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1.
Plant Dis ; 104(1): 94-104, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31738690

RESUMO

In this study, 3,426 grafted grapevines ready to be planted from 15 grapevine nursery fields in Northern Spain were inspected from 2016 to 2018 for black-foot causing pathogens. In all, 1,427 isolates of black-foot pathogens were collected from the asymptomatic inner tissues of surface sterilized secondary roots and characterized based on morphological features and DNA sequence data of the nuclear ribosomal DNA-internal transcribed spacer region, histone H3, translation elongation factor 1-alpha and ß-tubulin genes. Eleven species belonging to the genera Dactylonectria, Ilyonectria, Neonectria, and Thelonectria were identified, including Dactylonectria alcacerensis, D. macrodidyma, D. novozelandica, D. pauciseptata, D. torresensis, Ilyonectria liriodendri, I. pseudodestructans, I. robusta, Neonectria quercicola, Neonectria sp. 1, and Thelonectria olida. In addition, two species are newly described, namely D. riojana and I. vivaria. Twenty-four isolates representing 13 black-foot species were inoculated onto grapevine seedlings cultivar 'Tempranillo'. The pathogenicity tests detected diversity in virulence among fungal species and between isolates within each species. The most virulent species was D. novozelandica isolate BV-0760, followed by D. alcacerensis isolate BV-1240 and I. vivaria sp. nov. isolate BV-2305. This study improves our knowledge on the etiology and virulence of black-foot disease pathogens, and opens up new perspectives in the study of the endophytic phase of these pathogens in grapevines.


Assuntos
Variação Genética , Hypocreales , Doenças das Plantas , Vitis , Genes Fúngicos/genética , Hypocreales/classificação , Hypocreales/citologia , Hypocreales/genética , Doenças das Plantas/microbiologia , Doenças das Plantas/estatística & dados numéricos , Espanha , Especificidade da Espécie , Virulência , Vitis/microbiologia
2.
Nature ; 575(7781): 109-118, 2019 11.
Artigo em Inglês | MEDLINE | ID: mdl-31695205

RESUMO

The current trajectory for crop yields is insufficient to nourish the world's population by 20501. Greater and more consistent crop production must be achieved against a backdrop of climatic stress that limits yields, owing to shifts in pests and pathogens, precipitation, heat-waves and other weather extremes. Here we consider the potential of plant sciences to address post-Green Revolution challenges in agriculture and explore emerging strategies for enhancing sustainable crop production and resilience in a changing climate. Accelerated crop improvement must leverage naturally evolved traits and transformative engineering driven by mechanistic understanding, to yield the resilient production systems that are needed to ensure future harvests.


Assuntos
Produção Agrícola/métodos , Produção Agrícola/estatística & dados numéricos , Produtos Agrícolas/genética , Abastecimento de Alimentos/métodos , Abastecimento de Alimentos/estatística & dados numéricos , Aquecimento Global/estatística & dados numéricos , Desenvolvimento Sustentável/tendências , Aclimatação/genética , Aclimatação/fisiologia , Animais , Produtos Agrícolas/crescimento & desenvolvimento , Produtos Agrícolas/microbiologia , Produtos Agrícolas/virologia , Fertilizantes , Humanos , Doenças das Plantas/genética , Doenças das Plantas/prevenção & controle , Doenças das Plantas/estatística & dados numéricos , Chuva
3.
Plant Dis ; 103(8): 1876-1883, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31161932

RESUMO

Soybean cyst nematode (SCN; Heterodera glycines Ichinohe) is a major pathogen of soybean [Glycine max (L.) Merr.] in the United States. The spatial distribution of SCN in 10 naturally infested research sites in North Dakota was examined between 2006 and 2009. Egg densities were measured in plots and expressed as arithmetic means or grouped into classes using two categorical scales based on the effect of SCN on yield. Data were used to determine spatial distribution, egg cluster sizes, minimum plot sizes, and replications in field experiments. SCN populations varied among plots from undetected to 25,800 eggs/100 cm3 of soil, and differences between adjacent plots were as high as sixfold. Mean to median ratios and Lloyd's index of patchiness suggested an aggregated distribution in nine of the 10 sites. SCN cluster sizes varied in five of the 10 sites and optimum plot size over all sites varied depending on calculation methods. The minimum number of replications needed to detect specific differences among plots varied between field sites. Grouping data into either of the two categories generally increased the ability to detect differences between plots. The spatial distribution of SCN can be a critical factor affecting design and outcomes of field experiments.


