Pseudomonas protegens MP12: A plant growth-promoting endophytic bacterium with broad-spectrum antifungal activity against grapevine phytopathogens.

Pseudomonas sp. MP12 was isolated from a soil sample collected in a typical warm-temperate deciduous forest near Brescia, Northern Italy. Phylogenetic analysis identified the species as Pseudomonas protegens. We evidenced in this strain the presence of the genes phlD, pltB and prnC responsible for the synthesis of the antifungal compounds 2,4-diacetylphloroglucinol (2,4-DAPG), pyoluteorin and pyrrolnitrin, respectively. P. protegens MP12 was also shown to produce siderophores and ammonia, yielded positive results with the indole-3-acetic acid test, and was capable of phosphate solubilization. Moreover, P. protegens MP12 exhibited inhibitory effects on in vitro mycelial growth of prominent grapevine (Vitis vinifera) phytopathogens such as Botrytis cinerea, Alternaria alternata, Aspergillus niger, Penicillium expansum and Neofusicoccum parvum. The strain showed activity even against Phaeomoniella chlamydospora and Phaeoacremonium aleophilum, which cause the devastating tracheomycosis/esca disease of grapevine trunks for which no efficacious control methods have been demonstrated so far. Furthermore, the MP12 strain manifested in vivo antifungal activity against B. cinerea on grapevine leaves. Culture-dependent and culture-independent analysis revealed the ability of P. protegens MP12 to efficiently and permanently colonize inner grapevine tissues. These results suggest that P. protegens MP12 could be worth of exploitation as an antifungal biocontrol agent for applications in viticulture.