Scherm H, Yang X B, Lundeen P
Department of Plant Pathology, University of Georgia, Athens 30602.
Department of Plant Pathology, Iowa State University, Ames 50011.
Plant Dis. 1998 Oct;82(10):1152-1157. doi: 10.1094/PDIS.1998.82.10.1152.
Sudden death syndrome, caused by Fusarium solani f. sp. glycines, has increased in prevalence in soybean production regions in the North-Central United States. Little is known about soil factors and environmental conditions that influence disease severity in this pathosystem. We studied associations between biological, chemical, and physical soil variables and severity of foliar symptoms of sudden death syndrome in nine commercial soybean fields in Iowa during 1995 and 1996. Disease was patchy in all fields, and soil samples were collected in each field along a transect that ran from a symptomless area through a diseased area. There were 25 sampling stops along each transect, separated by distances of 1.5 to 2.5 m. At each stop, soil samples were collected and soil strength, soil moisture, and foliar disease severity (at plant growth stage R6) were measured. Soil samples were assayed for population densities of F. solani f. sp. glycines, cysts of the soybean cyst nematode (Heterodera glycines), and for chemical variables (soluble salts, pH, organic matter, cation exchange capacity, and concentrations of P, K, Ca, Mg, Mn, and Fe). Cross-correlation analyses were carried out to test for associations between soil variables and disease severity in individual fields, while discriminant analysis was used to assess the effects of soil variables across all fields. Disease severity showed consistent associations with F. solani f. sp. glycines populations (strong effect) and H. glycines cyst counts (minor effect). Available K was identified as a possible disease-enhancing factor, but the magnitude of its effect was dependent on the overall K-concentrations in the fields. For example, as the median K-concentration increased, the correlation between K and disease decreased. None of the other soil variables showed consistent associations with disease. The results suggest that localized presence or absence of F. solani f. sp. glycines is the chief reason for the patchiness of sudden death syndrome in affected fields. Thus, manipulation of soil nutrient status or fertility level appears to have limited potential for reducing disease in the high-yield soybean production environment of Iowa. Instead, producers should focus on preventing the establishment or reducing populations of F. solani f. sp. glycines and H. glycines in their fields.
由大豆尖镰孢菌引起的猝死综合征在美国中北部大豆产区的发病率有所上升。对于影响该病害系统中病害严重程度的土壤因素和环境条件，人们了解甚少。我们于1995年和1996年在爱荷华州的9个商业化大豆田中研究了生物、化学和物理土壤变量与猝死综合征叶部症状严重程度之间的关联。所有田块中的病害分布都呈斑块状，在每个田块中沿着一条从无症状区域穿过患病区域的样带采集土壤样本。每条样带设有25个采样点，相邻采样点间距为1.5至2.5米。在每个采样点采集土壤样本，并测量土壤强度、土壤湿度和叶部病害严重程度（在植株生长阶段R6）。对土壤样本检测大豆尖镰孢菌的种群密度、大豆孢囊线虫（大豆异皮线虫）的孢囊以及化学变量（可溶性盐、pH值、有机质、阳离子交换容量以及P、K、Ca、Mg、Mn和Fe的浓度）。进行交叉相关分析以检验各个田块中土壤变量与病害严重程度之间的关联，同时使用判别分析来评估所有田块中土壤变量的影响。病害严重程度与大豆尖镰孢菌种群（强效）和大豆孢囊线虫孢囊数量（弱效）呈现出一致的关联。有效钾被确定为一个可能的病害加重因素，但其影响程度取决于田块中的总体钾浓度。例如，随着钾浓度中位数的增加，钾与病害之间的相关性降低。其他土壤变量均未显示出与病害的一致关联。结果表明，大豆尖镰孢菌的局部存在与否是受影响田块中猝死综合征呈斑块状分布的主要原因。因此，在爱荷华州高产大豆生产环境中，通过操控土壤养分状况或肥力水平来降低病害的潜力似乎有限。相反，生产者应专注于防止大豆尖镰孢菌和大豆孢囊线虫在其田块中定殖或减少其种群数量。
