Effect of Different Media and Growth Regulators on Micropropagation of GF677

GF677 is a widely used rootstock for peach, nectarine and almond. It is vigourous and adapts well to limestone soils and drought. Due to low efficiency of propagation trough cutting, tissue culture is a good and fast method for propagation of disease-free plants of GF677. In vitro multiplication efficiency in GF677 is widely dependent on the type of culture medium and growth regulators. Therefore, the aim of this study was to determine the conditions required to optimize micropropagation methods for GF677 rootstock from nodal explants.

This experiment was conducted during 2015 at the laboratory of plant tissue culture at Agricultural and Natural Resources Research Center of Kermanshah, using a factorial in a completely randomized design with three replications. Sterile nodal explants were cultured onto different media of MS, WPM and B5 supplemented with benzyl adenine (BA) at concentrations of 0.25, 0.5, 1, 2 and 4 mg/L and indole-3-butyric acid (IBA) at concentrations of 0, 0.1, 0.25 and 0.5 mg/L. Elongated shoots of GF677 were cultured on MS medium supplemented with 0.25, 0.5, 1.0 and 2.0 mg/l IBA and 0.0, 0.1, 0.2 and 0.5 mg/l BA for rooting. Factorial analysis of variance was carried out and differences between means were scored with LSD tests.

The effect of different culture media (MS, B5 and WPM) and plant growth regulators (BA and IBA) on a number of shoots per proliferated explant of GF677 proved that the highest rate of adventitious shoot initiation, percentage of egeneration, shoot length and diameter, number and length of nodal, leaf number and multiplication was obtained in MS medium containing 1 mg/l BA + 0.5 mg/l IBA. Cytokinin stimulates the initiation and activity of axillary meristems, which result in shoot formation. This study showed that the number of shoots increased as concentration of BA increased to a certain amount. As concentration of BA increased to 1 mg/l, the number of shoots increased, too. It seems that there is a positive correlation between concentration of BA and the number of shoots to a certain concentration of BA. At concentrations higher than 1 mg/l BA the number of shoots increased. One of the possible reasons can be the reductive effect of higher concentrations of BA. Apparently, a certain amount of BA is required to obtain the best effect. Higher concentrations of BA cause formation of high amount of callus, which is not appropriate in tissue culture. The results of this experiment confirmed the positive influence of the growth regulator on the number of roots per shootlet. Among the various plant growth regulators used, the highest rate of rooting (33%) and the number of roots per shootlet (1.62) were obtained on MS medium containing 1.0 mg/l IBA and 0.5 mg/l BA. The concentration of auxin during rooting period strongly influenced the quality of root system during the rooting period. Rooted plants were transferred to a combination of terrestrial environments, including perlite, sand and soil in the ratio of 1: 2: 1, respectively. Among rooted plantlets that were acclimatized and transferred to the potting mix successfully, 90% survived and grew naturally after strengthening and transferring to the soil.

The shoot multiplications are influenced by the media and growth regulators. The MS medium gave the best results for the proliferation of cultures from explant among the tested media (MS, B5 and WPM). Growth regulators compounds have significant effects on different traits and these changes depend on type and concentration of hormone. Both cytokinin and auxins are important in micropropagation for GF677 rootstock.