Bacterial Spot Susceptibility in Low Chilling Peaches

Abstract

Bacterial spot caused by Xanthomonas pruni(E. F. Sm.) Dows. is a major disease of peach in the more temperate regions of the Eastern United States. Breeding for resistance has been a goal in improvement programs and many new peach and nectarine cultivars have relatively high levels of resistance. Bacterial spot is common in peach growing areas of central Georgia, much less common in North Florida and until 1979 had not been observed in North-central Florida. It was mistakenly thought that the bacterium was not adapted to the North-central Florida climate but it now appears that the breeding program (about 30 years) and industry (about 15 years) were not old enough for the bacteria to have time to establish itself. However, it is conceivable that new strains of the bacteria have developed which are now adapted to lower and warmer latitudes. Finally, it may be environmental conditions have recently been unusually favorable for development of the disease, especially in 1979-80. If this is the case, a remission in bacterial spot would be expected in the following years. Seven selections and cultivars became seriously affected in 1979 in the variety test orchard of the University of Florida at Gainesville. A major outbreak of bacterial spot occurred in the same orchard in 1980 and an evaluation of susceptible and resistant germplasm was made.