Caracterização epidemiológica da podridão mole da couve-chinesa causada por Pectobacterium aroidearum

Abstract

Among the various olerocaric species produced in Brazil, those belonging to the Brassicaceae family are characterized as the most abundant; it’s major economic expression, richness in minerals and vitamins, as well as low production costs. Among the botanical species belonging to the Brassicaceae family, Chinese cabbage stands out as one of the most produced vegetables in the state of Pernambuco. However, the yield of Chinese cabbage can be reduced due to the occurrence of a number of diseases, in which soft rot stands out. This disease is very frequent in Brazil, being a limiting factor for Chinese cabbage cultivation in the state of Pernambuco. However, the yield of this crop can be reduced due to the occurrence of several diseases, among which soft rot is highlighted. The objective of this work was to determine the ideal temperature for the in vitro growth of the isolates, to analyze the influence of inoculum concentration, temperature and duration and onset of high humidity on the aggressiveness of five isolates of Pectobacterium aroidearum (PA). Inoculate concentrations of 103 to 104, 105, 106, 107, 108 and 109 CFU / mL were evaluated; temperatures of 15, 20, 25, 28, 30, 35, 40 °C; treatments with humid chamber for 0, 6, 12, 24 and 48 h, with the beginning of the treatments immediately after the inoculations; and treatments with beginning of the humid chamber at 0, 6, 12, 24 and 48 h after inoculations. The data obtained were submitted to linear and non-linear regression analysis to relate the temperature, inoculum concentration, duration and beginning of high humidity to the lesion sizes induced by P. aroidearum isolates. The choice of the model for each experiment was determined by the significance of the regression (P≤0.05), determination coefficient (R2>0.95), residue distribution and mean squared error. The values of the variables estimated by the regression models in each experiment were submitted to analysis of variance and the averages were compared by the LSD test (P≤0.05). The ideal in vitro growth temperature for P. aroidearum isolates was 24.5 °C. The conditions that predisposed the severity of soft rot in Chinese cabbage were high inoculum concentration of 109 CFU / mL, together with temperature of 32 °C and high relative humidity, close to 100%, during 48 h. To our knowledge, this is the first study to determine the environmental factors favorable to the development of soft rot caused by P. aroidearum in Chinese cabbage in the state of Pernambuco. In addition, the knowledge obtained here will help in the understanding of epidemics of soft rot and the development of efficient strategies for the management of the disease.