Effect of fungicides in the viability of potential biocontrol agents against Fusarium head blight in wheat

PALAZZINI J.M; RAMIREZ M L; TORRES A. M.; CHULZE , S.N

Villa Carlos Paz

Congreso; VI Congreso Argentino de Microbiologia General; 2009

Sociedad Argentina de Microbiologia General

Fusarium Head Blight (FHB) caused by Gibberella zeae (anamorph = Fusarium graminearum) is a devastating disease that causes extensive yield and quality losses to wheat in humid and semi-humid regions of the world. Different strategies have been used to reduce the impact of FHB including crop rotation, tillage practices, fungicide application and the planting of less susceptible cultivars. None of these strategies by themselves are able to substantially reduce the impact of the disease. Biological control offers an additional strategy and can be used as part of an integrated management of FHB. In previous studies three bacteria, Bacillus subtilis RC 218, Brevibacillus sp. RC 263 and Streptomyces sp. RC 87B were selected by their potential to control the growth and deoxynivalenol (DON) production by F. graminearum. These microorganisms were able to control FHB and DON production in greenhouse trials. The goal of this work was: - to test the effect of common fungicides, utilized to control Fusarium head blight, on the viability of the potential biocontrol agents Bacillus subtilis RC 218, Brevibacillus sp. RC 263 and Streptomyces sp. RC 87B. Three different fungicides were used in the bioassay (prothioconazole, tebuconazole and metconazole) at concentrations ranging from 0.5 to 80 µg/ml. A single colony of each bacterial strain was used to inoculate 100 ml of the basal medium in 250 ml Erlenmeyer flasks and incubated for 12 h (overnight culture) at 28 ºC in a rotatory shaker (150 rpm) in order to obtain mid-log phase cells (approximately 106 cells ml-1). Cells counting was done in a haemocytometer chamber and adjusted to 2 x 103 cells ml-1. An aliquot of 0.1 ml of each bacterial strain was inoculated in Petri dishes using the spread plating technique containing the solid basal medium (agar 2%) with the different fungicides. Inoculated plates were incubated at 28 ºC for 48 h. Colony counting were done at 24 and 48h. Controls without fungicides were used for each strain. Differences in the viability of the three bacteria were observed in the presence of the fungicides. Bacillus subtilis RC 218 and Streptomyces sp. RC 87B showed better tolerance to fungicides than Brevibacillus sp. RC 263. Complete inhibition of growth was observed at concentrations of 20 µg/ml for metconazole, 40 µg/ml for tebuconazole and 80 µg/ml for prothioconazole. Results obtained indicate the possibility to use biocontrol agents in combination with fungicides as part of an integrated management to control FHB of wheat.