RESUMEN
Watermelon is affected by diseases such as Fusarium wilt, gummy stem blight, and root-knot nematode (RKN). Succinate dehydrogenase inhibitors (SDHIs) with potential fungicide and nematicide activity provide the opportunity to control multiple diseases with one compound. In this study, we aimed to determine the sensitivity of Meloidogyne incognita race 4 (MI4), Fusarium oxysporum f. sp. niveum (FON), and Stagonosporopsis citrulli (SCIT) to existing SDHIs: benzovindiflupyr, fluopyram, cyclobutrifluram, and pydiflumetofen. All SDHIs had fungicidal activity against 19 SCIT isolates in mycelial growth assays, but isolates were most sensitive to pydiflumetofen (median EC50 = 0.41 µg/ml). Most of the 50 FON isolates tested were sensitive to cyclobutrifluram for mycelial growth (median EC50 = 4.04 µg/ml) and conidial germination (median EC50 = 0.2 µg/ml) assays but were not sensitive to fluopyram. MI4 was most sensitive to cyclobutrifluram for egg hatch (mean EC50 = 0.0019 µg/ml) and J2 motility (mean EC50 = 1.16 µg/ml) assays but was not sensitive to pydiflumetofen. Significant positive correlations between the sensitivity of SCIT (mycelial growth) and FON (mycelial growth and conidial germination) for cyclobutrifluram and benzovindiflupyr (SCIT r = 0.88; FON r = 0.7; P < 0.0001) and cyclobutrifluram and pydiflumetofen (SCIT r = 0.83; FON r = 0.67 and 0.77; P < 0.0001) indicate a potential for cross-resistance between these SDHIs for these fungal pathogens. Overall, results suggest that cyclobutrifluram may be used for managing RKN, whereas it should be used judiciously for Fusarium wilt of watermelon and gummy stem blight due to the existence of insensitive isolates to the fungicide.
Asunto(s)
Citrullus , Fungicidas Industriales , Fusarium , Enfermedades de las Plantas , Succinato Deshidrogenasa , Tylenchoidea , Fusarium/efectos de los fármacos , Enfermedades de las Plantas/parasitología , Enfermedades de las Plantas/microbiología , Tylenchoidea/efectos de los fármacos , Citrullus/microbiología , Citrullus/parasitología , Animales , Succinato Deshidrogenasa/antagonistas & inhibidores , Fungicidas Industriales/farmacología , Inhibidores Enzimáticos/farmacología , Antinematodos/farmacologíaRESUMEN
Landscape management affects species interactions and can have notable effects on food web structure. Local parasitoid populations in greenhouses usually migrate from outside crops; biological control of greenhouse aphids may be thus highly dependent on the composition of surrounding landscape. However, it is less clear how surrounding landscape composition affects primary-hyperparasitoid food webs and pest control services in greenhouses. We investigated the food web of parasitoids on melon-cotton aphid (Aphis gossypii Glover) in watermelon greenhouses in two suburban Beijing counties over two years. We used the quantitative food web metrics (generality, vulnerability, link density, and interaction evenness) to assess the effects of landscape composition on primary-hyperparasitoid food web structure. We found that landscape with more cropland within 1-3 km tended to have more primary parasitoids per hyperparasitoid species (generality). Higher proportions of woodland at the 0.5 km scale were negatively correlated with the mean numbers of hyperparasitoid per primary parasitoid species (vulnerability), as well as with hyperparasitism rate and hyperparasitoid richness. Link density, interaction evenness and aphid mortality caused by parasitoids (parasitism rate) were not affected by landscape factors. However, active primary parasitism (biocontrol potential) increased with the proportion of woodland. This suggested that the bottom-up effect induced by primary parasitoids might benefit hyperparasitoids, thus exerting little influence of primary parasitoids on pest control. The top-down effect of hyperparasitoids may reduce with increasing woodland proportion. To enhance the effects of primary parasitoids, landscape management programs should also target, and thus limit the impact of hyperparasitoids.
