Fall M L, Van der Heyden H, Beaulieu C, Carisse O
Biology Department, University of Sherbrooke, Sherbrooke, QC, Canada J1K 2R1 and Horticulture Research and Development Centre, Agriculture and Agri-Food Canada, St-Jean-sur-Richelieu, QC, Canada J3B 3E6.
Compagnie de Recherche Phytodata Inc., Sherrington, QC, Canada J0L 2N0.
Plant Dis. 2015 Jul;99(7):1010-1019. doi: 10.1094/PDIS-05-14-0548-RE. Epub 2015 Jun 5.
More than 80% of Canadian lettuce production is located in the province of Quebec. Yet most of our knowledge on the epidemiology of lettuce downy mildew (Bremia lactucae) is derived from controlled-condition experiments or field experiments conducted in subtropical climates and, thus, cannot readily be applied to Quebec lettuce production. The influence of temperature and leaf wetness duration on the infection efficiency (IE) of B. lactucae was studied for 4 years (2003, 2004, 2012, and 2013) under field and growth-chamber conditions. IE was defined as the ratio of the number of lesions/leaf to the airborne conidia concentration (ACC). B. lactucae ACC was measured with rotating-arm samplers three times/week. In addition, 72 lettuce trap plants/sampling day were exposed to the potential airborne B. lactucae inoculum and disease intensity was assessed after 7 days of incubation in greenhouse. Under growth-chamber conditions, an ACC of 1 conidium/m was sufficient to cause 1 lesion/leaf, and IE ranged from 0.25 to 1.00. Under field conditions, an ACC of 10 to 14 conidia/m was required to cause 1 lesion/leaf, and IE ranged from 0.02 to 0.10, except in 2004, when IE ranged from 0.03 to 1.00. IE increased with increasing leaf wetness duration but decreased with increasing temperature. Also, considering an observed average temperature range from 10 to 20°C in the area of Quebec, 2 h of leaf wetness was sufficient for infection by B. lactucae. Therefore, under Quebec lettuce production conditions, a leaf wetness period of 2 h and an ACC of 10 to 14 conidia/m can be used as risk indicators to facilitate disease management decisions. Also, under typical Quebec weather conditions, measuring both morning and evening leaf wetness events could be used to improve the reliability of leaf wetness duration as a downy mildew risk indicator. Further research is needed to validate these risk indicators for integration into management strategies.
加拿大80%以上的生菜产量集中在魁北克省。然而，我们对生菜霜霉病（Bremia lactucae）流行病学的了解大多来自于在亚热带气候下进行的控制条件实验或田间实验，因此不能直接应用于魁北克的生菜生产。在田间和生长室条件下，对温度和叶片湿润持续时间对生菜霜霉病菌感染效率（IE）的影响进行了为期4年（2003年、2004年、2012年和2013年）的研究。IE定义为病斑数/叶片数与空气中分生孢子浓度（ACC）的比值。使用旋转臂采样器每周三次测量生菜霜霉病菌ACC。此外，每天设置72株生菜诱捕植株暴露于潜在的空气中生菜霜霉病菌接种物中，并在温室中培养7天后评估病害严重程度。在生长室条件下，ACC为1个分生孢子/立方米就足以导致1个病斑/叶片，IE范围为0.25至1.00。在田间条件下，导致1个病斑/叶片需要ACC为10至14个分生孢子/立方米，IE范围为0.02至0.10，但2004年除外，当年IE范围为0.03至1.00。IE随着叶片湿润持续时间的增加而增加，但随着温度的升高而降低。此外，考虑到魁北克地区观测到的平均温度范围为10至20°C，2小时的叶片湿润时间足以让生菜霜霉病菌感染。因此，在魁北克生菜生产条件下，2小时的叶片湿润期和10至14个分生孢子/立方米的ACC可作为风险指标，以促进病害管理决策。此外，在魁北克典型的天气条件下，同时测量早晨和傍晚的叶片湿润情况可用于提高叶片湿润持续时间作为霜霉病风险指标的可靠性。需要进一步研究来验证这些风险指标，以便将其纳入管理策略。
