Analysis of the temporal and spatial disease progress of Bemisia tabaci-transmitted Cucurbit yellow stunting disorder virus and Cucumber vein yellowing virus in cucumber

Ruiz, Leticia; Janssen, D.; Martín, German; Velasco, Leonardo; Segundo, E.; Cuadrado, I. M.

Analysis of the temporal and spatial disease progress of Bemisia tabaci-transmitted Cucurbit yellow stunting disorder virus and Cucumber vein yellowing virus in cucumber

2006

Cucurbit yellow stunting disorder virus (CYSDV) has been present in greenhouse-grown cucumber in Spain since 1992. However, in the autumn of 2000 Cucumber vein yellowing virus (CVYV) was introduced, leading to mixed infections of both Bemisia tabaci-transmitted viruses. The temporal and spatial spread of disease symptoms were monitored in experimental plastic-covered greenhouses during six consecutive cucumber plantings from 2000 to 2002. Using linear regression analysis of 46 disease-progress curves, the Gompertz model best described the CYSDV epidemics in 2000, whereas the logistic model best described the development of CYSDV and CVYV epidemics in 2001 and 2002. The fitted models were used to calculate the amount of degree Celsius-days at half-maximum infection in the greenhouses (°D0·5). After multiple regression analysis, 56% of the variation in °D0·5 of CYSDV was related to the numbers of whiteflies infesting the cucumber crops, and was independent of the mean temperatures in the greenhouses. In contrast, 76% of the variation in °D0·5 of CVYV was related to both the numbers of vectors present and maximum temperature. Symptom expression in cucumbers mechanically inoculated with CVYV was most prevalent when plants were grown at regimes of at least 28°C day temperature. According to analysis of spread using Taylor's power law, beta-binomial distribution fitting, and the ordinary runs test, the prevalence of CVYV showed significant overdispersion, whereas that of CYSDV did not. The χ2 test of independence and Spearman's rank correlation coefficient were used to measure co-occurrence and covariation, respectively, during the first half of the cultivation period. These results showed that the two diseases were not associated. © 2006 BSPP.

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