Studies on inoculum sources of angular leaf spot of beans caused by Phaeoisariopsis griseola in Uganda

Abstract

Angular leaf spot of beans caused by Phaeoisariopsis griseola is a major problem on this crop in Eastern Africa. The sources of inoculum for this disease were investigated. The causal fungus was confirmed as seedborne in all the cultivars tested. The fungus caused seed discolouration but not all infected seeds were discoloured. Seed to seedling transmission was low. The fungus survived in infected crop debris for a maximum of nine and four to six months under indoor and outside conditions respectively. Under soil, the fungus survived for only two months. Infected offseason crops and volunteer plants were present at the time of planting the seasons’ crops and were an obvious source of the inoculum. It is concluded that the seed, crop debris, off‐season crops and volunteer plants are all possible sources of P. griseola infection under the local conditions.     

玉米麦根腐平脐蠕孢叶斑病的发生与病原鉴定

在河北省春播玉米WN2000和山东省夏播普通玉米上发现一种叶斑病,其病斑圆形或椭圆形,中心灰白色,边缘褐色,有黄褐色褪绿圈,糯玉米WN2000病斑较大,(3~10)mm×(3~5)mm;普通玉米病斑较小,(1~2)mm×(2~3)mm。通过病原菌分离培养、致病性测定、形态特征观察及r DNA-ITS和1,3,8-三羟基萘还原酶基因(3HNR)序列分析,证明两种大小病斑是由同一种病原菌—麦根腐平脐蠕孢(Bipolaris sorokiniana)引起。田间调查结果表明,在山东省夏播玉米各品种苗期叶片上均有不同程度的发病,发病率最高的为冠玉6号,病株率52%,最低的为五岳88,病株率2%;鲜食玉米仅在河北春播玉米WN2000上发生,发病率为32%。麦根腐平脐蠕孢侵染不同玉米品种产生两种大小不同的病斑在国内外尚属首次报道。     

Sibling species of cercospora associated with gray leaf spot of maize

ABSTRACT Monoconidial isolates of the fungus causing gray leaf spot of maize were obtained from diseased leaves collected throughout the United States and analyzed for genetic variability at 111 amplified fragment length polymorphism (AFLP) loci. Cluster analysis revealed two very distinct groups of Cercospora zeae-maydis isolates. Both groups were found to be relatively uniform internally with an average genetic similarity among isolates of approximately 93 and 94%, respectively. The groups were separated from each other by a genetic distance of approximately 80%, a distance greater than that separating each group from the sorghum pathogen, C. sorghi (67 to 70%). Characteristics and dimensions of conidia and conid-iophores produced on infected plants or nutrient media were unreliable criteria for taxonomic differentiation of isolates composing the two groups of C. zeae-maydis. Nucleotide sequences of 5.8S ribosomal DNA (rDNA) and the internal transcribed spacer (ITS) regions were identical within each group but different between the two groups and different from C. sorghi. Restriction fragment length polymorphisms generated by digestion of the 5.8S rDNA and ITS regions with TaqI readily distinguished each group and C. sorghi. Isolates in one group were generally distributed throughout maize-producing regions of the United States; isolates in the other group were localized in the eastern third of the country. Both types were present in the same fields at some locations. The genetic distance based on AFLP profiles and different ITS nucleotide sequences between the two morphologically indistinguishable groups indicate that they are sibling species. Although it is unlikely that breeding for resistance to gray leaf spot will be confounded by local or regional variation in the pathogen, a vigilant approach is warranted, because two pathogenic species exist with unknown abilities to evolve new pathotypes.     

