BIOLOGICAL CONTROL OF FIRE BLIGHT ON APPLE BLOSSOMS AND SHOOTS WITH EPIPHYTIC AND SOIL BACTERIA

The protective activity of four bacterial isolates originating from the apple phyllosphere (B90, 35M, 43M, 48M) and two isolates from the soil environment (L16, 3M) was evaluated on blossoms and shoots of greenhouse-grown apple trees. These isolates were selected from a collection of 151 isolates based on their ability to suppress fire blight on pear fruitlets. Their efficacy, evaluated on 9^th day after inoculation on 'Idared' blossoms, ranged from 53.8 to 73.0%. On the 11^th day the isolate 35M appeared to be the most effective (59.5%). It was slightly better than strains A506 and C9-1, which were used for comparison. On shoots of M.26 apple rootstock, the evaluation on the 17^th day after inoculation showed that the highest efficacy gave isolates 35M (96.8%), 48M (91.5%) and 43M (92.8%). On ‘Gala Must’ isolates L16 and 35M almost entirely protected shoots against infection. Detection of Erwinia amylovora in tissue surrounding visually healthy wounds on shoots protected with isolates 35M and L16 was performed using conventional and PCR-based methods. In the case of isolate 35M, the presence of the pathogen was confirmed in 4 of 15 samples only by PCR while in shoots treated with isolate L16, 7 of 11 examined samples contained fire blight bacterium and its population was high enough for detection using conventional methods. A co-culture experiment that paired the selected isolates with E. amylovora on five microbiological media (Nutrient Agar with sucrose, Nutrient Agar with glycerol, King B, LB and PYGA) showed that L16, 3M and 35M inhibited growth of the pathogen on almost all of media while 43M, 48M and B90 did not show such activity. It was also found that isolates 3M, 35M and 48M produced lactones of homoserine (AHL). Phenotypic characterization and molecular analysis allowed for classification of the isolate 35M to species Pseudomonas syringae, L16 to Pseudomonas fluorescens, 43M to Citrobacter farmeri, 48M and B90 to Pantoea agglomerans and 3M to Pseudomonas chlororaphis.