Assuntos
Doenças das Plantas , Soja , Tylenchoidea , Animais , North Dakota , Doenças das Plantas/parasitologia , Doenças das Plantas/estatística & dados numéricos , Soja/parasitologia , Tylenchoidea/fisiologia
4.
PLoS One ; 14(5): e0215066, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31112545

RESUMO

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an airborne fungal disease which always destructs leaf and leads to stagnation of grain filling, decreasing of kernel weight, thin seed and yield loss. Winter wheat Huixianhong is a special germplasm with special characteristics of tolerance or resistance against stripe rust. In order to understand the effect on Huixianhong from stripe rust, we designed two kinds of treatment, inoculation of stripe rust fungi (IH) and artificial immune by bactericide (CK) to study the dynamic of disease process, the grain filling and the thousand-kernel weight (TKW). Our results showed that the incubation period of Hongxinahui was 13.5 days. The prevalence increased from 32.9% at 15 days after jointing to 80.0% at 9 days after booting, and reached to 97.0% at the heading stage. The infection type (IT) was 7 to 9 at the beginning of anthesis. The severity, leaf withered area ratio and disease index at the 15th day after anthesis were 67.17%, 98.17% and 0.6717, respectively. The IH maximum increasing rate of leaf necrosis and chlorosis area was from heading beginning stage to anthesis beginning stage, which increased from 18.66 mm2·d-1 to 21.04 mm2·d-1. The maximum rate of grain filling was 1.25 mg·d-1 at the 18th day after anthesis, which was earlier than that of CK by 3.3 days. The IH thousand-kernel weight Loss (TKWL) was more than that of CK by 6.19%, the stage of heading and amature were 3.0 days and 4.5 days earlier than CK, respectively. The stripe rust infection seriously destructed the photosynthetic function of leaf at the earlier stage of grain filling, i.e. at the beginning of anthesis, which led to the most important biomass loss and the grain filling rate decrease. As far as stripe rust is concerned, Huixianhong is a high susceptible, easily been infected, seriously showing symptoms and most quickly epidemic type but can successfully complete grain filling in high quality. It is a very useful germplasm for creating and selecting special breeding materials against stripe rust.


Assuntos
Basidiomycota/patogenicidade , Grão Comestível/fisiologia , Doenças das Plantas/microbiologia , Triticum/crescimento & desenvolvimento , Anti-Infecciosos/farmacologia , Basidiomycota/efeitos dos fármacos , Biomassa , Fotossíntese , Doenças das Plantas/estatística & dados numéricos , Folhas de Planta/metabolismo , Folhas de Planta/microbiologia , Sementes/microbiologia , Sementes/fisiologia , Triticum/metabolismo , Triticum/microbiologia
5.
Phytopathology ; 109(9): 1614-1627, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31066347

RESUMO

The oomycete Phytophthora infestans is an important plant pathogen on potato and tomato crops. We examined the genetic structure of extant 20th and 21st century U.S. lineages of P. infestans and compared them with populations from South America and Mexico to examine genetic relationships and potential sources of lineages. US-23, currently the most prevalent lineage detected in the United States, shared genetic similarity primarily with the BR-1 lineage identified in the 1990s from Bolivia and Brazil. Lineages US-8, US-14, and US-24, predominantly virulent on potato, formed a cluster distinct from other U.S. lineages. Many of the other U.S. lineages shared significant genetic similarity with Mexican populations. The US-1 lineage, dominant in the mid-20th century, clustered with US-1 lineages from Peru. A survey of the presence of RXLR effector PiAVR2 revealed that some lineages carried PiAVR2, its resistance-breaking variant PiAVR2-like, or both. Minimum spanning networks developed from simple sequence repeat genotype datasets from USABlight outbreaks clearly showed the expansion of US-23 over a 6-year time period and geographic substructuring of some lineages in the western United States. Many clonal lineages of P. infestans in the United States have come from introductions from Mexico, but the US-23 and US-1 lineages were most likely introduced from other sources.


Assuntos
Phytophthora infestans , Solanum tuberosum , Brasil , Estruturas Genéticas , México , Phytophthora infestans/fisiologia , Doenças das Plantas/estatística & dados numéricos , Estados Unidos
6.
Plant Dis ; 103(4): 601-618, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30789318

RESUMO

Between 2002 and 2015, a comprehensive survey of sunflower fields across seven Midwestern U.S. states was conducted 12 times and continues to be conducted every other year. The surveyors collected data on yield, agronomic management factors, disease, insect, weed, and bird damage. All surveyors were volunteers and came from universities (extension and research staff), USDA-ARS, and seed and chemical companies. In the 12 years the survey was conducted, data from 2,267 fields were collected. The results are presented annually at the National Sunflower Association Research Forum and are used to set sunflower research priorities. While 10 diseases are surveyed annually, we focus this article on the importance, findings, implications, and impacts of the five most important: downy mildew, Phomopsis stem canker, rust, Rhizopus head rot, and Sclerotinia head rot. This survey is unique among field crops in both scope and scale, and this manuscript discusses salient and clandestine benefits of intense and long-term disease surveys.