杨树角斑病病原菌分离及其培养特性研究

对杨树角斑病菌进行分离和鉴定,并研究不同培养条件对其培养特性的影响,以获得病原菌的纯培养并筛选出最佳培养条件,为杨树角斑病防治提供理论参考。分别采用组织和单孢分离法分离病原菌,根据子实体形态和病菌rDNA ITS序列对其进行鉴定。观察不同培养基、温度、光照、pH对病原菌生长的影响。结果表明,自然条件下,用杨树角斑病菌的分生孢子分离较病组织分离易成功。根据病菌的形态特征和rDNA ITS序列分析,将病菌鉴定为柳假尾孢[Pseudocercospora salicina(Ell.&Ev.)Deighton]。培养基、温度、光照、pH等因素影响病菌在培养基上的生长。燕麦培养基、pH6～7、25℃、黑暗条件是适合的培养条件。     

Evaluation of fungicide application rates,spray schedules and alternative management options for rust and angular leaf spot of snap beans in Uganda

Yield losses due to rust and angular leaf spot (ALS) of snap beans may reach 100% in Eastern Africa. Where susceptible varieties are grown, farmers control these diseases with routine fungicide applications. To determine an optimum application rate and spray schedule for Orius® (tebuconazole 250 g/L), we sprayed 10 mL and 20 mL Orius® per 15 L spray water twice at two trifoliate leaf stage and 50% flowering, and three times at the same stages, with an additional application at pod initiation. In farmers’ fields, we tested the effect of fungicide sprays, use of resistant variety, intercropping, increased plant spacing and farmyard manure on rust and ALS diseases. Application three times of 20 mL Orius® per 15 L spray water reduced rust severity scores by 5.7 and 2.4 in 2010 and 2011, respectively. Lowest rust and ALS severities were observed when a resistant variety, fungicide or farmyard manure was used. Pod yield increments due to disease management ranged between 13% and 242%. Prophylactic fungicide application, use of resistant varieties and farmyard manure can be used to reduce disease severity and improve snap bean quality on smallholder farms.     

A new leaf spot of maize incited byCurvularia clavata

In September 1969 a leaf spot of maize Composite Jawahar, incited byC. lavata Jain, was observed at the College Farm of the Banaras Hindu University, Varanasi. The fungus seriously damages maize leaves and considerably reduces its fodder value. The symptoms of the disease and taxonomic characters of the pathogen are being described in detail.Samenvatting Een belangwekkende bladvlekkenziekte op Composite Jawahar maïs, veroorzaakt doorCurvularia clavata Jain, werd waargenomen op de College Farm van de Banaras Hindu University te Benares in september 1969. De schimmel brengt ernstige schade toe aan maïsbladeren en vermindert aanzienlijk de waarde als voedergewas. Een beschrijving van de ziektesymptomen en van de schimmel wordt gegeven.     

Fungicide responses of maize hybrids to grey leaf spot

Grey leaf spot disease of maize (Cercospora zeaemaydis) has seriously decreased grain yields in the province of KwaZulu-Natal, South Africa, and has spread to infect maize in neighbouring provinces. No commercial hybrids, resistant to the disease have so far been identified, and fungicides have been shown to reduce disease severity. The response of sixty-four commercial hybrids to grey leaf spot under fungicide treatment were studied over two seasons. Overall, fungicides reduced disease severity and linear regression of gain in yield against disease severity enables the identification of hybrids with optimum responses to fungicides. Under low disease levels hybrids responded less to fungicides than under high disease levels. The most susceptible hybrids had the highest responses in control of leaf-blighting and gain in yield. Hybrids with lower-than-predicted leaf-blighting also had lower-than-predicted yield responses, indicating these to be less susceptible to grey leaf spot. These less susceptible hybrids are likely to require fewer fungicide treatments than more susceptible hybrids and are at lesser risk of serious yield losses.Abbreviations GLS grey leaf spot - AUDPC area under disease progress curve     

低频电流处理种子防治玉米小斑病研究

玉米小斑病(Bipolarismaydis)是玉米上的1种重要病害,近年来发生愈来愈重。2002～2005年参照电处理种子具有刺激作物生长、增强抗逆力、提高产量的原理,引用作为防治玉米小斑病的措施之一,进行了试验研究。结果表明,低频电流处理种子有促进生长、抑制病情发展、提高产量的作用。     

Infection of sesame seed by Alternaria sesami (Kawamura) Mohanty and Behera and severity of Alternaria leaf spot in Kenya

