Horticultural Crops Research Laboratory, U.S. Department of Agriculture Agricultural Research Service, Corvallis, OR 97330.
Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR 97331.
Plant Dis. 2020 Jun;104(6):1841-1850. doi: 10.1094/PDIS-08-19-1672-RE. Epub 2020 May 5.
Rhododendron root rot is a severe disease that causes significant mortality in rhododendrons. Information is needed about the incidence and identity of soilborne and species causing root rot in Pacific Northwest nurseries in order to better understand the disease etiology and to optimize disease control strategies. The last survey focusing solely on soilborne oomycete pathogens in rhododendron production was conducted in 1974. Since then, advances in pathogen identification have occurred, new species may have been introduced, pathogen communities may have shifted, and little is known about species affecting this crop. Therefore, a survey of root-infecting and species was conducted at seven nurseries from 2013 to 2017 to (i) document the incidence of root rot damage at each nursery and stage of production, (ii) identify soilborne oomycetes infecting rhododendron, and (iii) determine whether there are differences in pathogen diversity among nurseries and production systems. Rhododendrons from propagation, container, and field systems were sampled and and species were isolated from the roots and collar region. Root rot was rarely evident in propagation systems, which were dominated by species. However, severe root rot was much more common in container and field systems where the genus was also more prevalent, suggesting that species are the primary cause of severe root rot and that most contamination by these pathogens comes in after the propagation stage. In total, 20 species and 11 species were identified. , aff. , , and were the most frequently isolated species and the results showed that has become much more common than in the past. diversity was also greater in field systems than in propagation or container systems. Risks for contamination were commonly observed during the survey and included placement of potting media in direct contact with field soil, the presence of dead plants that could serve as continuous sources of inoculum, and the presence of excess water as a result of poor drainage, overirrigation, or malfunctioning irrigation equipment. In the past, research on disease development and root rot disease control in rhododendron focused almost exclusively on . More research is needed on both of these topics for the other root-infecting species identified in this survey.
杜鹃根腐病是一种严重的疾病，会导致杜鹃死亡率显著增加。为了更好地了解病因并优化防治策略，需要了解西北太平洋苗圃中引起杜鹃根腐病的土壤传播和种类的发病率和身份。最后一次专门针对杜鹃生产中土传卵菌病害的调查是在 1974 年进行的。此后，病原菌鉴定方面取得了进展，可能引入了新的物种，病原体群落可能发生了变化，而且对影响该作物的物种知之甚少。因此，从 2013 年到 2017 年，在七个苗圃进行了根侵染和物种的调查，以：(i)记录每个苗圃和生产阶段的根腐病损害发生率；(ii)鉴定侵染杜鹃的土壤卵菌；(iii)确定苗圃和生产系统之间的病原体多样性是否存在差异。从繁殖、容器和田间系统中采集杜鹃，并从根部和茎部区域分离和物种。繁殖系统中很少出现根腐病，以物种为主。然而，在容器和田间系统中，根腐病更为常见，而且属也更为普遍，这表明物种是严重根腐病的主要原因，而且这些病原体的大多数污染发生在繁殖阶段之后。总共鉴定出 20 个种和 11 个种。aff. 、、、和是最常分离的种，结果表明比过去更为常见。田间系统中的多样性也大于繁殖或容器系统。在调查过程中，经常观察到种污染的风险，包括将盆栽介质直接放置在田间土壤中、存在可能作为连续接种体来源的死植物，以及由于排水不良、过度灌溉或灌溉设备故障导致的积水过多。过去，杜鹃病害发展和根腐病防治的研究几乎完全集中在属上。本调查中鉴定的其他根侵染种需要对这两个主题进行更多研究。
