Early Blight Of Potato Research Articles

Differential Expression of Induced Resistance Genes by Abscisic Acid (ABA) Against Potato Early Blight Disease

Abscisic acid (ABA), a plant hormone involves in various plant physiological processes including, response to biotic and abiotic stress conditions. ABA was tested to study its ability to enhance disease resistance of two potato cultivars i.e., Nicola and Spunta, to the infection by the early blight fungus Alternaria solani (A. solani) under greenhouse conditions. Treatment with ABA solution (10 μM) reduced the early blight disease severity for both cultivars compared to the untreated infected plants. Differential display gene analysis for treated plants revealed three clear bands. These bands showed significant homology to well-known genes in the GenBank database and identified as superoxide dismutase (CuZnSOD), WRKY transcription factor (StWRKY) and Endoglucanase from potato genome. Real-Time PCR was used to detect the changes in gene expression of CuZnSOD and WRKY-type genes after infection with A. solani for both Nicola and Spunta potato cultivars and in different time intervals. The expression level of CuZnSOD and WRKY genes in potato leaves of both cultivars were increased for ABA treated and infected plants and for untreated/infected plants compared to the untreated/uninfected plants. Both genes were over expressed in infected plants treated with ABA than untreated ones and reached the maximum level of expression after two days of inoculation. The highest increase of both genes expression was observed in potato leaves of cv. Nicola compared to cv. Spunta.

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Induced Synthesis of Defense Enzymes during Induced Resistance against Early Blight of Potato Using Plant Extracts as Inducer

Induced Synthesis of Defense Enzymes during Induced Resistance against Early Blight of Potato Using Plant Extracts as Inducer

First Report of Alternaria Blight of Potatoes in Nomal Valley, Gilgit-Baltistan Pakistan

Gilgit-Baltistan (GB) having unique geographic and climatic conditions was free from plant diseases. Since the disease resistant traditional varieties of plants have been replaced by high yielding varieties. As a result major threats come in the form of diseases such as Late blight and Early blight of potato and tomato crops, Grey mold of Grapes, Powdery mildew of cucumbers, Botrytis leaf virus in onions, Crown gall disease of cherries and nematodes of potatoes. The introduction of handful of high yielding varieties have also reduced the genetic diversity. Potatoes are highly valuable, nutritious vegetable and major cash crop grown in Gilgit-Baltistan (GB) Pakistan. Recently early blight disease has severely infected the potato fields of Nomal valley of GB. Early blight is an important foliar disease under diverse climatic conditions of GB. Over the past few years, early blight became a major threat to potato crops in GB and highest incidences were recorded in Nomal Valley of GB. Nomal Valley has been divided into six major sectors or Mohallahs. The Mohallahs are as; Mohallah Jigot, Mohallah Batot, Mohallah Majini, Mohallah Das and Mohallah Sigal. During June-July, 2016 a survey were carried out in randomly selected five fields of each Mohallah of Valley Nomal. Within each field five potato plants were randomly selected and observed for typical early blight symptoms. Moreover at harvesting stage tubers were also observed for early blight symptoms. The disease incidence and disease severity were recorded. The highest percent disease severity (66.4) was recorded in potato fields of Mohallah Jigot followed by potato fields of Mohallah Sigel (63.2%), Mohallah Majini (42%) and Mohallah Batot (36%). Meanwhile the minimum percent disease severity was recorded on the potato fields of Mohallah Das (12%). It can be concluded from the present study that early blight is serious threat to potato production in Nomal Valley of GB.

2,4-Dichlorophenoxy acetic acid, abscisic acid, and hydrogen peroxide induced resistance-related components against potato early blight (Alternaria solani, Sorauer)

Induction of acquired resistance activates defense-related genes. Current study aimed to (a) initiate potato acquired resistance to the Early Blight disease caused by Alternaria solani through treating potato plants with low and repetitive doses of 2,4-dichlorophenoxy acetic acid (2,4-D), abscisic acid (AB), and hydrogen peroxide (H2O2) and (b) test the success of the use of the chemical inducers along with the application of fungicides. Potato cultivars Nicola and Spunta were treated once per wk for 6wk and challenged 1wk later by in the control of A. solani. Results showed that peroxidase (POD), phenylalanine ammonia lyase (PAL), and polyphenoloxidase (PPO) enzyme activities and gene regulation were significantly increased after 1d of infection and lasted for more than 15d. The 2,4-D and H2O2 inducers significantly increased both enzyme activities and gene expression of PAL, PPO, and POD for more than 15d post inoculation. PAL was the most increased at the enzyme activity and gene expression levels. Incorporation of such in-expensive treatments might reduce management costs and reduce the environmental pollution.

