Optimization of medium composition for apple rootstocks

Abstract

Impact of medium composition (plant growth regulators, mineral nutrients) on multiplication rate, shoot elongation, callusing and rooting of apple rootstocks ('M9', 'M27', and 'MM106') cultured on gelled basal Murashige and Skoog (MS) medium were investigated. Multiplication rate was mainly dependent upon kind of plant growth regulators especially, 6-benzylaminopurine (BA), mineral concentration and genotypes. The best shoot production in terms of shoot number and shoot quality was obtained using 4.4 μM BA and 2.27 μM thidiazuron (TZD) during the shoot multiplication phase, but 8.8 μM BA + 1.14 μM TZD and 2.8 μM gebberllic acid (GA₃) during the shoot elongation phase for all genotypes. Application of high (2.8 μM) concentration of GA₃ increased the elongation of adventitious shoots than low concentrations. The highest multiplication rate (5.7 No.//shoot) and the highest amount of total fresh weight (2.25 g/jar), as growth rate, were produced by applying 4.4 μM BA + 2.27 μM TDZ for ‘M27’ genotype. Micropropagation potential of ‘M27’ genotype was higher than other genotypes. 'MM106' genotype had the lowest multiplication rate (0.7 No./month), when 0 μM BA+9.08 μM TDZ was applied. Multiplication of explants from the 1st subculture was more sensitive to BA than that from the 3th or 4th subculture. The rooting of explants was promoted by indole-3-butyric acid (IBA) significantly and the best result for rooting was achieved in the half-strength MS medium containing 5.4 μM IBA and 1.2 μM 2,4-dichlorophenoxyacetic acid (2, 4-D). The highest percentage (64%) rooting was produced for ‘MM106’ genotype and the lowest (11%) for ‘M9' after 3 months. Root formation was increased with decreasing concentrations in cytokinins, but increasing auxins (IBA). Rooting percentage of shoot cultures in the low 1/2X-MS medium was significantly more than shoot cultures in the high 2X-MS medium.

Key words: Apple rootstocks, medium composition, multiplication rate, plant growth regulators (PGRs).