In the United States, combined annual yield losses caused by the major yield and seed quality reducing pathogens are estimated to be nearly $1.3 billion. Yield losses due to these pathogens have remained relatively high because no commercial resistant soybean cultivars have been available to soybean growers.

The overarching goal for this research is to provide producers with technologies to minimize soybean yield and seed quality losses to the top three soybean diseases causing economic damage to the midsouthern US including Tennessee. These diseases include charcoal rot, Frogeye leaf spot, and Phomopsis Seed Decay. We have made significant progress on all three fronts. Even though there is no complete resistance to charcoal rot resistance, we have soybean lines with acceptable agronomic traits with moderate resistance. This is also true for Phomopsis seed decay. However, we have several lines identified for Frogeye resistance.

In 2018, 75 lines of roundup ready and 105 conventional soybean lines were screened for charcoal rot resistance. Result from 2018 charcoal rot resistance evaluation is still being processed but based on data of the same lines planted in 2017, 30 lines among the 170 tested were resistant. However repeated testing is necessary to ensure and validate the resistance of these lines.

Charcoal rot screening and assessment was made at the West Tennessee Research and Education Center at Jackson, TN. The soybean lines were grown and screened in a field known to have charcoal rot fungus in the soil. Soybean stem were longitudinally split and severity rating based on a 1-5 scale was given, where 1 is resistant and 5 is susceptible. Based on such rating the lines are categorized as resistant, moderately resistant, moderately susceptible or susceptible.

Soybean lines for Frogeye leaf spot were screened at the West Tennessee Research and Education Center in Milan, TN. A total of 114 soybean lines were planted in field that were irrigated at flowering using central pivot system. The test location has a known natural infection every year. Evaluation for resistance was based on percent leaf area covered by frogeye leaf spot.

i. Validation of resistance to charcoal rot on individual soybean plant selections within breeding lines and Soybean Cyst Nematode germplasms.
ii. Screening of commercial Roundup Ready and conventional soybean cultivars for charcoal rot.
iii. Simultaneous evaluation of resistance to charcoal rot and drought tolerance.
iv. Screening of conventional and breeding lines against Phomopsis seed decay.
v. Evaluation of soybean accessions and breeding lines for frogeye leaf spot resistance.

Note: Objective iii has been added to this proposal because of the recent finding that breeding lines selected for drought tolerance can be further selected for charcoal rot resistance under non-irrigated (rain-fed) environments. Thus enabling identification for these two important traits.

The overall goal of this research is to provide producers with technologies to minimize soybean yield loss to the top three soybean diseases (charcoal rot, Frogeye leaf spot and Phomopsis seed decay) causing economic damage to Tennessee and the Midsouthern U.S.