Showing papers on "Leaf spot published in 2017"

A gene encoding maize caffeoyl-CoA O-methyltransferase confers quantitative resistance to multiple pathogens

Abstract: Alleles that confer multiple disease resistance (MDR) are valuable in crop improvement, although the molecular mechanisms underlying their functions remain largely unknown. A quantitative trait locus, qMdr9.02, associated with resistance to three important foliar maize diseases-southern leaf blight, gray leaf spot and northern leaf blight-has been identified on maize chromosome 9. Through fine-mapping, association analysis, expression analysis, insertional mutagenesis and transgenic validation, we demonstrate that ZmCCoAOMT2, which encodes a caffeoyl-CoA O-methyltransferase associated with the phenylpropanoid pathway and lignin production, is the gene within qMdr9.02 conferring quantitative resistance to both southern leaf blight and gray leaf spot. We suggest that resistance might be caused by allelic variation at the level of both gene expression and amino acid sequence, thus resulting in differences in levels of lignin and other metabolites of the phenylpropanoid pathway and regulation of programmed cell death.

Genetic Dissection of Novel QTLs for Resistance to Leaf Spots and Tomato Spotted Wilt Virus in Peanut (Arachis hypogaea L.)

Abstract: Peanut is an important crop, economically and nutritiously, but high production cost is a serious challenge to peanut farmers as exemplified by chemical spray to control foliar diseases such as leaf spots and thrips, the vectors of tomato spotted wilt virus (TSWV). The objective of this research was to map the quantitative trait loci (QTLs) for resistance to leaf spots and TSWV in one recombinant inbred line (RIL) mapping population of “Tifrunner × GT-C20” for identification of linked markers for marker-assisted breeding. Here, we report the improved genetic linkage map with 418 marker loci with a marker density of 5.3 cM/loci and QTLs associated with multi-year (2010–2013) field phenotypes of foliar disease traits, including early leaf spot (ELS), late leaf spot (LLS), and TSWV. A total of 42 QTLs were identified with phenotypic variation explained (PVE) from 6.36 to 15.6%. There were nine QTLs for resistance to ELS, 22 QTLs for LLS, and 11 QTLs for TSWV, including six, five, and one major QTLs with PVE higher than 10% for resistance to each disease, respectively. Of the total 42 QTLs, 34 were mapped on the A sub-genome and eight mapped on the B sub-genome suggesting that the A sub-genome harbors more resistance genes than the B sub-genome. This genetic linkage map was also compared with two diploid peanut physical maps, and the overall co-linearity was 48.4% with an average co-linearity of 51.7% for the A sub-genome and 46.4% for the B sub-genome. The identified QTLs associated markers and potential candidate genes will be studied further for possible application in molecular breeding in peanut genetic improvement for disease resistance.

Early sensing of peanut leaf spot using spectroscopy and thermal imaging

Abstract: Early and late leaf spot are the most devastating, important fungal foliar diseases affecting peanut. The economic loss caused by peanut diseases justifies the necessity to develop more reliable detection methods. Point and image spectroscopy and thermal imaging were used in this study for the early detection of peanut leaf spot. The spectral reflectance factors differ significantly according to the health condition. The leaves of the healthy peanut showed a decreasing reflection in 1015 nm, whereas the heavily diseased leaves showed an increasing reflection. At the thermal infrared range, affected plants show a higher temperature than healthy ones. A presymptomatic decrease in leaf temperature using thermal imagery was found about 1.3°C lower than the healthy leaves. However, the diseased plant’s temperature was 2.2°C higher than that of the healthy one. The temperature difference allowed the discrimination between the infected and healthy leaves before the appearance of visible necrosis on leave...

RNA-Seq analysis of resistant and susceptible sub-tropical maize lines reveals a role for kauralexins in resistance to grey leaf spot disease, caused by Cercospora zeina.

