Fire Blight Disease

The fire blight bacterium, named Erwinia amylovora, was the first to be associated with a plant disease in 1878 when growers noted a problem on their pears.  To this day, pears still cannot be grown in some regions in California because the environment is too conducive for the disease. It is a pathogen well adapted to attack plants.  It can invade through natural openings such as nectarthodes in flowers and sometimes the pores of young leaves called hydathodes.  The bacterium is disseminated in many ways ranging from rain splashing the bacteria around, by bees and other flower-visiting insects, and by threads of bacterial ooze that float in the wind. Once it is deposited on a plant, it like many bacteria have a sensory system that detects nutrients from the plants and then seek out the natural openings.  They use their flagella to propel themselves when moisture is present. The importance of flagella in the infection process was proven using motile and non-motile bacterial mutants in experiments.  The number of lesions cause by motile bacteria was up to 12 times more than those from non-motile counterparts.

After infection, the disease travels into stems and then to major branches. Although the bacteria overwinter in cankers, the bacteria may die off for unknown reasons but there always is a source somewhere on the tree or another nearby plant such as the common pyracantha.

The control methods for this disease are available in the fire blight narrative.  It includes non-chemical methods but the use of non-pathogenic bacteria as a bio-control was not included even though field tests were quite promising for two years. But on the third year, there was a serious outbreak of  the disease and the chemicals were far better. Schroth, the major researcher, at that time was not able to continue that line of research for lack of funds. This approach is now used by some growers to spray the flowers and especially those that grow organic fruit.

Panopoulos, and M. N. Schroth.  Role of flagella motility in the invasion of bean leaves by Pseudomonas phaseolicola.  Phytopathology, Vol. 64. 1974.

Thomson, S. V., M. N. Schroth, W. J. Moller, and W. O. Reil.  Efficacy of bactericides and saprophytic bacteria in reducing colonization and infection of pear flowers by Erwinia amylovora.  Phytopathology 66: 1457-1459. 1976.