scholarly journals Evaluation of a Model for Predicting the Infection Risk of Squash and Cantaloupe by Pseudoperonospora cubensis

Plant Disease ◽  
2018 ◽  
Vol 102 (5) ◽  
pp. 855-862
Author(s):  
Katie N. Neufeld ◽  
Anthony P. Keinath ◽  
Peter S. Ojiambo
Keyword(s):  
Downy Mildew ◽  
Roc Curve ◽  
Infection Risk ◽  
Economic Damage ◽  
Pseudoperonospora Cubensis ◽  
Threshold Probability ◽  
Classification Rate ◽  
Disease Symptoms ◽  
Disease Occurrence ◽  
Successful Infection

Infection risk models of downy mildew of cucumber caused by Pseudoperonospora cubensis were evaluated for their performance in predicting the infection risk of squash and cantaloupe plants under field conditions. Experiments were conducted from 2012 to 2014 in Clayton, NC and Charleston, SC, where disease-free potted plants were exposed to weather conditions during a 24- and 48-h period (hereafter 24- and 48-h models, respectively) within a plot with naturally occurring inoculum. Exposed plants were subsequently placed in a growth chamber where they were monitored for disease symptoms, which was indicative of a successful infection. Disease severity was assessed after 7 days as the proportion of leaf area with disease symptoms. Two predictor variables, day temperature and hours of relative humidity >80% during each exposure were used as inputs to generate model predictions that were compared with observed data. The threshold probability on the receiver operating characteristic (ROC) curve that minimized the overall error rate for the 24-h model was 0.85 for both squash and cantaloupe. The 24-h model was consistently more accurate than the 48-h model in predicting the infection risk for the two hosts. The accuracy of the 24-h model as estimated using area under ROC curve ranged from 0.75 to 0.81, with a correct classification rate ranging from 0.69 to 0.74 across the two hosts. Specificity rates for the model ranged from 0.81 to 0.84, while the sensitivity rates ranged from 0.58 to 0.67. Optimal decisions thresholds (POT) developed based on estimates of economic damage and costs of management showed that POT was dependent on the probability of disease occurrence, with the benefit of using the 24-h model for making management decisions being greatest at low levels of probability of disease occurrence. This 24-h model, previously developed using cucumber as the host, resulted in accurate estimates of the daily infection risk of squash and cantaloupe and could potentially be useful when incorporated into a decision support tool to guide fungicide applications to manage downy mildew in these other cucurbit host types.

scholarly journals Relationships Between Airborne Pseudoperonospora cubensis Sporangia, Environmental Conditions, and Cucumber Downy Mildew Severity

Plant Disease ◽  
2014 ◽  
Vol 98 (5) ◽  
pp. 674-681 ◽  
Author(s):  
L. L. Granke ◽  
J. J. Morrice ◽  
M. K. Hausbeck
Keyword(s):  
Leaf Area ◽  
Downy Mildew ◽  
Disease Severity ◽  
Leaf Wetness ◽  
Pseudoperonospora Cubensis ◽  
Disease Occurrence ◽  
Benton Harbor ◽  
Cucumber Downy Mildew ◽  
High Disease Severity ◽  
Symptomatic Leaf

Airborne Pseudoperonospora cubensis sporangia were collected 0.5 m above the ground from May to late September or early October 2010 and 2011 in unsprayed cucumber (Cucumis sativus) fields in Benton Harbor and Frankenmuth, MI. Cucumber downy mildew incidence and severity were evaluated weekly within each field from June until September or October. The first airborne sporangium was detected before the crop was planted for each site-year. The greatest numbers of airborne sporangia were detected when moderate to high disease severity (≥5% symptomatic leaf area) was detected within the field. Fewer airborne sporangia were present with low disease severity (<5% symptomatic leaf area), and even fewer were detected prior to planting the cucumber crop. The number of airborne sporangia detected, time post planting, planting number (first versus second versus third planting), temperature, and leaf wetness were positively associated and solar radiation was negatively associated with disease occurrence for at least one site-year. Michigan growers currently use an aggressive, calendar-based fungicide program to manage cucumber downy mildew. Because airborne sporangium concentrations were one of the most important factors identified in this study, the current fungicide recommendation of decreasing the spray interval following disease detection in an area is warranted.

