Russo Nicole L, Robinson Terence L, Fazio Gennaro, Aldwinckle Herb S
Department of Plant Pathology.
Department of Horticultural Sciences, Cornell University, Geneva, NY 14456.
Plant Dis. 2008 Mar;92(3):385-391. doi: 10.1094/PDIS-92-3-0385.
Erwinia amylovora, the causal agent of fire blight, can cause a fatal infection of apple rootstocks known as rootstock blight. Budagovsky 9 (B.9) apple rootstock is reported to be highly susceptible when inoculated with E. amylovora, although results from multiple trials showed that B.9 is resistant to rootstock blight infection in field plantings. Conflicting results could stem from genetic variation in the B.9 population, appearing as phenotypic differences in rootstock material. However, genetic testing, using 23 microsatellite loci, confirmed the clonal uniformity of B.9 in commerce. Variation in growth habit between B.9 rootstocks originating from two nurseries also has been discounted as a source of disease resistance. Instead, results indicate a possible novel resistance phenotype in B.9 rootstock. B.9 rootstock was susceptible to leaf inoculation by E. amylovora, statistically similar to the susceptible rootstock Malling 9 (M.9). Conversely, inoculation assays targeting woody 4- to 5-year-old tissue revealed a high level of resistance in B.9, whereas M.9 remained susceptible. Although the mechanism by which B.9 gains resistance to E. amylovora is unknown, it is reminiscent of age-related resistance, due to an observed gain of resistance in woody rootstock tissue over succulent shoot tissue. Durable fire blight resistance correlated with tissue development could be a valuable tool for rootstock breeders.
梨火疫病菌（Erwinia amylovora）是火疫病的致病因子，可导致苹果砧木发生一种致命感染，即砧木疫病。据报道，芽接9号（B.9）苹果砧木接种梨火疫病菌后高度感病，尽管多项试验结果表明，B.9在田间种植中对砧木疫病感染具有抗性。相互矛盾的结果可能源于B.9群体中的遗传变异，表现为砧木材料的表型差异。然而，使用23个微卫星位点进行的基因检测证实了商业上B.9的克隆一致性。源自两个苗圃的B.9砧木在生长习性上的差异也被排除为抗病性的来源。相反，结果表明B.9砧木可能存在一种新的抗性表型。B.9砧木对梨火疫病菌的叶片接种敏感，在统计学上与感病砧木马林9号（M.9）相似。相反，针对4至5年生木质组织的接种试验显示B.9具有高度抗性，而M.9仍然易感。尽管B.9对梨火疫病菌产生抗性的机制尚不清楚，但由于观察到木质砧木组织比多汁嫩枝组织获得了抗性，这让人联想到与年龄相关的抗性。与组织发育相关的持久火疫病抗性可能是砧木育种者的一个有价值的工具。