Assuntos
Ascomicetos , Helianthus , Doenças das Plantas , Pesquisa , Mapeamento Cromossômico , Doenças das Plantas/microbiologia , Doenças das Plantas/estatística & dados numéricos , Pesquisa/normas , Pesquisa/tendências , Inquéritos e Questionários
7.
Plant Dis ; 103(5): 818-824, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30806574

RESUMO

Maize and sugarcane are two economically important crops often grown in adjacent fields or co-cultivated in the northern guinea savannah agroecological zone, a major cereal production region of Nigeria. This study was conducted to determine the prevalence of mosaic disease in sugarcane and maize fields in the northern guinea savannah agroecological zone and to molecularly characterize the associated sugarcane mosaic virus (SCMV, genus Potyvirus) isolates. Surveys were conducted from June to July 2015, and sugarcane mosaic disease (SCMD) incidence was assessed across 21 farmer's fields. Mean SCMD incidence varied across states with ∼82% (308/376), ∼66% (143/218), and ∼67% (36/54) recorded in Kaduna, Kano, and Katsina states, respectively. RT-PCR analysis of 415 field-collected samples using genus-specific primers confirmed potyvirus infection in 63.7% (156/245) of sugarcane, 29.7% (42/141) of maize crops, and 45% (13/29) of itch grass samples. Cloning and sequencing of gene-specific DNA amplicons from a subset of 45 samples (sugarcane = 33, maize = 9, itch grass = 3) confirmed their specificities to SCMV. Phylogenetic analysis of the partial gene sequences showed that they all belong to a single monophyletic clade of SCMV. These results were supported by analysis of complete polyprotein sequences of representative maize and sugarcane isolates from Nigeria. Both isolates shared 94.9%/97.3% complete polyprotein nucleotide (nt)/amino acid (aa) identities with each other and 75.2%/97.6% nt/aa identities with corresponding sequences of global SCMV isolates. The detection of identical populations of SCMV isolates in both crop species and a weed host suggests possible vector mediated interspecies spread within cereal landscapes in the study area with implications for the integrated and sustainable management of SCMD in cereal cropping systems in Nigeria.


Assuntos
Genoma Viral , Doenças das Plantas , Potyvirus , Genoma Viral/genética , Nigéria , Filogenia , Doenças das Plantas/estatística & dados numéricos , Doenças das Plantas/virologia , Potyvirus/genética , Prevalência
8.
Plant Dis ; 103(3): 484-494, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30632469

RESUMO

The influence of environmental and management factors on the occurrence of foliar pathogens of watermelon was analyzed using survey-sampling data collected from commercial farms in South Carolina in spring 2015 and spring and fall 2016. A stratified two-stage cluster sampling design was used to sample symptomatic watermelon leaves from 56 fields of 27 growers in seven counties representing the main watermelon-producing areas in the state. In the sampling design, counties corresponded to strata, growers to first-stage clusters, and fields to second-stage clusters. Pathogens were identified on 100 leaves collected per field based on reproductive structures that formed on the leaves. Information about previous crops, fruit type, field size, transplanting date, first harvest date, and fungicides applied within 7 days and within 7 to 14 days prior to sampling was obtained from growers. Field alignment was determined with a compass. Survey-specific logistic regression procedures were used to analyze the effect of these factors on the probabilities of pathogen occurrence. Five fungal pathogens, Stagonosporopsis spp., Podosphaera xanthii, Cercospora citrullina, Colletotrichum orbiculare, and Myrothecium sensu lato (s.l.), and the oomycete Pseudoperonospora cubensis were included in the analyses. Among the factors we analyzed, there was a consistent increased probability of occurrence of Stagonosporopsis spp. in fields with a previous cucurbit crop, increasing probabilities of pathogen occurrence with increasing plant age, a lower probability of occurrence of some pathogens on triploid cultivars compared with diploid cultivars, and a decrease in probability of pathogen occurrence in fields aligned toward southwest or west. Application of fungicides significantly reduced the probability of observing C. citrullina, P. cubensis, and Stagonosporopsis spp. in 2015 and P. xanthii in spring 2016. This study emphasizes the importance of crop rotation and fungicide applications to manage foliar diseases of watermelon, particularly gummy stem blight, powdery mildew, and downy mildew. Crop age, cultivar type, and field alignment also were found to significantly influence the probability of pathogen occurrence. To the best of our knowledge, this is the first study examining the influence of various factors on foliar pathogens of watermelon with data collected from commercial fields.


