SHOOT TISSUE CULTURE OF APPLE: COMPARATIVE RESPONSE OF FIVE CULTIVARS TO CYTOKININ AND AUXIN

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Abstract
Shoot cultures of five apple cultivars, M.27, M.9, M.26, MM.111 and Macspur, a strain of McIntosh, were established in vitro and their response to different concentrations of cytokinin (benzyladenine, BA) and auxin (naphtheleneacetic acid, NAA) were measured. At the three BA concentrations tested (1.0, 5.0 and 10 μM) cultivars differed in the number of shoots produced and in their requirements for BA for optimum shoot production. M.27 produced the most shoots followed by Macspur, M.9 and M.26. The best concentration of BA for shoot production was 5.0 μM for Macspur and M.26 but slightly higher for M.27 and M.9. Rooting response was tested at NAA concentrations of 0.1, 0.33, 1.0, 3.3, 10 and 33 μM. The range of concentrations in which rootstock cultivars rooted was broader than for the scion cultivar Macspur and the percent rooting of rootstocks (about 85%) was higher than Macspur (58%). The most rooting occurred at 1.0 or 3.3 μM NAA. M.9 produced callus, which prevented rooting, when chronically exposed to NAA so a procedure of acute treatment was used. This allowed root initials to form but avoided callogenesis. Possible reasons for the different responses of the cultivars to cytokinin and auxin are discussed.

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