Since the summer 2017, severe decline symptoms have been observed on 10‐ to 25‐year‐old avocado trees in almost all commercial orchards planted in the Mediterranean coastal region of Turkey. Young, newly planted trees in infected orchards were also affected by the disease. Affected trees showed wilting, leaf discoloration, defoliation and severe dieback. Some trees were completely desiccated. Although fine roots of symptomatic trees usually were decayed, reddish brown cankers also occurred on taproots and lateral roots of heavily infected trees. The pathogens were isolated from necrotic root and soil samples of symptomatic trees, using selective medium and soil baiting, and were identified based on morphological features and DNA sequences of the internal transcribed spacer (ITS) region. One isolate each of Phytophthora cryptogea and P. palmivora was identified, while all other isolates were P. cinnamomi. In addition, a subcortical fan‐shaped mycelium, characteristic of Armillaria spp., was observed in the stem base of a symptomatic tree and identified as Armillaria gallica by DNA sequences of the internal transcribed spacer (ITS) and the translational elongation factor 1‐α (EF 1‐α) gene regions. Pathogenicity of Phytophthora isolates was tested by stem inoculation on one‐year‐old avocado seedlings. Two months after inoculation, canker lesions developed on stems of seedlings inoculated by any of the three Phytophthora spp. In contrast, collenchyma callus formed over the wound points on control plants over the same time period. This is the first report of P. cinnamomi, P. cryptogea, P. palmivora and A. gallica causing root rot of avocado trees in Turkey. In addition, P. cryptogea and A. gallica are reported for the first time associated with disease on this host. Due to the severe symptoms and widespread occurrence, P. cinnamomi should be considered a potential threat to avocado cultivation and natural ecosystems of this region of Turkey.

中文翻译：

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肉桂疫霉爆发导致土耳其南部鳄梨树严重衰退

自 2017 年夏季以来，在土耳其地中海沿岸地区种植的几乎所有商业果园中，10 至 25 年树龄的鳄梨树都出现了严重的衰退症状。受感染果园中新种植的幼树也受到这种疾病的影响。受影响的树木表现出枯萎、叶片变色、落叶和严重枯死。一些树完全干枯了。虽然有症状的树木的细根通常已经腐烂，但在严重感染的树木的主根和侧根上也会出现红褐色的溃疡病。使用选择性培养基和土壤诱饵从有症状的树木的坏死根和土壤样本中分离病原体，并根据内部转录间隔区 (ITS) 区域的形态特征和 DNA 序列进行鉴定。分别分离出 Phytophthora cryptogea 和 P. 鉴定出棕榈草，而所有其他分离株均为肉桂假单胞菌。此外，在一棵有症状的树的茎基部观察到一种具有蜜环菌属特征的皮质下扇形菌丝体，并通过内部转录间隔区 (ITS) 和翻译延伸因子 1-α 的 DNA 序列将其鉴定为 Armillaria Gallica (EF 1-α) 基因区域。通过对一年生鳄梨幼苗进行茎接种来测试疫霉属分离株的致病性。接种两个月后，三种疫霉属中任何一种接种的幼苗茎上出现溃疡病灶。相比之下，在同一时间段内，在对照植物的伤口点上形成了厚皮愈伤组织。这是 P. cinnamomi、P. cryptogea、P. palmivora 和 A. Gallica 在土耳其导致鳄梨树根腐病的第一份报告。此外，P。cryptogea 和 A. Gallica 首次被报道与该宿主的疾病有关。由于症状严重且广泛发生，肉桂假单胞菌应被视为对土耳其该地区鳄梨种植和自然生态系统的潜在威胁。