Enhancement of Populus alba tolerance to Venturia tremulae upon inoculation with endophytes showing in vitro biocontrol potential

Abstract

Several studies have provided evidence that endophytes of forest trees can provide the trees with protection against pests and pathogens, but more experimental evidence is still needed to better understand if endophytes could be utilized in biocontrol of forest diseases. Here, we tested the hypothesis that fungal endophytes of Populus alba L. contribute to tree tolerance to Venturia tremulae Aderh., causal agent of shoot dieback in trees within Populus section. Fungal endophytes were isolated from twigs of two healthy P. alba trees, and classified according to their morphology and ITS sequence. Pleosporales, Dothideales and Eurotiales were the main fungal orders represented. Twelve isolates were challenged by the pathogen in in vitro dual assays and 10 of them reduced the growth rate of the pathogen. A mixed cell suspension from these endophytes was applied as a preventive treatment to P. alba seedlings growing in the greenhouse with the exception of positive control plants. Fifteen days later, plants were treated with a V. tremulae spore suspension. An additional control group of Populus x canescens (Aiton) Sm. seedlings were also inoculated with V. tremulae. Although the overall incidence of symptoms was low, both the incidence and severity of damages were lower in P. alba plants pretreated with endophytes than in controls (43.18 and 12.16% of incidence and severity reduction, respectively). Incidence of symptoms was higher in P. x canescens than in P. alba seedlings, evidencing the higher tolerance of P. alba to Venturia shoot blight. The results suggest that P. alba endophyte community may reinforce the host’s tolerance to the pathogen.