Assuntos
Ascomicetos , Citrullus , Oomicetos , Ascomicetos/fisiologia , Citrullus/microbiologia , Citrullus/parasitologia , Análise por Conglomerados , Oomicetos/fisiologia , Doenças das Plantas/microbiologia , Doenças das Plantas/parasitologia , Doenças das Plantas/estatística & dados numéricos , Folhas de Planta/microbiologia , Folhas de Planta/parasitologia , Fatores de Risco , South Carolina
9.
Environ Sci Pollut Res Int ; 26(7): 6503-6516, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30627995

RESUMO

The meadow froghopper, Philaenus spumarius L., is endemic in Italy and was not considered a harmful species until 2014, when the olive quick decline syndrome (OQDS) showed up in Apulia (southern Italy). It was immediately suspected and then verified as the main vector of Xylella fastidiosa, the bacterium responsible for the disease. Currently, EU Directives consider the fight against P. spumarius compulsory in member states and recommend Integrated Pest Management (IPM), both in uncultivated and cultivated infested areas, to minimise the environmental impact of chemical pesticides. This should be based on an improved knowledge of the vector with its seasonal trends and feeding habits linked to specific herbaceous species. In this context, our field study was aimed to improve the understanding of the vector nutritional behaviour, especially at its critical nymph stage, by monitoring its presence on different herbaceous target species, using its typical feeding foams as key indicator. The study area was in Lazio region (central Italy), dedicated to olive growing and still unaffected by the X. fastidiosa plague. Over two years, during the nymph development period, field data have been acquired over the test area and then analysed by coupling statistical (ANOVA), geographical information system (GIS) and geo-referenced field sampling approaches. Results highlighted that P. spumarius exhibits significant preferences for specific herbaceous plants, especially at its early development stages, detectable by tenuous spittle. This indicates female oviposition activity, which seems also not influenced by olive tree proximity. Furthermore, the non-host plant species identified here could be suitable for creating green barriers for limiting the vector diffusion to contiguous areas where sensible plantations are growing. In the final section, applied implications arising from the present findings for P. spumarius population management are discussed.


Assuntos
Hemípteros/fisiologia , Insetos Vetores , Olea/microbiologia , Xylella/crescimento & desenvolvimento , Animais , Feminino , Hemípteros/microbiologia , Itália , Ninfa , Doenças das Plantas/estatística & dados numéricos
10.
J Sci Food Agric ; 99(7): 3459-3466, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30620392

RESUMO

BACKGROUND: As one of China's important economic crops, tea is economically damaged due to its large yield. The overall goal of this study is to develop an effective, simple, apt computer vision algorithm to detect tea disease area using infrared thermal image processing techniques and to estimate tea disease. RESULTS: This paper finds that the area of tea disease has certain regularity with its infrared image gray distribution. Using this rule, we extracted two characteristic parameters into a classifier to help achieve rapid tea disease detection, which increases the accuracy of detection a small amount. The tea disease detection algorithm consisted of the following steps: classify canopy infrared thermal image; convert red, green and blue image to hue, saturation and value; thresholding; color identification; noise filtering; binarization; closed operation; and counting. A correlation coefficient R2 of 0.97 was obtained between the tea disease detection algorithm and counting performed through human observation, which is 2% higher than traditional algorithms without classifiers. CONCLUSIONS: This article provides guidance for monitoring the condition of tea gardens with airborne thermal imaging cameras. © 2019 Society of Chemical Industry.


Assuntos
Camellia sinensis/efeitos da radiação , Processamento de Imagem Assistida por Computador/métodos , Doenças das Plantas/estatística & dados numéricos , Algoritmos , Camellia sinensis/crescimento & desenvolvimento , Cor , Humanos , Raios Infravermelhos , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/efeitos da radiação
11.
Plant Dis ; 102(12): 2465-2472, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30307836

RESUMO

Yellow dwarf viruses (YDVs) form a complex of economically important pathogens that affect cereal production worldwide, reducing yield and quality. The prevalence and incidence of YDVs including barley yellow dwarf viruses (BYDV-PAV and BYDV-MAV) and cereal yellow dwarf virus (CYDV-RPV) in cereal fields in Victoria, Australia were measured. As temperature decreases and rainfall increases from north to south in Victoria, fields in three geographical regions were evaluated to determine potential differences in virus prevalence and incidence across the weather gradient. Cereal samples randomly collected from each field during spring for four consecutive years (2014-2017) were tested for BYDV-PAV, BYDV-MAV, and CYDV-RPV using tissue blot immunoassay. BYDV-PAV was the most prevalent YDV species overall and had the highest overall mean incidence. Higher temperature and lower rainfall were associated with reduced prevalence and incidence of YDVs as the northern region, which is hotter and drier, had a 17-fold decrease in virus incidence compared with the cooler and wetter regions. Considerable year-to-year variation in virus prevalence and incidence was observed. This study improves our understanding of virus epidemiology, which will aid the development of more targeted control measures and predictive models. It also highlights the need to monitor for YDVs and their vectors over multiple years to assess the level of risk and to make more informed and appropriate disease management decisions.


