Showing papers on "Leaf spot published in 2019"
13 Mar 2019
TL;DR: A novel way of training and methodology was used to expedite a quick and easy implementation of the convolutional neural network system in practice and was able to recognise three different types of maize leaf diseases out of healthy leaves.
Abstract: Plant leaf diseases can affect plant leaves to a certain extent that the plants can collapse and die completely. These diseases may drastically decrease the supply of vegetables and fruits to the market, and result in a low agricultural economy. In the literature, different laboratory methods of plant leaf disease detection have been used. These methods were time consuming and could not cover large areas for the detection of leaf diseases. This study infiltrates through the facilitated principles of the convolutional neural network (CNN) in order to model a network for image recognition and classification of these diseases. Neuroph was used to perform the training of a CNN network that recognised and classified images of the maize leaf diseases that were collected by use of a smart phone camera. A novel way of training and methodology was used to expedite a quick and easy implementation of the system in practice. The developed model was able to recognise three different types of maize leaf diseases out of healthy leaves. The northern corn leaf blight (Exserohilum), common rust (Puccinia sorghi) and gray leaf spot (Cercospora) diseases were chosen for this study as they affect most parts of Southern Africa’s maize fields.
98 citations
27 Mar 2019
TL;DR: The purpose of the proposed system is to identify the leaf spot using image processing techniques and the classifier used in this paper is neural network (NN) classifier.
Abstract: Agricultural productivity plays a major role in an Indian economy; therefore the disease detection in the field of agriculture is important. Farmers struggle a lot for proper crop production due to multiple diseases affecting the plant so there is a need to detect the disease at initial stage. One major disease in the crop is leaf spot. The purpose of the proposed system is to identify the leaf spot using image processing techniques. In this research the disease detection is done in four stages, image acquisition, image segmentation, feature extraction and classification. For image segmentation is done with K-means clustering method and features are computed from disease affected cluster. Features such as Contrast, Correlation, Energy, Homogeneity, Mean, Standard Deviation and Variance are extracted. The extracted features from disease cluster are given as classifier inputs to classify the disease. The classifier used in this paper is neural network (NN) classifier. It is observed that the accuracies for bacterial leaf spot and target spot of cotton leaf diseases as 90% and 80% respectively. For tomato leaf diseases- septoria leaf spot and leaf mold as 100%.
83 citations
05 Feb 2019
TL;DR: One order, seven families, 28 new genera, 72 new species, 13 new combinations, four epitypes, and interesting new host and / or geographical records are introduced in this study.
Abstract: One order, seven families, 28 new genera, 72 new species, 13 new combinations, four epitypes, and 21 interesting new host and / or geographical records are introduced in this study. Pseudorobillardaceae is introduced for Pseudorobillarda (based on P. phragmitis). New genera include: Jeremyomyces (based on J. labinae) on twigs of Salix alba (Germany); Neodothidotthia (based on N. negundinicola) on Acer negundo (Ukraine); Neomedicopsis (based on N. prunicola) on fallen twigs of Prunus padus (Ukraine); Neophaeoappendicospora (based on N. leucaenae) on Leucaena leucocephala (France) (incl. Phaeoappendicosporaceae); Paradevriesia (incl. Paradevriesiaceae) (based on P. americana) from air (USA); Phaeoseptoriella (based on P. zeae) on leaves of Zea mays (South Africa); Piniphoma (based on P. wesendahlina) on wood debris of Pinus sylvestris (Germany); Pseudoconiothyrium (based on P. broussonetiae) on branch of Broussonetia papyrifera (Italy); Sodiomyces (based on S. alkalinus) from soil (Mongolia), and Turquoiseomyces (incl. Turquoiseomycetales and