Four main aspects of the halo-blight problem have been studied, (1) Identification of the pathogen. (2) Sources of infection and their detection. (3) Studies of the disease in the field and its control by foliar sprays. (4) Investigation of seed treatments. Prom a study of methods of identification of Ps. phaseolicola it was concluded that both phage and antiserum tests provided specific, rapid and easily applied techniques for the routine identification of isolates from plant and seed material. Using these tests, a laboratory method for the detection of the pathogen in seed was developed. The method, which will detect low levels of seed borne infection, has been used in a statistical procedure (the most probable number method) to give an estimate of percentage infection. There was no evidence to suggest that the bacteria could survive from one season to the next in the soil or on plant debris in the soil. Studies were made of disease incidence in field plots in two years with widely differing weather patterns. The plots were sown with varying proportions of infected seeds and the effect of initial inoculum on final disease intensity was determined. In 1968 and 1969 the disease was successfully controlled by sprays of streptomycin sulphate and copper oxychloride (0.1% a.i., 60 gal/acre). These were applied soon after emergence and then at 10 day intervals until most of the plants were flowering. Numerous tests of seed treatments failed to reveal any which would provide a practical control measure.
|Date of Award||1970|