THE EFFECT OF SOLAR HEATING OF SOIL ON NATURAL AND INOCULATED AGROBACTERIA

Solarization trials were carried out over 3 years and in two countries to control crown gall disease on fruit trees and eliminate Agrobacter ium. In 1992, agrobacteria in naturally infested soils of two Italian nurseries were monitored before and after solarization. Agrobacteria p opulations decreased by 99% and 92% after the treatment; however, crow n gall incidence did not decrease. In 1993 and 1994 solarization was t ested in Oregon in fields artificially infested with two marked strain s of A. tumefaciens. In sandy loam soil, the target bacteria were elim inated in 4 weeks, while in silty clay soil the populations were marke dly reduced after 2 months of treatment. Crown gall incidence on cherr y rootstocks transplanted to the field at the end of 1993 was 3.7% in the sandy loam soil control plots, while no tumours were observed on p lants from solarized plots. The use of solarization in combination wit h reduced doses of metham-sodium was also evaluated.