Infection levels of Alternaria sesami in sesame (Sesamum indicum L.) seeds collected from farmers in western districts of Kenya were detected using the oatmeal agar plate method. Infection levels varied from 9% in Kakamega to 24% in Siaya. Samples from Busia had a mean infection level of 11.69%. Alternaria leaf spot was monitored in plots planted with Alternaria sesami infected seed at six different infection levels at Kibwezi to determine the effect of transmission of the fungus by seed on disease severity. Increase in per cent leaf area blighted and per cent defoliation fit more closely the Gompertz model than the logistic model. Rates of disease increase in blighted leaf areas and defoliation, and areas under disease progress curves (AUDPC), varied among the six seed infection levels. Infection levels with larger AUDPC generally had faster rates of disease progress. Disease was most severe on plants established from seeds with 8% infection and least on plants established from seeds with 0% infection. Disease severity increased with increased seed infection level.     

云南省玉米灰斑病菌的分子鉴定

本研究利用ITS区、tef1基因、cmdA基因和HIS基因4个基因部分序列对2009-2011年间采自云南省主要灰斑病发生区域和吉林省部分区域的玉米灰斑病菌进行比较分析。结果表明,无论是4个基因序列单独聚类还是拼接序列聚类均把云南省灰斑病发生区域采集的菌株与Cercospora zeina聚为一群,而吉林省采集的灰斑病菌则与Cercospora zeae maydis聚为一群。聚类分析还表明云南省不同玉米产区的灰斑病菌遗传背景单一,在所有聚类树中均聚为一群,且自举支持值均>99%。     

玉米灰斑病抗性鉴定技术

对玉米灰斑病菌孢子产生、病菌接种和寄主抗病性测定技术的研究结果表明，应用玉米叶粉碳酸钙琼脂和玉米叶粉琼脂两种培养基，温度24～25℃，培养5天，病菌可大量产生分生孢子；于植株喇叭口期，用注射器将病菌孢子悬浮液注射于植株喇叭口中，获得了理想的发病效果；对20个玉米自交系注射接种鉴定结果表明，玉米自交系间抗病性差异明显，但未发现免疫自交系。     

Angular leaf spot of phaseolus beans: relationships between disease, healthy leaf area, and yield

ABSTRACT Five field experiments were conducted to investigate the relationship between the severity of visible disease (X), area under the disease progress curve (AUDPC), healthy leaf area index on any given day (HLAI), radiation intercepted by healthy leaf area on any given day (HRI), healthy leaf area duration (HAD), total healthy leaf area absorption (HAA), and yield of Phaseolus beans, cultivars Rosinha and Carioca, inoculated with Phaeoisariopsis griseola at several doses. In general, yield was not related to disease severity (X) or AUDPC. In contrast, the highest yields were always related to the highest values of HAD and HAA. The relationship between yield and HAD was linear in each of five trials (29.9 < R(2) < 70.2%, P < 0.001). The relationship between yield and HAA was linear in four of the trials (52.3 < R(2) < 70.3%, P < 0.001) and exponential in one of them (in which the plant canopy was the largest). Singlepoint models using HRI to estimate yield at various times during the crop season were developed. The slope of the yield-HRI relationship proved to be stable (26.8 +/-2.4 g MJ(-1)), regardless of cultivar, locale, planting date, and bean growth stage (from R5 to R8). The yield-HLAI relationship proved to be less consistent. HRI is proposed as a key explanatory variable for a transportable system of disease management; it may be useful in producing precise recommendations at the farm level.     

