S. Afr. J. Enol. Vitic., Vol. 29, No. 1, 2008 50 Interactive Effect of Ethephon and Shading on the Anthocyanin Composition of Vitis vinifera L. cv. Crimson Seedless M. A. Human and K. A. Bindon* Department of Viticulture and Oenology, University of Stellenbosch, Stellenbosch 7600, South Africa Submitted for publication: February 2008 Accepted for publication: May 2008 Key words: Crimson Seedless, table grape, colour, Vitis vinifera, anthocyanin, peonidin, cyanidin, shading, ethephon, Ethrel, 2-CEPA Abbreviations: Peonidin – Pn; Malvidin – Mv; Cyanidin – Cn; Delphinidin – Dn; Petunidin – Pt; glucoside – gluc The Vitis vinifera cultivar Crimson Seedless primarily accumulates the anthocyanin peonidin-3-glucoside. The research undertook the study of two factors which could inluence the accumulation of anthocyanin in grape berry skins: ethephon application and shade. Ethephon treatment at 200ppm applied one week post-véraison signiicantly increased the concentration of all anthocyanins in berry skins. Peonidin-3-glucoside was found to increase most signiicantly in response to ethephon application, and was increased 150% compared with an untreated control. The proportion of 3-monoglucoside anthocyanins increased in response to ethephon application. A shading treatment did not affect total anthocyanin concentration in berry skins, but the anthocyanin cyanidin-3-glucoside was decreased signiicantly by shade. Its content was 50% of a sun-exposed control. The observed effects were found to occur at two sites at which the experiment was performed in the Hex River and Paarl regions. Colour development in the Vitis vinifera cultivar Crimson Seedless does not appear to be inluenced signiicantly by bunch shading. The use of commercial growth regulators like ethephon exert a strong inluence on anthocyanin production in grape skins of this cultivar, and are therefore a more likely solution to overcome poor colour development in its production. Vitis vinifera L. cv. Crimson Seedless is a late ripening, red seed- less cultivar which can be highly proitable as it ills a niche gap in the market, as it is a seedless alternative for the red seeded grape, ‘Emperor’. It is one of the most important table grape cultivars currently produced in South Africa and is widely cultivated in ta- ble grape producing regions, such as the Berg River and Hex Riv- er Valleys. However, a concern in the commercial production of this cultivar is that it has been observed to lack adequate size and colour required for export, and that practices which improve size, such as girdling and gibberellic acid application, reduce the col- our even more (Jensen et al., 1975; Carreno et al., 1997; Cantos et al., 2002; Peppi & Dokoozlian, 2003; Avenant & Avenant, 2006; Peppi et al., 2006; Yahuaca et al., 2006; Cantín et al., 2007; Peppi et al., 2007). Various reasons for inferior colour development in wine and table grapes have been reported for the conditions prevalent in South Africa, such as high temperatures (Kliewer & Torres, 1972; Kliewer 1977; Mori et al., 2005; Yahuaca et al., 2006) and vigorous growth with dense, shaded canopies (Smart et al. 1988; Hunter et al., 1991). Apart from environmental factors which inluence colour de- velopment in grapes, genetic factors also pre-dispose certain cul- tivars to accumulate lower levels of anthocyanin. Cantos et al. (2002) investigated the polyphenol proiles of seven table grape cultivars, and of the four red cultivars examined Crimson Seed- less was found to have the lowest anthocyanin content. The most abundant anthocyanin in most table grape varieties studied was peonidin-3-glucoside (Pn-gluc), followed by cyanidin-3-gluco- side (Cn-gluc), which contrasts with V. vinifera winegrape culti- vars in which the most abundant anthocyanin has been reported to be malvidin-3-glucoside (Mv-gluc) (Mazza, 1995; Cantos et al., 2002; Peppi & Dokoozlian, 2003). In an effort to increase colour and colour uniformity of Crim- son Seedless, it has become common practice for producers to apply plant bio-regulators (Avenant & Avenant, 2006; Cantin et al., 2007). Ethylene-releasing compounds like ethephon, applied at véraison, have been used successfully in many Vitis vinifera L. cultivars to improve the colour of red grapes (Jensen et al., 1975; Szyjewicz et al., 1984; Roubelakis-Angelakis & Kliewer, 1986; Fitzgerald & Patterson, 1994; El-Kereamy et al., 2000; Delgado et al., 2004; Gallegos et al., 2006; Yahuaca et al., 2006). Earlier work by Steenkamp et al. (1977) also showed that ethe- phon increased phenylalanine-ammonia-lyase (PAL) activity in table grapes which was accompanied by increased colour deve- lopment. Ethephon treatments have also been shown to enhance gene expression for enzymes involved in anthocyanin biosyn- thesis such as UDP glucose-lavonoid 3-o-glucosyl transferase (UFGT) with concomitant increases in anthocyanin accumulation in Vitis vinifera cv. Cabernet Sauvignon (El-Kereamy et al., 2002; El-Kereamy et al., 2003). Higher anthocyanin levels at harvest in ethylene-treated Cabernet Sauvignon grapes were due to in- creased synthesis of anthocyanins, namely Mv-gluc (El-Kereamy et al., 2002; El-Kereamy et al., 2003). The effect of cluster shading and/or exposure to sunlight is a subject which has been extensively documented for both ta- ble grapes (Kliewer & Antcliff, 1970; Wicks & Kliewer, 1983) and wine grapes (Crippen & Morrison, 1986a, b, Bledsoe et al., *Corresponding author: E-email address: bindonk@sun.ac.za Acknowledgements: The authors acknowledge the National Research Foundation (NRF, Thuthuka).