Abstract In the spring of 2018, necrotic and canker symptoms were observed on stems of young apple trees that were bench-grafted by growers on four rootstocks (EMLA 9, Supporter 4, M9-T337 and Pajam 2) in Annapolis Valley, Nova Scotia. The objective of this study was to isolate and identify the causal organism of the disease on apple rootstocks. The diseased tissue obtained from eight infected plants of the four rootstocks showing visible necrotic and canker symptoms was used for microorganism isolation on potato dextrose agar (PDA). More than 90% of the isolates on PDA yielded a similar type of fungal colony. Based on the colony and spore morphology and presence of both α and β spores, Diaporthe was proposed as a major pathogen from the symptomatic tissue. Analysis of partial sequences of four unlinked loci DNA-lyase (APN2), histone-3 (HIS), translation elongation factor 1 alpha (TEF1-α) and the internal transcribed spacer (ITS) 5.8S region of rDNA of the representative fungal isolates from young apple trees confirmed its identity as D. eres (Phomopsis fukushii). The pathogenicity of the representative D. eres isolate was confirmed on 1-year-old young apple trees bench-grafted on four different rootstocks in greenhouse tests. Necrotic and sunken canker symptoms like those observed on the nursery-grown young apple trees appeared on stems of all inoculated plants. The necrotic and canker lesions were observed 3 days after inoculation; they spread both directions from the inoculation point and led to the death of the young plants after 4 weeks. To our knowledge, this is the first report of D. eres causing stem canker and death of young apple rootstock in Canada.

中文翻译：

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Diaporthe eres 导致加拿大的年轻苹果砧木发生茎溃疡和死亡

摘要 2018 年春季，在新斯科舍省安纳波利斯谷的四种砧木（EMLA 9、支持者 4、M9-T337 和 Pajam 2）上，种植者在台栽苹果幼树的茎上观察到坏死和溃疡症状。本研究的目的是在苹果砧木上分离和鉴定该病害的致病微生物。从表现出可见坏死和溃疡症状的四种砧木的八株感染植物中获得的患病组织用于在马铃薯葡萄糖琼脂（PDA）上进行微生物分离。PDA 上 90% 以上的分离株产生了相似类型的真菌菌落。根据菌落和孢子形态以及 α 和 β 孢子的存在，建议 Diaporthe 作为来自有症状组织的主要病原体。分析四个未连接位点 DNA 裂解酶 (APN2)、组蛋白 3 (HIS)、来自年轻苹果树的代表性真菌分离株的 rDNA 的翻译延伸因子 1 α (TEF1-α) 和内部转录间隔区 (ITS) 5.8S 区域证实其身份为 D. eres (Phomopsis fukushii)。代表性 D. eres 分离株的致病性在温室试验中在四种不同砧木上的 1 年龄苹果幼树上得到证实。所有接种植物的茎上都出现了坏死和凹陷溃疡症状，就像在苗圃种植的年轻苹果树上观察到的那样。接种3天后观察坏死和溃疡病灶；它们从接种点向两个方向传播，并在 4 周后导致幼苗死亡。据我们所知，这是加拿大第一次报告 D. eres 导致茎溃疡和年轻苹果砧木死亡。