Assuntos
Grão Comestível/virologia , Luteovirus/isolamento & purificação , Doenças das Plantas/virologia , Geografia , Doenças das Plantas/estatística & dados numéricos , Vitória
12.
Plant Dis ; 102(12): 2560-2570, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30346246

RESUMO

Rhododendrons are an important crop in the ornamental nursery industry, but are prone to Phytophthora root rot. Phytophthora root rot is a continuing issue on rhododendrons despite decades of research. Several Phytophthora species are known to cause root rot, but most research has focused on P. cinnamomi, and comparative information on pathogenicity is limited for other commonly encountered oomycetes, including Phytophthora plurivora and Pythium cryptoirregulare. In this study, three isolates each of P. cinnamomi, P. plurivora, and Py. cryptoirregulare were used to inoculate rhododendron cultivars Cunningham's White and Yaku Princess at two different inoculum levels. All three species caused disease, especially at the higher inoculum level. P. cinnamomi and P. plurivora were the most aggressive pathogens, causing severe root rot, whereas Py. cryptoirregulare was a weak pathogen that only caused mild disease. Within each pathogen species, isolate had no influence on disease. Both P. cinnamomi and P. plurivora caused more severe disease on Cunningham's White than on Yaku Princess, suggesting that the relative resistance and susceptibility among rhododendron cultivars might be similar for both pathogens. Reisolation of P. cinnamomi and P. plurivora was also greater from plants exhibiting aboveground symptoms of wilting and plant death and belowground symptoms of root rot than from those without symptoms. Results show that both P. cinnamomi and P. plurivora, but not Py. cryptoirregulare, are important pathogens causing severe root rot in rhododendron. This study establishes the risks for disease resulting from low and high levels of inoculum for each pathogen. Further research is needed to evaluate longer term risks associated with low inoculum levels on rhododendron health and to explore whether differences among pathogen species affect disease control.


Assuntos
Phytophthora/fisiologia , Doenças das Plantas/estatística & dados numéricos , Pythium/fisiologia , Rhododendron/parasitologia , Suscetibilidade a Doenças , Doenças das Plantas/parasitologia , Raízes de Plantas/genética , Raízes de Plantas/imunologia , Raízes de Plantas/parasitologia , Rhododendron/genética , Rhododendron/imunologia
13.
Plant Dis ; 102(12): 2592-2601, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30334675

RESUMO

In soybean, Sclerotinia sclerotiorum apothecia are the sources of primary inoculum (ascospores) critical for Sclerotinia stem rot (SSR) development. We recently developed logistic regression models to predict the presence of apothecia in irrigated and nonirrigated soybean fields. In 2017, small-plot trials were established to validate two weather-based models (one for irrigated fields and one for nonirrigated fields) to predict SSR development. Additionally, apothecial scouting and disease monitoring were conducted in 60 commercial fields in three states between 2016 and 2017 to evaluate model accuracy across the growing region. Site-specific air temperature, relative humidity, and wind speed data were obtained through the Integrated Pest Information Platform for Extension and Education (iPiPE) and Dark Sky weather networks. Across all locations, iPiPE-driven model predictions during the soybean flowering period (R1 to R4 growth stages) explained end-of-season disease observations with an accuracy of 81.8% using a probability action threshold of 35%. Dark Sky data, incorporating bias corrections for weather variables, explained end-of-season disease observations with 87.9% accuracy (in 2017 commercial locations in Wisconsin) using a 40% probability threshold. Overall, these validations indicate that these two weather-based apothecial models, using either weather data source, provide disease risk predictions that both reduce unnecessary chemical application and accurately advise applications at critical times.


Assuntos
Ascomicetos/fisiologia , Fungicidas Industriais/farmacologia , Doenças das Plantas/estatística & dados numéricos , Soja/microbiologia , Algoritmos , Ascomicetos/efeitos dos fármacos , Flores/microbiologia , Carpóforos , Modelos Logísticos , Doenças das Plantas/microbiologia , Análise de Regressão , Esporos Fúngicos , Tempo (Meteorologia) , Wisconsin
14.
Plant Dis ; 102(12): 2453-2464, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30334680

