Frateuria defendens reduces yellows disease symptoms in grapevine under field conditions

Yellows diseases in grapevine, associated with the presence of different phytoplasmas, are a major problem for growers, with no environmentally friendly means of control. Frateuria defendens (Frd), a bacterium with endophytic traits, has been shown to reduce yellows symptoms in grapevine plantlets under laboratory conditions. The objective of this study was to test whether similar effects could be achieved under field conditions. A trial was conducted in a heavily infected vineyard in northern Israel for two consecutive years. A suspension of Frd cells (108·mL-1) was applied bi-weekly by foliar spray on grapevines from bud burst to leaf senescence. Frd penetrated the leaves during the growing period but not during leaf senescence and could be detected in the leaves by PCR analysis up to 14 days post-spraying. The rate of yellows infection was lower in the treated grapevines compared to its increase in untreated grapevines and the yield of symptomatic plants was improved by 10 to 20 %. Taken together, the results suggest Frd acted as a biological control agent in vineyards under the experimental conditions tested

Microbe Relationships with Phytoplasmas in Plants and Insects

The hosts of phytoplasmas, i.e. plants and insect vectors, are inhabited by diverse microorganisms having interactions spanning from mutualism to parasitism. When the pathogens colonize a host, they may thus be exposed to diverse interac- tions with complex microbial communities. These relations are still poorly recog- nized for phytoplasmas, even though many beneficial or harmful interactions have been described for other plant pathogens. The knowledge on traits of microbial relations involving phytoplasmas in insects and plants is regarded as a valuable tool for designing new control methods against the diseases associated with these patho- gens, by displaying direct antagonistic activities, altering the vector fitness or com- petence for transmission, or promoting plant immune response or growth. In insect vectors, which mainly host bacterial associates, with few yeast-like symbionts, direct interactions with phytoplasmas were described for bacteria of the genera Frauteria in Hyalesthes obsoletus and Asaia in Euscelidius variegatus. In plants, the most studied systems are grapevine, apple and coconut palm, along with model organisms such as Catharanthus roseus and in vitro micropropagated plants. Here, many bacteria, mainly of the genera Pseudomonas, Burkholderia and Paenibacillus, as well as the fungal endophyte Epicoccum nigrum, were shown to inhibit phyto- plasma growth and related symptoms in the plant hosts. Overall, the recent advances concerning the knowledge on microbial symbioses in phytoplasma plant and insect hosts can consistently support future research regarding the phytoplasma infection process, and eventually drive new control strategies against phytoplasma-associated diseases