Farmers' perceptions and practices for managing tomato leaf curl virus disease in southern India

A survey of 174 tomato farmers in five districts of Karnataka State, South India, was conducted between March and July 1998 with the objectives of assessing farmers' knowledge and perceptions of tomato leaf curl virus disease (ToLCVD) and examining their current control practices. The findings showed that farmers were familiar with ToLCVD and regarded it as a serious constraint upon production, particularly in the hot season. However, only 2% of farmers were aware that tomato leaf curl virus (ToLCV) was transmitted by a whitefly vector, Bemisia tabaci . A similarly small number of farmers knew that ToLCVD was caused by a virus, whilst 86% of farmers believed that it was caused by high temperatures. Approximately 90% of farmers relied primarily on pesticides for control of ToLCVD. Few ToLCV-resistant varieties were available but one such variety, Avinash II, was grown by 13% of farmers in the hot season when incidence of the disease is highest. Farmers visiting experimental trials at a farmer field day, showed a strong interest in new advanced breeding tomato lines with resistance to ToLCV. Factors affecting the adoption of ToLCV-resistant varieties by tomato farmers are discussed.     

Cassava Bacterial Blight in Uganda

Abstract

Cassava bacterial blight (CBB) is a major problem of cassava in Uganda. It was first recorded in Terego County, Nile Province in 1976, and a disease survey indicated that CBB is now present in over half of the country. Losses of 90–100% have been observed on susceptible varieties in parts of the Nile, North and Eastern provinces. Symptoms include angular leaf spots, blight, wilt dieback and gum exudations. Planting of infected materials, rainfall, hailstorms, wind and insects are major factors in the spread of the disease. Restriction of movement of infected cassava cuttings to non-infected areas, planting of resistant varieties and healthy cuttings, encouragement of mixed cropping and crop rotation are recommended for control.     

Displacement of US‐1 clonal lineage by a new lineage of Phytophthora infestans on potato in Kenya and Uganda

Phytophthora infestans, the pathogen responsible for causing late blight in potato and tomato, is a rapidly evolving and highly adaptable pathogen. Following the appearance of a new clonal genotype in Kenya (KE‐1 lineage) in 2007, there was a need to document possible displacement of the US‐1 genotype by the newer lineage. Samples from Kenya (260) collected on potato and from Uganda collected on potato (134) and tomato (32) were genotyped with simple sequence repeat (SSR) and mitochondrial DNA haplotype (mtDNA) markers. Results show that, four years after its discovery, the KE‐1 lineage has completely displaced the US‐1 lineage on potato in Kenya. The KE‐1 lineage has also migrated into Uganda through the eastern part of the country that borders western Kenya. All potato samples from eastern Uganda were of the KE‐1 lineage. Moreover, samples from eight fields in western Uganda were also of the KE‐1 lineage, which is in agreement with an ongoing westward displacement. However, the new lineage has not displaced the old lineage on tomato, as all samples from tomato were US‐1. Principal coordinate analysis (PCA) scatter plots revealed clustering that indicated separation between the lineages and also between the subpopulations of the US‐1 lineage on potato and tomato.     

Assessment of the impact of mid-season late blight infection on disease development and yield of potato variety Russet Norkotah in Maine

Development of late blight of potatoes caused by Phytophthora infestans (US 8 fungal genotype, A2 mating type) was monitored in two Russet Norkotah commercial fields at Fort Fairfield in 1996 and Duncan Farm in 1997. Experimental plots representing various disease treatments (low, moderate, high and random late blight severity levels) were established in two fields in 1996. In 1997, only low and high disease treatments were established. The application of fungicides for late blight control was conducted in both years. Late blight incidence and severity were assessed in each plot of each treatment. Components of late blight disease development, tuber blight incidence and tuber yields were determined from each plot. Progress of late blight disease was rapid in 1996 but not in 1997. During the 1996 cropping season, mean disease incidence and severity in the random disease treatment plots were 84 and 21% respectively within 10 days of disease detection. In 1997, low levels of late blight severity were detected in the field plots. Average numbers of late blight leaf and stem lesions on infected plant and fungal sporangia on the diseased leaf were not significantly affected by disease treatment. Late blight foliar severity significantly affected potato tuber yields. Lowest tuber yield was obtained in plots with high disease levels and highest yields were recorded in plots with low late blight severity in 1996. Late blight severity was significantly correlated with tuber yield but not with per cent tuber blight.     