Quantitative phenotyping of grey leaf spot disease in maize using real-time PCR

Grey leaf spot is an important maize foliar disease caused by the fungal pathogens Cercospora zeae-maydis and Cercospora zeina. Although methods exist to detect these Cercospora species in maize, current techniques do not allow quantification of the fungi in planta. We developed a real-time SYBR® Green PCR assay for quantification of grey leaf spot disease in maize based on the amplification of a fragment of a cytochrome P450 reductase (cpr1) gene. In planta fungal DNA content was normalised to a maize glutathione S-transferase III gene (gst3) to yield values of ng Cercospora DNA/mg maize DNA. The assay was specific to the two Cercospora spp., and we observed no amplification of the cpr1 fragment in non-target maize leaf pathogens or saprophytes. The assay was employed to quantify C. zeina in glasshouse inoculated maize plants and grey leaf spot infected field plants of resistant and susceptible maize lines. In both instances, C. zeina DNA content correlated with symptomatic leaf lesion area, and the susceptible maize line contained significantly more C. zeina DNA than the resistant line. Sequence differences between the C. zeina and C. zeae-maydis cpr1 amplicons enabled us to perform melt curve analyses to identify the Cercospora species causing grey leaf spot at a particular location. This assay has application in the early detection and quantification of Cercospora spp., both of which are important tools in grey leaf spot disease management and maize breeding programmes.     

玉米灰斑病菌的可溶性蛋白质及同工酶多态性

利用聚丙烯酰胺凝胶电泳技术,对采自北方玉米主产区的23个玉米灰斑病菌菌株进行可溶性蛋白质和同工酶电泳图谱分析及聚类分析,从蛋白质和酶学的多态性水平上分析玉米灰斑病菌的生理分化特征.研究表明,玉米灰斑病菌在可溶性蛋白质和SOD、MDH、PPO、POD、EST、CAT等的同工酶谱存在差异,不同菌株之间某些同工酶谱带数和同一迁移率谱带的亮度和色泽差异非常显著,说明菌株间的多态性可在同工酶水平上得到反映.研究还发现,来自不同地区的菌株同工酶谱带无明显的变化规律,反映出病菌同工酶的变异与地理位置关系不密切,也表明该病菌可能具有较广泛的地域适应性.     

我国玉米灰斑病菌的种类及其分布调查

为了监测我国玉米灰斑病菌的种群及其分布,本研究于2016年－2019年从全国17省（直辖市）87地市（自治州）采集了1 341份玉米灰斑病样本,分离病原菌进行形态学和分子生物学鉴定。共分离到菌株4 186株,从中鉴定出玉蜀黍尾孢Cercospora zeae-maydis 3 272株、玉米尾孢C. zeina 914株。结果表明,引起我国玉米灰斑病的病原菌有玉蜀黍尾孢C. zeae-maydis和玉米尾孢C. zeina两个种,而且这两个种在我国的分布有一定的地域性。黑龙江、吉林、辽宁、内蒙古、河北、北京、天津、山东、山西和安徽地区的玉米灰斑病菌均为玉蜀黍尾孢;河南的西、南部和陕西的中、南部是玉蜀黍尾孢和玉米尾孢混合发生;湖北、四川和湖南虽然分离到了玉蜀黍尾孢和玉米尾孢两种菌,但以玉米尾孢为主;贵州和云南的玉米灰斑病菌均为玉米尾孢。     

玉米弯孢叶斑病研究现状、问题与展望

玉米弯孢叶斑病[Curvularia lunata(Wakker)Boed]是我国近几年玉米上发生的一种重要病害,对玉米高产稳产构成严重威胁。本文介绍了玉米弯孢叶斑病病原、发生规律、危害损失、抗病机制以及防治技术等主要研究进展及其存在问题。     

外引玉米种质对3种玉米叶斑病的抗性鉴定与评价

2012-2013年,应用田间人工接种的方法对引进的165份国外玉米种质进行了玉米大斑病、灰斑病、弯孢菌叶斑病等3种病害同步抗性鉴定与评价,结果表明:引进的国外玉米种质对3种玉米叶斑病的抗性表现均存在差异,表现抗病的种质较少,大部分种质表现感病或高度感病;抗性种质均以中抗为主,表明国外玉米种质对3种叶斑病的抗病能力较低。筛选出一批单抗性种质和兼抗2种或3种叶斑病的多抗性种质37份,为抗病育种提供了重要基础材料。