Department of Plant Pathology, University of Stellenbosch, Private Bag X1 Matieland, 7602, South Africa.
Plant Protection Division, ARC Infruitec-Nietvoorbji, Private Bag X5026, Stellenbosch, 7599, South Africa.
Plant Dis. 2019 Dec;103(12):3129-3141. doi: 10.1094/PDIS-04-19-0867-RE. Epub 2019 Oct 22.
Canker and wood rot pathogens cause dieback and, in severe cases, the death of young apple trees. Recently, a higher occurrence of cankers was observed on 1-year-old apple trees in the Western Cape Province of South Africa. This study aimed to assess the phytosanitary status of nursery trees and propagation material as possible inoculum sources for canker pathogens. Thirteen 1-year-old apple orchards showing canker or dieback symptoms were sampled. Certified nursery apple trees were collected from four nurseries as well as scion and rootstock mother plant material. Isolations were made from the discoloration observed in the vascular tissue of the plant parts and from asymptomatic material. Possible canker and wood rot species were identified with PCR and sequence comparisons of the relevant gene regions and phylogenetic analyses. Similar canker and wood rot species were isolated from 1-year-old diseased apple trees, nursery apple trees, and the propagation material. Forty-five fungal species associated with canker or wood rot symptoms were identified. The top five most abundant fungal species found causing disease on commercial 1-year-old trees were also found in high numbers causing latent infection in certified apple nursery trees. These species were sensu lato, , , , and , with sensu lato being the dominant species in both sampling materials. In all, 65% of certified nursery apple trees, 5% of scion shoots used for budding, and 21% of rooted rootstock cuttings from layer blocks had latent infections of canker and wood rot pathogens. Pathogenicity trials were conducted with isolates of 39 species, inoculated onto 2-year-old branches of 14-year-old Golden Delicious trees. All species caused lesions that were significantly longer than the control. This study confirmed the presence of canker and wood rot pathogens in apple propagation material as well as certified nursery apple trees, which will aid the improvement of management practices in nurseries.
溃疡和木腐病菌会导致苹果树枯死，严重时会导致幼树死亡。最近，南非西开普省的一年生苹果树出现了更高的溃疡病发生率。本研究旨在评估苗圃树木和繁殖材料作为溃疡病原菌接种体来源的植物检疫状况。对表现出溃疡或枯萎症状的 13 个 1 年生苹果园进行了采样。从四个苗圃收集了经过认证的苹果苗圃树，以及接穗和砧木母株材料。从植物组织的变色部位和无症状部位进行分离。通过 PCR 和相关基因区域的序列比较以及系统发育分析来鉴定可能的溃疡和木腐病物种。从 1 年生患病苹果树、苗圃苹果树和繁殖材料中分离出了相似的溃疡和木腐病物种。鉴定出与溃疡或木腐病症状相关的 45 种真菌。在商业 1 年生树上引起疾病的前 5 种最丰富的真菌物种也在大量发现的导致经认证的苹果苗圃树潜伏感染的物种中发现。这些物种是 sensu lato ， ， ， ， 和 ，其中 sensu lato 是两种采样材料中的优势种。在所有经过认证的苹果苗圃树中，65%的树、用于芽接的接穗的 5%和层块生根砧木插条的 21%都存在溃疡和木腐病原菌的潜伏感染。用 39 种分离物进行了致病性试验，将其接种到 14 年生金冠苹果树的 2 年生枝条上。所有物种都导致了比对照明显更长的病变。本研究证实了溃疡和木腐病原菌在苹果繁殖材料和经认证的苗圃苹果树中的存在，这将有助于改善苗圃管理实践。