Asunto(s)
Áfidos/fisiología , Citrullus/parasitología , Cadena Alimentaria , Animales , Áfidos/metabolismo , Áfidos/patogenicidad , Citrullus/crecimiento & desarrollo , Parasitología de Alimentos , Bosques , HumanosRESUMEN
Insect vector behavior and biology can be affected by pathogen-induced changes in the physiology and morphology of the host plant. Herein, we examined the temporal effects of Squash vein yellowing virus (family Potyviridae, genus Ipomovirus) infection on the settling, oviposition preference, and feeding behavior of its whitefly vector, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), formerly known as B. tabaci biotype B. Settling and oviposition behavioral choice assays were conducted on pairs of infected and mock-inoculated watermelon (Citrullus lanatus (Thunb) Matsum and Nakai) (Cucurbitales: Cucurbitaceae) at 5-6 days post inoculation (DPI) and 10-12 DPI. Electropenetrography, or electrical penetration graph (both abbreviated EPG), was used to assess differences in feeding behaviors of whitefly on mock-inoculated, 5-6 and 10-12 DPI infected watermelon plants. Whiteflies showed no preference in settling or oviposition on the infected and mock-inoculated plants at 5-6 DPI. However, at 10-12 DPI, whiteflies initially settled on infected plants but then preference of settling shifted to mock-inoculated plants after 8 h. Only at 10-12 DPI, females laid significantly more eggs on mock-inoculated plants than infected plants. EPG revealed no differences in whitefly feeding behaviors among mock-inoculated, 5-6 DPI infected and 10-12 DPI infected plants. The results highlighted the need to examine plant disease progression and its effect on vector behavior and performance, which could play a crucial role in Squash vein yellowing virus spread.
Asunto(s)
Conducta Alimentaria , Hemípteros/fisiología , Hemípteros/virología , Potyviridae/fisiología , Animales , Citrullus/parasitología , Citrullus/virología , Electrofisiología/métodos , Femenino , Insectos Vectores/fisiología , Insectos Vectores/virología , Oviposición/fisiología , Enfermedades de las Plantas/virologíaRESUMEN
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.
Asunto(s)
Ascomicetos , Citrullus , Oomicetos , Ascomicetos/fisiología , Citrullus/microbiología , Citrullus/parasitología , Análisis por Conglomerados , Oomicetos/fisiología , Enfermedades de las Plantas/microbiología , Enfermedades de las Plantas/parasitología , Enfermedades de las Plantas/estadística & datos numéricos , Hojas de la Planta/microbiología , Hojas de la Planta/parasitología , Factores de Riesgo , South CarolinaRESUMEN
Plants with shorter internodes are suitable for high-density planting, lodging resistance and the preservation of land resources by improving yield per unit area. In this study, we identified a locus controlling the short internode trait in watermelon using Zhengzhouzigua (long internode) and Duan125 (short internode) as mapping parents. Genetic analysis indicated that F1 plants were consistent with long internode plants, which indicates that the long internode was dominant over the short internode. The observed F2 and BC1 individuals fitted the expected phenotypic segregation ratios of 3:1 and 1:1, respectively. The locus was mapped on chromosome 9 using a bulked segregant analysis approach. The region was narrowed down to 8.525 kb having only one putative gene, Cla015407, flanking by CAPS90 and CAPS91 markers, which encodes gibberellin 3ß-hydroxylase (GA 3ß-hydroxylase). The sequence alignment of the candidate gene between both parents revealed a 13 bp deletion in the short internode parent, which resulted in a truncated protein. Before GA3 application, significantly lower GA3 content and shorter cell length were obtained in the short internode plants. However, the highest GA3 content and significant increase in cell length were observed in the short internode plants after exogenous GA3 application. In the short internode plants, the expression level of the Cla015407 was threefold lower than the long internode plants in the stem tissue. In general, our results suggested that Cla015407 might be the candidate gene responsible for the short internode phenotype in watermelon and the phenotype is responsive to exogenous GA3 application.
Asunto(s)
Citrullus , Ligamiento Genético , Oxigenasas de Función Mixta/genética , Nematodos , Enfermedades de las Plantas , Proteínas de Plantas/genética , Animales , Mapeo Cromosómico , Citrullus/genética , Citrullus/parasitología , Estudios de Asociación Genética , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/parasitologíaRESUMEN
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.
