Leaf Speck Research Articles

Grape Pseudocercospora Leaf Specked Area Estimation Using Hybrid Genetic Algorithm and Recurrent Neural Network

Grapes are prone to Pseudocercospora vitis fungus which causes Isariopsis leaf speck disease to the crop’s leaves, flower, and most importantly the fruit. Typical manual inspection of vineyard farmers is normally ineffective, destructive, and laborious. To address this, the use of integrated computer vision, machine learning, and computational intelligence techniques were realized to sort out healthy grape leaf image from a fungus-specked leaf image and to estimate the specked area percentage (SAP). A dataset made up of 343 normally healthy and 200 fungus-specked grape leaf images were initially pre-processed and segmented via graph cut prior to feature extraction and selection. Significant features were identified using classification tree (CTree). A multigene genetic programming tool called GPTIPSv2 was utilized to generate the fitness function needed for the optimization process done via genetic algorithm (GA). An optimal hidden neuron counts of 110, 50, and 10 were selected for a three-layered GA-optimized recurrent neural network (GA-RNN). Linear discriminant analysis (LDA) topped other disease recognition models with an accuracy of 99.99%. The developed GA-RNN model outperformed Gaussian process regression (GPR), regression tree (RTree), regression support vector machine (RSVM), and linear regression (RLinear) in performing leaf specked area estimation with an R2 value of 0.822. The developed CTree-LDA2-GA-RNN2 hybrid model has been proven to be the most viable model for this task.

Transcriptomic and genetic approaches reveal an essential role of the NAC transcription factor SlNAP1 in the growth and defense response of tomato

With global climate change, plants are frequently being exposed to various stresses, such as pathogen attack, drought, and extreme temperatures. Transcription factors (TFs) play crucial roles in numerous plant biological processes; however, the functions of many tomato (Solanum lycopersicum L.) TFs that regulate plant responses to multiple stresses are largely unknown. Here, using an RNA-seq approach, we identified SlNAP1, a NAC TF-encoding gene, which was strongly induced by various stresses. By generating SlNAP1 transgenic lines and evaluating their responses to biotic and abiotic stresses in tomato, we found that SlNAP1-overexpressing plants showed significantly enhanced defense against two widespread bacterial diseases, leaf speck disease, caused by Pseudomonas syringae pv. tomato (Pst) DC3000, and root-borne bacterial wilt disease, caused by Ralstonia solanacearum. In addition, SlNAP1 overexpression dramatically improved drought tolerance in tomato. Although the SlNAP1-overexpressing plants were shorter than the wild-type plants during the early vegetative stage, eventually, their fruit yield increased by 10.7%. Analysis of different hormone contents revealed a reduced level of physiologically active gibberellins (GAs) and an increased level of salicylic acid (SA) and abscisic acid (ABA) in the SlNAP1-overexpressing plants. Moreover, EMSAs and ChIP-qPCR assays showed that SlNAP1 directly activated the transcription of multiple genes involved in GA deactivation and both SA and ABA biosynthesis. Our findings reveal that SlNAP1 is a positive regulator of the tomato defense response against multiple stresses and thus may be a potential breeding target for improving crop yield and stress resistance.

Association of the Carrot Pathogen Alternaria dauci With New Diseases, Alternaria Leaf Speck, of Lettuce and Celery in California

In 2014 an unidentified disease was found on lettuce and celery grown in the Salinas Valley, Monterey Co., CA. Lettuce leaf symptoms were round to oval spots, 2 to 4 mm in diameter, white to tan, with a brown border. Celery leaf spots were round to oval, 2 to 4 mm in diameter, white to tan, with a chlorotic border. Initially it was thought that the damage was caused by chemical drift; however, field personnel noted the association of the disease with nearby carrots infected with Alternaria leaf blight. Microscopic examination of lettuce and celery leaves showed obclavate, brown, multicelled conidia in the spot centers, and a fungus was consistently isolated from this tissue. Cultural, morphological, and molecular analyses confirmed the fungus to be Alternaria dauci. Isolates of A. dauci from lettuce, celery, and carrot were pathogenic on all three crops. Field surveys showed that disease severity was greatest on the side of the lettuce or celery field closest to carrots. This is the first documentation that the carrot pathogen A. dauci can cause a disease on lettuce and celery grown in the field. The disease is designated as Alternaria leaf speck. Alternaria dauci was consistently isolated from nearby spinach plants showing identical symptoms and signs. However, pathogenicity tests were inconsistent and additional studies are needed to document A. dauci on spinach.