Severe outbreaks of late blight on potato and tomato in South India caused by recent changes in the Phytophthora infestans population

Late blight, caused by Phytophthora infestans, has emerged as the most destructive disease of potato and tomato in South India since 2008. One hundred and fifty‐seven isolates of Phytophthora infestans, 63 from potato and 94 from tomato, were collected from major potato and tomato production areas of South India between 2010 and 2012. Their phenotypic and genotypic characteristics were determined and compared with reference isolates. Isolates were characterized based on mating type, in vitro metalaxyl sensitivity, mitochondrial DNA haplotype, RG57 DNA fingerprinting patterns, SSR markers and aggressiveness on potato and tomato, in order to monitor population changes in P. infestans. All isolates were A2 mating type, metalaxyl resistant, mtDNA haplotype Ia and had RG57 and SSR fingerprints almost identical to the 13_A2 clonal lineage reported in Europe. Variation at the D13 and SSR4 loci allowed discrimination of minor variants, designated as 13_A2_3, 13_A2_3b, 13_A2_3c and 13_A2_1. A comparison of the lesion diameters caused by 157 isolates on detached leaflets of three potato and tomato cultivars showed all isolates to be equally aggressive, confirming that the same clonal population is infecting both hosts. This study demonstrates that the 13_A2 lineage was responsible for severe late blight outbreaks on potato and tomato in South India and has replaced the prior population represented by the US‐1 and other genotypes. Revised management strategies will be required to combat this destructive 13_A2 clonal lineage and monitoring of the population across other potato‐ and tomato‐growing regions of India is warranted.     

An advisory service for the occurrence of Phytophthora infestans on tomato in Emilia-Romagna region1

The Emilia-Romagna region is one of the leading areas in Italy for its high production of industrial tomatoes. A warning service for the occurrence of late blight caused by Phytophthora infestans has been operating for 3 years in the region. Its aim is to reduce the number of sprays which are usually carried out on tomato crops to prevent the disease (7–8 sprays depending on year and area). Climatic data from weather stations covering all the region is used by the warning service to inform farmers every week of the risk of disease occurrence and provide them with precise spray recommendations for blight control. A forecasting model based on climatic data (IPI Model; Infection Potential Index) has been elaborated by the Plant Protection Service of Emilia-Romagna region and is now used together with a network of unsprayed tomato plots and, in the high-risk areas, with aerobiological monitoring of P. infestans sporangia. The IPI Model uses daily data on temperature, RH and precipitation, and shows good reliability for ‘negative prognosis’ of the disease; the other forecasting parameters become more important when the risk is higher. This warning service has allowed growers to reduce sprays by 50% on average. Further reduction in treatments should be possible, especially in low blight-risk areas.     

生物源杀菌剂与化学药剂协调防控番茄病害

为了阐明化学药剂与生防菌剂及植物源杀菌剂交替使用对番茄病害发展的影响,田间试验检测了交替施药的防病效果及病害发展曲线下面积.结果表明,枯草芽孢杆菌BAB-1水剂及化学药剂交替喷施7次对番茄灰霉病、叶霉病、晚疫病和早疫病的防效分别为86.9%,61.0%,72.3%和77.2%.植物源杀菌剂1-氧-乙酰基大花旋覆花内酯(ABL)乳油与化学药剂及生防菌剂枯草芽孢杆菌BAB-1水剂交替喷施9次对上述病害的防效分别为88.6%,87.4%,85.4%和83.2%,相当于不同作用机制的化学药剂交替喷施9次的防效.此外,化学药剂与BAB-1水剂及ABL乳油交替喷施明显延缓了这4种病害的发展,减少了化学药剂施用次数.     