Asunto(s)
Ascomicetos/aislamiento & purificación , Citrullus/microbiología , Oomicetos/aislamiento & purificación , Enfermedades de las Plantas/estadística & datos numéricos , Citrullus/parasitología , Análisis por Conglomerados , Ambiente , Granjas , Modelos Estadísticos , Enfermedades de las Plantas/microbiología , Enfermedades de las Plantas/parasitología , Hojas de la Planta/microbiología , Hojas de la Planta/parasitología , Estaciones del Año , South CarolinaRESUMEN
A protocol for identifying tospovirus and thrips species in an individual thrips sample was successfully developed. First, an individual thrips was soaked in an RNA stabilization solution to preserve protein and nucleic acids and ground in a carbonate buffer containing 0.2% sodium diethyldithiocarbamate. Initially, the thrips extracts were screened for tospovirus infection by dot blot analysis using antibodies to nucleocapsid (N) proteins of tospoviruses. Thrips extracts with positive results by dot blot analysis were further subjected to RNA extraction. Next, tospovirus species were identified by reverse transcription-polymerase chain reaction (RT-PCR) using species-specific primers for the N genes of four tospoviruses known to occur in Thailand, including Capsicum chlorosis virus (CaCV), Melon yellow spot virus (MYSV), Tomato necrotic ringspot virus (TNRV) and Watermelon silver mottle virus (WSMoV). The residual genomic DNA in the thrips RNA extract was used as a template to identify thrips species by PCR with species-specific primers to the internal transcribed spacer 2 regions of the rRNA of Ceratothripoides claratris, Frankliniella intonsa, Scirtothrips dorsalis and Thrips palmi. This protocol was initially validated against laboratory-reared thrips and then used to determine the occurrence of viruliferous thrips species collected from tomato, pepper, watermelon and cucumber fields in Thailand.
Asunto(s)
Entomología/métodos , Immunoblotting/métodos , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Thysanoptera/clasificación , Thysanoptera/virología , Tospovirus/clasificación , Virología/métodos , Animales , Antígenos Virales/análisis , Capsicum/parasitología , Citrullus/parasitología , Cucumis sativus/parasitología , Solanum lycopersicum/parasitología , ARN Ribosómico/análisis , ARN Ribosómico/genética , ARN Viral/análisis , ARN Viral/genética , Tailandia , Thysanoptera/genética , Tospovirus/genética , Tospovirus/inmunologíaRESUMEN
Thrips-borne tospoviruses cause numerous plant diseases that produce severe economic losses worldwide. In the disease system, thrips not only damage plants through feeding but also transmit causative agents of epidemics. In addition, thrips are infected with tospoviruses in the course of virus transmission. Most studies on the effect of tospoviruses on vector thrips have focused on the Tomato spotted wilt virus-Frankliniella occidentalis system. Thus, we focused on another thrips-borne tospovirus, Watermelon silver mottle virus (WSMoV), to examine the effect of virus infection on its vector, Thrips palmi. In this study, the direct and indirect effects of WSMoV on the life history traits and feeding preference of T. palmi were examined. The survival rate and developmental time of the WSMoV-infected larval thrips did not differ significantly from those of the virus-free thrips. Comparing the developmental time of larval thrips fed on the healthy plants, thrips-damaged plants, and thrips-inoculated plants (the WSMoV-infected plants caused by thrips feeding), feeding on the thrips-damaged plants reduced the developmental time, and the WSMoV infection in host plants partially canceled the effect of thrips damage on the developmental time. In addition, no significant variations between the virus-free and WSMoV-infected adult thrips regarding longevity and fecundity were observed. These results implied that WSMoV did not directly affect the life history traits of T. palmi, but the WSMoV infection indirectly affected the development of T. palmi through the virus-infected plants. Furthermore, feeding preference tests indicated that T. palmi preferred feeding on either the thrips-damaged plants or the thrips-inoculated plants to the healthy plants. The effect of tospoviruses on the life history and feeding preference of vector thrips might vary among host plants, virus species, vector species, and environmental factors.
