Technical Yearbook 2023

Three foliar treatments of LalVigne ProHydro™ were applied at the equivalent dose of 1 kg/ha at these phenological stages: fruit set (19 June), pea-size (3 July), and cluster closure (17 July). Control vines were treated with water only at the same time point. All the plants were kept under full irrigation conditions (90% of pot capacity) for up to three days after the last treatment (20 July), when half of the vines from each sample were subjected to water stress, keeping maximum water capacity at 40%. On 8 August (a few days before veraison), 90% of maximum water availability was restored for all plants until the end of the season. Photosynthesis (Pn), stomatal conductance (gs), water use efficiency (WUE), photochemical efficiency of PSII (Fv/Fm), and chlorophyll content (SPAD units), as well as quantitative and compositional parameters of the grapes at harvest (12 September), were recorded. Results The data that emerged show how treatment with LalVigne ProHydro™ was able to limit the effects of water and heat stress during the year. From a climatic perspective, the study was conducted in a period with maximum temperatures (T max) above 35°C for over 22 days (figure 3A-B). It can be seen that regardless of the water regime implemented, all the plants in the trial were subjected to significant thermal stress during the season. The physiological data and, in particular, photosynthesis data show how, in response to the first and second treatment with LalVigne ProHydro™, there was increased photosynthesis compared to the untreated control. These differences decreased when lower temperatures were recorded on 15 July (figure 3A-B). In the samples not subjected to water stress, after the third treatment, following seven consecutive days with T max above 35°C, treated vines showed better photosynthesis than control vines (figure 3A). In the same period, with vines subjected to water stress, the treated plants showed a higher level of photosynthesis than the control, respectively +48% on 25

July (five days from the beginning of water stress) and +21% on 1 August (12 days of stress) (figure 3B). When full water volumes were restored, the treated plants responded promptly with a fast and consistent recovery of Pn (+56%) and WUE (+40%), which returned to pre-stress levels, while the untreated plants never recovered full photosynthetic rates (figure 3B-D). This suggests that during the stress period, the treated plants did not suffer permanent or irreversible damage to the photosynthesis system, as shown by the photochemical efficiency data evaluated through the Fv/Fm fluorescence ratio (figure 4A). This parameter has a threshold value of 0.65, below which there is an irreversible loss of efficiency of chloroplast photosystem II, evident as leaf yellowing, chlorosis and necrosis (photo 2), the result of hydrogen peroxide and other phytotoxic molecules accumulation under severe stress conditions. The plants treated with LalVigne ProHydro™ maintained a higher photochemical efficiency than the control, staying above the threshold value of 0.65 for the entire trial. Conversely, the control vines fell below this value, triggering chronic photoinhibition processes. No photoinhibition phenomena occurred in the irrigated plants, either in the treated or control plants (data not shown). In addition to rapidly recovering photosynthetic efficiency after the period of stress, the treated vines maintained their foliar system in activity longer, ensuring good photosynthesis levels until harvest. This observation is also confirmed by the higher content of chlorophyll found in the treated vines both during the hottest days in the irrigated trials (data not reported) and in those subjected to water stress (figure 4B). The better physiological performance of the treated vines allowed a better allocation of dry matter and reduction of grape dehydration phenomena, as shown by the average weight of the berries and yield per vine, higher than the control, both in the irrigated and in the stressed vines (table 1). At the same time, treatment supported sugar accumulation and concentration of polyphenols in plants subject to water stress (table 2).

TABLE 1. Production parameters recorded at harvest. Treatment with LalVigne ProHydro™ avoided losses due to dehydration enabling better average berry weight both in situations of good water supply and in situations of concomitant thermal and water stress. Different letters indicate statistically significant differences between treatments (p < 0.05). Sangiovese Average cluster weight (g) Berry weight (g) Yield (kg/vine) Irrigated control 210 b 1.29 b 1.68 b Irrigated ProHydro™ 256 a 1.55 a 2.05 a Control water stress 205 b 1.14 c 1.40 c ProHydro™ water stress 236 ab 1.36 b 1.65 b Conclusions

the natural biosynthesis of endogenous proline in the leaves, which allows a higher level of cell turgor and avoids the biosynthesis of phytotoxic molecules, such as hydrogen peroxide and other reactive oxygen species.

LalVigne ProHydro™ is a new microbial derivative capable of ensuring greater photosynthesis and fostering a faster plant recovery in case of water stress. The treatment stimulates

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TECHNICAL YEARBOOK 2023