Touriga Naçional x environment interaction in the Little Karoo region of South Africa

[摘要] ENGLISH ABSTRACT: The Little Karoo region of South Africa stretches from Montagu in the west, through Barrydaleon the Langeberg Mountain, towards Ladismith, Calitzdorp, Oudtshoorn and De Rust in theeast, with the Swartberg mountain range in the north.The Wine of Origin district of Calitzdorp is a small, demarcated area around Calitzdorp inthe Little Karoo, surrounded by the Rooiberg, Swartberg and Kleinberg mountains.With a mean February temperature (MFT) of 23.7ºC and a low annual rainfall of 233 mm,the district of Calitzdorp has a similar climate to that of the Douro Demarcated Region (DDR).The MFT is comparable to the DDR mean July temperature, and it seems that the DouroSuperior sub-region to the east of the DDR has a mean July temperature of higher than 25°C. Inthe Cima Corgo sub-region (in the centre of the DDR), and the Baixo Cargo sub-region, themean July temperatures are ±25°C and ±22°C respectively. Annual rainfall in the DDR is muchhigher, with Baixo Cargo recording 1 018 mm, Cima Corgo recording 658 mm and DouroSuperior in the east recording only 437 mm.Touriga Naçional is one of the highest quality Portuguese red grape varieties. It produceshigh-quality port-style wine as well as table wines. Excellent quality Touriga Naçional wineshave a dark black/purple colour, good extract, high, elegant tannin content and intense aromas,with typical plum, raisin, wild fruit, mulberry, 'fynbos and cherry aromas.The most suitable terroir for Touriga Naçional in the DDR has been found to be on sites thatrestrain the natural vigour of the grapevine. Soils with moderate to low water-holding capacity, inassociation with low rainfall, result in water deficits during the growing season and areconsidered optimal to restrict growth vigour.A steep, northern middle slope is ideal in the southern hemisphere for high temperaturesand sunlight interception. Warm temperatures (25 to 30 °C) during the day and coolertemperatures during the night are optimal for photosynthesis and colour development.In order to study factors affecting the quality of Touriga Naçional in Calitzdorp, two Vitisvinifera L. cv. Touriga Naçional commercial vineyards in the Calitzdorp district were selected.Each vineyard was divided into two separate management blocks based on their empiricallydetermined quality of production. Two crop-reduction treatments, the standard 50% cropreduction (which was considered to be the control) and a further less drastic treatment of 25%crop reduction, were applied.Significant differences were found in viticultural performance between the two adjacentTouriga Naçional management blocks in each vineyard, especially with respect to vigour. Theupper management blocks, which provided grapes for reserve-quality port-style wines,experienced a higher water deficit due to the moderate soil water-holding capacity and highertemperatures in comparison to the lower sites. The higher water deficits had a restraining effecton the Touriga Naçional vines, and therefore the upper sites had lower vigour, whichcontributed to better quality of both the wine and port-style wine, and this could be recognisedsensorially. However, it was not reflected in the chemical analytical results.Crop load also appeared to have an effect on the Touriga Naçional grapevines, but thisappeared to be dependent on the management block. The 50% crop reduction had a significantpositive effect on the sensory analyses, but did not significantly affect the chemical analyses.Calitzdorp terroir has a similar effect on Touriga Naçional compared to the DDR terroir, andthat is why Calitzdorp can produce good table and port-style wines from Touriga Naçional.

[发布机构] Stellenbosch University