Department of Plant Pathology, Kearney Agricultural Research and Extension Center, University of California Davis, Parlier, CA 93648.
Phytopathology. 2022 Jul;112(7):1454-1466. doi: 10.1094/PHYTO-10-21-0434-R. Epub 2022 Jun 15.
Dieback caused by spp. is an emerging disease in California citrus groves. A large-scale survey with emphasis on seasonal variations of latent infections was conducted throughout citrus orchards in Fresno, Kern, and Tulare counties in 2019 and 2020. Latent infections on citrus leaves and twigs varied markedly between years. Isolates of spp. were obtained from asymptomatic tissue, and two groups were formed based on colony and spore morphology. The morphological groups were further identified based on multigene sequence analysis using the DNA regions ITS1-5.8S-ITS2, TUB2, and GAPDH. Results revealed that isolates belong to two phylogenetic species, and , being more frequently isolated. Representative isolates of each species were further selected and characterized based on the response of physiological variables to temperature. Both species had similar optimum growth temperatures but differed in maximum growth rates, with exhibiting a greater growth rate than that of on media. Pathogenicity tests on citrus trees demonstrated the ability of and to cause lesions on twigs and no differences in aggressiveness. A fungicide screening performed in this study determined that the DMI fungicides were the most effective in reducing the mycelial growth of and . The QoI fungicides showed a remarkably inhibitory impact on spore germination of both species. On average, was more sensitive to the DMI fungicides than . The findings of this study provide new information to understand the dieback of citrus.
由 spp. 引起的枯萎病是加利福尼亚柑橘果园中的一种新兴疾病。2019 年和 2020 年，在弗雷斯诺、克恩和图莱里县的柑橘果园中进行了一项大规模调查，重点是潜伏感染的季节性变化。柑橘叶片和嫩枝上的潜伏感染在不同年份差异显著。从无症状组织中获得了 spp. 的分离物，并根据菌落和孢子形态将其分为两组。根据 ITS1-5.8S-ITS2、TUB2 和 GAPDH 区的 DNA 多基因序列分析进一步鉴定了形态组。结果表明，分离物属于两个系统发育种， 和 ， 更频繁地被分离。根据生理变量对温度的响应，进一步选择和表征了每种物种的代表性分离物。两种物种的最佳生长温度相似，但最大生长速率不同， 比 生长速度更快。对柑橘树的致病性测试表明， 和 能够在嫩枝上引起病变，且侵略性没有差异。本研究中的杀菌剂筛选确定，DMI 杀菌剂在抑制 和 的菌丝生长方面最有效。QoI 杀菌剂对两种真菌的孢子萌发都有显著的抑制作用。平均而言， 比 对 DMI 杀菌剂更敏感。本研究的结果提供了新的信息，以了解柑橘的 枯萎病。
