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ISHS Acta Horticulturae 839: I International Symposium on Biotechnology of Fruit Species: BIOTECHFRUIT2008

IMPROVED MICROPROPAGATION OF WALNUT (JUGLANS REGIA L.) ON MEDIA OPTIMIZED FOR GROWTH BASED UPON MINERAL CONTENT OF WALNUT SEED

Authors:   K. Vahdati, E. Najafian Ashrafi, H. Ebrahimzadeh, M. Mirmasoumi
Keywords:   walnut, seed, minerals, micropropagation, medium
Abstract:
Tissue culture success is strongly dependent on the chemical composition of the culture medium. Micropropagation of walnut has been partially limited by the lack of an appropriate culture medium. We hypothesized that minerals in proportions similar to those found in walnut seeds could provide an optimum medium for shoot micropropagation. The mineral composition of seed of five walnut cultivars ‘Serr’, ‘Pedro’, ‘Lara’, ‘Hartley’ and ‘Ron de Montignac’ were analyzed by Inductive Couple Plasma-Omission Spectroscopy (ICP-OES). In addition, the effect of Cu and myo-inositol on shoot length and rooting rate of explants was determined. The concentrations of minerals in walnut seeds were 2 to 26 times higher than in Driver and Kuniyuki Walnut (DKW) medium. Based upon the minimum mineral concentration observed in seeds, two new media with ×1.5 and ×2 DKW macro and micro nutrients (×1.5 and ×2 DKW, respectively) were formulated. The explants cultured on ×2 DKW and ×1.5 DKW formed shoots having green-colored leaves but produced callus similar to those cultured on DKW medium. Better growth was observed on ×1.5 DKW medium. Multiplication rates were different among the cultivars and ‘Vina’ had the maximum stem length and number of auxiliary buds on ×1.5 DKW. The number of auxiliary buds per shoot and stem length were enhanced with higher concentrations of Cu and myo-inositol. In vitro rooting percentage for ‘Sundland’, ‘Hartley’ and ‘Vina’ were 50, 31 and 16% in the DKW medium, respectively, but decreased in ×2 DKW and ×1.5 DKW (5-17%). Better rooting (up to 70%) was obtained when shoots were placed in media containing Cu at 10× and myo-inositol at 2× concentrations. The results suggested that some walnut cultivars need to be grown in media with higher mineral concentrations than DKW medium, and that higher levels of Cu and myo-inositol can be effective in improving the growth rate and rooting percentage of walnut explants.
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