ROOTING AND MULTIPLICATION ABILITY OF PERSIAN WALNUT AS INFLUENCED BY MOTHERSTOCK VIGOR AND PRECOCITY

Abstract

Based on the frequent existence of precocious and dwarf walnut (J. regia L.) genotypes in Iran nurseries, different studies were conducted to collect and evaluate these valuable genotypes for various aspects, including consistency of growth under in vitro and in vivo conditions and impacts of seedling vigor on the walnut rooting and grafting. In the present study, the stability of seedling vigor under in vitro conditions and multiplication and rooting ability of the microcuttings were tested. To this, nodal explants of newly grown shoots derived from 5-year-old seedlings previously classified into three different clusters according to their vigor, were surface sterilized and cultured on DKW medium. The explants were subcultured monthly, up to 13 times, to increase the number of microcuttings. Results of the in vitro study showed that number of shoots derived from the dwarf and semi-dwarf genotypes was higher in comparison to the high vigor ones (3.3 vs. 2.3). The low vigor genotypes also showed shorter internodes, smaller shoot size (2.6 vs. 4.5 cm) and lower callus formation as well as higher rooting percentage (63.5% vs. 37.1%) and in vitro flowering. These results are consistent with the field observations, suggesting basitonic tendency, easy rooting and dwarf stability of low vigor genotypes under in vitro conditions. In conclusion, we suggest a simultaneous recurrent selection program for both dwarfing and rooting ability (selection of dwarf/semi-dwarf as well as easy-to-root clones) to utilize their advantages in a high-density orchard system.