Abstract: Cercospora zeina is a foliar pathogen responsible for maize grey leaf spot in southern Africa that negatively impacts maize production. Plants use a variety of chemical and structural mechanisms to defend themselves against invading pathogens such as C. zeina, including the production of secondary metabolites with antimicrobial properties. In maize, a variety of biotic and abiotic stressors induce the accumulation of the terpenoid phytoalexins, zealexins and kauralexins. C. zeina-susceptible line displayed pervasive rectangular grey leaf spot lesions, running parallel with the leaf veins in contrast to C. zeina-resistant line that had restricted disease symptoms. Analysis of the transcriptome of both lines indicated that genes involved in primary and secondary metabolism were up-regualted, and although different pathways were prioritized in each line, production of terpenoid compounds were common to both. Targeted phytoalexin analysis revealed that C. zeina-inoculated leaves accumulated zealexins and kauralexins. The resistant line shows a propensity toward accumulation of the kauralexin B series metabolites in response to infection, which contrasts with the susceptible line that preferentially accumulates the kauralexin A series. Kauralexin accumulation was correlated to expression of the kauralexin biosynthetic gene, ZmAn2 and a candidate biosynthetic gene, ZmKSL2. We report the expression of a putative copalyl diphosphate synthase gene that is induced by C. zeina in the resistant line exclusively. This study shows that zealexins and kauralexins, and expression of their biosynthetic genes, are induced by C. zeina in both resistant and susceptible germplasm adapted to the southern African climate. The data presented here indicates that different forms of kauralexins accumulate in the resistant and susceptible maize lines in response to C. zeina, with the accumulation of kauralexin B compounds in a resistant maize line and kauralexin A compounds accumulating in the susceptible line.

Evaluation of biochemical changes in leaves of tomato infected with Alternaria alternata and its metabolites.

Abstract: The present study was carried out to evaluate the biochemical changes occurring in tomato leaves following treatment with leaf spot disease causing pathogen Alternaria alternata and two of its phytotoxic metabolites. Results revealed that the pathogen treatment caused severe foliar necrosis and by 10th day of treatment almost 3/4th of the leaf area was necrotized. A significant decline in the chlorophyll content was observed in the leaves treated with the pathogen and its metabolites. Reducing sugars showed a visible decline in the treated leaves in comparison to the control leaves. When compared with the control an increase in total soluble protein was observed in leaves treated with the pathogen and its metabolites. In case of phenol, a significant enhancement in phenol content of the pathogen and metabolite treated leaves was observed than the amount detected in control leaves. The results indicate that infection of tomato by the leaf spot pathogen Alternaria alternata and its metabolites causes severe alterations in the amount of various biochemical components.

Leaf disease detection on cucumber leaves using multiclass Support Vector Machine

Abstract: In India, smart organic farming is gaining importance. There may be problems due to environment, temperature, humidity or nutrient deficiency in this farming. If we have a monitoring system for this farming it is possible to produce healthy plant. The aim is to address this issue using computer aided image processing technique. Main solution is to create an automation system which can detect the disease present in the leaf of the plant. In this paper, a first level attempt is made to detect diseases present in the leaf of salad cucumber. The most common diseases which are present in salad cucumber are Alternaria leaf blight, Bacterial wilt, Cucumber green mottle mosaic, Leaf Miner, Leaf spot, Cucumber Mosaic Virus (CMV) disease and so on. K-means clustering, an unsupervised algorithm along with Support Vector Machine(SVM) is used in this work to address this problem.

Analysis of the Fungal Diversity in Citrus Leaves with Greasy Spot Disease Symptoms.

Abstract: Citrus greasy spot (CGS) is a disease of citrus with worldwide distribution and recent surveys have revealed a high level of incidence and severity of symptoms of the disease in Sicily, southern Italy. Although Mycosphaerel la citri (anamorph Zasmidium citri-griseum) and other related species are generally considered as causal agents, the etiology of CGS is still unclear. Here, we report the use of an amplicon metagenomic approach to investigate the fungal communities on citrus leaves symptomatic or asymptomatic for CGS from an orchard in Sicily showing typical CGS symptoms. A total of 35,537 high-quality chimeric free reads were obtained and assigned to 176 operational taxonomic units (OTUs), clustered at 99 % similarity threshold. Data revealed a dominating presence of the phylum Ascomycota (92.6 %) over other fungal phyla. No significant difference was observed between symptomatic and asymptomatic leaves according to both alpha and beta diversity analyses. The family Mycosphaerellaceae was the most abundant and was represented by the genera Ramularia, Mycosphaerella, and Septoria with 44.8, 2.4, and 1.7 % of the total detected sequences, respectively. However, none of the species currently reported as causal agents of CGS was detected in the present study. The most abundant sequence type (ST) was associated to Ramularia brunnea, a species originally described to cause leaf spot in a perennial herbaceous plant of the family Asteraceae. Results exclude that CGS symptoms observed in Sicily are caused by Z. citri-griseum and, moreover, they indicate that a considerable part of the fungal diversity in citrus leaves is still unknown.