Post-infection activity of fungicides against <Emphasis Type="Italic">Phytophthora infestans</Emphasis> on tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.)

Late blight caused by Phytophthora infestans is the most devastating disease of tomato (Solanum lycopersicum L.) and causes important economically losses if not properly controlled. Control is achieved mainly by preventive fungicide applications. However, even if curative applications are discouraged because they increase the risk of resistance development in the target pathogens, in practice fungicides may be applied also when the disease is already present, a situation that commonly occurs in the field. The aim of this work was to study the curative activity of several fungicides toward P. infestans to determine their efficacy when applied after the infection process. Nine trials were performed in greenhouse using potted tomato plants that were treated 24 h after inoculation. Disease severity was assessed three times from the development of the symptoms on the untreated plants and data analysed using a linear mixed model. Differences in post-infection control between the different chemical classes were found. Metalaxyl-M and cymoxanil showed the best curative activity while among the CAA fungicides, a good efficacy was expressed by dimethomorph. Interestingly, evidence of synergy between active ingredients having different modes of action was observed such as in the mixtures containing dimethomorph?+?ametoctradin, dimethomorph?+?pyraclostrobin and fosetyl-Al?+?propamocarb. This study provided useful information on the post-infection activity of some fungicides used to control tomato late blight and should be taken into account to perform more in depth studies at the field level and to improve the management strategies of the disease.     

<Emphasis Type="Italic">Clavibacter michiganensis</Emphasis> subsp. <Emphasis Type="Italic">michiganens</Emphasis>is strains virulence and genetic diversity. a first study in Argentina

Tomato leaves showing severe leaf spot symptoms have been observed and sampled in the central west and southwest Taiwan during 2015 and 2016. The symptoms were similar to those of bacterial leaf spot/late blight diseases, but only Stemphylium-like fungi were consistently isolated from the diseased tomato. Upon spray inoculation of tomato, Stemphylium-like isolates caused leaf spot symptoms identical to those of naturally infected plants, and the pathogenic isolates were successfully re-isolated from inoculated leaves. The tomato-pathogenic isolates were identified as S. lycopersici based on morphological characterization and molecular identification. S. lycopersici has been previously reported to cause gray leaf spot of tomato in the temperate regions, but the majority of S. lycopersici-caused lesions were black/dark brown rather than gray in our surveillance. Accordingly, it is suggested that S. lycopersici-caused disease of tomato is named Stemphylium leaf spot of tomato more appropriately than tomato gray leaf spot. Moreover, S. lycopersici-caused leaf spot disease on tomato has been distributed in major tomato production regions in Taiwan. The information provided by our study will be important for future breeding of tomato cultivars, especially for tomato producers in Taiwan.     

氟铃脲对番茄晚疫病的防治作用

通过药效试验发现氟铃脲对番茄晚疫病有一定的防治效果。室内离体试验结果表明,氟铃脲对番茄晚疫病菌的EC50为65.69 μg/mL;盆栽试验结果表明,6.25～200 μg/mL氟铃脲对番茄晚疫病均表现出一定的预防效果;田间小区试验200 μg/mL氟铃脲对番茄晚疫病的防效达到了64.42%。     

Phytophthora infestans: a review of past and current studies on potato late blight

