Influence of pre-harvest elicitors treatment during ripening period on phenolic composition in Monastrell grapes

Abstract

Phenolic compounds are very importants in crop plants, which is why there have been the subject of a large number of studies. There are three main reasons for optimising the level of phenolic compounds in crop plants: their physiological role in the plants, their technological significance for food processing, and their nutritional characteristics. 

Several techniques have been applied to improve the phenolic content of grapes. One such strategy developed in recent years is to apply elicitors, molecules that are able to trigger plant defence responses, thus contributing to plant resistance against pathogen attacks, and to activate secondary pathways, resulting in the accumulation of phenolic and aromatic compounds. In agricultural practice, elicitor treatment may represent an effective alternative to conventional agrochemicals [1]. 

In recent years, elicitor treatments of several grape varieties and consequent modifications in the corresponding grape and wine composition have been reported. For example, the pre-harvest application of BTH to Monastrell grapes led to increase levels of phenolic compounds in the treated grapes and the corresponding wines. [1]. It can be said that elicitation is a good strategy for inducing the synthesis of different classes of bioactive secondary metabolites, although the efficacy of such treatment mainly depends on individual plant genetics, the nature of the elicitor and the dose used. 

Our research group has focused its interest on the effect of the pre-harvest application (at veraison) of two elicitors: benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) and methyl jasmonate (MeJ), and a mixture of both on the phenolic composition during ripening period in two consequtives seasons (2016 and 2017); in order to be assessed whether veraison is the best moment for applying the elicitor or whether the application date could be optimised to obtain a maximum phenolic contents at harvest. 

The results were differents in function of the year study, obtaining higher concentrations of phenolic compounds in 2016 compared to 2017. On the other hand, the treatments showed higher results in all phenolic compounds studied excepted in the stilbenes when there were compared to the control grapes. Finally, some of the phenolic compounds analyzed obtained higher concentrations before harvest date. Therefore, our future objective will be to optimise the moment of elicitor application in order to obtain their maximum effect at the moment of harvest, probably by delaying the application until some weeks after veraison. 

[1] Ruiz-García, Y. et al. Journal of Agricultural and Food Chemistry, 2012, 60, 1283.