Potential of ethyl acetate fractions of Stryphnodendron adstringens shells and fruit extracts of Caesalpinia ferrea to control bacterial leaf speck and on the potentiation of defense enzymes in tomato

Considering the importance of bacterial leaf speck (Pseudomonas syringae pv. tomato) in reducing tomato yield and difficulties in disease control, this study investigated the effects of fractions of shells extract of Stryphnodendron adstringens (Sa) and fruit extract of Caesalpinia ferrea (Cf) compared to Acibenzolar-S-Methyl (ASM) on reducing bacterial leaf speck symptoms and on the potentiation of the activities of defense enzymes. The number of lesions per plant (NLP) was significantly lower in plants treated with the ethyl acetate fraction (EAF) of S. adstringens (Sa) and ASM compared to other treatments (EAF of Cf, n-butanol fractions of Sa and Cf, aqueous fractions of Sa and Cf and sterile distilled water). The bacteria were inhibited by the EAF of Sa and EAF of Cf and n-butanol fractions of Sa and Cf according to the bioautography assay. Saponins and tannins were the two major compounds found in these fractions based on the phytochemical analysis. Peroxidase (POX), polyphenoloxidase (PPO), β-1,3-glucanase (GLU) and phenylalanine ammonia-lyase (PAL) activities were determined on the leaves of plants treated with EAF Sa, ASM and sterile distilled water. Both POX and PAL activities were higher at 3 and 6 days after inoculation (dai), while the PPO and GLU activities were higher from 9 to 12 dai. It is suggested that saponins increased tomato resistance to P. s. pv. tomato because no antimicrobial activity against the bacteria was observed. In conclusion, the EAF Sa was very efficient in reducing bacterial leaf speck symptoms in conditions where the POX, PPO, PAL and GLU activities played a pivotal role in increasing tomato resistance to the disease.

Systemic resistance induced in Arabidopsis thaliana by Trichoderma asperellum SKT‐1, a microbial pesticide of seedborne diseases of rice

Trichoderma asperellum SKT-1 is a microbial pesticide of seedborne diseases of rice. To investigate the mechanisms of disease suppression in SKT-1, the ability to induce systemic resistance by SKT-1, or its cell-free culture filtrate (CF), was tested using Arabidopsis thaliana Col-0 plants. Both SKT-1 and its CF elicit an induced systemic resistance against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 in Col-0 plants. Involvement of plant hormones in the induced resistance by SKT-1 and CF was assessed using Arabidopsis genotypes such as the jasmonic acid (JA)-resistant mutant jar1, the ethylene (ET)-resistant mutant etr1, the plant impaired in salicylic acid (SA) signalling transgenic NahG and the mutant npr1 impaired in NPR1 activity. In soil experiments using SKT-1, no significant disease suppression effect was observed in NahG transgenic plants or npr1 mutant plants. Expression levels of SA-inducible genes such as PR-1, PR-2 and PR-5 increased substantially in the leaves of Col-0 plants. Expression levels of JA/ET-induced genes such as PDF1.2a, PR-3, PR-4 and AtVsp1 were also induced, but the levels were not as high as for SA-inducible genes. In a hydroponic experiment using CF from SKT-1, all Arabidopsis genotypes showed an induced systemic resistance by CF and increased expression levels of JA/ET- and SA-inducible genes in leaves of CF-treated plants. The SA signalling pathway is important in inducing systemic resistance to colonisation by SKT-1, and both SA and JA/ET signalling pathways combine in the signalling of induced resistance by CF. These results indicate that the response of A. thaliana is different from that found in root treatments with barley grain inoculum and CF from SKT-1.

Systemic resistance to bacterial leaf speck pathogen in Arabidopsis thaliana induced by the culture filtrate of a plant growth-promoting fungus (PGPF) Phoma sp. GS8-1

The culture filtrate (CF) from the plant growth-promoting fungus Phoma sp. GS8-1 was found to induce systemic resistance in Arabidopsis thaliana against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 (Pst), and the underlying mechanism was studied. Roots of A. thaliana were treated with CF from GS8-1, and plants expressed a clear resistance to subsequent Pst infection; disease severity was reduced, and proliferation of pathogen was suppressed. Various mutants of A. thaliana were used to test whether the CF induced resistance through one of the known signaling pathways: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). The CF was fully protective against Pst in Arabidopsis mutants jar1 and ein2 similar to wild-type plants. However, its efficacy was reduced in plants containing transgene NahG. Examination of systemic gene expression revealed that CF modulates the expression of SA-inducible PR-1, PR-2 and PR-5 genes, the JA/ET-inducible ChitB gene, and the ET-inducible Hel gene. Moreover, the expression of these genes was further enhanced upon subsequent stimulation after attack by Pst. Our data suggest that in addition to a partial requirement for SA, the signals JA and ET may also play a role in defense signaling in Arabidopsis.

