Hay Frank, Heck Daniel W, Klein Audrey, Sharma Sandeep, Hoepting Christy, Pethybridge Sarah J
Plant Pathology & Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell AgriTech, Cornell University, Geneva, NY 14456.
Cornell Vegetable Program, Cornell Cooperative Extension, Albion, NY 14424.
Plant Dis. 2022 May;106(5):1381-1391. doi: 10.1094/PDIS-07-21-1587-RE. Epub 2022 Apr 6.
Stemphylium leaf blight (SLB) caused by is the dominant foliar disease affecting large-scale onion production in New York. The disease is managed by fungicides, but control failures are prevalent and are attributed to fungicide resistance. Little is known of the relative role of inoculum sources in initiation and spread of SLB epidemics. Plate testing of 28 commercially available organic onion seedlots from 2016 and 2017 did not detect . This finding suggests that although has been reported as seed-transmitted, this is unlikely to be a significant inoculum source in commercially available organic seed lots and even less so in fungicide-treated seed used to establish conventional fields. The spatial and spatiotemporal dynamics of SLB epidemics in six onion fields were evaluated along linear transects in 2017 and 2018. Average SLB incidence increased from 0 to 100% throughout the cropping seasons with an average final lesion length of 28.3 cm. Disease progress was typical of a polycyclic epidemic and the logistic model provided the best fit to 83.3% of the datasets. Spatial patterns were better described by the beta-binomial than binomial distribution in half of the datasets (50%) and random patterns were more frequently observed by the index of dispersion (59%). Geostatistical analyses also found a low frequency of datasets with aggregation (60%). Spatiotemporal analysis of epidemics detected that the aggregation was influenced by disease incidence. However, diseased units were not frequently associated with the previous time period according to the spatiotemporal association function of spatial analyses by distance indices. Variable spatial patterns suggested mixed inoculum sources dependent upon location, and likely an external inoculum source at the sampling scale used in this study. A small-plot replicated trial was also conducted in each of 2 years to quantify the effect of -infested onion residue on SLB epidemics in a field isolated from other onion fields. SLB incidence was significantly reduced in plots without residue compared with those in which residue remained on the soil surface. Burial of infested residue also significantly reduced epidemic progress in 1 year. The effect of infested onion residue on SLB epidemics in the subsequent onion crop suggests rotation or residue management may have a substantial effect on epidemics. However, the presence of an inoculum source external to fields in onion production regions, as indicated by a lack of spatial aggregation, may reduce the efficacy of in-field management techniques.
由[病原菌名称未给出]引起的匍柄霉叶枯病（SLB）是影响纽约州大规模洋葱生产的主要叶部病害。该病通过杀菌剂进行防治，但防治失败的情况很普遍，这归因于杀菌剂抗性。对于接种源在匍柄霉叶枯病流行起始和传播中的相对作用，人们了解甚少。对2016年和2017年28个市售有机洋葱种子批次进行平板检测，未检测到[病原菌名称未给出]。这一发现表明，尽管[病原菌名称未给出]已被报道可通过种子传播，但在市售有机种子批次中，这不太可能是一个重要的接种源，在用于建立常规田块的经杀菌剂处理的种子中就更不可能了。2017年和2018年，沿着线性样带对六个洋葱田块中匍柄霉叶枯病的空间和时空动态进行了评估。在整个种植季节，匍柄霉叶枯病的平均发病率从0增加到100%，平均最终病斑长度为28.3厘米。病害进展是典型的多循环流行，逻辑模型对83.3%的数据集拟合最佳。在一半的数据集（50%）中，β-二项分布比二项分布能更好地描述空间格局，并且通过离散指数更频繁地观察到随机格局（59%）。地统计分析还发现数据集聚集的频率较低（60%）。对病害流行的时空分析检测到聚集受到发病率的影响。然而，根据距离指数的空间分析的时空关联函数，患病单元与上一个时间段并不经常相关。可变的空间格局表明接种源混合，这取决于位置，并且在本研究使用的采样尺度上可能存在外部接种源。还在连续两年的每一年中进行了小区重复试验，以量化受[病原菌名称未给出]侵染的洋葱残体对与其他洋葱田块隔离的一块田块中匍柄霉叶枯病流行的影响。与土壤表面残留有残体的小区相比，没有残体的小区中匍柄霉叶枯病的发病率显著降低。在一年中，掩埋受侵染的残体也显著降低了病害流行进程。受侵染的洋葱残体对后续洋葱作物中匍柄霉叶枯病流行的影响表明，轮作或残体管理可能对病害流行有重大影响。然而，如缺乏空间聚集所表明的，洋葱生产区域田块外部存在接种源可能会降低田间管理技术的效果。
