Studies on bacterial canker of tomato caused by Corynebacterium michiganense

Abstract

In initial studies the symptoms of the disease bacterial canker of tomato caused by Corynebacterium michiganense were followed, and methods of inoculation were assessed. The morphological and physiological characters of c. michiganense isolations were studied and a modified selective medium was developed. Transmission of the disease by artificially-infected seeds varied depending on the conditions of the experiment. The number of diseased plants were less than the plants with 'resident phase' of C. michiganense. The disease is disseminated by infected debris and through commercial practices (handling diseased plants, using contaminated knives) but not with insects. The survival of c. michiganense in water varied but cells in high concentration, low temperature and anaerobic conditions survived more than one year. The pathogen survived at least 20 days on tomato leaves without symptoms; survival depended on relative humidity.The disease ratings were higher in succulent tissue of young plants, young parts of mature plants and in plants grown in light soils with excess fertiliser. The pathogen can cause hypersensitive reaction (HR) in tobacco leaves similar to one caused by pseudoraonads as the external and ultra-structural changes showed. The ultrastructural changes of tomato leaves infiltrated with saprophyte Pseudomonas aeruginosa, heterologous P. syringae and homologous c. michiganense were followed and compared. The development of foliage spots was followed by scanning electron microscopy. Studying the development of C. michiganense and other selected heterologous and saprophytic bacteria it was found that only C. michiganense multiplied from low inocula to high final populations. Some saprophytes could inhibit homologous and heterologous bacteria if they were inoculated earlier and in a ratio of 10:1 or higher. No host more sensitive than tomato was found. One infected seed in2000 or more could be detected by leaf infiltration techniques and a 10-4 pathogen cells ml-1 by using fluorescent substrate(3-0-methylfluorescein) in ELISA double antibody sandwich method.