RESUMO

Soil samples were collected from 425 corn fields in 28 Ohio counties between growth stages V3 and V6 during the 2013 and 2014 growing seasons. Ten morphological groups of plant-parasitic nematodes, namely spiral, lesion, lance, dagger, stunt, pin, ring, stubby-root, cyst, and "tylenchids" (several genera morphologically similar to members of the subfamily Tylenchinae [NCBI Taxonomy] including Cephelenchus, Filenchus, Malenchus, and Tylenchus) were identified. Eight species belonging to six of these groups were characterized. Spiral, tylenchids, lesion, pin, lance, stunt, and dagger nematodes were detected in 94, 96, 80, 57, 48, 48, and 37% of the fields, respectively, whereas the stubby-root, cyst, and ring nematodes were present in fewer than 14% of the samples. Averaged across fields, the spiral, tylenchids, and pin nematodes had the highest mean population densities. For all groups, incidence and population density varied among counties, and in some cases, among soil regions and cropping practices. Both population parameters were heterogeneous at multiple spatial scales, with the lowest heterogeneity among soil regions and the highest among fields within county and soil region. Estimated variances at the soil region level were not significantly different from zero for most of the nematodes evaluated. Stunt and lance were two of the most variable groups at all tested spatial scales. In general, the population densities were significantly more heterogeneous at the field level than at the county level. Findings from this study will be useful for developing sampling protocols and establishing on-farm trials to estimate losses and evaluate nematode management strategies.


Assuntos
Nematoides/isolamento & purificação , Doenças das Plantas/parasitologia , Solo/parasitologia , Zea mays/parasitologia , Animais , Geografia , Modelos Lineares , Nematoides/crescimento & desenvolvimento , Ohio , Doenças das Plantas/estatística & dados numéricos , Densidade Demográfica , Análise Espacial
15.
Plant Dis ; 102(12): 2494-2499, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30281420

RESUMO

Target spot, caused by Corynespora cassiicola, has recently emerged as a problematic foliar disease of cotton. This pathogen causes premature defoliation during boll set and maturation that can subsequently impact yield, and on certain cotton cultivars loss can be substantial. This study sought to better understand target spot epidemics and disease-incited yield losses on cotton. In order to establish a range of disease, varying numbers of fungicide applications were made to each of two cotton cultivars in each of four site-years. Target spot intensity was rated over several dates beginning in late July or early August and continuing into September. Yield of seed plus lint (seed cotton) was recorded at harvest. When analyzed across cultivars, a second or third fungicide application increased yield compared with no treatment. Lack of significant yield response with a single fungicide application may have been due to timing of that application which preceded disease onset. The cultivar PhytoGen 499 WRF had consistently greater defoliation than any of the three Deltapine cultivars grown in each site-year. However, yields of both cultivars responded similarly to the fungicide regimes. Yield loss models based on late August defoliation were only predictive at site-years where conditions favored target spot development, i.e., abundant rain and moderate temperatures. Epidemic development fit the Gompertz growth model better than it did a logistic model. Knowledge of the underlying mathematical character of the epidemiology of target spot will prove useful for development of a predictive model for the disease.


Assuntos
Ascomicetos/fisiologia , Gossypium/microbiologia , Doenças das Plantas/estatística & dados numéricos , Fungicidas Industriais , Gossypium/crescimento & desenvolvimento , Modelos Estatísticos , Doenças das Plantas/microbiologia , Sementes/crescimento & desenvolvimento , Sementes/microbiologia , Tempo (Meteorologia)
16.
Plant Dis ; 102(11): 2296-2307, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30169137

RESUMO

Fungal rots in sugar beet roots held in long-term storage can lead to considerable sucrose loss but the incidence and distribution of fungal rots inside sugar beet piles and pathogenicity for some species is poorly understood. Thus, Idaho sugar beet held in five outdoor and two indoor piles in 2014 and 2015 were investigated. The root surface area covered by fungal growth and discolored and healthy tissue were assessed in nine 1-m2 areas per pile using a stratified random sampling design. Pathogenicity was evaluated indoors via plug inoculation in 2015 and 2016. Botrytis cinerea covered more root surface area inside indoor piles (6 to 22%) than outdoor piles (0 to 3%) (P < 0.0001). No trends were evident for the Athelia-like sp. (0 to 15%) and Penicillium-type spp. (0 to 8%). Penicillium-type isolates comprised the following species: 60% Penicillium expansum, 34% P. cellarum, 3% P. polonicum, and 3% Talaromyces rugulosus. Trace levels (<1% of root surface) of other fungi, including Cladosporium and Fusarium spp., were evident on roots and in isolations. Based on sample location in a pile, there were no trends or differences; however, two outdoor piles (OVP1 and OVP2) had more healthy tissue (90 to 96%) than other piles (28 to 80%) (P < 0.0001). When the pathogenicity tests were analyzed by species, all were significantly different from each other (P < 0.0001), except for P. polonicum and P. expansum: B. cinerea (61 mm of rot), P. polonicum (36 mm), P. expansum (35 mm), P. cellarum (28 mm), Athelia-like sp. (21 mm), T. rugulosus (0 mm; not different from check), and noninoculated check (0 mm). The OVP1 and OVP2 piles had negligible fungal growth on roots after more than 120 days of storage under ambient conditions, which indicates that acceptable storage can be achieved over this time period through covering piles with tarps and cooling with ventilation pipe.


