IMPACT OF NEW BIO STIMULANTS ON GRAPE SECONDARY METABOLITES UNDER CLIMATE CHANGE CONDITIONS

Abstract

In a context of climate change and excessive use of agrochemical products, sustainable approaches for environmental and human health such as the use of bio stimulants in viticulture represent a potential option, against abiotic and biotic threats. Bio stimulants are organic compounds, microbes, or a combination of both, that stimulate plant’s vital processes, allowing high yields and good quality products. In vines, may trigger an innate immune response leading to the synthesis of secondary metabolites, key compounds for the organoleptic properties of grapes and wines. During this research the prospect of foliar application of bio stimulants to improve the aromatic and polyphenolic potential of the grapes was investigated in two consecutive years, characterized by hot and dry summers. Two different products, prepared with specific fractions of inactivated yeasts, were compared, and applied in different points during veraison with two- or three-time application protocol. The experiment involved two cultivars cultivated in Tuscany, a white (Vermentino) and a red one (Sangiovese). Quali-quantitative determination of the aromatic composition of the grapes was carried out using GC-MS, whereas polyphenols in skins and seeds were analyzed by spectrophotometry and HPLC methods. The bio stimulants did not affect the vine yield, but higher berry weight and reduced sugar contents were noted at harvest in the grapes from treated with respect to the control vines. All treatments enhanced polyphenolic potential in berry skins of red grapes, whereas modifications on anthocyanins percentages and reduction of flavonols were also observed, suggesting a protective effect of the treatments against solar radiation stress. Moreover, grapes from treated vines differ significantly for the lower content of polyphenolic compounds in their seeds. As regards aroma precursors, three-time application triggered significantly higher contents for almost all chemical classes of aromatic precursors for Vermentino whereas all treatments enhanced the accumulation of terpenoids and benzenoids in the berries of San-giovese. Bio stimulants thus, improved the qualitative parameters of the grapes, but their effect was different based on the frequency and the timing of the application, the chemical class of the compounds and the cultivar examined. Further future investigation is necessary to optimize bio stimulant application to contrast stress conditions and improve grape quality.