Characterization of Septoria brown spot disease development and yield effects on soybean in Illinois

Brown spot, caused by <i>Septoria glycines</i> Hemmi, is a highly prevalent foliar disease of soybean (<i>Glycine max</i> (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 (<i>r</i> = −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.

由大豆壳针孢（Septoria glycines）Hemmi引起的褐斑病是大豆（Glycine max (L.) Merr.）上一种分布极为广泛的叶部病害。尽管该病害分布范围极广，但大豆壳针孢褐斑病的发生发展过程及其与产量损失的关联仍未得到充分解析。本研究通过设置重复多地点接种田间试验，系统表征了该病害的发展特征，并评估了其与大豆产量的相关关系。研究期间每周对多项病害及产量相关指标进行评级，以刻画病害的动态发展进程。结果显示，杀菌剂处理对季末病害的垂直扩展程度与褪绿面积的评级具有显著影响；在所有病害组分（包括坏死面积与落叶速率）的病情发展曲线下面积（AUDPC）方面，不同杀菌剂处理间同样存在显著差异。大豆产量与病害垂直扩展程度呈显著负相关（r = -0.36）。其中，季末病害评级的垂直扩展程度对产量的线性预测效果最优，其决定系数R²=0.08；而基于病情发展曲线下面积的预测决定系数为R²=0.2。对试验数据的方差分量分析表明，试验地点是最关键的影响因子，体现了当地环境条件对病害发生的显著调控作用。杀菌剂处理对大豆产量未产生统计学意义上的显著效应。功效分析结果显示，若要检测出269 kg·ha⁻¹的产量效应，至少需要设置8个试验地点。本研究结果可为该病害的发生发展特征解析及产量损失评估提供重要的参考依据。