Grape Ripening Is Regulated by Deficit Irrigation/Elevated Temperatures According to Cluster Position in the Canopy

Abstract

The impact of water deficit on berry quality has been extensively investigated during the last decades. Nonetheless, there is a scarcity of knowledge on the performance of varieties exposed to a combination of high temperatures/water stress during the growing season and under vineyard conditions. The objective of this research was to investigate the effects of two irrigation regimes, sustained deficit irrigation (SDI, 30% ETc) and regulated deficit irrigation (RDI, 15% ETc) and of two cluster positions within the canopy (east- and west-exposed sides) on berry ripening in red Aragonez (Tempranillo) grapevines. The study was undertaken for two successive years in a commercial vineyard in South Portugal, monitoring the following parameters: pre-dawn leaf water potential, berry temperature, sugars, polyphenols, abscisic acid (ABA) and related metabolites. Additionally, expression patterns for different transcripts encoding for enzymes responsible for anthocyanin and ABA biosynthesis (VviUFGT, VvNCED1, VvβG1, VviHyd1, VviHyd2) were analyzed. In both years anthocyanin concentration was lower in RDI at the west side (RDIW- the hottest one) from véraison onwards, suggesting that the most severe water stress conditions exacerbated the negative impact of high temperature on anthocyanin. The down-regulation of VviUFGT expression revealed a repression of the anthocyanin synthesis in berries of RDIW, at early stages of berry ripening. At full-maturation, anthocyanin degradation products were detected, being highest at RDIW. This suggests that the negative impact of water stress and high temperature on anthocyanins results from the repression of biosynthesis at the onset of ripening and from degradation at later stages. On the other hand, berries grown under SDI displayed a higher content in phenolics than those under RDI, pointing out for the attenuation of the negative temperature effects under SDI. Irrigation regime and berry position had small effect on free-ABA concentration. However, ABA catabolism/conjugation process and ABA biosynthetic pathway were affected by water and heat stresses. This indicates the role of ABA-GE and catabolites in berry ABA homeostasis under abiotic stresses. Principal component analysis (PCA) showed that the strongest influence in berry ripening is the deficit irrigation regime, while temperature is an important variable determining the improvement or impairment of berry quality by the deficit irrigation regime. In summary, this work shows the interaction between irrigation regime and high temperature on the control of berry ripening.

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“…The plot C) shows the averaged effect of canopy side (East vs West) on anthocyanin accumulation in the grape berry skin of exposed clusters The bars with different letter suffixes indicate significant differences (p<0.05). Adapted from [21]). …”

“…The experimental layout is a randomized complete block design with two irrigation treatments (Sustainable Deficit Irrigation (SDI -control; ~30% ETc) and Regulated Deficit Irrigation (RDI; ~15% ETc), and 4 replications per treatment. For more details check [21,26]. Soil and plant assessments were similar in the two experiments.…”

“…However, when comparing the maximum berry temperature per irrigation treatment, berries from west exposed clusters presented maximum temperatures 5 to 8 ºC and 2.5 to 9 ºC higher than those from east exposed clusters in SDI and RDI treatments, respectively. Consequently the berries from west exposed clusters accumulated a higher number of hours of temperature above 35ºC than berries from east exposed clusters [21]. Figure 6B presents an example of the daily evolution of exposed berries temperature during three hot days of the ripening period for RDI treatment, showing that from mid-morning to mid-afternoon the temperature of exposed berries (East and West) was above 35ºC and that the highest temperatures were attained at the west exposed berries during the afternoon.…”

“…Berry temperature was also assessed with thermocouples installed in different cluster positions within the canopy and then related to berry composition (for more detailed data see [21]). Using berry temperature from berry pea-size to full maturation, the work of [21] showed that irrigation treatment has a slight effect on the temperature of berries from clusters at similar exposure.…”

“…Using berry temperature from berry pea-size to full maturation, the work of [21] showed that irrigation treatment has a slight effect on the temperature of berries from clusters at similar exposure. However, when comparing the maximum berry temperature per irrigation treatment, berries from west exposed clusters presented maximum temperatures 5 to 8 ºC and 2.5 to 9 ºC higher than those from east exposed clusters in SDI and RDI treatments, respectively.…”