Assuntos
Beta vulgaris/microbiologia , Fungos/isolamento & purificação , Doenças das Plantas/microbiologia , Botrytis/genética , Botrytis/isolamento & purificação , Botrytis/patogenicidade , Cladosporium/genética , Cladosporium/isolamento & purificação , Cladosporium/patogenicidade , Armazenamento de Alimentos , Fungos/genética , Fungos/patogenicidade , Fusarium/genética , Fusarium/isolamento & purificação , Fusarium/patogenicidade , Idaho , Penicillium/genética , Penicillium/isolamento & purificação , Penicillium/patogenicidade , Filogenia , Doenças das Plantas/estatística & dados numéricos , Raízes de Plantas/microbiologia
17.
Plant Dis ; 102(11): 2285-2295, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30207511

RESUMO

A survey of foliar pathogens of watermelon based on two-stage cluster sampling was conducted on commercial farms in South Carolina in spring 2015, spring and fall 2016, and fall 2017. In total, 60 fields from 27 different growers in seven counties representing the main watermelon-producing areas in the state were sampled, using a stratified two-stage cluster sampling approach. In the sampling design, counties corresponded to strata, growers to first-stage clusters, and fields to second-stage clusters. In each field, 100 symptomatic leaves were collected at five equidistant sampling points along four transects encompassing a square shape of 2,500 m2. After collection, pathogens were identified based on reproductive structures formed on leaves during >12 h incubation. Estimates were obtained for the statewide probability of pathogen occurrence and associations between pathogen pairs. Six fungal pathogens, Stagonosporopsis spp., Podosphaera xanthii, Cercospora citrullina, Colletotrichum orbiculare, Myrothecium sensu lato (s.l.), and Corynespora cassiicola; the oomycete Pseudoperonospora cubensis; and three viral pathogens were identified on the examined leaves. With the exception of fall 2017, Stagonosporopsis spp. was the most prevalent pathogen in every season, followed by P. xanthii. The highest occurrence of P. cubensis was in spring 2015; it did not occur in 2016. The highest occurrence of C. orbiculare was in spring 2016; it did not occur in spring 2015. Myrothecium s.l. was the most common pathogen in fall 2017 and the second most common pathogen occurring by itself in fall 2016. The third most common pathogen in fall 2017, Corynespora cassiicola, was not observed in any other season. Eight of the 80 isolates of Stagonosporopsis spp. collected were identified as S. caricae, the rest as S. citrulli. All isolates of S. caricae were found in spring 2015 and originated from two fields in different counties. A total of three positive and five negative associations were found between pathogen pairs co-occurring on the same leaf. A positive association between Stagonosporopsis spp. and C. citrullina was the only significant association between pathogens found in two seasons, spring 2015 and spring 2016. Based on estimates of probability of pathogen occurrence across seasons, Stagonosporopsis spp. and P. xanthii are the most common pathogens on watermelons in South Carolina. This is the first report of C. cassiicola, S. caricae, and Myrothecium s.l. on watermelon in South Carolina.


Assuntos
Ascomicetos/isolamento & purificação , Citrullus/microbiologia , Oomicetos/isolamento & purificação , Doenças das Plantas/estatística & dados numéricos , Citrullus/parasitologia , Análise por Conglomerados , Meio Ambiente , Fazendas , Modelos Estatísticos , Doenças das Plantas/microbiologia , Doenças das Plantas/parasitologia , Folhas de Planta/microbiologia , Folhas de Planta/parasitologia , Estações do Ano , South Carolina
18.
Plant Dis ; 102(11): 2253-2257, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30145949

RESUMO

In the last 5 years, asparagus acreage in Canada has increased by over 25%. Stemphylium leaf spot, caused by Stemphylium vesicarium, has emerged as the predominant foliar pathogen of asparagus. Typically, contact fungicides are applied every 14 days; however, regardless of the number of applications, growers are not achieving adequate control of the disease. The TOM-CAST forecasting model is used widely in Michigan asparagus fields, but it has never been assessed for suitability in Ontario or in the popular cultivar, Guelph Millennium. Six field trials were conducted in 2012 and 2013 to evaluate the TOM-CAST forecasting model in two asparagus cultivars. The fungicides chlorothalonil or azoxystrobin/difenoconazole were applied according to the forecasting model or on a 14-day interval. The effectiveness of the forecasting model differed between sites and cultivars. Even though TOM-CAST is used in all cultivars in Michigan, TOM-CAST was not effective on Guelph Millennium. In the cultivar Jersey Giant, however, TOM-CAST with a 20 disease severity value spray interval improved control of Stemphylium leaf spot without increasing the number of sprays, compared with a 14-day treatment. The results in Guelph Millennium differed between sites. At one site, TOM-CAST maintained similar levels of Stemphylium leaf spot, but increased the number of applications, compared with a 14-day application interval. Of more concern, none of the fungicide treatments differed greatly from the untreated control at the other site. Our results show that forecasting models need to be validated locally in asparagus cultivars relevant to production today.


