Mizuho Nita

Reliability and accuracy of visual estimation of phomopsis leaf blight of strawberry.

ABSTRACT Six different individuals (raters) assessed the severity of Phomopsis leaf blight on strawberry leaflets in five experimental repetitions over 2 years by making a direct visual estimation of the percentage of diseased area of each leaflet or by using the Horsfall-Barratt (H-B) disease scale. Intra-rater and inter-rater reliability and accuracy were determined, and then the relationship between visually estimated severity values and actual severity values was evaluated. Agreement in estimated disease severity values between assessment times by the same raters (i.e., intra-rater reliability), and agreement in disease severity values among raters at a single assessment time (i.e., inter-rater reliability), were both high, with most correlation coefficients being greater than 0.85. The intra-class correlation for overall agreement among raters ranged from 0.80 to 0.96 for the five repetitions. Based on the concordance coefficient calculated for each rater in each repetition, agreement between estimated and actual severity (i.e., accuracy) was somewhat lower than reliability. The relationship between estimated and actual severity was linear, and there was a slight trend to overestimate disease severity. The H-B scale was not more reliable or accurate than direct estimation of severity, and the linear relationship between estimated and actual severity did not support the principles underling the H-B scale. Both size of leaflets and number of lesions per leaflet slightly affected the error in estimate of disease severity.

Plant Pathogens as Indicators of Climate Change

Publisher Summary Plant disease risk is strongly influenced by environmental conditions. While some animal hosts may provide their pathogens with a consistent range of body temperatures, plant pathogens are generally much more exposed to the elements. Plant diseases will tend to respond to climate change, though a number of interactions taking place among host, pathogen, and potential vectors. In some cases, the actions of land managers may also complicate interpretation of climate change effects. This chapter presents a brief introduction to plant diseases and a synthesis of research in plant pathology related to climate change. It discusses the types of evidence for climate change impacts that might be observed in plant disease systems and evaluates what evidence of climate change fingerprints currently exists. The battle against plant disease is not a new one, and plant disease management is essential to feed a growing human population. Plant pathogen groups include fungi, prokaryotes, oomycetes, viruses and viroids, nematodes, parasitic plants, and protozoa. The very different life histories of this diverse group of organisms and their different interactions with host plants produce a wide range of responses to environmental and climatic drivers. Pathogen species may quickly develop resistance to pesticides or adapt to overcome plant disease resistance, and may also adapt to environmental changes, where the rate of adaptation depends on the type of pathogen. Pathogen populations may explode when weather conditions are favorable for disease development. The potentially rapid onset of disease makes it difficult to anticipate the best timing of management measures, especially in areas with high levels of interannual variability in climatic conditions.

Characterization of Components of Partial Resistance, Rps2, and Root Resistance to Phytophthora sojae in Soybean.

ABSTRACT Phytophthora root and stem rot of soybeans caused by Phytophthora sojae is a serious limitation to soybean production in the United States. Partial resistance to P. sojae in soybeans is effective against all the races of the pathogen and is a form of incomplete resistance in which the level of colonization of the root is reduced following inoculation. Other forms of incomplete resistance include the single dominant gene Rps2 and Ripleys root resistance, which are both race-specific. To differentiate partial resistance from the other types of incomplete resistance, the components lesion length, numbers of oospores, and infection frequency were measured in eight soybean genotypes inoculated with two P. sojae isolates. The Rps2 and root-resistant genotypes had significantly lower oospore production and infection frequency compared with the partially resistant genotype Conrad, while the root-resistant genotype also had significantly smaller lesion lengths. However, the high levels of partial resistance in Jack were indistinguishable from Rps2 in L76-1988, based on the evaluation of these components. Root resistance in Ripley and Rps2 in L76-1988 had similar responses for all components measured in this study. Partial resistance expressed in Conrad, Williams, Jack, and General was comprised of various components that interact for defense against P. sojae in the roots, and different levels of each component were found in each of the genotypes. However, forms of incomplete resistance expressed via single genes in Ripley and Rps2 in L76-1988, could not be distinguished from high levels of partial resistance based on lesion length, oospore production, and infection frequency.

