Greer, D. H.

Rogiers, S. Y.

Steel, C. C.

English

JKI Open Journal Systems (Julius Kühn-Institut)

Vitis 45 (3), 147–148 (2006)sunburn (category 1-2) was assessed as lesions <5 mm diameter and light brown; moderate sunburn (category 3) <6 mm diameter and mid-intensity brown and severe sun-burn (category 4-5) as >6 mm diameter and dark brown in colour. The number of berries in each category was then counted.Berries with different sunburn categories were col-lected and a slice of skin (6 mm diameter) cut from the sunburn lesion of two berries from each category. The slice was attached to a brass stub, frozen at -170 oC on the cold stage of a scanning electron microscope (JEOL Australasia, Sydney, Australia). The appearance of epicuticular waxes covering the sunburn lesion was assessed microscopically from the scanning images.Data analyses were carried out using general linear models with SAS 9.1 (SAS Institute, Cary NC) and means and standard errors calculated.Results and Discussion: Sunburn of Chardonnay grapes was characterized by brown lesions that increased in size and depth of colour with increasing severity. The most severe lesions were probably associated with cell death in the epidermal layers of the skin. Well-exposed bunches in one year had up to 35 % of berries per bunch with sunburn of symptoms of varying severity while shad-ed bunches had less than 1 % with sunburn. In the second year, 22 % (43/197 kg) of the overall crop had moderate to severe sunburn. These results conform with high extents of sunburn reported anecdotally for grapes in Australia but in keeping with estimates for other crops (WÜNSCHE et al. 2001, MELGAREJO et al. 2004). Variation in sunburn between the two years could relate to differences in maxi-mum temperatures prior to harvest which on average were 40.8 oC (2003) compared with 30.8 oC (2004) while net radiation ranged between13.8 MJ m-2 d-1 and 15.5 MJ m-2 d-1. These results support the conclusion of BERGQVIST et al. (2001) that effects of radiation on grapes are highly tem-perature-dependent.Berry chlorophyll fluorescence changed little early in the season (Fig. 1) although Fm’ of sun-exposed berries was significantly lower than in shaded berries. However, shortly after veraison, there was a marked decline, notably in Fm’, and thereafter fluorescence from the Chardonnay berries became negligible in both shaded and sun-exposed bunches. Similar results occurred in dark-acclimated and sun-exposed berries of the cv. Kerner (DÜRING and DAV-TYAN 2002), i.e. a sharp decline occurred after veraison. This may relate to decreases in chlorophyll concentration occurring shortly after ripening commenced (HARDIE et al. 1996), especially as the fluorescence decline coincided in shaded and sun-exposed berries.There was a curvilinear relationship between chloro-phyll fluorescence and the severity of sunburn in Chardon-nay berries as shown elsewhere (WÜNSCHE et al. 2001). The highest fluorescence occurred on grapes with no sunburn and decreased mostly between control berries and those with slight to moderately severe sunburn. With more se-vere sunburn, fluorescence became relatively steady at about 30 % of that for control berries. The tightest rela-tionship between sunburn and fluorescence occurred with Research NoteSusceptibility of Chardonnay grapes to sunburnD. H. GREER, S. Y. ROGIERS and C. C. STEELNational Wine and Grape Industry Centre, Charles Sturt University, Wagga Wagga, AustraliaK e y   w o r d s :  Chlorophyll fluorescence, epicuticular waxes, sunburn.Introduction: Fruit of many horticulturally important crops (MA and CHENG 2004) including some grape varie-ties (SPAYD et al. 2002) are susceptible to high-light, high-temperature-induced sunburn. This is characterized by pigment changes in the skin that result in yellow, bronze or brown lesions (SCHRADER et al. 2003), often associat-ed with loss of chlorophyll (MERZLYACK et al. 2002). For grapes in commercial production areas of Australia, little is known about the incidence of sunburn. Anecdotal evidence suggests 5-15% of grapes are affected as a consequence of high summer temperatures.Recently, WÜNSCHE et al. (2001) demonstrated that chlorophyll fluorescence from fruit declined in concert with increasing severity of sunburn. Chlorophyll fluores-cence could, therefore, serve as a useful probe for sunburn on other fruit such as grapes, especially as it is more objec-tive than visual assessment of sunburn.Thus, the objectives of the study were to assess the incidence and severity of sunburn in Chardonnay grapes and to assess chlorophyll fluorescence as a tool to quantify sunburn in grapes.Material and Methods: The study was carried in 2003 and 2004 at the Charles Sturt University Vineyard in Wagga Wagga, NSW, Australia, using Chardonnay grapes. Three vines were allocated to two treatments; control vines where bunches were shaded and exposed vines where bunches were well sunlit throughout the growing season. Ten bunches in