Statistical analysis of 'White Riesling' (<i>Vitis vinifera</i> ssp. <i>sativa</i> L.) clonal performance at 16 locations in the Rheinland-Pfalz region of Germany between 1971 and 2007

Abstract

Performance trials have been evaluated of 30 'White Riesling' clones grown at 16 locations in the Rheinland-Pfalz region between 1971 and 2007. A mixed linear model approach was used to handle the highly-unbalanced data structure. Environmental factors accounted for about 95 % of the variation for individual observations. Genotypic clone variation contributed only 0.65 % to the total variation for grape yield, 0.29 % for total soluble solids (TSS) and 0.22 % for acidity. F-tests for clonal differences showed significant F-values for each characteristic. Estimated clone means ranged from 107.4 to 130.8 kg·ar^-1 (1 ar = 100 m²) for grape yield, from 72.0 to 75.2 °Oechsle for TSS and from 12.5 to 13.4 g·l^-1 for acidity. Significant mean differences were found only for clones located near the lower and upper extremes of the performance range. Long-term time trends of clonal performance are also present. On average over the 36 year period, grape yields increased by 2.00 kg·ar^-1 each year and TSS by 0.87 °Oechsle each year, whereas acidity decreased by 0.21 g·l^-1 each year.
No significant deviations of individual clones from the general long-term trends were verifiable for grape yield but some clones showed significant deviations for TSS and acidity.
A closer look at the linear trend for grape yield displayed a discontinuity around 1989. Before 1989 a linear gain of about 3.99 kg·ar^-1 was apparent whereas, after this time a very slight decrease of 0.28 kg·ar-1 was observed. For mean daily temperature, the long-term trend was remarkably parallel to that of grape yield and TSS. For the Rheinland-Pfalz region, daily temperature increased significantly by 0.046 °C per year, whereas average daily sunshine showed a no significant change over time.