Asunto(s)
Citrullus/parasitología , Conducta Alimentaria , Preferencias Alimentarias , Estadios del Ciclo de Vida , Thysanoptera/crecimiento & desarrollo , Thysanoptera/virología , Tospovirus/fisiología , Animales , Fertilidad , Longevidad , Hojas de la Planta/parasitología , Pupa/crecimiento & desarrollo , Pupa/virología , Plantones/parasitología , Análisis de SupervivenciaRESUMEN
Zucchini yellow mosaic virus (ZYMV, genus Potyvirus) causes important crop losses in cucurbits worldwide. In France, ZYMV epidemics are sporadic but occasionally very severe. This contrasts with Watermelon mosaic virus (WMV, genus Potyvirus) which causes regular and early epidemics. Factors influencing ZYMV epidemiology are still poorly understood. In order to gain new insights on the ecology and epidemiology of this virus, a 5-year multilocation trial was conducted in which ZYMV spread and populations were studied in each of the 20 plot/year combinations and compared with WMV. Search for ZYMV alternative hosts was conducted by testing weeds growing naturally around one plot and also by checking ZYMV natural infections in selected ornamental species. Although similar ZYMV populations were observed occasionally in the same plot in two successive years suggesting the occurrence of overwintering hosts nearby, only two Lamium amplexicaule plants were found to be infected by ZYMV of 3459 weed samples that were tested. The scarcity of ZYMV reservoirs contrasts with the frequent detection of WMV in the same samples. Since ZYMV and WMV have many aphid vectors in common and are transmitted with similar efficiencies, the differences observed in ZYMV and WMV reservoir abundances could be a major explanatory factor for the differences observed in the typology of ZYMV and WMV epidemics in France. Other potential ZYMV alternative hosts have been identified in ornamental species including begonia. Although possible in a few cases, exchanges of populations between different plots located from 500 m to 4 km apart seem uncommon. Therefore, the potential dissemination range of ZYMV by its aphid vectors seems to be rather limited in a fragmented landscape.
Asunto(s)
Citrullus/virología , Cucurbita/virología , Filogenia , Enfermedades de las Plantas/virología , Potyvirus/genética , ARN Viral/genética , Animales , Áfidos/fisiología , Conducta Animal , Citrullus/parasitología , Cucurbita/parasitología , Conducta Alimentaria , Francia , Haplotipos , Especificidad del Huésped , Interacciones Huésped-Parásitos , Insectos Vectores/fisiología , Epidemiología Molecular , Filogeografía , Enfermedades de las Plantas/parasitología , Malezas/parasitología , Malezas/virología , Potyvirus/clasificación , Potyvirus/aislamiento & purificaciónRESUMEN
Spatial distribution patterns of adult squash bugs were determined in watermelon, Citrullus lanatus (Thunberg) Matsumura and Nakai, during 2001 and 2002. Results of analysis using Taylor's power law regression model indicated that squash bugs were aggregated in watermelon. Taylor's power law provided a good fit with r2 = 0.94. A fixed precision sequential sampling plan was developed for estimating adult squash bug density at fixed precision levels in watermelon. The plan was tested using a resampling simulation method on nine and 13 independent data sets ranging in density from 0.15 to 2.52 adult squash bugs per plant. Average estimated means obtained in 100 repeated simulation runs were within the 95% CI of the true means for all the data. Average estimated levels of precision were similar to the desired level of precision, particularly when the sampling plan was tested on data having an average mean density of 1.19 adult squash bugs per plant. Also, a sequential sampling for classifying adult squash bug density as below or above economic threshold was developed to assist in the decision-making process. The classification sampling plan is advantageous in that it requires smaller sample sizes to estimate the population status when the population density differs greatly from the action threshold. However, the plan may require excessively large sample sizes when the density is close to the threshold. Therefore, an integrated sequential sampling plan was developed using a combination of a fixed precision and classification sequential sampling plans. The integration of sampling plans can help reduce sampling requirements.