Callus formation as affected by air temperature under different variants of walnut stratification

In this paper the effect of different stratification variants on callus formation onset in five walnut cultivars and selections (Šeinovo, Ovčar, Elit, G-139 and G-286) was studied. In all variants stratification, temperatures 28-29 deg C during 2004 initiated earlier onset on callus formation as compared to those 2003 (26-28 deg C). Callusing was first observed in the variant that included dipping the scion and union and covering with polyethylene foil. Callusing was then observed in the variant that included dipping the scion and union into paraffin, with the stratification in the sawdust up to the scion top. Callusing was observed latest in the variant without paraffin by complete covering with coniferous sawdust. Classified by cultivars and selections, callus formation was first observed in Šeinovo and selections Ovčar and G-286, whereas it was only later recorded in selections G-139 and Eliot.