Moore M J, Ostry M E, Hegeman A D, Martin A C
Northern Research Station, USDA Forest Service, St. Paul, MN.
Department of Horticulture, University of Minnesota, St. Paul.
Plant Dis. 2015 Mar;99(3):401-408. doi: 10.1094/PDIS-06-14-0642-RE.
A rapid and reliable technique is needed for identifying butternut trees (Juglans cinerea) with resistance to butternut canker. We investigated the potential of a bark extract bioassay to detect levels of resistance to Ophiognomonia clavigignenti-juglandacearum (Oc-j), the causal agent of butternut canker. Both reagent grade naphthoquinones and crude bark extracts of Juglans species inhibited germination of Oc-j conidia. A disc diffusion bioassay was used to study the level of inhibition by these bark extracts and results indicated extensive variation within and between butternut and other species of Juglans tested. In many months over a 3 year period, bark from butternut trees selected for apparent disease resistance could be distinguished from that of unselected trees. Inhibition of conidia germination roughly correlated to the level of resistance observed in field inoculations of the trees. Quantification of the naphthoquinone compounds juglone and plumbagin in butternut bark was performed using ultra-high performance liquid chromatography mass spectrometry. While the concentrations of these two compounds varied by month and by individual tree, juglone levels correlated well with the bark extract bioassay in some months. These results suggest that juglone concentration may account in part for the observed range of inhibition observed in the bioassay and variation in canker resistance among selections of butternut field inoculated with Oc-j. The bark extract bioassay described in the following report may have potential use for selecting resistant butternut for conservation and restoration purposes.
需要一种快速可靠的技术来鉴定对胡桃溃疡病具有抗性的白核桃树（Juglans cinerea）。我们研究了树皮提取物生物测定法检测对白核桃溃疡病病原菌——胡桃间座壳菌（Ophiognomonia clavigignenti-juglandacearum，Oc-j）抗性水平的潜力。试剂级萘醌和胡桃属物种的粗树皮提取物均能抑制Oc-j分生孢子的萌发。采用纸片扩散生物测定法研究这些树皮提取物的抑制水平，结果表明，在所测试的白核桃和其他胡桃属物种内部及之间存在广泛差异。在3年的许多个月里，被选为具有明显抗病性的白核桃树的树皮与未选树木的树皮可以区分开来。分生孢子萌发的抑制大致与在田间接种树木中观察到的抗性水平相关。使用超高效液相色谱质谱法对白核桃树皮中的萘醌化合物胡桃醌和扁蓄醌进行定量。虽然这两种化合物的浓度因月份和单株树木而异，但在某些月份，胡桃醌水平与树皮提取物生物测定法相关性良好。这些结果表明，胡桃醌浓度可能部分解释了生物测定中观察到的抑制范围以及接种Oc-j的白核桃田间选种中溃疡病抗性的差异。以下报告中描述的树皮提取物生物测定法可能在选择抗性白核桃用于保护和恢复目的方面具有潜在用途。
