ENDOPHYTIC BACTERIA AS A BIOCONTROL AGENT AGAINST PHYTOPLASMA IN GRAPEVINES

Bacteria from the genus Phytoplasma pose a major threat to many agricultural crops including grapevine. The conventional application of chemical sprays for controlling phytoplasma and other phloem restricted pathogens is inefficient, and the role of endophytes in the induction of plant resistance against such pathogens as well as direct inhibition of Phytoplasma by endophytes has been suggested. However, in order to proceed towards practical application, such a candidate should be cultivable and able to penetrate and survive within the plant for a reasonable time. We hypothesized that since phytoplasma are transferred by phloem feeding insects, the vectors, as well as the host plants, may serve as reservoirs of potentially beneficial bacteria. Different bacteria were isolated from the insect on artificial agar. One of these isolates belonged to the bacterial family Xanthomonadaceae. This isolate was introduced to healthy and phytoplasma-infected plants (Chardonnay) and was detected in the grapevine phloem three weeks post inoculation. The presence of the isolate seems to affect the morphology of the infected plants but not the healthy ones. In some parameters, the effect of phytoplasma on plant morphology was markedly reduced. We further investigated this isolate and found it secreting substances that suppress Spiroplasma (a model pathogenic bacterium). The facts that the isolate inhabits the same location as phytoplasma and that it has the ability to secret antimicrobial substances makes it a good candidate for phytoplasma control in grapevine.