Inoculum production and evaluation of temperature and leaf wetness for Passalora sojina inoculation in soybean

ABSTRACT The objective of this study was to develop a methodology for inoculum production and inoculation of Passalora sojina in soybean to assess the reaction to frogeye leaf spot. Thus, sporulation of fungal races was quantified in five substrates under two light regimes. The temperature and the leaf wetness period that resulted in greater infection efficiency were also determined. Petri dishes containing the culture media Oat Flour Agar (OFA), Tomato Juice (FTJ), V8 agar juice (V8), Infant Food (IF) and Potato Sucrose Agar (PSA) plus isolates of P. sojina races 23, 24 and 25 were subjected to 12-h photoperiod and 24-h continuous dark. Inoculated plants were incubated at temperatures of 15, 20, 25, 30 and 35 ºC and leaf wetness periods of 12, 24, 36, 48 and 72 hours. Experimental design was completely randomized with five replicates. There was interaction among isolate, culture medium and photoperiod. The highest sporulation (conidia/cm2) was obtained in the culture media FTJ (race 23) and V8 (races 24 and 25) under 12-h photoperiod. The optimum temperature for the disease development was 27oC under 72 hours of continuous leaf wetness.

摘要 本研究旨在建立一套大豆蛙眼叶斑病（frogeye leaf spot）病原菌大豆柱隔孢（Passalora sojina）的接种物制备与接种技术体系，以评估大豆对该病害的抗病反应。为此，我们在两种光照制度下，对五种培养基上的真菌菌株产孢量进行了定量分析，并测定了可实现最高侵染效率的温度与叶片保湿时长。
将分别接种大豆柱隔孢菌株23、24、25号的燕麦粉琼脂（Oat Flour Agar, OFA）、番茄汁培养基（Tomato Juice, FTJ）、V8汁琼脂（V8 agar juice）、婴儿食品培养基（Infant Food, IF）及马铃薯蔗糖琼脂（Potato Sucrose Agar, PSA）培养皿，分别置于12小时光照周期与24小时全黑暗条件下培养。
对接种后的植株，设置15、20、25、30、35℃共5个温度梯度，以及12、24、36、48、72小时共5个叶片保湿时长梯度进行培养。实验采用完全随机设计，设置5次重复。
数据分析显示菌株、培养基与光照周期三者间存在交互作用。在12小时光照周期条件下，菌株23的最高产孢量（分生孢子/平方厘米）出现在FTJ培养基中，菌株24与25的最高产孢量则出现在V8汁琼脂培养基中。该病害发展的最适温度为27℃，此时需配合72小时连续叶片保湿处理。