Turquoiseomycetaceae) (based on T. eucalypti) on leaves of Eucalyptus leptophylla (Australia); Typhicola (based on T. typharum) on leaves of Typha sp. (Germany); Xenodevriesia (incl. Xenodevriesiaceae) (based on X. strelitziicola) on leaves of Strelitzia sp. (South Africa). New species include: Bacillicladium clematidis on branch of Clematis vitalbae (Austria); Cercospora gomphrenigena on leaves of Gomphrena globosa (South Africa); Cyphellophora clematidis on Clematis vitalba (Austria); Exophiala abietophila on bark of Abies alba (Norway); Exophiala lignicola on fallen decorticated trunk of Quercus sp. (Ukraine); Fuscostagonospora banksiae on Banksia sp. (Australia); Gaeumannomycella caricicola on dead leaf of Carex remota (Germany); Hansfordia pruni on Prunus persica twig (Italy) (incl. Hansfordiaceae); Microdochium rhopalostylidis on Rhopalostylis sapida (New Zealand); Neocordana malayensis on leaves of Musa sp. (Malaysia); Neocucurbitaria prunicola on fallen twigs of Prunus padus (Ukraine); Neocucurbitaria salicis-albae on Salix alba twig (Ukraine); Neohelicomyces deschampsiae on culm base of dead leaf sheath of Deschampsia cespitosa (Germany); Pararoussoella juglandicola on twig of Juglans regia (Germany); Pezicula eucalyptigena on leaves of Eucalyptus sp. (South Africa); Phlogicylindrium dunnii on leaves of Eucalyptus dunnii (Australia); Phyllosticta hagahagaensis on leaf litter of Carissa bispinosa (South Africa); Phyllosticta austroafricana on leaf spots of unidentified deciduous tree host (South Africa); Pseudosigmoidea alnicola on Alnus glutinosa leaf litter (Germany); Pseudoteratosphaeria africana on leaf spot on unidentified host (Angola); Porodiplodia vitis on canes of Vitis vinifera (USA); Sodiomyces alkalinus from soil (Mongolia), Sodiomyces magadiensis and Sodiomyces tronii from soil (Kenya), Sympodiella quercina on fallen leaf of Quercus robur (Germany) and Zasmidium hakeicola on leaves of Hakea corymbosa (Australia). Epitypes are designated for: Cryptostictis falcata on leaves of E. alligatrix (Australia), Hendersonia phormii on leaves of Phormium tenax (New Zealand), Sympodiella acicola on needles of Pinus sylvestris (Netherlands), and Sphaeria scirpicola var. typharum on leaf of Typha sp. (Germany). Several taxa originally described from rocks are validated in this study. New taxa include: Extremaceae fam. nov., and new genera, Arthrocatena, Catenulomyces, Constantinomyces, Extremus, Hyphoconis, Incertomyces, Lapidomyces, Lithophila, Monticola, Meristemomyces, Oleoguttula, Perusta, Petrophila, Ramimonilia, Saxophila and Vermiconidia. New species include: Arthrocatena tenebrosa, Catenulomyces convolutus, Constantinomyces virgultus, C. macerans, C. minimus, C. nebulosus, C. virgultus, Exophiala bonariae, Extremus adstrictus, E. antarcticus, Hyphoconis sterilis, Incertomyces perditus, Knufia karalitana, K. marmoricola, K. mediterranea, Lapidomyces hispanicus, Lithophila guttulata, Monticola elongata, Meristemomyces frigidus, M. arctostaphyli, Neodevriesia bulbillosa, N. modesta, N. sardiniae, N. simplex, Oleoguttula mirabilis, Paradevriesia compacta, Perusta inaequalis, Petrophila incerta, Rachicladosporium alpinum, R. inconspicuum, R. mcmurdoi, R. monterosanum, R. paucitum, Ramimonilia apicalis, Saxophila tyrrhenica, Vermiconidia antarctica, V. calcicola, V. foris, and V. flagrans.
80 citations
TL;DR: Results suggest that Trichoderma sp.
60 citations
TL;DR: Findings reveal that competition, volatile antifungals, and enzyme activities are mechanisms involved in the biocontrol of leaf spot in lettuce by T. spirale T76-1.
53 citations
TL;DR: The results show that the DI detecting model based on the index could be used in peanut leaf spot detection in the absence of other stresses causing unhealthy symptoms and will provide a reliable, effective and accurate method for detecting leaf spot diseases in peanut through the analysis of hyperspectral data in the future.
39 citations
TL;DR: These products are involved in the antifungal activity against Colletotrichum sp.
33 citations
TL;DR: It is evident that alternaria leaf spot on canola across southern Australia is not solely caused by A. brassicae, but that a range of other Alternaria spp.