A survey on tomato leaf grey spot in the two main production areas of Argentina led to the isolation of Stemphylium lycopersici representatives which were genetically diverse and differed in their virulence

Abstract: Tomato gray leaf spot was first reported in Argentina in 1990 Since then, the disease has not only increased in endemic areas, but also disseminated in other tomato-growing areas In a survey of plants with typical symptoms of Tomato grey leaf spot disease we isolated 27 Stemphylium representatives from the two main tomato-growing areas of Argentina Cultural features such as sporulation, conidia morphometry among others revealed high variability between isolates, which was confirmed by Inter Simple Sequence Repeat (ISSR)-PCR technique A molecular phylogenetic analysis comprising the Internal Transcribed Spacer (ITS) and the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene partial sequences unambiguously identified all isolates as Stemphylium lycopersici Based on disease severity on detached leaves, isolates were grouped in three categories (high, medium and low virulent) No correlation was found between phenotypic or genotypic characters and the geographical origin of the isolates

NMR-Based Metabolic Profiling of Field-Grown Leaves from Sugar Beet Plants Harbouring Different Levels of Resistance to Cercospora Leaf Spot Disease.

Abstract: Cercospora leaf spot (CLS) is one of the most serious leaf diseases for sugar beet (Beta vulgaris L.) worldwide. The breeding of sugar beet cultivars with both high CLS resistance and high yield is a major challenge for breeders. In this study, we report the nuclear magnetic resonance (NMR)-based metabolic profiling of field-grown leaves for a subset of sugar beet genotypes harbouring different levels of CLS resistance. Leaves were collected from 12 sugar beet genotypes at four time points: seedling, early growth, root enlargement, and disease development stages. ¹H-NMR spectra of foliar metabolites soluble in a deuterium-oxide (D₂O)-based buffer were acquired and subjected to multivariate analyses. A principal component analysis (PCA) of the NMR data from the sugar beet leaves shows clear differences among the growth stages. At the later time points, the sugar and glycine betaine contents were increased, whereas the choline content was decreased. The relationship between the foliar metabolite profiles and resistance level to CLS was examined by combining partial least squares projection to latent structure (PLS) or orthogonal PLS (OPLS) analysis and univariate analyses. It was difficult to build a robust model for predicting precisely the disease severity indices (DSIs) of each genotype; however, GABA and Gln differentiated susceptible genotypes (genotypes with weak resistance) from resistant genotypes (genotypes with resistance greater than a moderate level) before inoculation tests. The results suggested that breeders might exclude susceptible genotypes from breeding programs based on foliar metabolites profiled without inoculation tests, which require an enormous amount of time and effort.

Effect of elevated atmospheric CO 2 and temperature on the chemical and biological control of powdery mildew of zucchini and the Phoma leaf spot of leaf beet

Abstract: The effects of increased temperature and CO2 levels on the effectiveness of four fungicides and one microbial treatment on disease development in zucchini-Podosphaera xanthii and leaf beet-Phoma betae pathosystems, kept under phytotron conditions, have been evaluated in this study Six CO2 and temperature combinations have been tested for each pathosystem in four experimental trials Penconazole and sulphur treatments, applied under a simulated CO2 and temperature increase scenario, have shown an efficacy in powdery mildew control that ranged from 850 to 889 % for penconazole and from 899 to 926 % for sulphur, and the treatments have therefore resulted to be equally effective compared to that observed under 400–450 ppm conditions The disease control provided by A quisqualis was significantly improved under an increased CO2 concentration of 800–850 ppm at 26–30 °C, by 233 % for disease incidence and 228 % for disease severity The effectiveness of both mancozeb and azoxystrobin against Phoma leaf spot is affected by high levels of CO2 The efficacy of mancozeb and azoxystrobin has been improved significantly by 153 % and 206 %, respectively, under 800–850 ppm of CO2 and 22–26 °C, compared to the efficacy observed under standard conditions of CO2 More attention should be paid to the efficacy of chemical and biological control measures considering the predicted future climate changes

