Plastochron index of 'Cabernet Sauvignon' and 'Chardonnay' grapevines in Fronteira Oeste, in the state of Rio Grande do Sul, Brazil

The objective of this work was to estimate the plastochron index of the 'Cabernet Sauvignon' and 'Chardonnay' grapevine varieties in Fronteira Oeste, in the state of Rio Grande do Sul, Brazil. The experiment was conducted in 2010, in a completely randomized design, using 'Cabernet Sauvignon' and ' Chardonnay' grapevines grown in the municipalities of Itaqui, Sao Borja, and Macambara, which were referred to as sites 1, 2, and 3, respectively. Phenological monitoring of the varieties was done from the beginning of sprouting until the pruning of canes (green trimming). The daily thermal sum (dTS, degrees C day) was calculated using the cardinal temperatures for node appearance in grapevines (10, 25, and 35 degrees C), whereas the accumulated thermal sum (aTS, degrees C day) was obtained by adding up the dTS. The plastochron index was estimated by the inverse of the angular coefficient of the linear regression between the number of nodes per cane and aTS. In all three sites, both 'Cabernet Sauvignon' and 'Chardonnay' required degree-days of 10 degrees C and aTS of 810 degrees C to complete the cycle from the beginning of sprouting until the end of flowering. The estimated plastochron indexes of the 'Cabernet Sauvignon' and 'Chardonnay' grapevines, in Fronteira Oeste, in the state Rio Grande do Sul, were 40.4 and 49.7 degrees C day per node, respectively.