Abstract: Studies were undertaken to determine Alternaria spp. associated with leaf spot symptoms on canola (Brassica napus) in two cropping seasons (2015, 2016) across southern Australia. Major allergen Alt a1 and plasma membrane ATPase genes were used to identify Alternaria spp. In 2015, 112 isolates of seven Alternaria spp. were obtained, with A. metachromatica predominating. In 2016, 251 isolates of 12 Alternaria spp. were obtained, with A. infectoria predominating. Alternaria spp. isolates were morphologically and phylogenetically identified and studies to determine their pathogenicity on both B. napus (cv. Thunder TT) and B. juncea (cv. Dune) confirmed 10 species (A. alternata, A. arborescens, A. brassicae, A. ethzedia, A. hordeicola, A. infectoria, A. japonica, A. malvae, A. metachromatica and A. tenuissima) as pathogenic on both Brassica species. Alternaria ethzedia, A. hordeicola and A. malvae were recorded for the first time in Australia on any host and the record of A. arborescens was the first for New South Wales (NSW) and South Australia (SA). Other first records included A. infectoria on B. napus in NSW; A. japonica on B. napus in NSW and Western Australia (WA); A. metachromatica on any host in NSW, Victoria (VIC), WA and SA; and A. tenuissima on B. napus in NSW, SA and WA. It is evident that alternaria leaf spot on canola across southern Australia is not solely caused by A. brassicae, but that a range of other Alternaria spp. are also involved to varying degrees, depending upon the year and the geographic locality.
29 citations
TL;DR: The tomato gray leaf spot resistance gene Sm was fine-mapped in a 185-kb region through a map-based cloning strategy and genome-wide association study; a candidate gene was proved to be involved in Sm-mediated resistance through transient gene silencing and seems to be a good candidate of the Sm locus.
Abstract: The tomato gray leaf spot resistance gene Sm was fine-mapped in a 185-kb region through a map-based cloning strategy and genome-wide association study; a candidate gene was proved to be involved in Sm-mediated resistance through transient gene silencing. Gray leaf spot, caused by Stemphylium spp., is a warm weather foliar disease in tomato (Solanum lycopersicum L). Resistance against gray leaf spot is conferred by a single incompletely dominant gene (Sm) located on chromosome 11. This study aimed to map and identify molecular marker tightly linked to the Sm gene for the use of marker-assisted selection in breeding. Using an F2 population derived from a cross between the resistant line ‘9706’ and the susceptible line ‘Heinz 1706’, the Sm gene was mapped to a 185-kb interval between two markers, InDel343 and InDel-FT-32 on chromosome 11, which was consistent with the result of a genome-wide association study using 289 diverse accessions. An ORF predicted in this region was proved to be involved in Sm-mediated resistance through transient gene silencing and seems to be a good candidate of the Sm locus. To clone the Sm gene, a bacterial artificial chromosome (BAC) library was screened and one BAC clone B80B15 containing the predicted ORF was identified. The analysis of sequence and structure characteristics demonstrated that the candidate gene was not a typical type resistance gene. Additionally, a co-dominant marker Sm-InDel, which produced a 122-bp or 140-bp fragment for resistant or susceptible alleles, respectively, was developed. This marker was validated in 289 germplasm and could be used in marker-assisted selection for gray leaf spot resistance.
20 citations
TL;DR: Thirty-six strains of Paramyrothecium- and Albifimbria-like fungi were isolated from affected plants belonging to eight different species, and the involvement of fungi previously considered saprophytic in the development of plant disease for the first time deserves particular attention.
Abstract: The genera Paramyrothecium and Albifimbria have been established from the former genus Myrothecium and they generally comprise common soil-inhabiting and saprophytic fungi. Within these genera, onl...
19 citations
30 Oct 2019
TL;DR: Results indicated that application of Trichoderma had higher propagules than non-inoculated control and neither varietal resistance nor the disease control methods used in this study impacted the yield or yield components of Jerusalem artichoke.
Abstract: The objectives of this study were to evaluate the efficacy of integrating resistant genotypes of Jerusalem artichoke with Trichoderma harzianum isolate T9 to control Alternaria leaf spot caused by Alternaria spp. under two fertilization regimes and to determine whether T9 application induced chitinase and β-1,3-glucanase activity in Jerusalem artichoke leaves. Six Jerusalem artichoke varieties (resistant varieties JA15, JA86, and JA116 and susceptible varieties HEL246, HEL293, and JA109) and three disease control methods (a non-inoculated control, application of T. harzianum T9, and fungicide sprays (propiconazole at a rate of 30 mL/20 L of water, 375 ppm)) was conducted in two separate trials (different fertilization regimes) at the experimental farm of the Faculty of Agriculture, Khon Kaen University, Khon Kaen, Thailand. Resistant genotypes controlled Alternaria leaf spot effectively. Application of Trichoderma showed low efficacy to control Alternaria leaf spot, but in specific susceptible genotypes—HEL246 and HEL293—the application of Trichoderma could reduce disease severity up to 10%. The application of Trichoderma was associated with a rise in production of chitinase and β-1,3-glucanase in HEL246 seedlings. The number of Trichoderma propagules in soil, as well as the extent of colonization of roots and leaves, were monitored. The results indicated that application of Trichoderma had higher propagules than non-inoculated control. Neither varietal resistance nor the disease control methods used in this study impacted the yield or yield components of Jerusalem artichoke.
