Comparison of current peanut fungicides against Athelia rolfsii through a laboratory bioassay of detached plant tissues

Authors: WEI, XING - Virginia Tech; LANGSTON, DAVID - Virginia Tech; Mehl, Hillary

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2022
Publication Date: 3/20/2022
Citation: Wei, X., Langston, D.B., Mehl, H.L. 2022. Comparison of current peanut fungicides against Athelia rolfsii through a laboratory bioassay of detached plant tissues. Plant Disease. 106(8):2046-2052. https://doi.org/10.1094/PDIS-12-21-2789-RE.
DOI: https://doi.org/10.1094/PDIS-12-21-2789-RE

Interpretive Summary: Peanut is an important oilseed crop that contains high-quality protein and oil content. However, peanut yields are reduced by several fungal diseases. Stem rot, caused by the soilborne fungus Athelia rolfsii, is one of the most economically important diseases of peanuts worldwide. Foliar-applied fungicides are commonly used to control this disease during the growing season, and several new fungicide products have recently been registered for stem rot control in peanuts. In this study, standard and new stem rot fungicides were evaluated using a laboratory bioassay of detached plant tissues inoculated with A. rolfsii. Overall, fungicides were similarly effective, and inhibition of fungal growth by the different fungicides decreased over time at a similar rate. After foliar application of the fungicides, untreated tissues of the same plant (e.g., stems) exhibited varied levels of fungal control, indicating differences between fungicides in their systemic movement within the plant. Properties of different peanut stem rot fungicides identified in this study are useful in developing fungicide application recommendations that will maximize their efficacy for disease control and protection of crop yields.

Technical Abstract: Southern stem rot of peanut, caused by Athelia rolfsii, is an important fungal disease that impacts peanut production worldwide. Foliar-applied fungicides are used to manage the disease, and several fungicides have been recently registered for southern stem rot control in peanuts. This study compared fungicidal, residual, and potential systemic activity of current fungicides against A. rolfsii using a laboratory bioassay. Peanut plants grown in the field were treated with eight fungicides ~90 days after planting, and plants were collected for the laboratory bioassay weekly for five weeks following application. Peanut plants were separated into the newest fully mature leaf present at sample collection, the second newest fully mature leaf present at the time of fungicide application, upper stem, and crown tissues. Each plant tissue was inoculated with A. rolfsii then incubated at 30°C for two days. Lesion length was measured, and percent inhibition of fungal growth by each fungicide relative to the control was calculated. All fungicides provided the greatest inhibition of A. rolfsii on leaf tissues that were present at the time of fungicide application, followed by the newly grown leaf and upper stem. Little inhibition occurred on the crown. Fungal inhibition decreased at similar rates over time for all fungicides tested. Succinate dehydrogenase inhibitors provided less basipetal protection of upper stems than quinone outside inhibitor or demethylation inhibitor fungicides. Properties of the fungicides characterized in this study, including several newly registered products, are useful for developing fungicide application recommendations to maximize their efficacy in controlling both foliar and soilborne peanut diseases.