Failures count too: effect of the application of commercial inoculum of arbuscular fungi in a vineyard during its plantation

Symbiosis with arbuscular mycorrhizal fungi (AMF) has long been recognized for its positive impact on plant health. Today, various companies market AMF-based commercial inoculants as biofertilizers or biostimulants for sustainable agriculture. However, their consistent efficacy in real-world field settings remains uncertain. This study investigated the influence of a commercial AMF inoculant on a newly planted vineyard featuring a local grape cultivar grafted onto a common rootstock (‘Ritcher 110’). Over two years, the physiological well-being, growth, and productivity of 20 inoculated vines compared to 20 control counterparts were monitored. The impact of inoculation on soil bacterial diversity and the infectivity of soil was assessed. Notably, AMF-inoculated plants exhibited consistently lower values in photosynthesis, growth, and grape production, although statistical significance was not always reached. Additionally, the total production remained unaffected, but there was a significant decrease in °Brix and pH values, suggesting delayed grape ripening in mycorrhizal plants, potentially promoting secondary metabolites accumulation. Regarding soil effects, the inoculation's impact was slight, with no substantial changes in soil mycorrhizal infectivity and only slight shifts in the microbial community's metabolic profile. Numerous studies highlight the context-dependent nature of AMF inoculation's effects, making it challenging to predict outcomes in field conditions. Failures found in trials like the present one provides valuable scientific information, contributing to determine the prerequisites for effective biofertilizer use in commercial viticulture. Ultimately, the effectiveness of AMF-based biofertilizers remains contingent on specific conditions, exposing the need for additional research to ensure their consistent and reliable application.