TL;DR: Testing the dual infection of AMF and Epichloë on perennial ryegrass growth and the physiological and biochemical indexes under limited soil conditions occurs in nature ecosystem showed that infection with B. sorokiniana significantly decreased plant growth and shoot N concentration, and this negative effect was exaggerated by AMF’s role.
Abstract: Both arbuscular mycorrhizal fungi (AMF) Claroideoglomus etunicatum and grass endophytes (Epichloe) could improve disease tolerance. Research is limited on the dual infection by AMF and Epichloe on plant diseases. Bipolaris sorokiniana is a fungal species that causes leaf spot in cereals, and also in perennial ryegrass (Lolium perenne), impacting its growth and production. This experiment tested the dual infection of AMF and Epichloe on perennial ryegrass growth and the physiological and biochemical indexes under limited soil conditions occurs in nature ecosystem. The results showed that infection with B. sorokiniana significantly decreased plant growth and shoot N concentration (P < 0.05), and this negative effect was exaggerated by AMF × Epichloe. The pathogen alone decreased AMF colonization (P < 0.05); however, the interactions of the pathogen and grass endophyte showed the highest value of perennial ryegrass AM colonization. Infection with AMF or Epichloe alone, or the combination of the two, suppressed the occurrence of leaf spot. Epichloe×AMF × B. sorokiniana had the highest amount of β-1,3-glucanase activity and jasmonic acid activity, whereas AMF and Epichloe alone or combined significantly increased the lignin content in diseased plants (P < 0.05). Limited soil nutrients did not affect the inhibition function of AMF and Epichloe for PRG leaf spot disease.
TL;DR: Post hoc analysis of the RIL subpopulation that was not utilized in the QTL mapping revealed that the flanking markers for these QTLs can successfully select for resistant and susceptible lines, confirming the effectiveness of pyramiding these resistance loci to improve host-plant resistance in peanut breeding programs using marker-assisted selection.
Abstract: Early and late leaf spots are the major foliar diseases of peanut responsible for severely decreased yield in the absence of intensive fungicide spray programs. Pyramiding host resistance to leaf spots in elite cultivars is a sustainable solution to mitigate the diseases. In order to determine the genetic control of leaf spot disease resistance in peanut, a recombinant inbred line population (Florida-07 x GP-NC WS16) segregating for resistance to both diseases was used to construct a SNP-based linkage map consisting of 855 loci. QTL mapping revealed three resistance QTLs for late leaf spot qLLSA05 (phenotypic variation explained, PVE=7-10%), qLLSB03 (PVE=5-7%), and qLLSB05 (PVE=15-41%) that were consistently expressed over multi-year analysis. Two QTL, qLLSA05 and qLLSB05, confirmed our previously published QTL-seq results. For early leaf spot, three resistance QTLs were identified in multiple years, two on chromosome A03 (PVE=8-12%) and one on chromosome B03 (PVE=13-20%), with the locus qELSA03_1.1 coinciding with the previously published genomic region for LLS resistance in GPBD4. Comparative analysis of the genomic regions spanning the QTLs suggests that resistance to early and late leaf spots are largely genetically independent. In addition, QTL analysis on yield showed that the presence of resistance allele in qLLSB03 and qLLSB05 loci might result in protection from yield loss caused by LLS disease damage. Finally, post hoc analysis of the RIL subpopulation that was not utilized in the QTL mapping revealed that the flanking markers for these QTLs can successfully select for resistant and susceptible lines, confirming the effectiveness of pyramiding these resistance loci to improve host-plant resistance in peanut breeding programs using marker-assisted selection.
TL;DR: C. fructicola is confirmed as the most frequent species causing GLS in Brazil and the diversity and pathogenicity of GLS-causing species worldwide is discussed.
Abstract: Glomerella leaf spot (GLS), caused by Colletotrichum spp., is one of the most important diseases of apple. In this study we aimed to identify Colletotrichum species associated with GLS from different apple-producing areas in Southern Brazil and assess their differential pathogenicity towards apple. Sequencing and multilocus phylogenetic analysis using partial gene regions of ITS, GAPDH, TUB2, ACT and HIS3 allowed the identification of eighteen isolates of Colletotrichum fructicola, and only one of Colletotrichum nymphaeae. All isolates were pathogenic to apple leaves, while C. nymphaeae did not cause symptoms. Worldwide, our literature review showed nine Colletotrichum species reported associated with GLS in different countries: C. fructicola, C. nymphaeae and C. karstii in Brazil; C. fructicola and C. aenigma in China; C. fructicola, C. aenigma and C. siamense in Japan, C. fructicola, C. alienum, C. gloeosporioides, C. siamense, C. tropicale and C. fioriniae in the USA, and only C. fructicola in Uruguay. Our study confirms C. fructicola as the most frequent species causing GLS in Brazil and discusses the diversity and pathogenicity of GLS-causing species worldwide.