Fungal diseases on tomato plant under greenhouse condition

Abstract: The cultivation of crops in the greenhouse is the most intensive form of horticultural production. Greenhouse climatic conditions provide an ideal condition for the development of many foliar, stem and soil-borne plant diseases. Diseases are a major limiting factor for vegetable that cause serious yield reduction leading to severe economic losses. Fungi enter plants through natural openings such as stomata and through wounds caused by pruning, harvesting, hail, insects, other diseases, and mechanical damage. This chapter provides an overview of the most important diseases of tomato plants. Some of the diseases that will cover in this chapter are the follow: Early blight late, Septoria leaf spot, Late blight, Fusarium wilt, Verticillium wilt, Anthracnose, Buckeye rot, and Southern blight . For each disease, main symptoms and disease development are described. This review is based on combined information derived from available literature and expertise knowledge.

Comportamento de cultivares de cafeeiro sob a incidência das doenças da ferrugem e cercosporiose em dois ambientes de cultivo

Abstract: Orange rust, caused by Hemileia vastatrix, is the main coffee disease in terms of scope and damage. The development of cultivars, resistant and/or tolerant to pests and diseases, has an important role in the productivity increase and production cost decrease. Thus, the aim of this study was to provide information about the reaction of ten commercial cultivars of C. Arabica to the incidence of rust and gray leaf spot in two important coffee regions of Minas Gerais state. The experiments were carried out in two important coffee regions of Minas Gerais (Southern Minas and Alto Paranaiba), being implemented in public experimental areas in the Experimental Farm of the Agricultural Research Company of Minas Gerais (Epamig) in Patrocinio-MG and Experimental Campus of the Federal University (Ufla) of Lavras-MG. The experimental design was of randomized blocks with three replicates and 10 plants per plot, when only six central plants were considered as a useful part. The adopted spacing was of 3.5 m between rows x 0.70 m between plants. Evaluations of both rust incidence and severity as well as gray leaf spot incidence were carried out monthly from January to August each year (2011/2012 and 2012/2013 crops). The incidence percentages of the disease were transformed into area below the incidence and rust severity (AACPIF, AACPSF) and gray leaf spot incidence (AACPIC) progress curve, according to criteria established by Campbell and Madden (1990). The Oeiras cultivar presents total loss of resistance to rust, Catigua MG2 cultivar presents immunity to the rust pathogen and the cultivars studied exhibit no resistance to gray leaf spot.

Characterization of Fusarium spp. associated with pineapple fruit rot and leaf spot in Peninsular Malaysia.

Abstract: Pineapple (Ananas comosus) is one the important fruit crops planted in Malaysia, and this study was conducted to determine Fusarium spp. associated with diseases of the fruit crop as Fusarium is prevalent in tropical countries. Our objective was to identify and characterize Fusarium spp. associated with pineapple fruit rot and leaf spot mainly found on the fruits and leaves in Peninsular Malaysia. Fusarium isolates (n = 108) associated with pineapple fruit rot and leaf spot were characterized by morphological, molecular and phylogenetic analyses, a mating study and pathogenicity testing. TEF-1α sequence analysis identified Fusarium proliferatum, Fusarium verticillioides, Fusarium sacchari and Fusarium sp. Mating was successful only between tester strains of F. proliferatum and F. verticillioides. Sexual crosses with standard tester strains showed that 82 isolates of F. proliferatum produced fertile crosses with mating population D (Gibberella intermedia) and three isolates of F. verticillioides were fertile with the tester strain of mating population A (Gibberella moniliformis). All isolates were pathogenic, causing pineapple fruit rot and leaf spot, thus fulfilling Koch's postulates.

First report of DMI-insensitive Cercospora beticola on sugar beet in Ontario, Canada.

Abstract: Cercospora leaf spot, caused by the fungal pathogen Cercospora beticola, is an economically important foliar disease of sugar beet in Ontario, Canada. The first demethylation inhibitor (DMI) fungicide registered for sugar beet in Canada …

Differential gene expression in leaf tissues between mutant and wild-type genotypes response to late leaf spot in peanut (Arachis hypogaea L.).

