ROOT DEVELOPMENT OF INVITRO HYBRID WALNUT MICROCUTTINGS IN A VERMICULITE-CONTAINING GELRITE MEDIUM

Quantitative and qualitative improvements in root development have been obtained in six clones of hybrid walnut trees propagated by tissue culture and selected for multiplication and rooting abilities. A mixture of diluted gelified medium (DKW, macroelements 1/4) and vermiculite, used in the proportions 250/200 (v/v), strongly promoted root elongation (two to seven-fold) and the development of secondary roots of induced shoots (IBA 24.6-mu-M) after 2 weeks of culture. Furthermore, rooting rates were enhanced (from 15 to 50%) and the number of primary roots per rooted explant was from two to six-fold higher. Distilled water added to vermiculite always gave the poorest rooting. Vermiculite promoted penetration and aeration of the roots more than gelrite alone, and its effect was better than that of perlite. This procedure resulted in 80-100% rooting for five hybrid clones.