Mayorquin Joey S, Wang Danny H, Twizeyimana Mathias, Eskalen Akif
Department of Plant Pathology and Microbiology, University of California, Riverside 92521.
Plant Dis. 2016 Dec;100(12):2402-2413. doi: 10.1094/PDIS-03-16-0362-RE. Epub 2016 Sep 20.
Several members of the families Botryosphaeriaceae and Diatrypaceae are known as canker and dieback pathogens of a number of woody hosts. Because desert citrus production in California can occur in proximity to table grape production, it was suspected that fungi associated with grapevine cankers might also be associated with citrus branch canker and dieback decline. To determine the fungi associated with branch canker and dieback disease of citrus in the southern California desert regions, surveys were conducted from 2011 to 2013 in the major citrus-growing regions of Riverside, Imperial, and San Diego Counties. Cankered tissues were collected from branches showing symptoms typical of branch canker and dieback. Various fungal species were recovered from necrotic tissues and species were identified morphologically and by phylogenetic comparison of partial sequences of the internal transcribed spacer (ITS) region (ITS1-5.8S-ITS2), β-tubulin gene, and elongation factor 1-α genes with those of other species in GenBank. Four fungi, including Neoscytalidium hyalinum, Eutypella citricola, E. microtheca, and an unnamed Eutypella sp., were associated with branch canker. N. hyalinum was the most frequently recovered fungus from symptomatic tissues (31%) followed by E. citricola (10%), E. microtheca (4%), and the Eutypella sp. (2%). In pathogenicity tests, all fungi caused lesions when inoculated on 'Lisbon' lemon (citrus) branches. Lesions caused by the Eutypella sp. were significantly longer than those of the other Eutypella spp.; however, they did not differ significantly from those produced by N. hyalinum. The most-parsimonious unrooted trees based on the combined data of ITS and partial β-tubulin gene region sequences showed three distinct clades of Eutypella spp. (E. citricola, E. microtheca, and an unidentified Eutypella sp.). Similarly, ITS and partial translation elongation factor 1-α gene region sequences differentiated two species of Neoscytalidium, N. hyalinum and N. novaehollandiae. Identifying the diversity, distribution, and occurrence of these fungal pathogens is useful for the management of citrus branch canker and dieback disease in the desert citrus-growing regions of California.
葡萄座腔菌科和座囊菌科的几个成员是许多木本寄主的溃疡病和枝枯病病原体。由于加利福尼亚州的沙漠柑橘产区可能与鲜食葡萄产区相邻，因此人们怀疑与葡萄溃疡病相关的真菌也可能与柑橘枝溃疡病和枝枯病衰退有关。为了确定与南加利福尼亚沙漠地区柑橘枝溃疡病和枝枯病相关的真菌，于2011年至2013年在河滨县、帝国县和圣地亚哥县的主要柑橘种植区进行了调查。从表现出典型枝溃疡病和枝枯病症状的枝条上采集溃疡组织。从坏死组织中分离出各种真菌物种，并通过形态学以及将内部转录间隔区（ITS）区域（ITS1-5.8S-ITS2）、β-微管蛋白基因和延伸因子1-α基因的部分序列与GenBank中的其他物种进行系统发育比较来鉴定物种。四种真菌，包括透明新座壳孢、柑橘真壳囊孢、微小真壳囊孢和一种未命名的真壳囊孢属真菌，与枝溃疡病有关。透明新座壳孢是从有症状组织中最常分离到的真菌（31%），其次是柑橘真壳囊孢（10%）、微小真壳囊孢（4%）和真壳囊孢属真菌（2%）。在致病性试验中，所有真菌接种到“里斯本”柠檬（柑橘）枝条上时都会引起病斑。真壳囊孢属真菌引起的病斑明显比其他真壳囊孢属真菌的病斑长；然而，它们与透明新座壳孢产生的病斑没有显著差异。基于ITS和部分β-微管蛋白基因区域序列的组合数据构建的最简约无根树显示，真壳囊孢属真菌有三个不同的进化枝（柑橘真壳囊孢、微小真壳囊孢和一种未鉴定的真壳囊孢属真菌）。同样，ITS和部分翻译延伸因子1-α基因区域序列区分了两种新座壳孢属真菌，即透明新座壳孢和新荷兰新座壳孢。确定这些真菌病原体的多样性、分布和发生情况，对于加利福尼亚沙漠柑橘种植区柑橘枝溃疡病和枝枯病的管理是有用的。
