Current Ideas on the Genetics and Regulation of the Synthesis of Phaseolotoxin in Pseudomonas Syringae PV. Phaseolicola

Abstract

The bacterium Pseudomonas syringae pv. phaseolicola is the causal agent of the “halo blight” disease of beans (Phaseolus vulgaris L.). This bacterium shares wide evolutionary relatedness with Pseudomonas savastonoi, and it was proposed that its taxonomic status be changed to P. savastanoi pv. phaseolicola; however, this proposal has been rejected and the organism has been maintained within the P. syringae group66. The disease attacks both foliage and pods, and is a major problem in temperate areas of the world. Leaf symptoms appear several days after infection as small water-soaked spots on the lower surface. At 7-10 days after infection, the lesions appear as greasy water-soaked points of infections. Pods can also be infected and lesions appear as brown or red water-soaked spots.Seeds may also become infected and the disease may be transmitted through the infected seed. At temperatures between 18°C and 23°C and high humidity, a zone of yellow-green tissue may develop around the initial site of infection after 3–8 days, giving rise to what is known as the chlorotic halo. In cases of severe infection, the chlorosis may become systemic. In fact, halo blight is considered to be a low-temperature disease and epidemic potential is greatest at temperatures ranging between 18°C and 22°C.