Smith V L
Department of Plant Pathology and Ecology, Connecticut Agricultural Experiment Station, New Haven 06504.
Plant Dis. 1999 Aug;83(8):782. doi: 10.1094/PDIS.1999.83.8.782B.
Powdery mildew of dogwood (Cornus florida L.) has been observed on landscape trees since 1992, and has been increasing in severity recently. In 1998, mildewed leaves (n = 100) were collected from each of four locations in Connecticut. White mildew colonies first appeared in the early summer, 4 to 6 weeks after leaf emergence, and the initial colonies rapidly coalesced to cover the entire adaxial leaf surface. Incidence on observed trees reached nearly 100%. Premature autumn coloration and defoliation occurred on those trees where incidence was highest; tree mortality due solely to powdery mildew was not observed. Cleistothecia were apparent on both adaxial and abaxial leaf surfaces within 4 to 6 weeks of initial infection. Mycelium was white in color, and conidiophores were three-celled with a slightly bent foot cell. Fibrosin bodies were not present in conidia (n = 400), which measured 14.1 m ± 0.80 × 28.1 m ± 1.60 (mean + standard error of the mean). Cleistothecia measured 114.7 m ± 1.77 in diameter, and had 4 to 10 dichotomously branched appendages, which measured 140.7 m ± 3.95 in length (1.23× cleistothecial diameter). The fungus was identified as Microsphaera pulchra based on mycelial, conidial, and cleistothecial characteristics (1). In addition, cleistothecia were found on twigs and on fallen leaves of dogwood; these overwintering cleistothecia contained mature asci and mature ascospores in March 1999. Microsphaera penicillata recently was redescribed to include only that species causing powdery mildew on Alnus spp., and having appendages 1.5× cleistothecial diameter (2). The fungus causing powdery mildew in Connecticut previously had been reported to be M. penicillata, which was not found in the present study. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer, New York, 1995.
自1992年以来，人们在景观树上观察到山茱萸（Cornus florida L.）白粉病，且病情最近愈发严重。1998年，从康涅狄格州的四个地点各采集了100片患病叶片。白色的霉菌菌落最早在初夏出现，即叶片长出4至6周后，最初的菌落迅速融合，覆盖了叶片的整个正面。观察到的树木发病率接近100%。发病率最高的那些树木出现了秋季提前变色和落叶的情况；未观察到仅由白粉病导致的树木死亡。在初次感染后的4至6周内，闭囊壳在叶片的正面和背面都很明显。菌丝体为白色，分生孢子梗为三细胞，基部细胞稍弯曲。分生孢子（n = 400）中没有纤维状小体，其大小为14.1μm ± 0.80 × 28.1μm ± 1.60（平均值 + 平均标准误差）。闭囊壳直径为114.7μm ± 1.77，有4至10个二叉状分枝的附属丝，长度为140.7μm ± 3.95（为闭囊壳直径的1.23倍）。根据菌丝体、分生孢子和闭囊壳的特征，该真菌被鉴定为美丽球针壳（Microsphaera pulchra）(1)。此外，在山茱萸的嫩枝和落叶上也发现了闭囊壳；这些越冬的闭囊壳在[具体年份]1999年3月含有成熟的子囊和成熟的子囊孢子。球针壳（Microsphaera penicillata）最近被重新描述，仅包括在桤木属植物上引起白粉病且附属丝为闭囊壳直径1.5倍的那个物种(2)。此前有报道称在康涅狄格州引起白粉病的真菌是球针壳，而在本研究中未发现该真菌。参考文献：(1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer, New York, 1995.
