Beale Julie W, Windels Carol E, Kinkel Linda L
Diagnostician/Research Specialist, University of Kentucky, Lexington 40546.
Professor, University of Minnesota, Northwest Research and Outreach Center, Crookston 56716.
Plant Dis. 2002 May;86(5):547-551. doi: 10.1094/PDIS.2002.86.5.547.
Spatial distribution of Aphanomyces cochlioides inoculum and disease was assessed in sugar beet fields located near Moorhead, MN and Wahpeton, ND. Soil samples were collected in June and July 1994 from two main plots (60 by 60 m) in each field. Samples were evaluated for A. cochlioides using a sugar beet seedling assay in the greenhouse to determine a root rot index value (0-to-100 scale), which served as an indirect estimate of relative activity and density of inoculum. Field evaluations of Aphanomyces root rot on sugar beet (0-to-7 scale) were made at harvest in September at each soil collection site. Greenhouse root rot index values correlated positively with field disease ratings for all plots. Variance-to-mean ratios of greenhouse root rot index values and of field disease ratings among samples within each plot were calculated to compare the spatial distribution of midseason inoculum with root rot at harvest. Ratios of greenhouse root rot indices indicated that inoculum of A. cochlioides was aggregated in the field at midseason, but root rot was uniform within plots by harvest. Wet weather in July through August was conducive to infection and development of symptoms. A uniform distribution of disease at harvest likely reflects a combination of factors, including root growth into inoculum foci, redistribution of inoculum, and inoculum densities that are spatially variable but all above some minimum threshold for infection.
在明尼苏达州莫尔黑德市和北达科他州瓦佩顿市附近的甜菜田中，评估了甜菜拟盘多毛孢菌接种体和病害的空间分布。1994年6月和7月，从每个田块的两个主要地块（60×60米）采集土壤样本。在温室中使用甜菜幼苗试验对样本进行甜菜拟盘多毛孢菌评估，以确定根腐病指数值（0至100分制），该值作为接种体相对活性和密度的间接估计。9月收获时，在每个土壤采集地点对甜菜根腐病进行田间评估（0至7分制）。所有地块的温室根腐病指数值与田间病害评级呈正相关。计算每个地块内样本间温室根腐病指数值和田间病害评级的方差均值比，以比较季中接种体的空间分布与收获时的根腐病情况。温室根腐病指数的比值表明，甜菜拟盘多毛孢菌接种体在季中田间呈聚集分布，但收获时地块内根腐病分布均匀。7月至8月的潮湿天气有利于感染和症状发展。收获时病害的均匀分布可能反映了多种因素的综合作用，包括根系向接种体病灶生长、接种体的重新分布以及接种体密度在空间上可变但均高于某个最低感染阈值。
