Field evaluation of Serratia marcescens IBC-CR18 as biocontrol agent of the Coffee leaf rust

Abstract

The aim of this work was to assess in the field the effect of Serratia marcescens strain IBC-CR18 as potential biocontrol agent of the coffee leaf rust (Hemileia vastratix), sprayed onto seven months-old Arabic coffee plants cv. “Marago”. We evaluated the crude culture of the strain (109 UFC mL-1 and metabolites) grown on nutrient broth during 72 h under static fermentation at 26 ºC (± 2 ºC) and the crude culture subjected to freeze-thaw 48 h before field spraying, with the objective to inactivate the bacterial cells. A conventional chemical treatment (85% cupper oxychloride as active ingredient, at a dose of 5 g L-1 of water), a commercial biofungicide based on Bacillus subtilis (Serenade® Opti, 5 g L-1) and a Control (water) were included. The repeated measures analysis of the infection indices revealed statistical differences between treatments (F4,437=4.47; P=0.0015), which were noticeable at the end of the field trial. After spraying of the treatments on coffee plants, the commercial biofungicide accumulated the lowest amount of disease (area under disease progress curve) in comparison to the rest of the treatments and control (F4,115=3.00; P=0.02), and caused a delay of the epidemics for 20.3 days as compared to Control. On the other hand, bacterial crude culture and freeze-thaw crude culture, delayed the disease progression for 12.2 y 15.3 days, respectively, in comparison to Control.