Effect of soil solarization on total Agrobacterium spp. population, inoculated Agrobacterium tumefaciens, and on the development of crown gall

Two experiments were carried out in different Jordanian locations to test the effect of solarization on populations of Agrobacterium spp., including Agrobacterium tumefaciens, the crown gall agent that was inoculated in the soil, as well as on crown gall incidence. The results of these experiments showed that solarization markedly decreased the populations of three Jordanian A. tumefaciens isolates that were used as inoculum in the trials. Bacterial population reduction was correlated with temperature and soil type. Agrobacterium spp. population decreased by 99% in the first three weeks after inoculation. Lower bacterial recovery was obtained from solarized plots in the Jordan Valley (silty clay soil and temperature ranging from 39 to 51degreesC) than from the comparable treatments carried out in the uplands (clay soil and temperature ranging from 29 to 46degreesC). Solarization did not completely eliminate Agrobacterium spp. from the soil, but the number of GF677 and bitter almond roostock seedlings with crown gall was significantly reduced in solarized plots in the Jordan Valley and uplands (by 89 and 94%, respectively) as compared with seedlings planted on non-solarized plots.