Abstract: Late leaf spot (LLS) is a major foliar disease in peanut (A. hypogaea L.) worldwide, causing significant losses of potential yield in the absence of fungicide applications. Mutants are important materials to study the function of disease-related genes. In this study, the mutant line M14 was derived from cultivar Yuanza 9102 treated with EMS. Yuanza 9102 was selected from an interspecific cross of cultivar Baisha 1016 with A. diogoi, and is resistant to several fungal diseases. By contrast, the M14 was highly susceptible to late leaf spot. RNA-Seq analysis in the leaf tissues of the M14 and its wild type Yuanza 9102 under pathogen challenge showed 2219 differentially expressed genes including1317 up-regulated genes and 902 down-regulated genes. Of these genes, 1541, 1988, 1344, 643 and 533 unigenes were obtained and annotated by public protein databases of SwissPort, TrEMBL, gene ontology (GO), KEGG and clusters of orthologous groups (COG), respectively. Differentially expressed genes (DEGs) showed that expression of inducible pathogenesis-related (PR) proteins was significantly up-regulated; in the meantime DEGs related to photosynthesis were down-regulated in the susceptible M14 in comparison to the resistant WT. Moreover, the up-regulated WRKY transcription factors and down-regulated plant hormones related to plant growth were detected in the M14. The results suggest that down-regulated chloroplast genes, up-regulated WRKY transcription factors, and depressed plant hormones related to plant growth in the M14 might coordinately render the susceptibility though there was a significant high level of PRs. Those negative effectors might be triggered in the susceptible plant by fungal infection and resulted in reduction of photosynthesis and phytohormones and led to symptom formation.

Corynespora cassiicola causes leaf spot disease on lettuce ( Lactuca sativa ) cultivated in hydroponic systems in Thailand

Abstract: Lettuce (Lactuca sativa) is an annual vegetable that is widely cultivated in hydroponic systems in Thailand. In 2016, a leaf spot disease was commonly found on hydroponically-grown lettuce plants in glasshouses in Songkhla province, southern Thailand. The morphology of the fungus that was consistently isolated from the leaf spots was identical to that described for Corynespora cassiicola. The identity of the fungus was confirmed by sequencing the ITS and LSU gene regions. Koch’s postulates were satisfied, proving that C. cassiicola was the causal agent of the recent outbreaks of leaf spot in hydroponically-grown lettuce in Thailand. This paper is the first report of the disease in this country.

Leaf spot disease adversely affects human health promoting constituents and withanolide biosynthesis in Withania somnifera (L.) Dunal

Abstract: Aims The present work investigates the implication of leaf spot disease on the antioxidant potentials and commercial value of pharmaceutically important constituents of Withania somnifera, a high valued medicinal plant. Methods and Results Leaf spot disease was induced in W. somnifera by inoculating Alternaria alternata (Fr.) Keiss. pathogen. Total polyphenolic content (TPC) and antioxidant potential showed a significant decrease during leaf spot disease. Evaluation of pharmaceutically active constituents withaferin A, withanone and withanolide A utilizing high-performance liquid chromatography (HPLC) showed a significant decrease in diseased samples as compared to healthy ones. Quantitative expression of major genes involved in withanolide biosynthesis also showed down-regulation in diseased samples. Alterations in the ultra-structure of chloroplasts were also analyzed under transmission electron microscopy (TEM) to get a better insight into the changes of withanolide biosynthesis in leaf during disease infestation. Conclusions The present work suggests that when the pathogenic fungus invades the host plants, it evokes multiple responses, which could be studied at various levels. The knowledge gained from this work will provide appropriate rationale for controlling the bio-deterioration of the pharmaceutically active metabolites in W. somnifera and development of suitable strategies against leaf spot disease. Significance and Impact of the Study The present work first time investigates the effect of leaf spot disease on the human health promoting constituents and withanolide biosynthesis in this high valued medicinal plant. This article is protected by copyright. All rights reserved.

Entyloma helianthi: identification and characterization of the causal agent of sunflower white leaf smut.

Abstract: White leaf smut is a minor foliar disease of sunflower (Helianthus annuus) in the United States. The disease occurs primarily in greenhouse-grown sunflowers in California and causes leaf spot, defoliation, and a reduction in yield and crop value. Historically, many Entyloma specimens with similar morphological characters, but infecting diverse plant genera including Helianthus, were called Entyloma polysporum. Recent comparative morphological and molecular work has shown that Entyloma species infect hosts within a single genus or species, suggesting that the sunflower Entyloma species may not be E. polysporum. In 2015, sunflower leaf smut material was collected from ornamental sunflowers in a greenhouse in Santa Barbara County, California. Morphologically, this species differed from E. polysporum in having smaller, more regular-shaped teliospores and prominently developed conidiophores with cylindrical conidia. The rDNA ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]) region of the sunflower leaf smut was phylogenetically distinct from all previously sequenced Entyloma species and found only on H. annuus. This study confirms that the sunflower leaf smut pathogen represents a novel species, Entyloma helianthi. Possible misidentification of the anamorphic stage of Entyloma helianthi as another leaf spot pathogen, Ramularia helianthi, is also discussed.