Phytophthora infestans is the causal agent of potato late blight. Genotypes of Japanese populations of P. infestans have been classified as US-1, JP-1, JP-2, JP-3, and JP-4 based on analyses of DNA polymorphisms. These populations may have been introduced to Japan by the migration of P. infestans from other countries and by domestic changes produced through sexual and asexual propagation. Resistance to late blight has been an ongoing desire of potato farmers in Japan and elsewhere. Recurrent backcrossing of Solanum demissum to varieties of S. tuberosum has been used to transfer late blight resistance. Many varieties carry the R1 gene, whereas others carry R2, R3, and/or R4. However, R genes provided only transient resistance to late blight. New races rapidly overcome R-gene-mediated resistance. The R genes of potato generally encode receptors that recognize secretory effector (Avr) proteins produced by P. infestans. These effector proteins induce robust resistance in potato varieties containing R genes, while they suppress resistance in potato varieties lacking R genes. Conserved molecules from Phytophthora species such as fatty acids, glucans, and elicitins also act as elicitors in Solanaceae species. These P. infestans-derived elicitors induce defensive reactions, including the accumulation of phytoalexins and hypersensitive cell death. A future challenge will be to combine our accumulated knowledge with that from other scientific fields to develop a disease management approach for late blight.     

Characterization of Egyptian <Emphasis Type="Italic">Phytophthora infestans</Emphasis> population using simple sequence repeat markers

The plant pathogenic oomycete, Phytophthora infestans, is the causal agent of late blight disease in tomato and potato. For characterizing Egyptian P. infestans isolates by DNA marker analysis, 40 isolates of P. infestans were collected from different locations in Egypt during two growing seasons (2012/2013 and 2013/2014). The 40 isolates were grouped into seven genotypes, in which 24 alleles were detected. The identified genotypes were not completely associated with geographic location and sample collection years. These results provide genetic and geographical information for developing a program to manage late blight disease.     

Metalaxyl resistance in Phytophthora infestans on greenhouse tomatoes in Greece

In winter/spring 1984 resistance to metalaxyl developed in Phytophthora infestans within tomato greenhouses in Preveza, Greece. The appearance of resistant isolates followed continuous applications of metalaxyl and prevalence of weather conditions favourable for late blight. The majority of resistant isolates grew on tomato leaf discs floated on solutions containing 100 μg/ml metalaxyl whereas sensitive isolates were inhibited at concentrations of 0.1 μg/ml.
In trials within polyethylene tunnels metalaxyl had no effect on the development of the late blight induced by resistant strains but both a mixture of this fungicide with mancozeb and mancozeb alone, gave satisfactory control of the disease when applied in a 7-day schedule.     

近年来中国马铃薯晚疫病的时空演变特征及防控情况分析

为系统全面地了解马铃薯晚疫病在我国的发生演变特征及防控情况,基于2008—2017年国家统计局官方数据、《中国农业统计资料》《全国植保专业统计资料》及全国马铃薯品种分布等数据,对全国及各马铃薯产区晚疫病的发生及防治情况进行综合量化分析。结果表明：马铃薯晚疫病在我国连年发生,年平均发生面积约197.47万hm²,占马铃薯总种植面积的40.66%;晚疫病造成马铃薯年平均产量损失占所有病害所致产量损失的63.54%,远高于其他病害,损失巨大;在我国马铃薯4大产区中,马铃薯晚疫病在北方一作区的年平均发生面积最大,约73.44万hm²,而在西南混作区造成的年平均产量损失最高,约14.29万t;晚疫病发生与马铃薯种植区域的重心在空间上呈现相似的迁移趋势;以费乌瑞它为代表的高感晚疫病品种在全国大面积种植,但近年来部分抗病品种的种植面积正在逐年增加;近年来我国对马铃薯晚疫病的防治面积大幅度提升,但仍太过依赖化学防治,应加大绿色防控技术的推广和应用力度。     

Detection and Identification of <Emphasis Type="Italic">Phytophthora</Emphasis> Species in Southern Italy by RFLP and Sequence Analysis of PCR-amplified Nuclear Ribosomal DNA