Perpetuation of <i>Alternaria solani</i> of Potato under Temperate Kashmir Valley Conditions

The present study on perpetuation of Alternaria solani , causing early blight of potato in Kashmir valley was conducted during 2009 and 2010. The perpetuation of the fungus A. solani was studied on diseased leaves by placing the leaves on ground surface and at 20 cm depth, as well as on diseased potatoes kept in ambient store. The pathogen perpetuated as mycelium and conidia throughout winter on diseased leaves left on the ground surface and on diseased potatoes kept in ambient store. The number of spores cm -2 leaf area and the viability of spores decreased with increase in depth of placement in soil. Maximum spores production on over wintered leaves was observed during first fortnight of June during the year 2009 and 2010, with maximum number of 294 and 323 spores, respectively. However, by the first fortnight of July, the number gradually declined to 160 and 220 spores, respectively. The highest spore viability of 44.3 and 49.3 per cent in leaves on ground surface was recorded in the first fortnight of June, 2009 and 2010, respectively. In potatoes kept in ambient store the average number of spores increased upto first fortnight of June, both in 2009 and 2010, with a maximum number of 430 and 508 spores, respectively. The number then gradually declined to 216 and 263 spores, respectively, till last observation recorded in the second fortnight of July.

Population genetic analysis reveals cryptic sex in the phytopathogenic fungus Alternaria alternata.

Reproductive mode can impact population genetic dynamics and evolutionary landscape of plant pathogens as well as on disease epidemiology and management. In this study, we monitored the spatial dynamics and mating type idiomorphs in ~700 Alternaria alternata isolates sampled from the main potato production areas in China to infer the mating system of potato early blight. Consistent with the expectation of asexual species, identical genotypes were recovered from different locations separated by hundreds of kilometers of geographic distance and spanned across many years. However, high genotype diversity, equal MAT1-1 and MAT1-2 frequencies within and among populations, no genetic differentiation and phylogenetic association between two mating types, combined with random association amongst neutral markers in some field populations, suggested that sexual reproduction may also play an important role in the epidemics and evolution of the pathogen in at least half of the populations assayed despite the fact that no teleomorphs have been observed yet naturally or artificially. Our results indicated that A. alternata may adopt an epidemic mode of reproduction by combining many cycles of asexual propagation with fewer cycles of sexual reproduction, facilitating its adaptation to changing environments and making the disease management on potato fields even more difficult.

Individual Participant Data Meta-Analysis of Foliar Fungicides Applied for Potato Early Blight Management

Foliar fungicides continue to be the primary means of early blight management on potato in the United States. Both premium-priced, single-site mode-of-action "specialty" fungicides and standard protectant multisite fungicides are applied, either alone or incorporated into fungicide rotation programs to combat early blight. Individual participant data meta-analysis was conducted to compare overall fungicide efficacy against early blight on potato, quantify tuber yields, and identify the most efficacious timing for fungicide applications. In this study, the specialty fungicide-based applications were compared against the standard fungicides chlorothalonil and mancozeb applied alone. Type 3 fixed effects indicated that there was a significant difference (P < 0.0001) in overall efficacy and yield among the treatments applied to manage early blight in potato. There was a significant difference (P < 0.0001) among treatments in early blight development during the growing season. Applications incorporating specialty fungicides, when compared with standard fungicides, significantly affected disease severity from vegetative growth initiation (P = 0.0139) to tuber maturation (P = 0.0009). Results demonstrate that the higher cost, specialty-fungicide-based applications were most effective for early blight management in North Dakota and Minnesota.

Functional Analyses of the Diels-Alderase Gene sol5 of Ascochyta rabiei and Alternaria solani Indicate that the Solanapyrone Phytotoxins Are Not Required for Pathogenicity.

