Harmon Philip F, Latin Richard
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907.
Plant Dis. 2005 Apr;89(4):412-418. doi: 10.1094/PD-89-0412.
Winter survival of Magnaporthe oryzae in north central Indiana was investigated in response to reports and observations of sporadic disease incidence. Survival of the fungus in perennial ryegrass residue was assessed. Time course studies were designed to assess the conidia production potential of infested perennial ryegrass residue exposed to ambient and predetermined treatments. Approximately 50,000 conidia per gram dry weight were produced initially on infested residue. In all years of the study, ambient winter conditions in Lafayette, IN, reduced conidia production on residue to fewer than 60 conidia per gram by spring. Unless residue was dried prior to treatment, storage of residue at all temperatures tested reduced conidia production potential. Airborne M. oryzae conidia, over the plot of perennial ryegrass where the winter survival studies were conducted, were estimated from particles collected with a volumetric air sampler. The stand of perennial ryegrass was inoculated with residue infested with M. oryzae in the summer of 2000 and late fall of 2000 and 2001. The stand of ryegrass was not inoculated in the summers of 200l or 2002. Conidia were captured with the air sampler each year in early July, before outbreaks had been observed in north central Indiana, but capture peaked in September when outbreaks most often occur. Cumulative conidia capture followed disease severity in 2000; however, no disease was observed in 2001 or 2002. Results of this study suggest poor survival of M. oryzae, and inadequate populations of viable pathogen limit disease development in north central Indiana. Disease risk assessment in north central Indiana should include an estimate of viable inoculum.
针对有关零星发病情况的报告和观察结果，对稻瘟病菌在印第安纳州中北部的冬季存活情况展开了调查。评估了该真菌在多年生黑麦草残体中的存活情况。设计了时间进程研究，以评估受侵染的多年生黑麦草残体在自然环境和预定处理条件下产生分生孢子的潜力。最初，每克干重的受侵染残体可产生约50,000个分生孢子。在研究的所有年份中，印第安纳州拉斐特市的冬季自然条件使残体上的分生孢子产量在春季降至每克少于60个。除非在处理前将残体干燥，否则在所有测试温度下储存残体都会降低分生孢子的产生潜力。通过用容积式空气采样器收集的颗粒，估算了进行冬季存活研究的多年生黑麦草地块上空的稻瘟病菌分生孢子数量。在2000年夏季以及2000年和2001年的深秋，用受稻瘟病菌侵染的残体对多年生黑麦草植株进行了接种。在2001年或2002年夏季未对黑麦草植株进行接种。每年7月初，在印第安纳州中北部尚未观察到病害爆发之前，用空气采样器捕获分生孢子，但捕获量在9月达到峰值，此时最常发生病害爆发。2000年，分生孢子的累积捕获量与病害严重程度相符；然而，在2001年和2002年未观察到病害。本研究结果表明，稻瘟病菌的存活率较低，且存活的病原菌数量不足限制了印第安纳州中北部病害的发展。印第安纳州中北部的病害风险评估应包括对存活接种体的估计。
