Impact of Japanese beetles (Popillia japonica Newman) on the chemical composition of two grape varieties grown in Italy (Nebbiolo and Erbaluce)

Abstract

The Japanese beetle, Popillia japonica Newman, is considered one of the most harmful organisms due to its ability to feed on more than 300 plant species. Symptoms indicative of adult beetles include feeding holes in host plants extending to skeletonization of leaves when population numbers are high. The vine is one of the species most affected by this beetle. However, the damaged plants, even if with difficulty, manage to recover, bringing the bunches of grapes to ripeness.

The idea of this study was to chemically characterize both grapes produced from healthy plants and those obtained from damaged plants. The purpose was to highlight how the plant was able to respond positively or negatively after its leaf surface has been heavily damaged by the beetle.

Nebbiolo (red) and Erbaluce (white) are the V. vinifera L. cultivars selected for this study. These were harvested in three different sampling points, during the last phase of berry development (vintage 2020) from the vineyard located in the Northern part of Piedmont Region. Samples collection was conducted on August 26th, September 3rd and September 9th, including both healthy and popillia-affected samples.
Both the phenolic and aromatic components were characterized in the samples for 93 analytical variables (58 VOCs, 22 phenolics, 13 anthocyanins) whose information has been subjected to statistical analysis.

To further understand the different between healthy and affected state, a PLS-DA model was built. A clear separation was observed between affected and healthy grapes independently of grape variety. From the data set used, 10 phenolics were identified with VIP score higher than 1.5, namely protocatechuic acid-O-hexoside, protocatechuic acid, hydroxy-caffeic acid dimer isomer 1, (E)-coutaric acid, (Z)-fertaric acid, procyanidin dimer, catechin, epicatechin, quercetin-3-O-glucuronide, and quercetin, which are the most significant analytes to explain the discrimination between affected and healthy grapes.