Populational fluctuation of Cercospora beticola conidia in the air and its relationship with the severity of Cercospora leaf spot of beets

ABSTRACT In a field trial in 2016 and 2017, the fluctuation of Cercospora beticola conidia was quantified, as well as its relationship with the severity of Cercospora leaf spot in beets. Beet seeds of cultivar Boro were sown in four replicates, resulting in the evaluation of 80 plants. Conidia were collected by a “vane”-type spore trap containing a microscopic slide smeared with petroleum jelly, which was weekly quantified under a microscope. The disease severity was analyzed through a diagrammatic scale to evaluate the percentage of leaf area affected by the disease. The number of conidia and the severity of Cercospora leaf spot of beets were subjected to the calculation of Pearson correlation coefficient (r). In 2016 and 2017, the collection of conidia occurred concomitantly with the manifestation of the disease, probably because there was inoculum concentration in the air. The correlation between the variables fluctuation of conidial population and disease severity was significant, showing r=0.762 and r=0.768 for 2016 and 2017, respectively. The severity of the disease in beets is influenced by the presence of conidia collected from the air.

摘要：2016年与2017年的田间试验中，本研究对甜菜尾孢菌（Cercospora beticola）分生孢子（conidia）的种群波动进行了定量检测，并分析其与甜菜尾孢叶斑病（Cercospora leaf spot）病情严重度的相关性。本试验选用品种‘Boro’的甜菜种子设置4次重复播种，最终共计评估80株甜菜植株。采用搭载涂抹有凡士林（petroleum jelly）的载玻片（microscopic slide）的风标式孢子捕捉器（vane-type spore trap）收集分生孢子，每周在显微镜下对孢子数量进行定量统计。通过病情分级标准图（diagrammatic scale）评估病害导致的叶片受害面积占比，以此计算病情严重度。针对甜菜分生孢子数量与尾孢叶斑病病情严重度两组数据，计算皮尔逊相关系数（Pearson correlation coefficient，r）。2016年与2017年，分生孢子的收集时间与病害显现时间同步，推测原因为空气中存在高浓度的接种体。分生孢子种群波动与病情严重度之间的相关性显著，2016年与2017年的皮尔逊相关系数分别为r=0.762与r=0.768。甜菜尾孢叶斑病的病情严重度受空气中捕获的分生孢子数量影响。