Elicitation of systemic resistance against the bacterial speck pathogen in Arabidopsis thaliana by culture filtrates of plant growth-promoting fungi

The potential for mediation of induced systemic resistance (ISR) and the mechanisms used by nonpathogenic beneficial microbes to mediate ISR are currently under intense investigation but have been overlooked in studies examining plant growth promoting fungi (PGPF) or their metabolites. Here, we examined whether culture filtrates (CFs) of three well-characterized PGPF isolates, which demonstrated different responses in hypersensitive reaction-like cell death and β-glucuronidase reporter gene expression of PR-1a and PDF 1.2 constructs, had the ability to induce systemic resistance against the bacterial leaf speck pathogen Pseudomonas syringae pv. tomato DC3000 (Pst) in Arabidopsis thaliana. Arabidopsis plants treated with CFs of Phoma sp. (GS6-2 and GS7-3) and sterile fungus (GU23-3) elicited ISR against the Pst pathogen, resulting in a reduction in the number of symptomatic leaves, restriction of disease severity, and suppression of pathogen proliferation, with the best results obtained with Phoma sp. To determine the mechanism used to induce systemic resistance, Arabidopsis genotypes expressing the bacterial salicylate hydroxylase gene or containing disruptions in the nonexpressor of pathogenesis-related genes 1 (NPR 1), jasmonic acid JA, and ethylene (ET) signaling were screened. We demonstrate that signal transduction leading to GS6-2-mediated ISR requires salicylic acid (SA) accumulation, whereas CF of GU23-3-mediated ISR stimulates a pathway dependent on JA signaling. However, GS7-3-mediated ISR does not require SA, JA, ET, or NPRl signaling. Our results suggest that ISR mediated by three PGPF isolates studied were divergent in the biochemical pathways affected.

EDR2 negatively regulates salicylic acid-based defenses and cell death during powdery mildew infections of Arabidopsis thaliana

BackgroundThe hypersensitive necrosis response (HR) of resistant plants to avirulent pathogens is a form of programmed cell death in which the plant sacrifices a few cells under attack, restricting pathogen growth into adjacent healthy tissues. In spite of the importance of this defense response, relatively little is known about the plant components that execute the cell death program or about its regulation in response to pathogen attack.ResultsWe isolated the edr2-6 mutant, an allele of the previously described edr2 mutants. We found that edr2-6 exhibited an exaggerated chlorosis and necrosis response to attack by three pathogens, two powdery mildew and one downy mildew species, but not in response to abiotic stresses or attack by the bacterial leaf speck pathogen. The chlorosis and necrosis did not spread beyond inoculated sites suggesting that EDR2 limits the initiation of cell death rather than its spread. The pathogen-induced chlorosis and necrosis of edr2-6 was correlated with a stimulation of the salicylic acid defense pathway and was suppressed in mutants deficient in salicylic acid signaling. EDR2 encodes a novel protein with a pleckstrin homology and a StAR transfer (START) domain as well as a plant-specific domain of unknown function, DUF1336. The pleckstrin homology domain binds to phosphatidylinositol-4-phosphate in vitro and an EDR2:HA:GFP protein localizes to endoplasmic reticulum, plasma membrane and endosomes.ConclusionEDR2 acts as a negative regulator of cell death, specifically the cell death elicited by pathogen attack and mediated by the salicylic acid defense pathway. Phosphatidylinositol-4-phosphate may have a role in limiting cell death via its effect on EDR2. This role in cell death may be indirect, by helping to target EDR2 to the appropriate membrane, or it may play a more direct role.

Reduction of bacterial speck (Pseudomonas syringae pv. tomato) of tomato by combined treatments of plant growth-promoting bacterium, Azospirillum brasilense, streptomycin sulfate, and chemo-thermal seed treatment

Inoculation of tomato seeds with the plant growth-promoting bacterium Azospirillum brasilense, or spraying tomato foliage with A. brasilense, streptomycin sulfate, or commercial copper bactericides, separately, before or after inoculation with Pseudomonas syringae pv. tomato, the casual agent of bacterial speck of tomato, had no lasting effect on disease severity or on plant height and dry weight. Seed inoculation with A. brasilense combined with a single streptomycin foliar treatment and two foliar bactericide applications at 5-day intervals (a third or less of the recommended commercial dose) reduced disease severity in tomato seedlings by over 90% after 4 weeks, and significantly slowed disease development under mist conditions. A. brasilense did not induce significant systemic resistance against the pathogen although the level of salicylic acid increased in inoculated plants. Treatment of tomato seeds that were artificially inoculated with P. syringae pv. tomato, with a combination of mild chemo-thermal treatment, A. brasilense seed inoculation, and later, a single foliar application of a copper bactericide, nearly eliminated bacterial leaf speck even when the plants were grown under mist for 6 weeks. This study shows that a combination of otherwise ineffective disease management tactics, when applied in concert, can reduce bacterial speck intensity in tomatoes under mist conditions.

Septoria Leaf Speck, a New Disease of Sunflower, Caused by Septoria helianthina sp. nov.

AbstractMany strains of a pathogenic fungus were isolated from diseased sunflower leaf tissue. According to their characteristics they belonged to the genus Septoria. Leaf speck symptoms, characteristic for spontaneous infection, were also reproduced by artificial inoculation of sunflower plants in the greenhouse.Comparing the morphological, cultural and pathogenic properties of the isolated fungus with other sunflower pathogens, it was indicated that the strains, originating from diseased sunflower leaves represented a new, so far not described species. Therefore, for the causal agent of this disease, the name Septoria helianthina Petrov & Arsenijevic was suggested.