Bacillus velezensis S26-loaded biochar boosts plant growth, alleviates copper stress and suppresses black foot disease in SO4 vine rootstock

Abstract

The excessive use of copper-based agrochemicals poses a serious concern to viticulture worldwide. As a consequence, vineyard soil can become contaminated, leading to reduced vine growth and increased susceptibility to soilborne pathogens. Black foot, caused by various pathogenic species, including Dactylonectria macrodidyma, is a fungal disease that impacts the trunk and roots of vines. Enhancing plant biomass and productivity can involve various strategies, such as utilizing beneficial bacteria immobilized in biochar. This study aimed to investigate the impact of applying biochars derived from grape bagasse and enriched with Bacillus velezensis S26 endospores on alleviating copper stress, controlling black foot disease, and promoting the growth of the vine rootstock SO4 (Vitis berlandieri × V. riparia). Initially, we assessed various methods for immobilizing bacterial endospores into fresh bagasse biochar (FBB) and composted bagasse biochar (CBB). Subsequently, the cell viability of incorporated B. velezensis S26 endospores was evaluated over a 180-day storage at 4 and 25 °C. Finally, a pot experiment was conducted using micropropagated SO4 plants to investigate the growth-promotion capacity and biocontrol potential of both biochar and biochar enriched with B. velezensis S26 endospores. Our findings revealed that refrigerated storage ensured the highest cell viability in CBB, while no statistically significant difference was observed among the evaluated treatments for FBB. The application of B. velezensis S26 endospores, FBB, and CBB, either as a single inoculation or combined treatments, resulted in increased plant growth measurements. In addition, both FBB and CBB enriched with B. velezensis S26 endospores enhanced the growth and biomass of SO4 rootstocks cultivated in substrates with high copper concentrations or inoculated with D. macrodidyma TD1110. Furthermore, the frequency of pathogen re-isolation decreased by 29 % and 31.5 % using fresh and composted grape bagasse biochars enriched with bacterial endospores, respectively. Therefore, the utilization of fresh and composted bagasse biochars not only contributed to improving rootstock development measurements and suppressing the effects of D. macrodidyma TD1110 in SO4 vine rootstocks but also to waste valorization and a more sustainable agriculture.