Ascochyta rabiei and Alternaria solani, the causal agents of Ascochyta blight of chickpea (Cicer arietinum) and early blight of potato (Solanum tuberosum), respectively, produce a set of phytotoxic compounds including solanapyrones A, B, and C. Although both the phytotoxicity of solanapyrones and their universal production among field isolates have been documented, the role of solanapyrones in pathogenicity is not well understood. Here, we report the functional characterization of the sol5 gene, which encodes a Diels-Alderase that catalyzes the final step of solanapyrone biosynthesis. Deletion of sol5 in both Ascochyta rabiei and Alternaria solani completely prevented production of solanapyrones and led to accumulation of the immediate precursor compound, prosolanapyrone II-diol, which is not toxic to plants. Deletion of sol5 did not negatively affect growth rate or spore production in vitro, and led to overexpression of the other solanapyrone biosynthesis genes, suggesting a possible feedback regulation mechanism. Phytotoxicity tests showed that solanapyrone A is highly toxic to several legume species and Arabidopsis thaliana. Despite the apparent phytotoxicity of solanapyrone A, pathogenicity tests showed that solanapyrone-minus mutants of Ascochyta rabiei and Alternaria solani were equally virulent as their corresponding wild-type progenitors, suggesting that solanapyrones are not required for pathogenicity.

Functional Analyses of the Diels-Alderase Gene sol5 of Ascochyta rabiei and Alternaria solani Indicate that the Solanapyrone Phytotoxins Are Not Required for Pathogenicity.

Ascochyta rabiei and Alternaria solani, the causal agents of Ascochyta blight of chickpea (Cicer arietinum) and early blight of potato (Solanum tuberosum), respectively, produce a set of phytotoxic compounds including solanapyrones A, B, and C. Although both the phytotoxicity of solanapyrones and their universal production among field isolates have been documented, the role of solanapyrones in pathogenicity is not well understood. Here, we report the functional characterization of the sol5 gene, which encodes a Diels-Alderase that catalyzes the final step of solanapyrone biosynthesis. Deletion of sol5 in both Ascochyta rabiei and Alternaria solani completely prevented production of solanapyrones and led to accumulation of the immediate precursor compound, prosolanapyrone II-diol, which is not toxic to plants. Deletion of sol5 did not negatively affect growth rate or spore production in vitro, and led to overexpression of the other solanapyrone biosynthesis genes, suggesting a possible feedback regulation mechanism. Phytotoxicity tests showed that solanapyrone A is highly toxic to several legume species and Arabidopsis thaliana. Despite the apparent phytotoxicity of solanapyrone A, pathogenicity tests showed that solanapyrone-minus mutants of Ascochyta rabiei and Alternaria solani were equally virulent as their corresponding wild-type progenitors, suggesting that solanapyrones are not required for pathogenicity.

Role of Weather Factors on Early Blight of Potato under Kashmir Valley Conditions

The effect of weather factors on development of early blight of potato studied during the year 2009 and 2010 , indicated maximum apparent infection rate of 0.155 (unit/day) and 0.165 (unit/day) respectively. The temperature 26.47 and 27.32 ℃ , relative humidity 92 and 91 per cent and precipitation 6.68 and 6.42 mm during 2009 and 2010, respectively, apparently favoured the maximum disease development during these periods. Temperature showed a significant and positive correlation with disease intensity, whereas relative humidity and precipitation showed positive but non significant correlation with disease intensity. Multiple regression analysis revealed that weather factors accounted for 65.5 per cent variation.

Effect of simulated rain on the efficiency of fungicides in potato late blight and early blight control

A resistencia de fungicidas a chuva no controle da requeima ( Phytophthora infestans ) e pinta preta ( Alternaria solani ) da batata foi avaliada em condicoes de casa-se vegetacao e laboratorio. Plantas de batata das cultivares Agata e Monalisa tratadas com fungicidas indicados para as duas doencas foram submetidas a chuva controlada de 20 mm durante 6 minutos aos 30 minutos, 1, 2 e 4 horas apos a pulverizacao. Apos a secagem das plantas, discos foliares foram coletados e transferidos para placas de Petri e inoculados com os patogenos. Em seguida as placas foram incubadas em câmara BOD a 18° C para P. infestans e 25 ° C para A. solani , sob fotoperiodo de 12 horas. A severidade foi avaliada atraves da porcentagem da area do disco afetada pelas doencas aos 5 e 7 dias apos a inoculacao, respectivamente. Os resultados obtidos permitiram concluir que os fungicidas sistemicos, translaminares ou com tenacidade inerente foram menos afetados pela chuva simulada quando comparados aos fungicidas de contato. O aumento do tempo de secagem promoveu maiores niveis de controle da requeima e pinta preta, evidenciando uma maior retencao ou absorcao dos produtos testados.

