Department of Plant Breeding and Genetics, Cornell University, Ithaca, NY, USA.
Phytopathology. 2011 Feb;101(2):290-8. doi: 10.1094/PHYTO-03-10-0087.
The agronomic importance of developing durably resistant cultivars has led to substantial research in the field of quantitative disease resistance (QDR) and, in particular, mapping quantitative trait loci (QTL) for disease resistance. The assessment of QDR is typically conducted by visual estimation of disease severity, which raises concern over the accuracy and precision of visual estimates. Although previous studies have examined the factors affecting the accuracy and precision of visual disease assessment in relation to the true value of disease severity, the impact of this variability on the identification of disease resistance QTL has not been assessed. In this study, the effects of rater variability and rating scales on mapping QTL for northern leaf blight resistance in maize were evaluated in a recombinant inbred line population grown under field conditions. The population of 191 lines was evaluated by 22 different raters using a direct percentage estimate, a 0-to-9 ordinal rating scale, or both. It was found that more experienced raters had higher precision and that using a direct percentage estimation of diseased leaf area produced higher precision than using an ordinal scale. QTL mapping was then conducted using the disease estimates from each rater using stepwise general linear model selection (GLM) and inclusive composite interval mapping (ICIM). For GLM, the same QTL were largely found across raters, though some QTL were only identified by a subset of raters. The magnitudes of estimated allele effects at identified QTL varied drastically, sometimes by as much as threefold. ICIM produced highly consistent results across raters and for the different rating scales in identifying the location of QTL. We conclude that, despite variability between raters, the identification of QTL was largely consistent among raters, particularly when using ICIM. However, care should be taken in estimating QTL allele effects, because this was highly variable and rater dependent.
培育持久抗性品种的农艺重要性促使人们对定量疾病抗性（QDR）进行了大量研究，特别是对疾病抗性的数量性状位点（QTL）进行了定位。QDR 的评估通常通过目测疾病严重程度进行，这引起了人们对目测估计的准确性和精密度的关注。尽管先前的研究已经研究了与疾病严重程度的真实值相关的影响目测疾病评估准确性和精密度的因素，但这种变异性对疾病抗性 QTL 识别的影响尚未得到评估。在这项研究中，在田间条件下生长的重组自交系群体中，评估了评估者变异性和评分尺度对玉米北部叶斑病抗性 QTL 作图的影响。使用直接百分比估计、0 到 9 的有序评分尺度或两者结合，由 22 位不同的评估者对 191 条系进行评估。结果发现，经验更丰富的评估者具有更高的精度，并且使用患病叶片面积的直接百分比估计比使用有序尺度产生更高的精度。然后，使用每位评估者的疾病估计值，使用逐步广义线性模型选择（GLM）和包容性复合区间作图（ICIM）进行 QTL 作图。对于 GLM，大多数 QTL 在评估者之间基本一致，尽管一些 QTL 仅由部分评估者识别。在鉴定的 QTL 处，估计等位基因效应的幅度差异很大，有时高达三倍。ICIM 在鉴定 QTL 的位置方面在评估者之间和不同评分尺度之间产生了高度一致的结果。我们得出结论，尽管评估者之间存在差异，但 QTL 的鉴定在评估者之间基本一致，特别是在使用 ICIM 时。然而，在估计 QTL 等位基因效应时应小心，因为这高度可变且依赖于评估者。
