Although biological control is not commonly used for foliar diseases, numerous organisms capable of antagonizing fruit and leaf pathogens have been reported in recent years. Formerly, little attention was given to bio-control of foliar pathogens, principally because the foliar microflora was known to consist of relatively few organisms whose populations fluctuate dramatically according to environmental conditions. These may be daily temperature, relative humidity and ultraviolet radiation, which vary amply and rapidly, especially in the Andean mountains. Additionally, the rapid growth of foliage provides better opportunities for pathogen growth rather than organisms in the phyllosphere (Fry, 1982).

One example of biological control of an airborne foliar disease is the use of the antagonistic bacteria Pseudomonas cepacia and Bacillus subtillis to control Monilia pod rot in cacoa. P. cepacia and B. subtillis, applied every two weeks from March to August 2001 in field studies in Los Rios, Ecuador, reduced the disease by 55 and 62%, respectively, compared to the untreated control (Falconí et al., 2002). Concurrently, formulations of biopesticides, tests for tolerance of the antagonists to agrochemicals and tests for toxicity of the antagonists to cacao were carried out. Cost-Benefit analysis demonstrated a major economic benefit in using biological control as compared to chemical control (Falconí et al., 2003).

Ramos et al. (1993) and Sanchez et al. (1998) reported that certain microorganisms in the phyllosphere are antagonistic to Phytophthora infestans. These include the yeast Sporobolomyces spp. and isolates of Pseudomonas spp. and Bacillus spp. Jongebloed et al. (Sanchez et al., 1998) found that P. fluorescens isolate 148 and Bacillus sp. isolate B39 inhibited P. infestans in tomato maintained in a growth chamber. De la Vega and Perez (2003) tested the efficiency of isolates of P. fluorescens antagonistic to P. infestans and their tolerance to the principal fungicides used to control potato late blight in the greenhouse. At least two of these isolates significantly reduced infection and had some tolerance to the systemic fungicide Fosetyl-Al.

Streptomyces violaceusniger strain YCED-9 was strongly antagonistic to isolates of P. infestans in vitro (Trejo et al., 1998). S. violaceusniger produces geldanamycin, a benzoquinoid polyketide highly inhibitory of mycelial growth of Pythium and Phytophthora spp.

Interest in the biological control of P. infestans abounds. Hopefully, more effort will be made to continue studying these organisms as a future component of integrated control of late blight.

--------------------------------------------------------------------------------

Prepared by Cesar Falconí, The Army Polytechnic School, Sangolqui, Ecuador.

Translated from Spanish by GILB

Literature cited

De la Vega V C and Perez M N. 2004. Seleción, dosificación y tolerancia a fungicidas de Pseudomonas flourescens en el manejo integrada de Phytophthora infestans en el cultivo de la papa, Solanum tuberosum. Thesis for professional title. Centro de Control Biológico de la ESPE. Facultad de Ciencias Agropecuarias. Quito, Ecuador.

Falconi C E, Paez G T, Oleas A R and Yanez V R. 2002. Biological control of Monilia pod rot in the field using epiphytic bacteria. Phytopathology 92:S24.

Falconi C E, Paez G T, Oleas A R and Yanez V R. 2003. [Biological strategies for the control of moniliasis in cacao] Estrategias biológicas para el control de la moniliasis del cacao. Reporte técnico – cientifico, Convenio ESP-PROMSA, IQ-CV-025. Centro Control Biológico de la Facultad de Ciencias Agroprecuarias de la ESPE. 54p.

Fry, W.E. 1982. Principles of Plant Managment. Academic Press Inc. USA. 378 p.

Ramos L, Ciampi L and Gonzales S. 1993. [Biological control of Phytophthora infestans in potato plants] Control biológico de Phytophthora infestans en plantas de Solanum tuberosum L. Simiente 63: 53–54.

Sanchez V, Bustamante, E and Shattock R. 1998. [Selection of antagonists for biological control of Phytophthora infestans in tomato] Selección de antagonistas para el control biológico de Phytophthora infestans en tomate. Manejo Integrado de Plagas: 25-34..

Trejo Estrada, S R, Paszczynski A and Crawford D. L. 1998. Antibiotics and enzymes produced by the biocontrol agent Streptomyces violaceusniger YCED-9. Journal of Industrial Microbiology and Biotechnology 21:81-90.