Efficacy of certain bio agents and fungicides against early blight of potato (Solanum tuberosum L.)

An experiment was conducted to evaluate the effect of bio agents (Trichoderma harzianum and Pseudomonas fluorescens) and fungicides (mancozeb) against early blight of potato caused by Alternariasolani (Ell. and Mart.) at the experimental field of Department of Plant Protection, Sam Higginbottom Institute of Agriculture, Technology and Sciences, Allahabad during Rabi Season of 2013-2014. Seven treatment including control with three replications were taken up using RBD. The treatments comprised of seed treatment and foliar spray (once and twice) of bio agents Trichoderma harzianum and Pseudomonas fluorescens while fungicide taken up was mancozeb and control (spray of plain water) was applied. Observation for per cent disease intensity was recorded at 60 and 80 days after sowing. Lowest disease intensity was recorded in mancozeb (15.07% and 18.40%, respectively) as compared to control which recorded highest disease intensity (20.91% and 33.80%, respectively).Mancozeb not only reduced disease intensity but also recorded highest yield (253.00 q/ha) as compared to control which recorded 157.83 q/ha.The bio agents Trichoderma harzianum and Pseudomonas fluorescens (seed treatment +foliar spray) were also effective in reducing the disease intensity and increasing tuber yield.

Quantification of disease progression of Alternaria spp. on potato using real-time PCR

Potato early blight and brown spot are important fungal diseases responsible for premature defoliation and yield loss of potato. Pathogens considered to be involved in leaf necrosis are Alternaria solani and A. alternata, respectively. Both diseases are commonly characterized by the visualization of leaf lesions. Current detection and identification methods for Alternaria species rely primarily on cultural and morphological characteristics, the assessment of which is time-consuming and not always suitable. Sensitive, reliable methods for estimating infection severity are therefore desirable. In this study, an Alternaria-specific real-time PCR assay was developed using primers based on internal transcribed spacers (ITS) 1 and 2. The assays facilitated species detection and clearly discriminated between A. solani and A. alternata. The use of real-time PCR allowed quantitative estimation of fungal biomass in plant tissues. Detection sensitivities were in the range of >100 fg. Real-time PCR applications used to accurately assess the extent of colonization by Alternaria spp. during disease development are reported here for the first time. Additionally, Alternaria genomic DNA levels were verified not only in potato leaves showing different levels of disease progress, but also in symptomless leaves. This assay provides a useful tool to quantify pathogen levels during initial latent stages of infection and will thus help in the early detection and quantification of Alternaria spp..

Large-spored Alternaria pathogens in section Porri disentangled

The omnipresent fungal genus Alternaria was recently divided into 24 sections based on molecular and morphological data. Alternaria sect. Porri is the largest section, containing almost all Alternaria species with medium to large conidia and long beaks, some of which are important plant pathogens (e.g. Alternaria porri, A. solani and A. tomatophila). We constructed a multi-gene phylogeny on parts of the ITS, GAPDH, RPB2, TEF1 and Alt a 1 gene regions, which, supplemented with morphological and cultural studies, forms the basis for species recognition in sect. Porri. Our data reveal 63 species, of which 10 are newly described in sect. Porri, and 27 species names are synonymised. The three known Alternaria pathogens causing early blight on tomato all cluster in one clade, and are synonymised under the older name, A. linariae. Alternaria protenta, a species formerly only known as pathogen on Helianthus annuus, is also reported to cause early blight of potato, together with A. solani and A. grandis. Two clades with isolates causing purple blotch of onion are confirmed as A. allii and A. porri, but the two species cannot adequately be distinguished based on the number of beaks and branches as suggested previously. This is also found among the pathogens of Passifloraceae, which are reduced from four to three species. In addition to the known pathogen of sweet potato, A. bataticola, three more species are delineated of which two are newly described. A new Alternaria section is also described, comprising two large-spored Alternaria species with concatenate conidia.