scholarly journals Diagrammatic scale to assess downy mildew severity in melon

2009 ◽  
Vol 27 (1) ◽  
pp. 76-79 ◽  
Author(s):  
Sami J Michereff ◽  
Marissônia A Noronha ◽  
Gaus SA Lima ◽  
Ígor CL Albert ◽  
Edilaine A Melo ◽  
...  
Keyword(s):  
Linear Regression ◽  
Leaf Area ◽  
Downy Mildew ◽  
Pseudoperonospora Cubensis ◽  
Northeast Brazil ◽  
Simple Linear Regression ◽  
Standard Methods ◽  
Accuracy And Precision ◽  
Severity Levels ◽  
Diagrammatic Scale

The downy mildew, caused by Pseudoperonospora cubensis, is an important melon disease in Northeast Brazil. Considering the lack of standard methods for its assessment, a diagrammatic scale was developed with 2, 4, 8, 16, 32, 64, 82, and 96% of affected leaf area. The scale was then checked for its accuracy, precision, and reproducibility in estimating downy mildew severity. The diagrammatic scale was validated by eight disease raters; using 50 leaves with different severity levels, previously measured using the software Assess®. Two evaluations were performed on the same set of leaves, but in a different sequence order, by the same raters, within a 15-day interval. The accuracy and precision of each rater was determined by simple linear regression between the actual and the estimated severity. The scale provided good levels of accuracy (means of 87.5%) and excellent levels of precision (means of 94%), with absolute errors concentrated around 10%. Raters showed great repeatability (means of 94%) and reproducibility (>90% in 90.3% of cases) of estimates. Therefore, we could conclude that the diagrammatic scale presented here was suitable for evaluating downy mildew severity in melon.

scholarly journals Host Preference of Mating Type in Pseudoperonospora cubensis, the Downy Mildew Causal Agent of Cucurbits

Plant Disease ◽  
2013 ◽  
Vol 97 (2) ◽  
pp. 292-292 ◽  
Author(s):  
Y. Cohen ◽  
A. E. Rubin ◽  
M. Galperin
Keyword(s):  
Downy Mildew ◽  
Mating Type ◽  
Host Preference ◽  
Practical Implication ◽  
Natural Infection ◽  
Primary Source ◽  
Pseudoperonospora Cubensis ◽  
Close Proximity ◽  
Detached Leaves ◽  
Classical Genetics

The A2 mating type of Pseudoperonospora cubensis was first discovered in Israel in May 2010 on butternut gourd (Cucurbita moschata) (1). We monitored the occurrence of the A2 mating type of P. cubensis in isolates collected during May 2010 through September 2012 from downy mildew-infected cucurbit crops growing along the coastal plain of Israel. Mating type was determined by oospore production in melon leaf discs co-inoculated with sporangia of a test isolate mixed with sporangia of A1 or A2 tester isolates (2). The A1 and A2 tester isolates were maintained at 14°C (14 h light/day) by repeated inoculation of detached leaves of cucumber and pumpkin, respectively. The 29 isolates that were collected from cucumber (Cucumis sativum) were all A1. Of the 33 isolates collected from pumpkin (Cucurbita maxima), squash (C. pepo), or butternut gourd (C. moschata), 88% were A2 and 12% were A1. The host preference of mating type in P. cubensis was monitored at Bar-Ilan University farm during April to July 2012, among about 800 plants of eight cucurbit species (~100 plants per species) that were grown side-by-side in three adjacent net-houses (two 6 × 50 m and one 6 × 100 m) and exposed to natural infection. Downy mildew developed on cucumber, melon, pumpkin, squash, and butternut gourd, but not on watermelon, sponge gourd (Luffa cylindrica), or Momordica balsamina. Three-hundred and three isolates of P. cubensis were collected and tested for mating type: 123 from cucumber, 53 from melon, 30 from pumpkin, 48 from butternut gourd, and 41 from squash. The cucumber isolates expressed A1, A2, and A1A2 at a ratio of 94.3%, 3.3%, and 2.4%, respectively; the melon isolates 58.5%, 26.4%, and 15.1%; the pumpkin isolates 0%, 96.7%, and 3.3%; the butternut isolate 7.3%, 87.3%, and 5.5%; and the squash isolates 2.4%, 97.6%, and 0%, respectively. A1A2 isolates produce oospores when crossed with either A1 or A2 tester isolates. This is the first evidence suggesting a preference of A1 isolates to Cucumis spp. and of A2 isolates to Cucurbita spp. similar preference was recently observed among Chinese isolates of this pathogen (unpublished data). The mechanism(s) controlling this preference is not known. Classical genetics is currently employed to P. cubensis in order to understand if it derives from true linkage. The practical implication for downy mildew management is that growing cucumber/melon in close proximity to pumpkin/squash/butternut gourd should be avoided as it may enhance oospore production in nature. Oospores in soil were recently shown to serve as a primary source of downy mildew infection in cucumber (3). References: (1) Y. Cohen, A. E. Rubin, and M.Galperin. Plant Dis. 95:874, 2011; (2) Y. Cohen and A. E. Rubin. Eur. J. Plant Pathol. 132:577, 2012; (3) Y. J. Zhang et al. J. Phytopathol. 160:469, 2012.