Effects of application of fungicide during the dormant period on phomopsis cane and leaf spot of grape disease intensity and inoculum production

Efficacy of application of the fungicides calcium polysulfide or fixed copper during the dormant period on control of Phomopsis cane and leaf spot of grape (Vitis spp.), caused by Phomopsis viticola, was examined under field conditions during the 2003 and 2004 growing seasons in Ohio. Dormant-period fungicide applications were made either in the fall (after leaf drop and periderm tissue formation on the first-year canes, mid-November), or spring (at bud-swell, mid-April), or both. Disease incidence and severity on leaves and internodes were examined. In addition, effects of dormant-period application on sporulation of P. viticola were determined by examining the number of conidia in rain-splashed water in the spring and formation of mature pycnidia on cane sections in the winter. Fall-and-spring and spring applications of calcium poly-sulfide provided 12 to 88% reduction in disease intensity (incidence or severity), whereas calendar-based protectant mancozeb applications reduced overall disease intensity by 47 to 100%. Fixed-copper applications did not provide a consistent reduction of the disease. Fall applications of dormant-period fungicide provided little or no effect by itself. There was a significantly lower number of conidia observed in collected splashed rain water from vines treated with fall-and-spring applications of calcium polysulfide than in rain water from nonsprayed vines. Fall-and-spring and spring applications of calcium polysulfide provided a significant reduction in the number of mature pycnidia formed on incubated cane sections compared with the nonsprayed control (5 versus 10 pycnidia/cm2), whereas fixed copper did not provide a significant reduction.

Evaluation of a Disease Warning System for Phomopsis Cane and Leaf Spot of Grape: A Field Study

A field evaluation of a warning system for Phomopsis cane and leaf spot of grape (Vitis spp.), caused by Phomopsis viticola, was conducted in Ohio over 3 years (2002 to 2004) by applying fungicides and fungicide-adjuvant combinations based on predicted infection events. Three different criteria for risk-light, moderate, and high-were evaluated with the warning system. The warning system is based on measured weather conditions (temperature and wetness duration following rain) and a model for risk of leaf and internode infection. Vines were sprayed with fungicides based on either the warning system or a calendar-based 7-day protectant program, from 2.5-cm shoot growth (Eichhorn-Lorenz [E-L] stage 7) to the end of the broom (E-L stage 27). Fungicides were tested with or without an adjuvant (JMS Stylet-Oil or Regulaid). In the controls, the mean percentage of leaves and internodes with infections ranged from 36 to 100%, the number of lesions per leaf ranged from 1 to 28, and percentage of internodes covered by lesions ranged from 1 to 12%. Both the calendar-based protectant treatment (based on use of mancozeb) and the warning system treatment based on spraying in response to light or moderate predicted infection events (especially with mancozeb + Regulaid) resulted in significantly less disease incidence and severity compared with the controls. The mean percent control (relative difference in disease between a treatment and the control) was higher for the protectant schedule (˜55% and ˜80% for incidence and severity, respectively, based on application of mancozeb) than for the warning system (˜36% and ˜60% for incidence and severity, respectively, based on application of mancozeb + Regulaid), but there were two to three times more fungicide applications with the protectant schedule than with the warning system.

Temporal Effects on the Incidence and Severity of Brown Marmorated Stink Bug (Hemiptera: Pentatomidae) Feeding Injury to Peaches and Apples during the Fruiting Period in Virginia.

ABSTRACT Exclusion cages were used to compare the incidence and severity of feeding injury from brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), on ‘Redhaven’ peaches, ‘Golden Delicious’ apples, and ‘Smoothee Golden’ apples at harvest, following sequential periods of exposure to natural H. halys populations during the 2011 and 2012 growing seasons in Virginia. The fruit used in these experiments were in orchards or on trees that were not managed for H. halys. Treatments were sets of 50 fruit that were always caged, never caged, or exposed during one interval during the fruiting period of peaches and apples in the Mid-Atlantic region of the United States. The cages effectively prevented feeding injury from H. halys. Peaches and apples that were never caged showed the highest percentages of injured fruit at harvest. Exposure treatment had a significant effect on the percentage of fruit showing external injury at harvest in both years for apples and in 2012 for peaches, and a significant effect on the percentage of apples and peaches showing internal injury at harvest in both years. There was no consistent effect of each exposure period on peach injury, but apples exposed during the mid- to latter portion of the season tended to show most injury. Across all exposure periods, more internal than external injuries were recorded at harvest from peaches, while apples tended to have equal or very similar numbers of both kinds of injury. The implications of these results to H. halys management in eastern apple orchards are discussed.

Variation in Disease Incidence of Phomopsis Cane and Leaf Spot of Grape in Commercial Vineyards in Ohio