Cultivation technology influences the occurrence of potato early blight (Alternaria solani) in an organic farming system

Nowadays, organically produced products have become more popular than ever and interest in them is still growing fast. The early blight causal pathogen Alternaria solani has not been considered a great threat to potato in northern climate conditions in the past and has not been routinely sprayed against. During our study early blight was evaluated in 2010 and 2011 on the plants of a potato cultivar ‘Reet’ in an organic farming experiment. In our study, both growing seasons were very favourable for early blight development. Significant differences between the two cultivation technologies were found (F1,12 = 4.84, p = 0.048). In 2010, the area under disease progress curve (AUDPC) value was 303 on cover crop (CC) plots and 990 on CC + M (manure) plots that is three times higher, whereas in 2011, the AUDPC value was 967 on CC plots and 1195 on CC + M plots. Our results confirm that potato early blight has become a serious problem in North-East European organic potato fields and thus susceptible potato cultivars cannot be recommended for growing in an organic farming system. However, it is possible to influence the development severity of early blight by selecting the proper growing technology. Since, in the changing climate conditions and in susceptible cultivars, early blight is a potato disease that can cause early defoliation of plants and crop death, there is a need for resistant potato cultivars.

First Report of Boscalid and Penthiopyrad-Resistant Isolates of Alternaria solani Causing Early Blight of Potato in Michigan.

Early blight of potato (Solanum tuberosum) is caused by Alternaria solani and occurs annually in Michigan. If left uncontrolled, it can result in yield losses exceeding 20% and impact stored potatoes. The disease is commonly managed using succinate dehydrogenase inhibitor (SDHI) fungicides (1). Unfortunately, recent studies have shown that SDHI resistance has increased dramatically over the past 2 years in A. solani populations (1,2). To investigate the occurrence of SDHI resistance in Michigan, potato leaves with early blight symptoms were collected from fields in Montcalm and Ionia counties, MI, in 2012. To obtain A. solani isolates from leaves, small pieces of leaf tissue (5 × 5 mm) were excised from the center of lesions and transferred on to water agar. Plates were incubated at 25°C overnight to allow conidia to germinate. Single germinated A. solani conidia were transferred to potato dextrose agar (PDA) and incubated at 25°C for 7 days. The identity of cultures was confirmed by colony and conidial morphology (3). Nineteen A. solani isolates were obtained and each was screened for sensitivity to the SDHI fungicides boscalid, penthiopyrad, and fluopyram, using a 50 ppm discriminatory dose based on EC50 values previously determined (2). Mycelial plugs (~5.5 mm) were transferred to amended and non-amended PDA plates that were incubated at 25°C for 7 days. An isolate was considered highly resistant if fungal growth relative to control plates exceeded 50%, moderately resistant if it was between 35 and 50%, and sensitive if it was less than 35% (2). A sensitive A. solani isolate (AS11) from Bonners Ferry, ID, was used as a control in these experiments. Of all isolates tested, 11% were highly resistant to both boscalid and penthiopyrad and 5% were moderately resistant to both fungicides, 21% were moderately resistant to penthiopyrad alone, and the remaining isolates (84 and 68% respectively) were sensitive to the two fungicides. None of the isolates tested were resistant to fluopyram. Recently, two major mutations, H227R in SdhB and H133R in SdhD, have been identified in highly resistant A. solani isolates in Idaho (2). Because the majority of the identified mutations occur near the 3' end of each subunit, this region was amplified and sequenced using the following primer sets: SdhB (5'-TACTGGTGGAACCAGGAGGAGTA-3' and 5'-CATACCACTCTAGGTGAAG-3'), SdhC (5'-CCAAATCACCTGGTACGCCTCG-3' and 5'-TCATCCGAGGAAGGTGTAGTAAAGGCTG-3'), and SdhD (5'-CCGACTCTATTCTCTGCGCCCT-3' and 5'-CTCGAAAGAGTAGAGGGCAAGACCCA-3'). In this study, all of the isolates that were highly resistant to both boscalid and penthiopyrad were found to contain the H133R mutation in SdhD, which correlated with the strongest resistance phenotype. To our knowledge, this is the first report of resistance to SDHI fungicides in populations of A. solani on potato in Michigan. These data are concerning as they indicate that the highly resistant isolates have already developed cross-resistance between boscalid and penthiopyrad, despite penthiopyrad not yet having regular use in Michigan. Although all of the isolates tested were sensitive to fluopyram, the discovery of isolates resistant to boscalid and penthiopyrad suggests that all SDHI fungicides should be considered at high risk of resistance development in Michigan.

