Murcha-de-fusário do tomateiro: levantamento da intensidade,amostragem,arranjo espacial,variabilidade de isolados de Fusarium oxysporum f.sp. lycopersici e seleção de cultivares resistentes

Abstract

Fresh tomato is very important in the Agreste Region of Pernambuco State, Brazil. However its production is impaired by the occurrence of Fusarium wilt caused by Fusarium oxysporum f.sp. lycopersyci. This study aimed to survey the disease intensity in planting areas of Camocim de São Félix county, Agreste of Pernambuco and to determine the ideal sample size for disease assessment, to analyze the disease spatial pattern in field, to characterize the variability of Fusarium oxysporum f.sp. lycopersyci populations and to select the resistance of tomato cultivars to races 1 and 2 of the pathogen. The disease survey in 50 planting areas showed high disease prevalence (72%) and average incidence of 17,15%. Using the incidence data from 36 areas as pilot-samples, the sample size for disease assessment was determined accordimg to the mean variability coefficient. The number of rows to be sampled was inversely related to disease incidence and acceptable error. To quantify the disease in future surveys, considering 10% error, each area should have 130rows and 12 plants/row sampled. The disease spatial pattern was studied in 11 planting areas in plots with 480 plants, using mapping, ordinary runs, fitting of β-binomial distribution and spatial autocorrelation analyses. Seven areas showed agregation of diseased plants and four areas presented the randomized pattern suggesting that there is not a single spatial pattern of the diasease in field.Thirty-six pathogen isolates were characterized in relation to epidemiological components, races and isoenzymatic patterns. The disease incidence separated isolates into two similarity groups but based upon the area under the disease progress curve (AUPDC) and progress rate there was three groups. Only one isolate belonged to race 1 while all the others were race 2 suggesting a small population variability regarding to races. The relative mobility of bands indicated six similarity groups for esterases and eight groups for fosfatase. There were no significant correlations among the relative mobility values for isozymes and the values for epidemiological components. In the resistance assay the disease temporal progress was analysed in 25 tomato cultivars inoculated with isolates of races 1 and 2. Race 2 isolates induced disease symptoms in all cultivars but race 1 isolates only induced symptoms in cultivars Santa clara I-5300, Jumbo AG-592, Barão Vermelho AG-591, Débora Plus AF-799, Débora and Viradouro. The cultivars Seculus and Rio Grande showedlonger incubation periods and smaller incidence values, progress rate and AUPDC, suggesting their use in programs of Fusarium wilt integrated management in Agreste of Pernambuco.