Spatial progress of bacterial blight in coffee nursery and environmental variables for “In vitro” cultivation of Pseudomonas syringae pv. garcae

Abstract

The Bacterial blight, whose etiologic agent is the bacterium Pseudomonas syringae pv. garcae has occurred in nurseries and crops of Coffea arabica, causing damage to the culture. The objectives of this thesis were to: compare the efficiency of inoculation methods, with and without injury, and their interaction with different concentrations of P. syringae pv. garcae on the intensity of the bacterial blight of coffee; to verify the interaction of different temperatures and photoperiods on the inoculum concentration of P. syringae pv. garcae and the expression of the symptoms of the Bacterial blight on coffee leaves; and, to characterize the spatio- temporal progress (P. syringae pv. garcae) in coffee seedlings (C. arabica) in the nursery using inoculum pre-set start. According to the results, the methods of inoculation by wounding the leaf of coffee plants to inoculate P. syringae pv. garcae provided higher incidence and severity of Bacterial blight. Among these, the inoculation methods with the highest incidence and severity of the disease are via inoculum injection, wound with a multi-needle set and sandblasting. For these methods, inoculum concentrations of 1.3x109 , 1.6x109 and 8.5x108 CFU/ml, respectively, provided maximum disease severity. The highest mean inoculum concentration was 1.22x109 CFU/ml obtained in the 12-hour photoperiod. Under these conditions at 23.3°C there was the highest inoculum production of 2.40x109 and 2.11x109 CFU/ml. Although there was a difference regarding the photoperiod in the production of inoculum, only the temperature influenced the AACPS, being higher at 23.7°C. The positive correlation of temperature with inoculum concentration and the latter with AACPS proved the importance of environmental variables, especially temperature, in obtaining the highest number of bacterial cells for the expression of symptoms. Larger bacterial cell dimensions occurred when incubation was performed under photoperiod conditions of continuous light and temperature of 28°C or continuous dark and temperature of 26°C. In the coffee seedling nursery, there was an epidemic of the Bacterial blight. The start was 15 days after the introduction of the initial inoculum in the pond, lasting eight weeks. There was spatial dependence of the diseased seedlings in relation to the initial inoculum, that is, the space-time progress of the disease was related to the introduction of infected plants. From these infected plants, the pathogen was disseminated more than 40 cm from the inoculum source in less than 40 days, with spatial dependence. This distance increased with the increase in the number of diseased plants in the main focus and/or secondary focus.