STUDIES OF HALO-BLIGHT SEED INFECTION AND DISEASE TRANSMISSION IN DWARF BEANS

The transmission of Pseudomonas phaseolicola from plant to seed was mainly by the penetration of bacteria from external pod lesions to the underlying seeds. There was no evidence for translocation of bacteria from other parts of the plant to the seed, and symptomless pods contained only healthy seeds. Although a small proportion of infected seeds showed obvious symptoms of infection, the majority showed either slight symptoms, which could be detected only by careful observation, or were symptomless. In tests of disease transmission from seed to seedling, seeds with slight symptoms, or those which were symptomless were responsible for 35% and 52% respectively of the total disease transmission compared to 13% for obviously infected seeds. The viability of bacteria in seed stored under relatively uncontrolled conditions (10–27 d̀C) declined by a factor of 250 per annum over the first 3 yr with extrapolation predicting effective extinction after c. 5 yr. The pathogen survived longer under controlled conditions (7–10 d̀C and 45–50% r.h.) but no viable bacteria were detected in seed stocks which were 10‐yr‐old and with one exception 6‐yr‐old stocks were also free of the pathogen. Copyright © 1979, Wiley Blackwell. All rights reserved