A statewide survey for incidence of Phomopsis cane and leaf spot of grape (caused by Phomopsis viticola) was conducted during the 2002 to 2004 growing seasons. Over the 3 years, disease was observed in all surveyed vineyards, and mean disease incidence for leaves and internodes was 42 and 50%, respectively. A hierarchical linear mixed model was used to evaluate effects of region, farm within region, vineyard within farm, sampling site (i.e., vine) within vineyard, and shoot (i.e., cane) within vine on disease incidence. Region of the state did not have a significant effect on incidence but there was significant variation at all other levels of the hierarchy (P < 0.05); the greatest variation was at the lowest scale (shoots within vines). The potential effects of weather and management practices on disease risk at the vineyard scale were determined by using nonparametric correlation and binary logistic analyses after first classifying mean incidence per vineyard as being below or above 20% (D20 = 0,1) and 40% (D40 = 0,1). Overall results indicated that variables for predicted number of moderate infection events (DM; based on ambient temperature and hours when either there was measured rainfall or relative humidity above 90%), the extent of fungicide application (C) during early- and mid-May (M1 and M2, respectively), and the use of a dormant-period application of fungicide (DOR) were the key factors in predicting disease risk (for either D20 or D40). Accuracy (percentage of high and low disease vineyards correctly predicted) and area under the receiver operating characteristic curve (an overall measure of the accuracy of a model) for a generic model combining these predictor variables were 74 and 0.84, respectively, for D40 and 87 and 0.97, respectively, for D20. Models based on management practices were as accurate as those that incorporated weather variables. Although the degree of control of this disease is inadequate in Ohio, based on the survey results for incidence, the results from the risk-model analysis showed that improved management might be obtained by applying fungicide early during the growing season.

Geographic distribution of cryptic species of Plasmopara viticola causing downy mildew on wild and cultivated grape in eastern North America.

The putative center of origin of Plasmopara viticola, the causal agent of grape downy mildew, is eastern North America, where it has been described on several members of the family Vitaceae (e.g., Vitis spp., Parthenocissus spp., and Ampelopsis spp.). We have completed the first large-scale sampling of P. viticola isolates across a range of wild and cultivated host species distributed throughout the above region. Sequencing results of four partial genes indicated the presence of a new P. viticola species on Vitis vulpina in Virginia, adding to the four cryptic species of P. viticola recently recorded. The phylogenetic analysis also indicated that the P. viticola species found on Parthenocissus quinquefolia in North America is identical to Plasmopara muralis in Europe. The geographic distribution and host range of five pathogen species was determined through analysis of the internal transcribed spacer polymorphism of 896 isolates of P. viticola. Among three P. viticola species found on cultivated grape, one was restricted to Vitis interspecific hybrids within the northern part of eastern North America. A second species was recovered from V. vinifera and V. labrusca, and was distributed across most of the sampled region. A third species, although less abundant, was distributed across a larger geographical range, including the southern part of eastern North America. P. viticola clade aestivalis predominated (83% of isolates) in vineyards of the European winegrape V. vinifera within the sampled area, indicating that a single pathogen species may represent the primary threat to the European host species within eastern North America.

Biological control for grapevine crown gall using nonpathogenic Rhizobium vitis strain ARK-1

Crown gall of grapevine, which is caused by tumorigenic Rhizobium vitis, is the most important bacterial disease of grapevine throughout the world. Screening tests of biological control agents resulted in the discovery of a nonpathogenic R. vitis strain ARK-1. By soaking grapevine roots with a cell suspension of strain ARK-1 prior to planting in the field, ARK-1 treatment significantly reduced the number of plants with crown gall symptoms. Several field trials result indicated that ARK-1 was very useful in the field, not only for grapevine but also for various other plant species. In experiments where a mixture of ARK-1 and a tumorigenic strain at a 1 : 1 cell ratio was examined in vitro and in planta, expression levels of the virulence genes virD2 and virE2 of the tumorigenic strain were significantly lower. The suppression of virulence genes, which can result in a reduction of gall formation and the pathogen population, seems to be a unique mechanism of ARK-1. These results indicated that ARK-1 is a promising new agent to control grapevine crown gall.

Synergistic Effect of a Mixture of Benzimidazole and Iminoctadine Triacetate for the Preharvest Control of Benzimidazole-Resistant Penicillium digitatum, a Causal Agent of Citrus Green Mold in Japan

Green mold, caused by Penicillium digitatum, is the leading cause of citrus decay in Japan. Due to a ban on the post-harvest fungicide application in Japan, the preharvest application of benzimidazoles has been used and demonstrated good efficacy since 1971. A benzimidazole resistant P. digitatum strain was first isolated from a packinghouse in 1974, and more cases were reported in subsequent years. On the other hand, very few cases were reported from the grove for two decades. However, by the mid-1990s, when the field incidences of benzimidazole resistant strain started to increase, the effect of benzuimidazoles became unstaible. An alternative to a benzimidazoles, iminoctadine triacetate, exhibited good antifungal activity against P. digitatum in vitro, but its efficacy was inconsistent in the field. We examined the efficacy of a mixed application of iminoctadine triacetate and benzimidazoles against each fungicide by itself based on five years of data from multiple locations. The results indicated a synergistic suppression on green mold, where the efficacy of the mixture was consistently greater than treatments with either fungicide alone. The improved efficacy was considered acceptable for a practical use by the industry, and lead to a development of a pre-mixed commercial product, Beftopsin flowable in 2006.