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

Incidence of 'Candidatus Liberibacter europaeus' and phytoplasmas in Cacopsylla species (Hemiptera: Psyllidae) and their host/shelter plants

Psyllids, as vectors of phloem-restricted plant pathogens, are serious agricultural pests. Fruit tree phytoplasmas are transmitted by different Cacopsylla spp., while other psyllids are known vectors of liberibacters. Recently, the bacterium \u2018Candidatus Liberibacter europaeus\u2019 was found in pear trees and in Cacopsylla pyri (Linnaeus), the vector of \u2018Ca. Phytoplasma pyri\u2019. This new species does not cause symptoms in plants and is probably a symbiont rather than a pathogen. Based on these findings and the assumption that \u2018Ca. Liberibacter europaeus\u2019 is widespread, we studied its distribution in the genus Cacopsylla and in the respective host and shelter plants (where psyllids aestivate and overwinter), as well as its possible copresence with \u2018Ca. Phytoplasma\u2019 spp. We tested 14 Cacopsylla species and 11 plant species from northwestern Italy, Hungary and Israel, characterized by warm oceanic, temperate continental and warm Mediterranean climatic conditions, respectively. \u2018Ca. Liberibacter europaeus\u2019 was common within the Cacopsylla genus, being present in nine of the 14 species screened as well as in most host plants, whereas none of the shelter plants tested positive for this bacterium. Altogether, these findings indicate the presence of \u2018Ca. Liberibacter europaeus\u2019 in continental zones, whereas it does not seem to be widespread in the Mediterranean region. Furthermore, lack of specific symptoms in all infected plants confirms an endophytic relationship with this bacterium, while its abundance in insects suggests a beneficial role for the host. Co-infections with phytoplasmas, observed in insects and plants, require further study to evaluate the possible interactions between them