Yakabe L E, Parker S R, Kluepfel D A
United States Department of Agriculture-Agricultural Research Service Crops Pathology and Genetics Research Unit, Department of Plant Pathology, University of California-Davis 95616.
Plant Dis. 2014 Jun;98(6):766-770. doi: 10.1094/PDIS-07-13-0742-RE.
The walnut rootstock 'Paradox' (Juglans hindsii × J. regia) is susceptible to Agrobacterium tumefaciens, which often results in a high incidence of crown gall in nursery or walnut production orchards. Though A. tumefaciens is susceptible to the commonly used preplant soil fumigants, crown gall incidence can rise above acceptable levels. We examined the ability of Paradox seed to acquire A. tumefaciens as a function of harvest method used prior to planting. Over a 2-year period at two participating commercial nurseries, Paradox seed were collected directly from the mother tree without contacting the soil or gathered after sitting on the orchard floor for up to 28 days. A. tumefaciens was never detected in or on the 2,650 seeds collected directly from the mother tree. Both virulent and avirulent A. tumefaciens strains were detected in and on the husk of nuts incubated on the orchard floor at a frequency directly proportional to the time spent on the orchard floor. Regardless of A. tumefaciens contamination in or on the husk, A. tumefaciens was never detected in the seed interior. Avoiding soilborne populations of A. tumefaciens at the time of seed collection will play an important role in managing crown gall.
核桃砧木“Paradox”（黑核桃×胡桃）对根癌土壤杆菌敏感，这常常导致苗圃或核桃生产果园中冠瘿病的高发病率。虽然根癌土壤杆菌对常用的种植前土壤熏蒸剂敏感，但冠瘿病发病率仍可能升至可接受水平之上。我们研究了Paradox种子获取根癌土壤杆菌的能力与种植前采用的收获方法之间的关系。在两年时间里，在两家参与的商业苗圃中，Paradox种子要么直接从母树上采集而不接触土壤，要么在果园地面放置长达28天后收集。直接从母树上采集的2650颗种子内部及表面均未检测到根癌土壤杆菌。在果园地面放置的坚果外壳上及内部均检测到了致病和非致病的根癌土壤杆菌菌株，其频率与在果园地面放置的时间成正比。无论坚果外壳上及内部是否存在根癌土壤杆菌污染，种子内部均未检测到根癌土壤杆菌。在种子采集时避免根癌土壤杆菌的土壤传播种群，对冠瘿病的管理将起到重要作用。
