Analysis of Vermentino plants with symptoms of chlorotic mottling and leaf deformation disease by molecular test and fluorimetric indices

Grapevine Pinot gris virus (GPGV; genus Trichovirus) is a single-stranded, positive-sense RNA virus infecting grapevine and associated with stunting, chlorotic mottling and leaf deformation. Symptomatic (S) and asymptomatic (A) plants are usually identified by visual approach in the field, while the virus detection is carried out by molecular test (RT-PCR). To detect out infected plants with an early and non-destructive analysis, the use of fluorescence analysis by a proximal sensor was tested. Monitoring was performed in a Vermentino vineyard (Olmedo, Sardinia, Italy) Guyot trained to characterize GPGV disease symptoms. In the summer 2021, 50 leaves by respective plants were tested by RT-PCR (Invitrogen) and classified in two groups: 20 plants A and 30 S. The same leaves were tested by a fluorometric proximal sensor, Multiplex 3.6 (FORCE-A, Orsay, France) using these indices: Sample Fluorescence Ratio (SFR_RG), linked to chlorophyll content; FLAV, linked to flavonols content; FER_RG, correlated to anthocyanins content devoid of chlorophyll. These indices were analysed in a statistical software (RStudio) by analysis of variance (ANOVA). Statistical differences between the A and S plants were found using only the FER_RG index. It has been observed that this index is significantly higher in S plants, indicating a lower chlorophyll content than in the A plants. By performing the inverse of the FER_RG index (FER_RG^−1), the corresponding index relating to the content of chlorophyll was obtained, which identifies a higher index in asymptomatic plants than in symptomatic ones.