Block C C, Hill J H, McGee D C
Plant Pathologist, USDA-ARS North Central Regional Plant Introduction Station.
Professor, Department of Plant Pathology.
Plant Dis. 1999 Jun;83(6):527-530. doi: 10.1094/PDIS.1999.83.6.527.
The relationship between the amount of foliar disease on maize plants and seed contamination by the causal bacterium, Pantoea stewartii, was studied by comparing disease severity on adult plants with results from laboratory seed tests. Seventy-seven naturally infected maize lines (25 in 1990 and 52 in 1992) were selected and assigned to one of six disease severity classes based on the percentage of ear leaf tissue killed by Stewart's wilt: trace to 2%, 6 to 14%, 25 to 34%, 35 to 49%, 50 to 74%, and 75 to 100%. Ears were harvested from 10 to 20 plants representative of the disease class for each maize line, and seeds were tested by enzyme-linked immunosorbent assay (ELISA) of bulk-seed samples. Seed infection percentages were estimated from the bulk-test results by using statistical equations for group testing. The accuracy of the bulk-seed method for estimating seed infection was validated by comparison with 300-kernel single-seed tests. Infected seed was detected only from seed of plants with ≥25% disease severity; however, 45 of 63 such seed lots had no infection. Three seed lots had >5% infected seeds, all from plants with >50% disease severity. The results suggest a possible threshold level between 15 and 25% disease severity for Stewart's wilt on leaves before bacteria are detected in seed. This study describes a relatively simple method for estimating the incidence of infected seeds in a seed lot and contributes additional evidence to indicate that the chance of spreading P. stewartii from U.S.-produced maize seeds is low.
通过比较成年植株上的病害严重程度与实验室种子检测结果，研究了玉米植株叶部病害数量与致病细菌斯氏泛菌（Pantoea stewartii）引起的种子污染之间的关系。选择了77个自然感染的玉米品系（1990年25个，1992年52个），并根据斯氏枯萎病致死的穗叶组织百分比将其分为六个病害严重程度等级之一：微量至2%、6%至14%、25%至34%、35%至49%、50%至74%以及75%至100%。从每个玉米品系的10至20株代表该病害等级的植株上收获果穗，并通过对混合种子样本进行酶联免疫吸附测定（ELISA）来检测种子。利用分组检测的统计方程从混合检测结果中估算种子感染率。通过与300粒单粒种子检测结果进行比较，验证了混合种子法估算种子感染情况的准确性。仅从病害严重程度≥25%的植株种子中检测到感染种子；然而，63个此类种子批次中有45个没有感染。有3个种子批次的感染种子>5%，均来自病害严重程度>50%的植株。结果表明，在种子中检测到细菌之前，叶片上斯氏枯萎病的病害严重程度可能存在15%至25%的阈值水平。本研究描述了一种相对简单的方法来估算种子批次中感染种子的发生率，并提供了更多证据表明从美国生产的玉米种子传播斯氏泛菌的可能性较低。