Bioefficacy of plant extracts and biocontrol agents against Alternaria solani

Three bioagents viz., Trichoderma harzianum Rifai, Trichoderma viride Pers. andTrichoderma virens (Miller et al) von Arx and five plant extracts viz., Artimesia absinthiumL., Datura stramonium L., Urtica dioica L., Juglans regia L. and Mentha arvensis L. were evaluated in vitro against Alternaria solani (Ellis and Martin) Jones and Grout causing early blight of potato through dual culture and poisoned food technique, respectively. Among bioagents, significantly higher mycelial growth inhibition of A. solani was recorded in the case of T. harzianum (71.85%), which was followed by T. viride (65.93%) and T. virens(58.65%) proved least effective in inhibiting the mycelial growth of A. solani. Among plant extracts, D. stramonium proved superior to all other botanicals, exhibiting (61.12%) mycelial growth inhibition of A. solani. This was followed by A. absinthium (58.54%).Urtica dioica (37.34%) proved least effective in inhibiting the mycelial growth of the test fungus. Key words: Bioagents, plant extracts, potato, Alternaria solani, dual culture, early blight.

Development and validation of a set of standard area diagrams to estimate severity of potato early blight

Standard area diagrams (SADs) to assess the severity of potato early blight (Alternaria grandis) on leaves of potato (Solanum tuberosum L.) were developed and validated. The proposed SADs include images of leaves with 10 distinct disease severities (0.1, 1, 3, 5, 10, 20, 40, 60, 80 and 100 %). The SADs were validated by 12 raters who had no previous experience in evaluating plant disease. Lin’s concordance correlation analysis of estimated vs. actual disease severity (based on image analysis) showed that precision and accuracy improved for most raters using the SADs, compared to assessments made without the SADs. The SADs improved accuracy (coefficient of bias, C b = 0.97 and 0.99, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ c = 0.91 and 0.98 without and with SADs, respectively) of the estimates of severity. Severity estimates were more reliable when using SADs (coefficient of determination, R 2 = 0.80 unaided and R 2 = 0.95 with SADs, and the intra-class correlation ρ = 0.86 without SADs and ρ = 0.97 using the SADs). The SADs improved raters’ ability to accurately, precisely and reliably estimate potato early blight severity, and as such can be used to assess severity for several purposes, including breeding for resistance, fungicide screening, and pathotype characterization.

Screening and characterization of resistance to succinate dehydrogenase inhibitors in Alternaria solani

Field isolates of Alternaria solani, which causes early blight of potato in Idaho, USA were evaluated in vitro for their sensitivity towards the succinate dehydrogenase inhibitor (SDHI) fungicides boscalid, fluopyram and penthiopyrad. A total of 20 isolates were collected from foliar‐infected tissue in 2009, 26 in 2010 and 49 in 2011. Fungicide sensitivity was tested using the spiral‐gradient end point dilution method. The frequency of boscalid‐resistant isolates (&gt;50% relative growth when using a spiral dilution gradient starting at 507 mg L−1) drastically increased over the duration of this study (15% in 2009, 62% in 2010 and 80% in 2011). Increasing resistance to fluopyram and penthiopyrad was observed. However, cross‐resistance was only observed between boscalid and penthiopyrad. The target site of this fungicide class is the succinate dehydrogenase (SDH) enzyme complex, which is vital for fungal respiration. Sequence analysis of the SDH complex revealed mutations in the subunits B and D that were correlated with the emergence of boscalid resistance in potato fields in Idaho. In particular, H277R and H133R were identified in SDH subunits B and D, respectively. The presence of restriction sites in the gene sequences allowed the development of a rapid PCR‐RFLP method to assess boscalid sensitivity in A. solani populations.