Bock C H, Parker P E, Cook A Z, Gottwald T R
University of Florida/USDA, 2001 S. Rock Rd., Ft. Pierce, FL 34945.
USDA-APHIS, Moore Air Base, Edinburg, TX 78539.
Plant Dis. 2008 Jun;92(6):927-939. doi: 10.1094/PDIS-92-6-0927.
Citrus canker is a disease of citrus and is caused by the bacterial pathogen Xanthomonas citri subsp. citri. Ways of managing the disease are being sought, and accurate, precise, reproducible disease assessment is needed for monitoring epidemics. The objective of this study was to investigate the characteristics of visual assessment of citrus canker symptoms compared with actual disease measured using image analysis (IA). Images of 210 citrus leaves with a range of incidence and severity of citrus canker were assessed by three plant pathologists (VR1-3) and by IA. The number of lesions (L), % area necrotic (%AN), and % area necrotic+chlorotic (%ANC) were assessed. The best relationships were found between %AN and %ANC (r = 0.41 to 0.87), and the worst between L and %AN (r = 0.27 to 0.66). Bland-Altman plots showed various sources of rater error in assessments, including under- and over-estimation, proportional error, and heterogeneity of variation dependent on actual disease magnitude. There was a tendency to overestimate area diseased, but not lesion counts, and this tendency was pronounced at lower disease severity, with a leaf having more lesions tending to be assessed as having greater area infected compared with a leaf with fewer lesions but equal actual area infected. The rater estimations of disease were less accurate or precise with increasing actual disease severity as indicated by the fit of a normal probability density function-the incidence of extreme values increases with increasing actual disease. For example, for %ANC the kurtosis of the distribution ranged from 17.92 to 1.18, 0.51, and 0.22 in actual disease category ranges of 0 to 10, 11 to 20, 21 to 30, and 31 to 40% area infected, respectively. The log variance of the estimates plotted against log actual disease for all three raters over two assessment occasions gave a linear relationship for L, %AN, and %ANC (r = 0.74, 0.65, and 0.74, respectively). Training should improve the accuracy, precision, and reproducibility of raters, and knowledge of the characteristics of disease assessment should help develop and target the training more appropriately and address specific causes and sources of error.
柑橘溃疡病是一种柑橘病害，由细菌病原体柑橘溃疡病菌引起。人们正在寻找该病的管理方法，而监测疫情需要准确、精确、可重复的病害评估。本研究的目的是调查与使用图像分析（IA）测量的实际病害相比，柑橘溃疡病症状的视觉评估特征。由三位植物病理学家（VR1 - 3）和IA对210片具有不同柑橘溃疡病发病率和严重程度的柑橘叶图像进行了评估。评估了病斑数量（L）、坏死面积百分比（%AN）和坏死 + 褪绿面积百分比（%ANC）。发现%AN和%ANC之间的相关性最好（r = 0.41至0.87），而L和%AN之间的相关性最差（r = 0.27至0.66）。布兰德 - 奥特曼图显示了评估中评分者误差的各种来源，包括低估和高估、比例误差以及取决于实际病害程度的变异异质性。存在高估病害面积的趋势，但病斑数量不存在这种趋势，并且这种趋势在病害严重程度较低时更为明显，与病斑较少但实际感染面积相同的叶片相比，病斑较多的叶片往往被评估为感染面积更大。如正态概率密度函数的拟合所示，随着实际病害严重程度的增加，评分者对病害的估计准确性或精确性降低——极端值的发生率随着实际病害的增加而增加。例如，对于%ANC，在实际病害类别范围为0至10%、11至20%、21至30%和31至40%感染面积时，分布的峰度分别为17.92、1.18、0.51和0.22。在两次评估中，针对所有三位评分者绘制的估计值对数与实际病害对数的关系图显示，L、%AN和%ANC呈线性关系（r分别为0.74、0.65和0.74）。培训应提高评分者的准确性、精确性和可重复性，并且了解病害评估的特征应有助于更适当地开展培训并确定培训目标，以及解决特定的误差原因和来源。