TL;DR: To evaluate the antimicrobial activities of an active compound isolated from the culture broth of Amphirosellinia nigrospora JS‐1675 against various plant pathogenic bacteria and fungi.
Abstract: Aims To evaluate the antimicrobial activities of an active compound isolated from the culture broth of Amphirosellinia nigrospora JS-1675 against various plant pathogenic bacteria and fungi. Methods and results While screening for bioactive secondary metabolites from endophytic fungi, we found that A. nigrospora JS-1675 showed strong in vitro antibacterial activity against Ralstonia solanacearum. One compound (1) was isolated and identified as (4S, 5S, 6S)-5,6-epoxy-4-hydroxy-3-methoxy-5-methyl-cyclohex-2-en-1-one. Growth of most of the tested phytopathogenic bacteria was inhibited by compound 1 and the ethyl acetate (EtOAc) layer except Pseudomonas syringae pv. lachrymans. Compound 1 also inhibited the mycelial growth of several plant pathogenic fungi. Both compound 1 and the EtOAc layer reduced bacterial leaf spot disease in detached peach leaves. They also suppressed the development of bacterial wilt on tomato seedlings quite effectively. Conclusions Amphirosellinia nigrospora JS-1675 showed antimicrobial activity against plant pathogenic bacteria and fungi by producing compound 1. Significance and impact of the study This is the first report on the occurrence of compound 1 in A. nigrospora JS-1675 and its efficacy against plant pathogenic bacteria and fungi. Their strong disease control efficacy against tomato bacterial wilt suggests that this fungus can be used as a microbial bactericide.
TL;DR: Identification and association of specific gene-expression will elucidate potential disease resistance mechanism in peanut and may facilitate the selection of breeding lines with high levels of leaf spot resistance.
Abstract: Peanut (Arachis hypogaea L.) is an important food and oilseed crop worldwide. Yield and quality can be significantly reduced by foliar fungal diseases, such as early and late leaf spot diseases. Acceptable levels of leaf spot resistance in cultivated peanut have been elusive due to environmental interactions and the proper combination of QTLs in any particular peanut genotype. Resistance gene analogs, as potential resistance (R)-genes, have unique roles in the recognition and activation of disease resistance responses. Novel R-genes can be identified by searches for conserved domains such as nucleotide binding site, leucine rich repeat, receptor like kinase, and receptor like protein from expressed genes or through genomic sequences. Expressed R-genes represent necessary plant signals in a disease response. The goals of this research are to identify expressed R-genes from cultivated peanuts that are naturally infected by early and late spot pathogens, compare these to the closest diploid progenitors, and evaluate specific gene expression in cultivated peanuts. Putative peanut R-genes (381) were available from a public database (NCBI). Primers were designed and PCR products were sequenced. A total of 214 sequences were produced which matched to proteins with the corresponding R-gene motifs. These R-genes were mapped to the genome sequences of Arachis duranensis and Arachis ipaensis, which are the closest diploid progenitors for tetraploid cultivated peanut, A. hypogaea. Identification and association of specific gene-expression will elucidate potential disease resistance mechanism in peanut and may facilitate the selection of breeding lines with high levels of leaf spot resistance.
TL;DR: Under conducive field conditions for disease development, A. japonica can cause serious seed-yield losses of a magnitude similar to those occurring with A. brassicae, and these findings explain observed acceleration of Alternaria leaf spot severity from A. Japonica through the growing season.
