Abstract

DA ROCHA JUNIOR, Otacílio M. et al. Spatial characterization of banana yellow sigatoka and its implications for sampling. Agrociencia [online]. 2010, vol.44, n.3, pp.351-361. ISSN 2521-9766.

Yellow sigatoka, caused by the fungus Mycosphaerella musicola, is a major disease of banana (Musa spp.) and is widely spread in Brazil. This study was conducted to apply spatial dispersion criteria of yellow sigatoka in a sampling system to estimate the disease severity in the Valley of Siriji in northeastern Brazil. The disease spatial pattern was characterized in three fields of cv Pacovan bananas, where 30 contiguous rows, 30 plants per row were considered, giving a total of 900 plants. Severity was analyzed by autocorrelation, Lloyd index and geostatistical interpolative maps. In spite of the narrow range of severity among plantations (44.2-34.5 %), they exhibited a moderately to strongly aggregate pattern with continuous spatial dependencies of 2, 14, and 27 order, implicating contagious distances of 81, 42, and 6 m. The aggregates had an elongated predominance in direction of the rows with lateral contagious distances of 39 to 3 m in two of the fields. Interpolations evidenced spatial generalization of aggregates, concurring with the low values of the Lloyd index (1.01-1.04). Systematic sampling was designed with intervals of selection of rows (k₁) and plants (k₂) of 6 units for a total n = 50, with which the entire production unit was explored, but giving priority to intra-row selection by the aggregative property. This sampling method was applied in an additional 30 i-fields to estimate the sample size using , where k is an estimator of aggregation of the negative binomial distribution and CV the acceptable error. With a 5 % error, n_i had a range of 111-6 plants and was inversely proportional to the level of severity. In an epidemiological survey, systematic sampling (k₁ =6, k₂ = 6) is proposed with a 5 % error and n = 34 plants ha^-1 , corresponding to 3.8 % of the population.

Keywords : Musa spp.; Mycosphaerella musicola; epidemiology; phytopathometry; sampling.

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