The Use of Mannans as a Sustainable Approach to Activate Vitis vinifera Innate Immunity in Response to Fungi Causing Grapevine Trunk Diseases (GTD)

Grapevine Trunk Diseases (GTDs) are caused by a wide variety of phytopathogenic fungal species that compromise grapevine productivity and wine quality. Each year they lead to major economic losses. Most GTD treatments currently available on the market are chemical-based and environ-mentally harmful. Given that one of the goals proposed by the European Green Deal is to develop sustainable agriculture which does not harm the environment, reduces pesticide use, and pro-motes rural area economies, an alternative to those treatments may be the use of elicitors such as oligosaccharides from fungal organisms. Indeed, many studies have confirmed that oligosaccha-rides play important roles in activating plants' innate immunity. Mannans are one possible type of such oligosaccharides. The present work analysed Vitis vinifera L. (cv. Tempranillo and cv. Airén) leaves and grapes to evaluate their physiological and molecular response to GTDs and how this response might be conditioned using different concentrations of mannans as elicitors. It was found that mannan addition to diseased vines was more positive for the leaves than for the grapes. In general, mannans increased the expression levels of chalcone synthase (CHS1, CHS3), phenylalanine ammonia lyase (PAL), superoxide dismutase (SOD), and polyphenol oxidase (PPO) in healthy leaves of both varieties. In diseased leaves, CHS3 and PAL decreased in both varieties, while CHS1 and PPO increased in Tempranillo but not in Airén. In the grapes, the expression pat-terns of the genes studied varied greatly due to the development of the disease. The mannan treatment seemed to reduce the oxidative stress caused by GTDs, although this response depend-ed on the variety and on the plant's phytosanitary status.