Control of bacterial spot on tomato in the greenhouse and field with h-mutant bacteriophages

A mixture of host-range mutant (h-mutant) bacteriophages specific for tomato race 1 (T1) and race 3 (T3) of the bacterial spot pathogen, Xanthomonas campestris pv, vesicatoria (Doidge) Dye was evaluated for biological control of bacterial spot on 'Sunbeam' tomato (Lycopersicon esculentum Mill.) transplants and field-grown plants for two seasons (Fall 1997 and Fall 1998), Foliar applications of bacteriophages were compared with similar applications of water (control) and of copper/mancozeb bactericides, the commonly used chemical control strategy for tomato seedling and field production. In 1997, the incidence of bacterial spot on greenhouse-grown seedlings was reduced from 40.5% (control) to 5.5% or 0.9% for bactericide- or bacteriophage-treated plants, respectively. In 1998, the incidence of bacterial spot was 17.4 % on control plants vs. 5.5 % and 2.7% for bactericide- and bacteriophage-treated plants, respectively, although these differences were not statistically significant at P less than or equal to 0.05, Applications of bacteriophages to field-grown tomatoes decreased disease severity as measured by the area under the disease progress curve (AUDPC) by 17.5% (1997) and 16.8% (1998) compared with untreated control plants. Preharvest plant vigor ratings, taken twice during each field season, were higher in the bacteriophage-treated plants than in either bactericide-treated plants or nontreated controls except for the early vigor rating in 1998, Use of bacteriophages increased total weight of extra-large fruit 14.9 % (1997) and 24.2 % (1998) relative to that of nontreated control plants, and 37.8 % (1997) and 23.9 % (1998) relative to that of plants treated with the chemical bactericides. Chemical names used: manganese, zinc, carboxy-ethylene bis dithiocarbamate (mancozeb).