Zhang Guirong, Thompson Arthur, Schisler David, Johnson Eric T
Crop Bioprotection Research Unit, USDA ARS, Peoria, IL, 61604, USA.
Heliyon. 2019 Jan 31;5(1):e01117. doi: 10.1016/j.heliyon.2019.e01117. eCollection 2019 Jan.
Basil downy mildew caused by is a disease of sweet basil () production worldwide. In this study, sweet basil was grown in plant growth chambers and inoculated with sporangia of harvested from previously infected plants. Plants were placed in closed, clear plastic bags and leaves harvested over time and observed using scanning electron microscopy. In most cases, sporangia germinated myceliogenically on abaxial and adaxial leaf surfaces as early as three days after inoculation. Germ tubes and the tips of hyphae ramifying on leaf surfaces directly penetrated basil leaves to initiate the infection process. Hyphal growth was not observed to gain entrance to the interior of leaves through stomata, though growth over these openings was observed. Most frequently, seven days after inoculation, one or more sporangiophores grew through stomata to produce new sporangia on both the abaxial and adaxial surfaces of leaves. Macroscopic signs of infection were visible on both sides of leaves approximately ten days after inoculation under the conditions of this study. These results contribute to a better understanding of the infection process and disease onset of and should help in the development of more effective measures for reducing basil downy mildew.
由[病原体名称未给出]引起的罗勒霜霉病是一种在全球范围内影响甜罗勒（[植物学名未给出]）生产的病害。在本研究中，甜罗勒种植于植物生长室，并接种从先前感染植株上采集的[病原体名称未给出]的孢子囊。将植株置于封闭的透明塑料袋中，随时间采集叶片，并使用扫描电子显微镜进行观察。在大多数情况下，接种后最早三天，孢子囊就在叶片的背面和正面以菌丝体方式萌发。萌发管和在叶表面分支的菌丝顶端直接穿透罗勒叶片以启动感染过程。未观察到菌丝通过气孔进入叶片内部生长，不过在这些开口处有生长现象。最常见的情况是，接种七天后，一个或多个孢子囊梗通过气孔生长，在叶片的背面和正面产生新的孢子囊。在本研究条件下，接种后约十天，叶片两面都出现了肉眼可见的感染症状。这些结果有助于更好地理解[病原体名称未给出]的感染过程和病害发生情况，并应有助于制定更有效的措施来减少罗勒霜霉病。
