ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
MANIPULATION OF THE EPIPHYTIC MICROBIAL COMMUNITY TO PROMOTE BIOLOGICAL CONTROL OF ERWINIA AMYLOVORA ON PEAR AND APPLE |
| Author: | T. van der Zwet |
| Abstract:
Since 1987, the Appalachian Fruit Research Station has made a renewed effort to study several phases in the application of biological control of Erwinia amylovora. A variety of microorganisms have been isolated from leaves of six different types of natine West Virginia flora (blackberry, honeysuckle, wild grape, tree of heaven, honey locust, and virginia creeper). One of these organisms, recorded as Le-15, proved to be an excellent antagonist of E. amylovora in vitro and in vivo on green pear fruit. An agar plug technique was used to screen the epiphytic microorganisms for inhibitory action against E. amylovora on plates. After an incubation period of 72 hours at 25°C, the diameter of the clear zones surrounding the plugs was measured in mm. Immature pear fruits were used to test the prospect antagonists in a live tissue system. Small wells (7x7mm), cut into the side of the fruit, were filled with 25 μl of an antagonist suspension, followed 30 min later with 25 μl of 105 cfu/ml aqueous suspension of E. amylovora. In basic nutritional requirement studies of pathogen and antagonist, we recently demonstrated that the growth of Le-15 was enhanced significantly through the use of 2-deoxy-D-ribose to the medium, which compound had no measurable effect on E. amylovora. This sugar was one of 32 carbohydrates tested at 0.4%, 0.2% and 0.1%. Biolog micro plates, containing a selective basal medium, were used to grow the organisms. In the wells a tetrazolium blue dye is reduced to purple by the respiring cells. With a high degree of substrate oxidation, a larger light absorbance value was recorded. Using a microplate colorimetric absorbance recorder equipped with a 492 nm filter, all absorbances were recorded for the plates at time 0 hrs. After shaking at 400 rpm, the absorbance values were recorded again at 24 and 48 hrs. Sucrose was used as a control. Optimal utilization of all carbohydrate solutions occurred at the highest concentration (0.4%, suggesting that this concentration can be used as the starting concentration for in vivo trials. Additional antagonists and other nutritional sources are being investigated in the biological control of Fire Blight. | |
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