Management of snap bean insect pests and diseases by use of antagonistic fungi and plant extracts.

Abstract: Use of synthetic pesticides reduces the competitiveness of Kenyan snap bean pods due to stringent regulations by importers as a result of presence of chemical residues. This study was conducted to determine the effectiveness of local biopesticides in managing insect pests and diseases of snap beans. Field experiments were set up in farmer's field where Trichoderma spp. and Paecilomyce spp. and plant extracts from turmeric, garlic, ginger and lemon were applied weekly as foliar sprays. Plant extracts reduced the population of whiteflies and thrips by up to 58% and 41% while antagonistic fungi had a corresponding 30% and 18% reduction, respectively. Trichoderma spp. reduced severity of angular leaf spot (37.5%), rust (67%) and anthracnose (20.7%). Plant extracts and antagonistic fungi increased marketable pod yield by 25.6% and 17.3%, respectively. Results demonstrated that local environments are potential sources of biopesticides that can be exploited for integrated management of pests and diseases.

Biological Control of Brown Leaf Spot Disease Caused by Curvularia lunata and Field Application Method on Rice Variety IR66 in Cambodia

Abstract: Curvularia lunata was found to cause a serious rice brown leaf spot in Cambodia. This is the first report of brown leaf spot on rice in Cambodia. All isolates were tested for pathogenicity. Dual culture antagonistic tests showed that Chaetomium cupreum inhibited sporulation of C. lunata when compared to the control. In a pot experiment , C. cupreum significantly reduced the incidence of brown leaf spot caused by C. lunata . After application of a spore suspension of C. cupreum , Chaetomium -biofungicide and chemical fungicide (tebuconazole) to rice seedlings inoculated with C. lunata , the disease was reduced by 68.79 %, 75.80 % and 72.41 %, respectively. In a field trial, the chemical method gave the best results in all plant parameters, followed by the good agricultural practice (GAP) and organic methods. The chemical method gave the highest panicle/plant, panicle length, panicle weight, grain weight/plant which were different from the GAP and organic methods. The chemical method also gave the best results in filled grain panicle -1 , unfilled grain panicle -1 , grain weight plot -1 , dry hay weight plot -1 , biomass weight plot -1 and harvest index, and was significantly better than the GAP and organic methods.

Prevalence of angular leaf spot disease and sources of resistance in common bean in eastern Democratic Republic of Congo

Abstract: Angular leaf spot ( Pseudocercospora griseola Crous U, Brown) is one of the most important diseases hindering common bean ( Phaseolus vulgaris L.) production in the Great Lakes Region of Africa, including the Democratic Republic of Congo. The disease causes extreme yield losses, estimated at 384.2 tonnes per year, in Sub-Saharan Africa. Little is known about the distribution, severity and incidence of the disease and the effect of agronomic practices and environmental factors on the disease prevalence in the country to facilitate interventions. A field survey was conducted during two crop seasons, February to June and September to January, in two main beans growing zones of eastern DRC namely; sub-humid highland and sub-humid mid altitude at low latitudes, in South and North Kivu, respectively. Severity and incidence of angular leaf-spot and other occurring diseases were assessed on common bean plants in farmers’ fields. Angular leaf spot in these fields had an average severity index (PSI) of 49.9%. PSI was significantly different (P<0.05) between districts and seasons. Using multiple regression analysis, independent variables: growth stage, cropping system, districts and altitude were shown to have significant influence on the observed PSI (P<0.05) with R 2 = 96.2%. The highest severity (PSI=59.7%) was observed in Kabare district, and the lowest in Uvira district (PSI=39.5%). Screening of a set of 37 released common bean varieties in DRC using virulent Andean and Mesoamerican isolates identified four resistant bean varieties; ARA 4, COD MLV 059, MLV 224/94B, LSA 144 and Mexico 54. Some of these varieties possess useful traits, in addition to acceptable seed market class, and are hence recommended as suitable parents for ALS resistant variety development and promotion in ALS prone environments. Keywords: Phaseolus vulgaris , Pseudocercospora griseola , severity