In four neighbouring regions of southern Italy, Basilicata, Campania, Apulia and Calabria, pepper and zucchini plants showing Phytophthora blight symptoms, tomato plants with either late blight or buckeye rot symptoms, plants of strawberry showing crown rot symptoms and declining clementine trees with root and fruit rot were examined for Phytophthora infections by means of polymerase chain reaction (PCR) assays, using primers directed to nuclear ribosomal DNA (rDNA) repeat sequences. All diseased plants and trees examined tested positive. The detected fungal-like organisms were differentiated and characterized on the basis of primer specificity as well as through extensive restriction fragment length polymorphism (RFLP) and sequence analysis of PCR-amplified rDNA. Phytophthora capsici was identified in diseased pepper and zucchini plants, P. infestans was identified in tomato with late blight symptoms whereas buckeye rot-affected tomatoes and diseased strawberry plants proved to be infected by P. nicotianae and P. cactorum, respectively. Declining clementine trees were infected with P. citrophthora and P. nicotianae in about the same proportion. Also, thirty-one pure culture-maintained isolates of Phytophthora which had previously been identified in southern Italy by traditional methods but were never examined molecularly, were examined by RFLP and sequence analysis of PCR-amplified nuclear rDNA. Among these, an isolate from gerbera which had previously been identified by traditional methods only at genus level, was assigned to P. tentaculata. For the remaining pure culture-maintained isolates examined, the molecular identification data obtained corresponded with those delineated by traditional methods. Most of the diseases examined were already known to occur in southern Italy but the pathogens were molecularly detected and fully characterized at nuclear rDNA repeat level only from other geographic areas, very often outside Italy. A new disease to southern Italy was the Phytophthora blight of zucchini. This is also the first report on the presence and molecular identification of P. tentaculata from Italy.     

Phytophthora infestans in a subtropical region: survival on tomato debris, temporal dynamics of airborne sporangia and alternative hosts

Little is known about inoculum dynamics of late blight caused by Phytophthora infestans in tropical/subtropical areas, particularly in Brazil. The objectives of the present study were to assess (i) the survival of the pathogen on stems, leaflets and tomato fruits, either buried or not in soil; (ii) the pathogenicity of P . infestans to mostly solanaceous plant species commonly found in Brazil that could act as inoculum reservoir; and (iii) the temporal dynamics of airborne sporangia. Phytophthora infestans survived in tomato plant parts for less than 36 days under greenhouse and field conditions. In greenhouse tests, pathogen structures were detected earlier on crop debris kept in dry than in wet soil conditions. Isolates of two clonal lineages of P. infestans , US-1 from tomato, and BR-1 from potato, were inoculated on 43 plant species. In addition to potato and tomato, Petunia  ×  hybrida and Nicotiana benthamiana were susceptible to the pathogen. Airborne inoculum was monitored with Rotorod and Burkard spore traps as well as with tomato and potato trap plants. Sporangia were sampled in most weeks throughout 2004 and in the first two weeks of 2005. Under tropical/subtropical conditions, airborne inoculum is abundant and is more important to late blight epidemics than inoculum from crop debris or alternative hosts.     

Spatial Analysis of Phytophthora infestans Genotypes and Late Blight Severity on Tomato and Potato in the Del Fuerte Valley Using Geostatistics and Geographic Information Systems

ABSTRACT Genetic structure of Phytophthora infestans, the causal agent of potato and tomato late blight, was analyzed spatially in a mixed potato and tomato production area in the Del Fuerte Valley, Sinaloa, Mexico. Isolates of P. infestans were characterized by mating type, allozyme analysis at the glucose-6-phosphate isomerase and peptidase loci, restriction fragment length polymorphism with probe RG57, metalaxyl sensitivity, and aggressiveness to tomato and potato. Spatial patterns of P. infestans genotypes were analyzed by geographical information systems and geo-statistics during the seasons of 1994-95, 1995-96, and 1996-97. Spatial analysis of the genetic structure of P. infestans indicates that geographic substructuring of this pathogen occurs in this area. Maps displaying the probabilities of occurrence of mating types and genotypes of P. infestans, and of disease severity at a regional scale, were presented. Some genotypes that exhibited differences in epidemiologically important features such as metalaxyl sensitivity and aggressiveness to tomato and potato had a restricted spread and were localized in isolated areas. Analysis of late blight severity showed recurring patterns, such as the earliest onset of the disease in the area where both potato and tomato were growing, strengthening the hypothesis that infected potato tubers are the main source of primary inoculum. The information that geostatistical analysis provides might help improve management programs for late blight in the Del Fuerte Valley.     