each were selected for study. When the berries were 5 mm diameter, chlorophyll fluorescence was measured in situ on two berries of each bunch. Measurements were repeated at approximately 15-d-intervals until harvest. Fluorescence (OS1-FL, Opti-sciences, Tyngsboro, USA) was measured at about 1500 µmol m-2 s-1 irradiance. The fibre-optic probe covered the sunburn lesion on each berry. Steady-state fluorescence, Ft was recorded and then a saturating flash (4000 µmol m-2 s-1 for 0.8 s) applied to determine maximum fluorescence, Fm’. Fluorescence yield was determined as (Fm’ - Ft) / Fm’. At harvest, grapes were sorted into 6 categories of sun-burn, based on size of lesion and depth of browning; slight Correspondence to: Dr. D. H. GREER, National Wine and Grape Industry Centre, Charles Sturt University, Locked Bag 588, Wag-ga Wagga, NSW 2678, Australia. Fax: +2-6933-2107. E-mail: DGreer@csu.edu.au148 D. H. GREER et al.This project was funded by a Charles Sturt University Com-petitive Grant for which we are most grateful. D. LA BORDE and N. DIMOS assisted with measurements. SAS Australia generously donated SAS 9.1 Academic Analysis Suite to the senior author to undertake the data analysis. BERGQVIST, J.; DOKOOZLIAN, N.; EBISUDA, N.; 2001: Sunlight exposure and temperature effects on berry growth and composition of Cabernet Sauvignon and Grenache in the Central San Joaquin Valley of Cali-fornia. Am. J. Enol. Vitic. 52, 1-7.DÜRING, H.; DAVTYAN, A.; 2002: Developmental changes of primary proc-esses of photosynthesis in sun- and shade-adapted berries of two grapevine cultivars. Vitis 41, 63-67.HARDIE, W. J.; AGGENBACH, S. J.; JAUDZEMS, V. G.; 1996: The plastid of the grape pericarp and their significance in isoprenoid synthesis. Aust. J. Grape Wine Res. 2, 144-154.MA, F.; CHENG, L.; 2004: Exposure of the shaded side of apple fruit to full sun leads to up-regulation of both the xanthophyll cycle and the ascorbate-glutathione cycle. Plant Sci. 166, 1479-1486.MELGAREJO, P.; MARTÍNEZ, J. J.; HERNÁNDEZ, F.; MARTÍNEZ-FONT, R.; BAR-ROWS, P.; EREZ, A.; 2004: Kaolin treatment to reduce pomegranate sunburn. Sci. Hortic. 100, 349-353.MERZLYAK, M. N.; SOLOVCHENKO, A. E.; CHIVKUNOVA, O. B.; 2002: Patterns of pigment changes in apple fruits during adaptation to high sunlight and sunscald development. Plant Physiol. Biochem. 40, 679-684.SCHRADER, L.; ZHANG, J.; SUN, J. S.; 2003: Environmental stresses that cause sunburn of apple. Acta Hortic. 618, 397-405.SPAYD, S. E.; TARARA, J. M.; MEE, D. L.; FERGUSON, J. C.; 2002: Separa-tion of sunlight and temperature effects on the composition of Vitis vinifera cv. Merlot berries. Am. J. Enol. Vitic. 53, 171-182.WÜNSCHE, J. N.; BOWEN, J.; FERGUSON, I.; WOOLF, A.; 2004: Sunburn on ap-ples - causes and control mechanisms. Acta Hortic. 636, 631-636.WÜNSCHE, J. N.; GREER, D. H.; PALMER, J. W.; LANG, A.; MCGHIE, T.; 2001: Sunburn - the cost of a high light environment. Acta Hortic. 557, 349-356.Received March 7, 2006maximum fluorescence (Fm’) and shows it can be used to quantify sunburn in grapes.The almost total loss of fluorescence occurring about 20 d prior to harvest of the Chardonnay berries coincided with increased appearance of visual sunburn symptoms. This loss of fluorescence could be attributed to increased skin browning of the berries as sunburn occurred. Sun-ex-posure of varieties such as Cabernet Sauvignon, Merlot, Grenache, Shiraz and Pinot Noir berries increased total phenolic concentrations (BERGQVIST et al. 2001, SPAYD et al. 2002). The brown appearance of the Chardonnay berry le-sions also suggests appearance of secondary phenolic com-pounds (WÜNSCHE et al. 2004). The high susceptibility of Chardonnay grapes to sun-burn may relate to changes in epicuticular waxes. In ber-ries with no sunburn, the waxes had an intricately arranged platelet structure orientated perpendicular to the surface of the berry (Fig. 2). With even the slightest symptoms of sun-burn, these waxes lost the crystalline structure and became relatively amorphous. The epicuticular waxes appeared to be very sensitive to the conditions causing sunburn and seem to be implicated in the susceptibility of Chardonnay grapes to high light and high temperature. 0 10 20 30 40 50 60 70 800.00.20.40.60.8HarvVerFluorescence yield B  F t and F m'Days from December 10100200300400500   AFig. 1: Changes in (A) steady-state (Ft), maximum (Fm’) fluo-rescence and (B) the fluorescence yield of Chardonnay exposed (circles) and shaded (squares) berries throughout two growing seasons. The arrows indicate veraison and harvest.Fig. 2: Scanning electron micrographs (x 2000 magnification) of epicuticular waxes on Chardonnay grapes. (A) Control grapes with no sunburn; (B) slight sunburn; (C) moderate sunburn; (D) severe sunburn.A BC D

Susceptibility of Chardonnay grapes to sunburn

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Susceptibility of Chardonnay grapes to sunburn

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