Identity of Epicoccum sorghinum Causing Leaf Spot Disease of Bletilla striata in China

Abstract: Bletilla striata (Thunb.) Rchb. f. (Orchidaceae), known as a traditional Chinese herb, has been widely used as hemostatic and anti-microbial. In May 2017, a leaf spot disease was observed on 20–30% of B. striata in commercial fields located in Ziyuan County, Guangxi, China. Small, circular, brown spots were early observed on leaves, enlarging and developing into irregular dark brown and necrotic lesions. Necrotic lesions caused leaf abscission and occurred frequently during the plant’s life cycle. Three symptomatic leaves from three individual plants were surface sterilized in 1% sodium hypochlorite for 2 min, rinsed 3 times in sterile water, plated on potato dextrose agar (PDA) medium and then incubated at 26°C for 3 days. Seven isolates recovered from diseased plants and the colonies were villose and regular, pale grey, secreting scarlet pigment to the media. After 15 days of incubation, subspheroical chlamydospores were observed, which were brown to black, with verrucose surface. Unicellular chlamydosp...

First Report of Leaf Spot on Taro Caused by Epicoccum sorghinum in China

Abstract: Colocasia esculenta (L.) Schoot (Araceae), commonly known as taro, is grown worldwide as a starch-rich tuber, and has been cultivated extensively in southern China. In May 2016, leaf spot symptoms of Guangxi Lipu (varying from 30–40 × 12–15 cm in size) were frequently observed on lower taro leaves in many commercial fields (paddy field soil) located in Zhangzhou, Fujian province, China (percentage of symptomatic plants and fields were 10% and 80%, separately) and disease severity was positively influenced by suitable temperatures (25°C to 30°C ) and high humidity. Symptoms first appeared as necrotic lesions, which then elongated and became yellowish to light-brown and the necrotic lesions became thinner and many black pycnidia were found. Then, leaf spots later coalesced, becoming large and irregular, with yellow margins and some lesions eventually perforated. In most spots, black pycnidia were found in the thinner mesophyll tissues, varying from 20–70 µm in diameter. Conidia were hyaline, unicellular, el...

Outstanding host resistance will resolve the threat from white leaf spot disease (Pseudocercosporella capsellae) to oilseed and vegetable Brassica spp.crops

Abstract: Field host resistance against the white leaf spot pathogen Pseudocercosporella capsellae was determined across one hundred and seventeen Brassica napus, eleven B. juncea, four B. rapa, five B. oleracea, eight B. fruticulosa and one B. carinata genotypes. Of the one hundred and seventeen B. napus, there were seven lines of B. napus containing weedy crucifer introgression, sixteen lines with B. carinata introgression, fifty six lines of synthetic B. napus from B. juncea into B. carinata and B. rapa into B. oleracea, while remaining B. napus were commercial varieties from Australia. There was wide and significant (P < 0.001) variation across the test genotypes in terms of relative disease development assessed either as % leaves diseased index (%LDI), values ranging from 0 to 68, or % leaves collapsed index (%LCI), with values ranging from 0 to 38. B. rapa subsp. oleifera ATC 95966 Bo was the most resistant genotype to white leaf spot disease (%LDI = 0, %LCI = 0). Very high resistance was observed in all five B. oleracea genotypes (%LDI < 13, %LCI ≤ 10) and of these B. oleracea var. gongylodes Tronchuda with %LDI = 1.0 and %LCI = 2.5 and B. oleracea var. sabellica Kailan with %LDI = 2.4 and %LCI = 2.0 were the most resistant. Eight B. fruticulosa genotypes showed high resistance with %LDI < 15 and ≤ 10 %LCI. While eight out of twelve B. juncea varieties were highly susceptible, there was a range in %LDI of 5–58 and %LCI of 10–30 and with both Montara and VT 535 G showing best resistance of this species. Amongst B. napus genotypes, more than ten of the Australian commercial cultivars demonstrated comparatively higher resistance to white leaf spot disease than the most resistant genotypes with weedy introgression or synthetic B. napus, with commercial cultivars Oscar and Stubby considered to be highly resistant. These resistances offer unique opportunities both for direct deployment where white leaf spot is severe and for oilseed and vegetable Brassica spp. breeding programs to develop commercial cultivars with effective resistance.