scholarly journals Virus and virus-like diseases of grapevine in Hungary

2011 ◽  
Vol 17 (3) ◽  
Author(s):  
J. Lázár ◽  
Gy. D. Bisztray
Keyword(s):  
Energy Metabolism ◽  
Host Cell ◽  
Particle Morphology ◽  
Plant Viruses ◽  
Diagnostic Methods ◽  
Economic Damage ◽  
Mixed Infections ◽  
Disease Symptoms ◽  
The World

Viruses and viroids are submicroscopic infectious particles which can cause disease symptoms on grapevine. These parasites are depending completely on the energy metabolism of the plant cell. To enter the host cell plant viruses depend on injuries or on transmission via invertebrates (insects, nematodes, etc.). Viruses are classified by many characters including particle morphology, host range and information content of the genome. At present about 70 viruses including 7 viroids infecting grapevine are known. In single or mixed infections they are potentially detrimental to the quality and quantity of grape production in any growing area of the world. Some viruses can cause severe economic damage in vineyards. In Hungary many important viruses and viroids have been detected in grape. This review summarises characteristics of viruses and the results of detection and characterization of virus and virus like diseases of grapevine in Hungary. The identification of the causal agent, its transmission, geographical distribution and the development of the diagnostic methods are also discussed.

scholarly journals Fungicides for Control of Downy Mildew on Pickling Cucumber in Michigan

2019 ◽  
Vol 20 (3) ◽  
pp. 165-169 ◽  
Author(s):  
Katelyn E. Goldenhar ◽  
Mary K. Hausbeck
Keyword(s):  
Downy Mildew ◽  
Untreated Control ◽  
Field Studies ◽  
Pseudoperonospora Cubensis ◽  
Relative Area ◽  
Disease Progress Curve ◽  
Cucurbit Downy Mildew ◽  
Disease Progress ◽  
Pickling Cucumber ◽  
Progress Curve

Michigan growers rely on fungicides to limit cucurbit downy mildew (CDM), incited by Pseudoperonospora cubensis; resistance of the pathogen to fungicides is a concern. We evaluated fungicides against CDM in Michigan field studies from 2015 to 2017. According to the relative area under the disease progress curve (rAUDPC), in 2015, mandipropamid, propamocarb, fluxapyroxad/pyraclostrobin, copper octanoate, and dimethomorph resulted in disease levels similar to the control. These treatments, along with cymoxanil, were similar to the control in 2016. Fungicides that were ineffective during 2015 and 2016 did not limit CDM in 2017. Famoxadone/cymoxanil and fluopicolide did not limit CDM in 2017. Each year, the following treatments were similar for disease based on rAUDPC data: oxathiapiprolin applied alone or premixed with chlorothalonil or mandipropamid, ametoctradin/dimethomorph, fluazinam, mancozeb/zoxamide, cyazofamid, and ethaboxam. An exception occurred in 2017, when ethaboxam was less effective than fluazinam, oxathiapiprolin/chlorothalonil, and oxathiapiprolin/mandipropamid. Mancozeb and chlorothalonil treatments were similar in 2015 and 2017, according to rAUDPC data. In 2017, yields were increased for oxathiapiprolin/chlorothalonil, oxathiapiprolin/mandipropamid, mancozeb, ametoctradin/dimethomorph, mancozeb/zoxamide, ethaboxam, cyazofamid, chlorothalonil, and fluazinam compared with the untreated control.

scholarly journals Transcriptional regulation of stilbene synthases in grapevine germplasm differentially susceptible to downy mildew