The tomato borer Tuta absoluta in South America: pest status,management and insecticide resistance

The tomato borer Tuta absoluta (Lepidoptera: Gelechiidae) has been a recognized pest in South America since the 1960s, quickly spreading to the major tomato‐producing countries in the region. A series of studies regarding this pest's biology, ecology and management were conducted to contain tomato losses within acceptable levels. Although cultural control methods were attempted against T. absoluta, as were the development of resistant tomato varieties and the use of pheromones and natural enemies, insecticides are still the main control method used. The sex pheromone of T. absoluta was identified, confirmed and synthesized in the late 1990s and it is currently used for detection and monitoring of this species, but improved sampling plans are still necessary for its use in decision‐making regarding insecticide use. Insecticide use has shifted from earlier reliance on organophosphates, pyrethroids, cartap and abamectin to insect growth regulators and, more recently, to novel insecticides. Unfortunately, the overreliance on insecticide use led to problems with insecticide resistance in the region, which is a current matter of concern not only in South America, but also elsewhere since introduced strains may carry insecticide‐resistance genes at high frequency even without local selection in the site of introduction.     

Farmers' perceptions of sorghum stem-borer and farm management practices in eastern Ethiopia

A survey of 90 farmers, randomly selected over six sorghum-growing districts in eastern Ethiopia was carried out during July to August, 2001 in the long rainy season. The study investigated farmers' perceptions of the importance of stem-borer and farm practices influencing the pest. Sorghum farming was characterized by smallholdings with an average land size of 4.3 ha, an average family size of 6 and an average yield of 878?kg ha^???1. Farmers cited pests, drought, and shortage of seed, land and labour as the main constraints upon sorghum production. Stem-borers were perceived to be the major pests requiring control. The majority of the farmers never applied chemical insecticides against stem-borers due to lack of capital and unavailability of insecticides. Because of restricted access to improved varieties, farmers largely used local cultivars of sorghum selected for yield potential but with little emphasis on insect resistance. Very few farmers destroyed sorghum residues after harvest. The majority of farmers grew sorghum under intercropping mainly due to the high yield expected. Crop rotation in sorghum fields was not widely practised due to land shortage.     

Late blight (Phytophthora infestans (Mont) De Bary) development from potato seed-pieces treated with fungicides

Fungicides were applied as seed-piece treatments to control potato late blight, caused by Phytophthora infestans, US8, A2 biotype in controlled environment and field experiments. Efficacy of seed treatments for controlling late blight was examined under three disease development regimes simulated by artifical inoculation; (a) seed-borne infection, (b) transmission of infection resulting from spread during the seed-cutting operation, and (c) infection of foliage by aerial inoculation. Emergence of plants from the seed-borne infection was uniformly low (<40%) in controlled environment and field experiments. In controlled environment experiments some of the plants that emerged from fungicide-treated seed-pieces were infected with late blight. Following exposure of tuber surfaces to P infestans, emergence rates from seed-pieces treated with formulated products that included mancozeb in the formulation were comparable to the untreated and non-inoculated control in controlled environment and field experiments. Plants that emerged from non-inoculated seed-pieces treated with fungicides that contained active ingredients known to be effective against foliar late blight had lower percentage foliar infection after inoculation than the untreated control. Leaves close to the base of the stem had fewer infections than leaves attached at the mid region of the main stem, 14 days after inoculation, in some of the controlled environment studies. In contrast, field experiments conducted under conditions conducive to late blight development showed that none of the seed treatments applied to late blight-free seed-pieces delayed the onset and severity of late blight infection. In potato production areas at risk of early season late blight, seed treatments applied to healthy seed may confer limited protection against late blight between planting and the first scheduled applications of prophylactic foliar fungicides. © 1999 Society of Chemical Industry