Assuntos
Ascomicetos/efeitos dos fármacos , Asparagus (Planta)/microbiologia , Fungicidas Industriais/administração & dosagem , Modelos Estatísticos , Doenças das Plantas/prevenção & controle , Dioxolanos/administração & dosagem , Previsões , Nitrilos/administração & dosagem , Ontário , Doenças das Plantas/microbiologia , Doenças das Plantas/estatística & dados numéricos , Folhas de Planta/microbiologia , Pirimidinas/administração & dosagem , Estrobilurinas/administração & dosagem , Triazóis/administração & dosagem
19.
Plant Dis ; 102(9): 1748-1758, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30125211

RESUMO

Current management of sudden death syndrome (SDS) of soybean, caused by Fusarium virguliforme, focuses on planting resistant varieties and improving soil drainage; however, these measures are not completely effective. A 6-year study evaluated the effects of cropping system diversification on SDS and soybean yield. SDS, root health, yield, and F. virguliforme density in soil were assessed in a naturally infested field trial comparing a 2-year cropping system consisting of a corn-soybean rotation and synthetic fertilizer applications with 3- and 4-year cropping systems consisting of corn-soybean-oat + red clover and corn-soybean-oat +alfalfa-alfalfa rotations, respectively, with both manure and low synthetic fertilizer rates. In 5 of 6 years, SDS incidence and severity were lower and yield higher in the 3- and 4-year systems than in the 2-year system. SDS severity and incidence were up to 17-fold lower in the diversified systems than in the 2-year system. Incidence and severity of SDS explained 45 to 87% of the variation in yield. Plants in the 2-year system generally showed more severe root rot and lower plant weights than plants in the diversified systems. F. virguliforme density in soil was up to fivefold greater in the 2-year system compared with the 4-year system. The processes responsible for the suppression of SDS and yield protection in the diversified cropping systems still need to be determined.


Assuntos
Fusarium/crescimento & desenvolvimento , Doenças das Plantas/prevenção & controle , Soja/microbiologia , Agricultura , Fusarium/patogenicidade , Incidência , Doenças das Plantas/microbiologia , Doenças das Plantas/estatística & dados numéricos
20.
Sensors (Basel) ; 18(6)2018 Jun 11.
Artigo em Inglês | MEDLINE | ID: mdl-29891814

RESUMO

In recent decades, rice disease co-epidemics have caused tremendous damage to crop production in both China and Southeast Asia. A variety of remote sensing based approaches have been developed and applied to map diseases distribution using coarse- to moderate-resolution imagery. However, the detection and discrimination of various disease species infecting rice were seldom assessed using high spatial resolution data. The aims of this study were (1) to develop a set of normalized two-stage vegetation indices (VIs) for characterizing the progressive development of different diseases with rice; (2) to explore the performance of combined normalized two-stage VIs in partial least square discriminant analysis (PLS-DA); and (3) to map and evaluate the damage caused by rice diseases at fine spatial scales, for the first time using bi-temporal, high spatial resolution imagery from PlanetScope datasets at a 3 m spatial resolution. Our findings suggest that the primary biophysical parameters caused by different disease (e.g., changes in leaf area, pigment contents, or canopy morphology) can be captured using combined normalized two-stage VIs. PLS-DA was able to classify rice diseases at a sub-field scale, with an overall accuracy of 75.62% and a Kappa value of 0.47. The approach was successfully applied during a typical co-epidemic outbreak of rice dwarf (Rice dwarf virus, RDV), rice blast (Magnaporthe oryzae), and glume blight (Phyllosticta glumarum) in Guangxi Province, China. Furthermore, our approach highlighted the feasibility of the method in capturing heterogeneous disease patterns at fine spatial scales over the large spatial extents.


Assuntos
Oryza/crescimento & desenvolvimento , Doenças das Plantas/estatística & dados numéricos , Tecnologia de Sensoriamento Remoto/métodos , Imagens de Satélites , Análise Discriminante , Análise dos Mínimos Quadrados , Folhas de Planta/anatomia & histologia , Folhas de Planta/química , Folhas de Planta/metabolismo
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