Abstract
Brown spot, caused by Septoria glycines Hemmi, is a highly prevalent foliar disease of soybean (Glycine max (L.) Merr.). Despite its wide distribution, the development of Septoria brown spot and its relationship with yield reduction remain poorly characterized. In this study, we conducted replicated multi-location inoculated field trials to characterize the disease development and evaluated the relationship between Septoria brown spot and soybean yield. Multiple components of disease and yield were rated weekly to characterize disease development. Fungicide treatments had a significant effect on ratings of vertical progress of the disease and chlorotic area at the end of the season. There were also significant differences between the fungicide treatments for the Area Under the Disease Progress Curve (AUDPC) of all the disease components, including necrotic area and defoliation rate. Soybean yield was negatively correlated with the vertical progress of the disease (r = −0.36). The vertical progress was the best linear predictor of yield with an R2 = 0.08 for the end of the season rating and an R2 = 0.2 for the AUDPC. A variance component analysis of the data showed that location was the most critical factor, illustrating the large effect of local environmental conditions on the disease. There was no statistically significant effect of the fungicide treatments on yield. Power analyses indicated that at least eight locations are needed to detect an effect of 269 kg ha−1. Our results provide useful information in the characterization of the disease development and for estimations of yield damage.
Highlights
Soybean (Glycine max (L.) Merr.) is one of the most important crops in the UnitedStates with a cultivated area of 35.75 million hectares, and an average yield of 3.5 metric tons/hectare (52.1 bushels/acre) in 2018 [1]
We focus on Septoria brown spot of soybeans, a highly prevalent disease in all soybean growing areas [2]
(2011) [4] reported a significant correlation between rain and yield response to fungicide application when rain occurred after pod formation (R3) and before seed formation (R5). These findings suggest that reducing foliar diseases, in general, could have a positive effect on yield under certain environmental circumstances
Summary
Soybean (Glycine max (L.) Merr.) is one of the most important crops in the UnitedStates with a cultivated area of 35.75 million hectares, and an average yield of 3.5 metric tons/hectare (52.1 bushels/acre) in 2018 [1]. An estimated 12% of soybean yield is lost to diseases every year in the U.S [2]. Hemmi) is one of the ten most destructive diseases associated with the yield losses [3]. This disease often occurs simultaneously with other late-season diseases such as frogeye leaf spot (Cercospora sojina Hara), and Cercospora leaf blight (Cercospora kikuchii (Mat and Tom) Gardner). Some authors consider them a complex of diseases [4]. These late-season diseases have not received much research attention yet assessing their individual effect on soybean yield is critical to precision management practices and our understanding of disease progression in the field
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