Micro-propagation of Most Important Walnut Cultivars and Stocks in Syria

Muhsen Al-Sewei 
General Commission for Scientific Agricultural Research-
Homs Research Center
Aleppo University, Faculty of Agriculture


This study has been carried out at the plant tissue culture laboratory at Aleppo Research Center during the period of 2003-2006 with the aim of developing an efficient method for micro-propagation of three important walnut cultivars (Hartley, Serr, Belhsen-2) in order to make these cultivars available for fruit growers for the aim of improving walnut production in Syria.
A full successful and detailed in vitro propagation system for the following walnut cultivars Hartley, Serr, and Belhsen-2 has been developed.
Shoot tips, single nodes and auxiliary buds excised from adult trees grown in the field under natural conditions at Gosea Al-Kharab Research Center, Homs Province were used as primary explants
which were surface-disinfected using HgCl2 or with sodium or calcium hypochlorite followed by three rinses with sterile distilled water. They were then placed onto three media (MS, DKW, WPM) containing a combination of growth regulators at different concentrations (Kinetin or BA at 0.5, 1 or 2 mg/l) each with IBA or NAA at 0.1 mg/l. Multiplication rate of 5-fold was achieved every 4 weeks.
Rooting was achieved within 2-4 weeks using 1.5-2 cm long shoot tips excised from proliferation cultures and grown on half or full strength agar-gelled media containing (IBA, NAA) at a concentration of 2, 3, 4 or 5 mg/l with a maximum rooting efficiency of 80 %. However, low concentrations of auxin decreased percentage of rooting 30-60%. But high concentrations decreased percentage of rooting and the callus formation.
On media containing 1/2MS + 4 mg/l IBA +Activated charcoal, a maximum rooting efficiency of 85% was obtained within 2-4 weeks.
Also dark treatment during the rooting phase has been studied, so that one week was the best treatment concerning the percentage of rooting.
Rooted plantlets were transplanted into pots with a mixture of 2:1 (v/v) peat:perlite and covered with a plastic bags and acclimatized gradually to field conditions by making holes in the bags throughout 5-6 weeks. Acclimatization took about 4 weeks where the bags were removed completely with 65-75 % efficiency.