Abstract: Studies were undertaken under controlled conditions into the effects of different foliage components (cotyledon, first, second and third leaf) at three plant ages (3, 5 and 7 weeks old) on development of Alternaria leaf spot disease, caused by Alternaria japonica or A. brassicae, in canola (Brassica napus cv. Thunder TT) and mustard (B. juncea cv. Dune). Alternaria japonica generally showed percentage disease index (%DI) values similar to A. brassicae across the two Brassica species, different foliage components and plant ages. %DI from either pathogen was greater in older plants than younger plants for the same foliage components in both cultivars. Field studies were then undertaken with canola to compare disease development from A. japonica and A. brassicae across different plant components (leaf, pod and stem) and the consequent adverse impact on seed yield. Alternaria japonica was more severe in terms of leaf area diseased (%LAD 62.6) and stem area diseased (%SAD 69.8) than pod area diseased (%PAD 25.5), whereas A. brassicae was more severe on leaves (%LAD 61.9) than on pods (%PAD 47.4) or stems (%SAD 41.0). Stem disease incidence was greater for A. japonica (%SDI 94.0) than for A. brassicae (%SDI 56.5), but pod disease incidence was greater for A. brassicae (%PDI 93.5) than for A. japonica (%PDI 86.1). For A. japonica, AUDPC values of leaf disease incidence (LDI, 283.5), leaf area diseased (LAD, 253.3) and leaf collapse (LCI, 149.5) resulted in a yield loss of 58.1%, similar to A. brassicae, where AUDPC values of LDI (277.8), LAD (247.2) and LCI (111.0) caused a yield loss of 59.4%. These findings explain observed acceleration of Alternaria leaf spot severity from A. japonica, as from A. brassicae, through the growing season as plants become more susceptible with increasing age, and as more susceptible, later developing leaves become abundant. For the first time, we demonstrate that under conducive field conditions for disease development, A. japonica can cause serious seed-yield losses of a magnitude similar to those occurring with A. brassicae.
TL;DR: The whole-genome sequence of D. segeticola will provide a resource for future research on host-pathogen interactions, determination of trait-specific genes, pathogen evolution and plant-host adaptation mechanisms.
Abstract: The fungal pathogen Didymella segeticola (basionym Phoma segeticola) causes leaf spot on tea (Camellia sinensis), which leads to a loss in tea leaf production in Guizhou Province, China. D. segeticola isolate GZSQ-4 was sequenced using Illumina HiSeq and Pacific Biosciences (PacBio) RS technologies, and then assembled to approximately 33.4 Mbp with a scaffold N50 value of approximately 2.3 Mbp. In total, 10,893 genes were predicted using the Nonredundant, Gene Ontology, Clusters of Orthologous Groups, Kyoto Encyclopedia of Genes and Genomes, and SWISS-PROT databases. The whole-genome sequence of D. segeticola will provide a resource for future research on host-pathogen interactions, determination of trait-specific genes, pathogen evolution, and plant-host adaptation mechanisms.
TL;DR: The highest initial inoculum was found in the lower part of the tree, but the highest rate of the disease progress in the upper, confirming the importance of dead leaves on the ground as main source of primary inoculum.
Abstract: Glomerella leaf spot (GLS) of apple is caused by three different Colletotrichum species complexes. This study evaluated the dispersal of Colletotrichum spores related to GLS temporal progress and d...
TL;DR: To confirm pathogenicity, detached healthy leaves of macadamia were superficially disinfected with 1% sodium hypochlorite solution for 2 min, washed with sterile water, air dried at room temperature, and then inoculated with the pathogen, thus satisfying Koch’s postulates.
Abstract: During March 2015, irregular light brown spots on leaves of macadamia (Macadamia integrifolia) were observed in Vitoria da Conquista, Bahia, Brazil. The disease severity was estimated at around 25%. Initial disease symptoms were characterized by small spots measuring 6 to 12 mm, which enlarged and coalesced, covering an extensive leaf area. Lesions showed abundant acervuli on the adaxial surface. From diseased leaves, direct isolations were performed by picking up conidia from acervuli and placing them on potato dextrose agar (PDA). Cultures were incubated at 25°C with a 12-h photoperiod for 10 days, and four single-spore isolates were obtained. Isolates showed similar morphological characteristics, and the representative isolate MAC-01 was further investigated. Fourteen-day-old colonies grown on PDA were white with cottony aerial mycelium and abundant black globular acervuli. Conidia were clavate to fusiform, four-septate, straight or slightly curved, and measured 17.9 to 27.5 µm long × 5.1 to 6.8 µm wide (n = 100). The three median cells were dark brown, whereas the basal and apical cells were hyaline. Conidia had a single basal appendage (3.5 to 7.4 μm long; n = 100) and two to three apical appendages (16.3 to 29.3 μm long; n = 100). Morphological features were consistent with those of Neopestalotiopsis clavispora reported by Maharachchikumbura et al. (2014). To confirm species identification, the internal transcribed spacer region (ITS), a partial sequence of the β-tubulin gene (TUB2), and a partial sequence of translation elongation factor 1-alpha gene (tef1-α) were polymerase chain reaction amplified and sequenced (Maharachchikumbura et al. 2014). The resulting sequences were deposited in GenBank under accession numbers KX721071 to KX721073. BLAST searches showed 98 to 100% identity with the existing sequences of N. clavispora deposited in GenBank (accession nos.: ITS, JX398978; TUB2, JX399013; and tef1-α, JX399044). Phylogenetic Bayesian inference analysis from a combined ITS, TUB2, and tef1-α sequence alignment showed that the examined isolate belonged to the N. clavispora species. The N. clavispora clade was well supported with a Bayesian posterior probability value of 1. To confirm pathogenicity, detached healthy leaves of macadamia were superficially disinfected with 1% sodium hypochlorite solution for 2 min, washed with sterile water, air dried at room temperature, placed in Petri dishes containing sterile filter paper moistened with sterile water, and then inoculated with the pathogen. For that, 5-mm mycelial plugs were excised from a 10-day-old colony grown on PDA and placed on the adaxial surface of 25 leaves. Plates were incubated at 25°C with a 12-h photoperiod for 10 days. As a control treatment, five additional detached leaves were mock inoculated with a PDA plug. The experiment was performed twice. Two days after inoculation, all inoculated leaves showed irregular light brown spots, measuring up to 8 mm, similar to those observed in the affected orchard. As the disease progressed, spots enlarged and acervuli were formed. Control leaves were asymptomatic. N. clavispora was reisolated from the symptomatic tissues and identified as previously described, thus satisfying Koch’s postulates. N. clavispora has been reported as the causal agent of leaf spot on Carya illinoinensis (Lazarotto et al. 2012) and Mangifera indica (Ismail et al. 2013). To our knowledge, this is the first report of N. clavispora causing leaf spot on macadamia in Brazil. Further studies are necessary to assess the geographic distribution and the importance of the disease in Brazilian macadamia orchards.
01 Mar 2019
TL;DR: In this study Deep Learning was used for the diagnosis of corn plant disease using the Convolutional Neural Network method, with an accuracy of 99%, in detecting disease in corn plants.
Abstract: Deep Learning is still an interesting issue and is still widely studied. In this study Deep Learning was used for the diagnosis of corn plant disease using the Convolutional Neural Network (CNN) method, with a total dataset of 3.854 images of diseases in corn plants, which consisted of three types of corn diseases namely Common Rust, Gray Leaf Spot, and Northern Leaf Blight. With an accuracy of 99%, in detecting disease in corn plants.
TL;DR: Results of this study suggest that relating HAD to Grain Yield could be an effective tool in order to improve the quantification and modelling of yield losses under foliar diseases infections.
TL;DR: To establish the baseline sensitivity of C. zeae-maydis isolates collected from different areas of the U.S. to pydiflumetofen using in vitro assays, a new succinate dehydrogenase inhibitor (SDHI) that currently is being registered for use on corn in the US is established.
TL;DR: Of particular interest are 27 wheat accessions that demonstrated resistance to spore inoculation by Ptr race 1, were characterized by insensitivity to ToxA and showed field resistance to the pathogen.
Abstract: Tan spot caused by the fungus Pyrenophora tritici-repentis is an important leaf spot disease in wheat growing areas throughout the world. The study aims to identify wheat germplasm resistant to tan spot based on phytopathological screening and molecular marker analysis. A collection of 64 common wheat germplasms, including cultivars and breeding lines from Kazakhstan and CIMMYT, was assessed for tan spot resistance in greenhouse conditions and characterized using the Xfcp623 molecular marker, diagnostic for the Tsn1 gene. All wheat cultivars/lines varied in their reaction to tan spot isolate race 1, ranging from susceptible to resistant. Most accessions studied (53 %) were susceptible to Ptr race 1. Spring wheat cultivars were more susceptible to race 1 than winter wheat cultivars. As a result of genotyping, an insensitive reaction to Ptr ToxA was predicted in 41 wheat cultivars (64 %). The tsn1 gene carriers identified included 27 Kazakhstani and 14 CIMMYT cultivars/lines, demonstrating insensitivity to Ptr ToxA. The majority of the Tsn1 genotype were sensitive to race 1 and showed susceptibility to the pathogen in the field. Disease scores from seedling stage positively correlated with field disease ratings. Of particular interest are 27 wheat accessions that demonstrated resistance to spore inoculation by Ptr race 1, were characterized by insensitivity to ToxA and showed field resistance to the pathogen. The results of this study will contribute to wheat breeding programs for tan spot resistance with Marker Assisted Selection using the closely flanking markers.
TL;DR: The remaining unclarified taxon among the seven known pathotypes of host-selective toxin (HST)-producing Alternaria alternata, namely, the strawberry pathotype (the strawberry black leaf spot pathogen), is taxonomically revised and re-described herein.
