2012 Annual Report
1a.Objectives (from AD-416):
Screening soybean varieties for resistance to Phomopsis seed decay (PSD)
1b.Approach (from AD-416):
Field screening and laboratory seed quality assays will be conducted to determine:.
1)The disease resistance of commercial available soybean varieties to PSD; and.
2)The virulence/aggressiveness of PSD isolates collected in Mississippi.
During this reporting period, 50 soybean lines including 34 commercial soybean varieties and 16 breeding lines (MG IV and MGV) were planted in Stoneville, Mississippi, on May 11, 2011, to evaluate them for resistance to Phomopsis seed decay (PSD). Two experiments were set up in a split-plot design for each maturity group IV and V, where the inoculation treatments (inoculated and non-inoculated) were the main units in a randomized completed design with four replications. Soybean varieties in each maturity group were the sub-unit, which was a repeated measure of two harvest times at R8 and R8+2weeks stages (normal vs. delayed). Seeds were planted in 10 ft long row plots with 8 seeds/ft of row on 40-in. row spacing. A total of 800 plots were planted. The inoculated plots were sprayed with Phomopsis spores at the R5 to R6 growth stage. Evaluations were conducted when the soybeans are mature, which included seed plating assay to determine the PSD incidence, germination tests , and visual seed quality scoring of seeds harvested from each field plots. In 2011, although the weather was dry, differences of the Phomopsis seed infection were still observed among soybean lines with some lines having no infection while others had levels as high as 11%. These differences between lines were reflected in visual seed quality and seed germination. The range for visual seed quality was from 1.1 to 3.4, and the seed germination rate was from 50.3% to 100%. Our previous experiments indicated that the seed germination was significantly negatively correlated with the Phomopsis seed infection. Maturity IV varieties Morsoy R2 491, Morsoy R2S 480, Pioneer 94Y90, and maturity V varieties Asgrow 5606, Asgrow 5831,Dyna-Gro 37RY52, Dyna-Gro 33C59, Progeny 5650, Progeny 5706, Terral59R16, and PI 42324B had over 95% germination rate in both inoculated and noninocuolated trials. Identification of these lines that have no or less Phomopsis seed infection, high germination rate, and good visual sores are of important because they produce high seed quality that is beneficial to soybean growers.
Results of this research alone with other projects on PSD were presented at the 39th Annual Meeting of Southern Soybean Disease Workers on March 8, 2012, entitled “Screening germplasm for resistance to Phomopsis seed decay: joint effort from USDA and university scientists”. Four quarterly and one annual progress reports have been submitted to Mississippi Soybean Promotion Board (MSPB). The milestone for evaluation soybean varieties for resistance to Phomopsis seed decay was fully met.