IN VITRO MICROPROPAGATION OF CG41 APPLE ROOTSTOCK

The apple production area in Uruguay is of approximately 4000 ha, with an average fruit production of 62,000 t per year. Apple is the most important crop within deciduous fruits, and has behaved as the most demanding, in crop technology, during the last years. Local climate and soil conditions in the south of the country, where the major apple producing area is located, can generate sanitary problems to apple trees. New rootstocks of CG series were introduced from Cornell University in 1996 by the Fruit Program of the National Agricultural Research Institute (INIA - Uruguay) with the purpose of evaluating new tools to solve some of these soil problems as Eriosoma lanigerum and Phytophthora sp. The rootstocks introduced were CG 16, CG 3041 and CG 5935. CG41 was selected through the results of the first trials since this rootstock showed to be well adapted, very precocious and productive, with similar vigor to M9, tolerant to Eriosoma lanigerum, and resistant to Phytophthora sp. This work was carried out to develop a protocol of in vitro propagation of CG41 rootstock, in order to generate faster plant availability to nurseries. Cytokinin (benzyladenine and thidiazuron) effect was evaluated during the multiplication phase. The multiplication rate obtained was higher than three and there was significant difference between the treatments compared. Thidiazuron was the most effective hormone in the phase of multiplication. However, thidiazuron used in successive sub-cultures generated deformations in explants and leaves of plantlets. Therefore its incorporation had to be alternated with other growth regulators. Also different elongation media were compared and the most effective included kinetin's addition. Finally, different rooting substrates were evaluated. At this level the cut in V at the base of the plant was critical, independently of its size.