TL;DR: Of all the agar media evaluated, fresh rice leaf extract amendment at 25 g/liter with no V8 supplementation consistently supported the greatest radial growth, and 10% V8-only medium resulted in greater sporulation of C. janseana than other media evaluated.
Abstract: Cercospora janseana is the causal agent of narrow brown leaf spot, one of the major diseases of rice in the United States In vitro studies were conducted to evaluate various plant-based agar media
TL;DR: To the authors' knowledge, this is the first report of L. theobromae causing leaf spot on tea plants in China and it was consistently reisolated from inoculated leaves.
Abstract: Tea plant (Camellia sinensis) has been widely grown in Guizhou Province in China in recent years A survey that was conducted from May to October 2016, in the main tea production fields in Huishui County (2622 °N, 10708 °E), southern Guizhou Province, revealed spots on tea leaves that were initially chlorotic and then brown, necrotic, and surrounded by slightly chlorotic halos Spots gradually enlarged, formed larger irregular shapes, and covered the entire width of the leaves The color of the lesion’s center changed to dark brown or black Tea leaves with extensive lesions gradually dried and dropped off the plant Disease incidence of leaves was estimated at 30 to 45%, depending on the field Disease severity on a plant basis was estimated to be 32 to 38% To identify the etiology of this disease, samples taken from the lesion margins were surface sterilized with 75% ethanol followed by 05% sodium hypochlorite for 30 s, rinsed with sterile water three times, and plated on potato dextrose agar (PDA) The plates were incubated at 25°C in darkness for 3 to 5 days, and then hyphal tips from the margin of a growing colony were successively transferred to fresh PDA plates to study their morphological and molecular characteristics The fungal colonies were initially white, with sparse aerial mycelia 2 days after the inoculation, and they later turned gray, with woolly aerial mycelia 7 days after the inoculation Globose to subglobose pycnidia were formed on 2- and 3-week-old cultures The immature conidia were initially ovoid, hyaline, and aseptate, 2583 (21 to 29) × 1459 (12 to 15) μm (n = 50) single spores Mature conidia became dark brown with striated cell walls and had a median septum These observed morphological features are in accordance with those previously described for Lasiodiplodia theobromae (Pat) Griffon & Maubl (Alves et al 2008) The internal transcribed spacer (ITS1-58S-ITS2) and part of the translation elongation factor 1-alpha genes of the isolates were further amplified following the methods described in Alves et al (2008) and then sequenced and deposited in GenBank BLAST algorithm-based analyses showed 99 and 100% identities between six isolates (MH151161 and MH151160, etc) and L theobromae (KX2703621 and KU8869561, respectively) To fulfill Koch’s postulates, PDA plugs with actively growing mycelia from three isolates were placed on wounded tea leaves using a sterile needle or a sterile scalpel, covered with wet cotton, and kept under 80% relative humidity until symptom development (n = 10 for each isolate) The light brown leaf spots formed 1 to 2 days after inoculation and then gradually enlarged with the color becoming black in the center of the lesion The spots resulted in a rapid necrosis and withered the entire leaf, as well as the top tender bud and fresh leaf, whereas the control leaves inoculated with PDA plugs without mycelia showed no symptoms L theobromae was consistently reisolated from inoculated leaves L theobromae is a plurivorous pathogen found worldwide, and it is transmitted in many ways It has been previously reported to cause root disease in tea bushes after pruning (Petch 1923; Punithalingam 1976), foliar diseases on tea oil Camellia (Zhu et al 2014) and on Parthenium (Kumar and Singh 2000), but not to cause disease on tea leaves in China To our knowledge, this is the first report of L theobromae causing leaf spot on tea plants in China This identification will help producers in Guizhou Province seek and adopt appropriate field management measures to prevent and control this disease
01 Dec 2019
TL;DR: Using digital image processing and machine learning technology to realize the automatic recognition of plant leaf diseases is of great significance to the prevention and control of crop diseases.
Abstract: Using digital image processing and machine learning technology to realize the automatic recognition of plant leaf diseases is of great significance to the prevention and control of crop diseases. In this paper, powdery mildew, bacterial leaf spot, black spot and downy mildew of sunflower leaves were studied. The image samples were denoised by morphological weight adaptive image denoising method. K-means + + clustering algorithm and watershed algorithm are used to segment the image of sunflower leaf disease. 19 feature values of color feature and texture feature are extracted from the diseased areas, and a random forest algorithm is constructed to identify the diseased areas. The overall recognition rate can reach 95%.