Michela Centinari

Shifts in xylem vessel diameter and embolisms in grafted apple trees of differing rootstock growth potential in response to drought

We investigated responses of plant growth rate, hydraulic resistance, and xylem cavitation in scion-rootstock-combinations of Malus domestica L. cv. Honeycrisp scions grafted onto a high-shoot vigor (HSV) rootstock, (semi-dwarfing Malling111), or onto a low-shoot vigor (LSV) rootstock, (dwarfing Budagovsky 9), in response to substrate moisture limitation. Adjustments in xylem vessel diameter and frequency were related to hydraulic resistance measurements for high- versus low- vigor apple trees. We observed a greater tolerance to water deficit in the high-shoot compared to the low-shoot vigor plants under water deficit as evidenced by increased growth in several plant organs, and greater scion anatomical response to limited water availability with ca. 25% increased vessel frequency and ca. 28% narrower current season xylem ring width. Whereas water limitation resulted in greater graft union hydraulic resistance of high-shoot vigor trees, the opposite was true when water was not limiting. The graft union of the low-shoot vigor rootstock exhibited higher hydraulic resistance under well-watered conditions. Scions of high-shoot vigor rootstocks had fewer embolisms at low plant water status compared to scions of low-shoot vigor rootstocks, presumably as a result of large differences in xylem vessel diameter. Our results demonstrated that anatomical differences were related to shifts in hydraulic conductivity and cavitation events, a direct result of grafting, under limited soil water.

Cover crop water use in relation to vineyard floor management practices

The aim of our study was to compare soil evaporation (Es) versus cover crop (Festuca arundinacea var. barfelix) evapotranspiration (ETcc) within a vineyard ecosystem and to investigate the effect of mowing in reducing cover crop evapotranspiration, and, hence, its below-ground competitiveness. The study was carried out in a 2-year-old Sangiovese (Vitis vinifera L.) vineyard, grafted to SO4, in Bologna, Italy. Mini-lysimeters and a portable gas-exchange chamber system were used to investigate cover crop evapotranspiration in relation to mowing and bare soil management practices. Our results show that, immediately after mowing, ETcc markedly decreased, with the percentage of reduction ranging from 35 to 49%, depending on the amount of clipped biomass. The extent of the ETcc reduction decreased over time as the cover crop regrew. Over the 28-day period following the mowing, soil evaporation was 35 and 48% lower than mowed and unmowed cover crop evapotranspiration, respectively. This study shows that mowing could be used as a water management strategy to decrease vine cover crop competition over a short time period.

Impact of Amigo Oil and KDL on Grapevine Postbudburst Freeze Damage, Yield Components, and Fruit and Wine Composition

Field studies were conducted in 2014 and 2015 on Vitis vinifera cvs. Lemberger and Riesling and on interspecific hybrid cvs. Noiret and Traminette to evaluate the effectiveness of two sprayable products for reducing postbudburst freeze damage without impacting grape production, fruit composition, wine chemistry, or sensory perception. The treatments consisted of a) one application of a vegetable oil-based adjuvant (Amigo) during the dormant season to delay budburst and reduce the chance of frost damage; and b) application of a potassium fertilizer (KDL) within 24 hrs before a predicted frost event to increase plant freeze resistance. Amigo oil application significantly delayed budburst in Lemberger and Riesling in both years (six to 11 days), but the delay was less pronounced in Noiret and Traminette (two to four days). A frost event (minimum temperature −3°C) occurred in late spring 2015 in the Noiret and Traminette vineyard. At that time, the percentage of buds that had reached budburst was no longer lower in the Amigo oil-treated vines than other treatments. Neither Amigo oil nor KDL reduced freeze damage and crop loss in the hybrid cultivars. The lower osmotic potential of Noiret KDL-treated leaves compared to the control did not translate into increased freeze resistance under our experimental conditions. The delay in budburst in Amigo oil-treated vines did not impact fruit composition at harvest in any of the cultivars tested or the sensory perception of Riesling wines. Amigo oil applied at 10% concentration caused, however, phytotoxic effects (i.e., reduced cluster weight and bud survival). Further studies are needed before Amigo oil can be recommended as a frost-avoidance strategy.

Impact of Fruit-Zone Leaf Removal on Rotundone Concentration in Noiret

Rotundone was recently identified as the compound that imparts the black pepper aroma in several winegrape cultivars. This two-year study aimed to identify the presence of rotundone in Noiret (interspecific hybrid of Vitis) and to determine the impact of fruit-zone leaf removal on rotundone concentrations in fruit and wine. The relationship between the intensity of black pepper aroma and rotundone concentration in Noiret wine was also explored. An undefoliated control (CON) was compared to a maintained fruit-zone sunlight exposure (MSE) treatment, where leaves were periodically removed from the fruit-zone. The influence of timing of fruit-zone leaf removal was assessed in a separate experiment by comparing preveraison leaf removal (LR) and postveraison leaf removal (PVLR) treatments. MSE vines had greater fruit-zone sunlight exposure compared to the CON throughout the season in 2015, both at the pre- and postveraison stages, but in 2014, only after veraison. PVLR increased fruit-zone sunlight exposure during ripening compared to LR in 2015 only. Rotundone could not be quantified in Noiret berries sampled before or at veraison (limit of quantitation = 0.16 μg/kg). Rotundone concentrations in harvested fruit and wines did not differ between treatments in 2014, but were significantly higher in MSE than in CON in 2015 (1.98 versus 1.28 μg/kg). PVLR temporarily increased rotundone concentration compared to LR, but differences disappeared by harvest. Black pepper aroma intensity, as determined by a sensory panel, was positively correlated (p = 0.023, r = 0.791) with rotundone concentration in wines made from imposed viticulture treatments, providing evidence that black pepper notes in Noiret are positively related to concentration of rotundone in the wine.