Bock Clive H, Grauke Larry J, Conner Patrick, Burrell Susan L, Hotchkiss Michael W, Boykin Debbie, Wood Bruce W
United States Department of Agriculture - Agriculture Research Service, Southeastern Fruit and Tree Nut Research Lab (USDA-ARS, SEFTNRL), Byron, GA 31008.
USDA-ARS Pecan Breeding and Genetics, Somerville, TX 77845.
Plant Dis. 2016 Sep;100(9):1937-1945. doi: 10.1094/PDIS-12-15-1398-RE. Epub 2016 Aug 9.
Pecan scab (caused by Fusicladium effusum) is the most economically destructive disease of pecan in the Southeast United States. Wet, humid conditions typical of the Southeast are known to provide conditions conducive to epidemics. A provenance collection of pecan from 19 locations representing the native range of the tree is located in Byron, Georgia, and was assessed for pecan scab severity in 1998, 2013, and 2014. There were significant differences among the 19 provenances (F = 5.6 to 62.5, P < 0.0001). Provenances from wetter locations (generally north of Texas) had the greatest proportion of scab resistant trees, while provenances from the drier southern areas (Texas and Mexico) tended to be the most susceptible to scab. The association with rainfall was borne out by correlation analysis (r = -0.625 to -0.823 [P < 0.0001 to 0.004]). Other factors consistently associated with scab severity included leaflet tilt and droop angle (r = -0.533 to -0.883 [P < 0.0001 to 0.02]). Multiple regression analysis demonstrated that leaflet droop angle was a particularly good predictor of provenance susceptibility. Leaflet characteristics vary with provenance location, and whether there is a direct relationship between scab severity and leaflet characteristics is not established. Estimates of heritability were not entirely consistent among years, but different methods were used to assess scab severity in 1998 (a 1 to 5 category scale) compared with 2013 and 2014 (the percent ratio scale). Despite using different methods, there was generally good agreement among years in regard to severity of disease on individual trees. In conclusion, trees from more northern populations (in areas with greater annual rainfall) are most likely to provide valuable and diverse sources of resistance to scab. The provenance collection contains a range of scab-resistant genotypes from diverse locations that can contribute to genetic improvement regarding scab resistance.
山核桃疮痂病（由扩散黑星孢引起）是美国东南部对山核桃经济破坏最严重的病害。美国东南部典型的潮湿、湿润环境已知会提供有利于该病流行的条件。在佐治亚州拜伦市有一个来自19个地点的山核桃种源收集区，这些地点代表了山核桃树的原生范围，并在1998年、2013年和2014年对山核桃疮痂病的严重程度进行了评估。19个种源之间存在显著差异（F = 5.6至62.5，P < 0.0001）。来自较湿润地区（一般在得克萨斯州以北）的种源中抗疮痂病的树木比例最高，而来自较干燥的南部地区（得克萨斯州和墨西哥）的种源往往最易感染疮痂病。相关性分析证实了与降雨量的关联（r = -0.625至 -0.823 [P < 0.0001至0.004]）。其他始终与疮痂病严重程度相关的因素包括小叶倾斜度和下垂角度（r = -0.533至 -0.883 [P < 0.0001至0.02]）。多元回归分析表明，小叶下垂角度是种源易感性的一个特别好的预测指标。小叶特征因种源地点而异，且疮痂病严重程度与小叶特征之间是否存在直接关系尚未确定。遗传力估计在不同年份并不完全一致，但1998年（采用1至5级分类量表）与2013年和2014年（采用百分比比例量表）评估疮痂病严重程度的方法不同。尽管使用了不同方法，但不同年份间关于单株树木疾病严重程度总体上有较好的一致性。总之，来自更北部种群（年降雨量更大地区）的树木最有可能提供对抗疮痂病有价值且多样的抗性来源。该种源收集区包含来自不同地点的一系列抗疮痂病基因型，可有助于在抗疮痂病方面进行遗传改良。
