora leaf blight, frogeye leaf spot, Septoria brown spot, and target spot in northeast MS, 2016

摘要

A field evaluation of 18 maturity group IV conventional and LibertyLink soybean cultivars to Cercospora leaf blight (CLB), frogeye leaf spot (FLS), Septoria brown spot (SBS), and target spot (TS) was performed at the North MS Research and Extension Center, Verona, MS. Soybean cultivars were planted in Leeper silty clay loam soil on 22 Apr. Plot size was two 8-in. twin rows on 38-in. beds, 20 ft. in length. The experimental design was a randomized complete block design with four replications. Diseaseseverity ratings were visually assessed on the presence of disease symptoms on the soybean plot canopy. Disease assessments were made based on a scale of 0 to 9, where 0 = no disease present and 9 = severe disease, characterized by approximately 90% leafcoverage. 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. Plots were harvested on 3 Oct by harvesting the middle two rows of soybean. Yield was calculated by standardizing moisture to 13%. 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.