The influence of culture dates, genotype and size and type of shoot apices on in vitro shoot proliferation of Vitis vinifera cvs Thompson Seedless, Ribier and Black Seedless

shown a marked influence on shoot proliferation rates for several species. However, in grapevines, only CHEE and PooL (1985) mention this fact and FANIZZA et al. (1984) found no seasonal differences when culturing grapevines apices in vitro. With respect to the explant position in the plant (axillary vs. apical buds), the results are contra­ dicting (YU and MEREDITH 1986; NOVAK and JUVOVA 1983; HWANG and KIM 1990; SUDARSONO and GOLDY 1991) probably due to its relation with the phenol content existing in the tissue (FANIZZA et al. 1984). The explant's size and physiological age are important factors in meristem selections for success in its survival and prolifera­ tion. However, no previous references were found in the literature concerning these aspects. The objective of this study was to evaluate the effect of the time (date) of cul­ ture as well as size and type of apex (apical or axillary) on the proliferation rate of shoots in three commercially important grapevine cultivars. Materials and methods: Apices from apical and axillary buds (0.5 and 1.5 mm) of the cvs Ribier, Thompson Seedless and Black Seedless were cultured. The following media and concentrations of growth regulators were used: a) Initiation phase: MS 3/4 plus BAP 2.0 mg/1; b) Proliferation phase: MS plus BAP 2.0 mg/1; c) Elongation phase: MS plus BAP 0.5 mg/1 plus GA 0.4 mg/1; d) Rooting phase: MS 3/4 plus IBA 0.5 mg/1. The culture was carried out in 6 different dates, every 15 d, starting on Sep. 27. The trial had a factorial design totalizing 72 treatments with 10 replications each. The cultures were kept at 26 ± 2 °C, under 16 h of light with an intensity of 30 J.. LE m-2s-1 PAR (photosynthetica lly active radiation) and were transferred to a fresh medium every 25 d. Shoots formed after each sub-culture were counted and the results were analyzed by ANOVA and Duncan test. For a commercial purpose, a potential amount of shoot/explant was calculated for each genotpype after a one-year period of culture considering the best culture date.