Walnuts are considered recalcitrant to tissue culture, with a great genetic determinism on all stages of micropropagation; while other factors, also with great impact, become more complicated with the reproduction of newly realized varieties. In this research, a holistic approach aimed to determine the influence of genotype and the nutritive formulation throughout the whole cycle of micropropagation of four Persian walnut varieties (Juglans regia L.) was presented. During the in vitro establishment it was determined that besides genotype and culture medium, the effect of collection season and the likely interaction amongst factors had a great influence on the successful introduction of all four genotypes. However, all cultures were affected by a deep decay, being necessary the introduction of ethylenediamine di-2-hydroxyphenyl acetate ferric, as iron source, and Phloroglucinol in both Murashige and Skoog (1962) and the corrected Driver and Kuniyuki (1987) formulations. These modifications allowed the stabilization of cultures, maintaining thereafter a steady quality. Either proliferation, rooting and ex vitro survival of four clones were affected by the culture medium, obtaining the best results with the corrected Driver and Kuniyuki (1987) formulation. Finally, in vitro plants produced from all clones were acclimated with high survival rates (75.9–91.1% for the best culture medium), depending of clone and the culture medium used. Microsatellite analysis showed that micropropagated plants maintained the same genetic profiles of their corresponding donor trees. These results might contribute to deepening of the understanding of factors that determine the success of micropropagation of walnuts, and the extents of its influence; whereas, it sets the basis for the commercial micropropagation of all four clones.

Walnut is one of the most common nuts in many countries of the world. It is used in cooking and in traditional medicine. Walnut cultivation on an industrial scale in Kazakhstan began only in 2016-2017, so Kazakhstan scientists in this field do not yet have any scientific experience. The article presents the results of studies on the influence of the nutrient medium compositions Murashige-Skoog and Driver-Kunzhuki on the microclonal propagation of different genotypes of the walnut Juglans regia L. Two varieties were selected as mother plants: the Uzbek variety Ideal and the Chinese variety Liaohe-1, adapted in the southeast Kazakhstan. In the course of work, we compared the growth rate of walnut shoots of two varieties on nutrient media Murasige-Skoog (MS) and Driver-Kunzhuki (DKW) with a concentration of 6-benzylaminopurine (BAP) of 1 and 1.5 mg / l. After a month of cultivation of shoots, positive growth dynamics was observed only on MS medium. On plants of both varieties, the growth rate was slow on DKW medium, the plants had yellow leaves, some shoots blackened and perished. To obtain high-quality material, as well as to increase the growth rate of shoots, DKW medium was supplemented with FeEDDHA (119 mg / L) and phloroglucinol (50 mg / L). As a result of phenological observations: the height of the main shoot, the number of internodes, the formation of additional shoots, and the state of the plants, it was found that the best nutrient medium for microclonal propagation of walnut Ideal and Liaohe-1 is a modified DKW medium. MS can only be used at the initial stage - an introduction to in vitro culture.