2019 ◽  
Vol 19 (1) ◽  
Author(s):  
Mario Ciaffi ◽  
Anna Rita Paolacci ◽  
Marco Paolocci ◽  
Enrica Alicandri ◽  
Valentina Bigini ◽  
...  
Keyword(s):  
Transcriptional Regulation ◽  
Downy Mildew ◽  
Transcriptional Activation ◽  
Constitutive Expression ◽  
Stilbene Synthase ◽  
Disease Symptoms ◽  
Adaptive Resistance ◽  
Genes Encoding ◽  
The Impact ◽  
Stilbene Biosynthesis

Abstract Background To limit the impact of the downy mildew disease of grapevine and reduce the need to recur to chemical treatments, an effective strategy might be recovering adaptive resistance traits in both cultivated and wild V. vinifera germplasm. Considering that stilbenes represent the most important class of phytoalexins in the Vitaceae, the constitutive expression and transcriptional activation of all the functional members of the stilbene synthase gene family were analysed in a group of nine grapevine genotypes following artificial infection with the oomycete Plasmopara viticola, the causal agent of the disease. In addition, in the same genotypes we analyzed the expression of genes encoding for two transcription factors involved in the transcriptional regulation of the stilbene synthase genes, namely VvMYB14 and VvMYB15, and of genes encoding for chalcone synthases. Results Downy mildew incidence and severity ranged from nihil to high in the grapevine genotypes considered, being low to moderate in a subgroup of V. vinifera genotypes. The constitutive expression of the stilbene synthase genes as well as the extent of their transcriptional activation following P. viticola inoculation appeared to be inversely related to the proneness to develop disease symptoms upon infection. In a specular manner, following P. viticola inoculation all the chalcone synthase genes were up-regulated in the susceptible grapevine genotypes and down-regulated in the resistant ones. The infection brought by P. viticola appeared to elicit a co-ordinated and sequential transcriptional activation of distinct stilbene synthase genes subsets, each of which may be regulated by a distinct and specific MYB transcription factor. Conclusions The present results suggest that the induction of stilbene biosynthesis may contribute to the basal immunity against the downy mildew of grapevine, thus representing an adaptive resistance trait to recover, in both cultivated and wild V. vinifera germplasm. During the early stages of P. viticola infection, an antagonistic interaction between flavonol and stilbene biosynthesis might occur, whose outcome might determine the subsequent extent of disease symptoms. Further studies are needed to decipher the possible regulatory mechanisms involved in the antagonistic crosstalk between these two metabolic pathways in resistant and susceptible genotypes in response to P. viticola.

scholarly journals Relationship Between Loci Conferring Downy Mildew and Powdery Mildew Resistance in Melon Assessed by Quantitative Trait Loci Mapping

2005 ◽  
Vol 95 (5) ◽  
pp. 556-565 ◽  
Author(s):  
L. Perchepied ◽  
M. Bardin ◽  
C. Dogimont ◽  
M. Pitrat
Keyword(s):  
Quantitative Trait Loci ◽  
Powdery Mildew ◽  
Downy Mildew ◽  
Resistance Genes ◽  
Quantitative Trait ◽  
Pseudoperonospora Cubensis ◽  
Podosphaera Xanthii ◽  
Resistance Qtl ◽  
Trait Loci ◽  
Artificial Inoculations

Partial resistance to downy mildew (Pseudoperonospora cubensis) and complete resistance to powdery mildew (Podosphaera xanthii races 1, 2, 3, and 5 and Golovinomyces cichoracearum race 1) were studied using a recombinant inbred line population between ‘PI 124112’ (resistant to both diseases) and ‘Védrantais’ (susceptible line). A genetic map of melon was constructed to tag these resistances with DNA markers. Natural and artificial inoculations of Pseudoperonospora cubensis were performed and replicated in several locations. One major quantitative trait loci (QTL), pcXII.1, was consistently detected among the locations and explained between 12 to 38% of the phenotypic variation for Pseudoperonospora cubensis resistance. Eight other Pseudoperonospora cubensis resistance QTL were identified. Artificial inoculations were performed with several strains of four races of Podosphaera xanthii and one race of G. cichoracearum. Two independent major genes, PmV.1 and PmXII.1, were identified and shown to be involved in the simple resistance to powdery mildew. Three digenic epistatic interactions involving four loci were detected for two races of Podosphaera xanthii and one race of G. cichoracearum. Co-localization between PmV.1, resistance genes, and resistance genes homologues was observed. Linkage between the major resistance QTL to Pseudoperonospora cubensis, pcXII.1, and one of the two resistance genes to powdery mildew, PmXII.1, was demonstrated.

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