Pathogenicity of Burkholderia cepacia (Pseudomonas cepacia) in four onion genotypes (Allium sp.)

Abstract

Onion is one of the major crops in Puerto Rico.The bacterium Burkholderia cepacia (basonym: Pseudomonas cepacia) is the causal agent of the onion disease sour skin. In Puerto Rico the strain B. cepacia UPR-5C has been reported as a biological control agent of various phytopathogenic fungi. At present, the pathogenic characteristics of this strain are unknown. The pathogenicity of B. cepacia UPR-5C was determined in four commercial onion genotypes, yellow, red scailions, white Spanish and slip, by using a complete randomized design with split plots. The onion genotypes were inoculated with bacteria of 10e CFU/ml from each growth phase and with the filtrates corresponding to each phase. Symptoms were evaluated seven days after inoculation.Treatments with cells, but not filtrates, induced symptoms in the yellow onion genotype. The red, white and slip genotypes were not susceptible, but the bacterium is pathogenic to yellow onions. There are, however, different levels of resistance within the species.