Levantamento da incidência da mancha-aquosa do melão nos municípios de Mossoró e Baraúna (Rio Grande do Norte, Brasil) e determinação do tamanho da amostra para quantificação da doença

Abstract

Melon is one of the most popular cucurbits in the world. The bacterial blotch of melon, caused by Acidovorax avenae subsp. citrulli has caused 40 to 50% losses in the production and made the fruits inappropriate for commercialization in the State of Rio Grande do Norte. This study aimed to survey the bacterial blotch incidence in 18 melon planting areas of the counties Mossoró and Baraúna in Rio Grande do Norte, and to determine the ideal sample size for disease assessment. Prevalence of 100% was reported in the studied fields. The incidence of the bacterial fruit blotch ranged from 4.30 to 47.29%. Incidence levels were under 20% in 50% of the areas and higher than 40% in 17% of the areas. There was significant difference for the variables melon type (P=0.01) and years of melon culture in the area (P=0.05). The t test showed the melon Piel de sapo was more susceptible than the yellow type and the disease incidence in areas with less than 10 years of melon cropping was higher than those with more than20 years. However, there were no significant differences (P=0.05) for disease incidence averages among areas planted with corn (18%) and corn plus other grasses (20%) between melon seasons. Using the incidence data from 18 areas as pilot-samples, the sample size for disease assessment was determined according to the mean variability coefficient. The Pierson test showed no significant correlations (P=0.05) between the levels of disease incidence and sample sizes. Based on the data obtained andconsidering 10% of acceptable error, it is recommended that in future surveys of melon bacterial blotch incidence in fields in Rio Grande do Norte, a sample composed by 12 subsamples comprising 100 m2/ha and 20 fruit evaluated per subsample must be analyzed.