WALNUT GRAFTING BY HEATING THE GRAFT-POINT DIRECTLY IN THE FIELD
A heating line has been arranged in order to graft and heat the seedlings directly in the field.
The heating line consisted in a 27° C. thermostating electrical cable positioned around the graft-point and sealed with a thin foil band to standardize the heat and to retain humidity. Two groups of grafted seedlings were compared: heating the graft union immediately after grafting or heating two days later. The effect of a humid cloth band, placed around the graft-point, in order to slow down the scion dehydration, was also tested. The results were compared with transplanted plants obtained by forcing the graft point in the Hot Callusing Pipe system.
Without covering the graft point with a cloth band, the plants bench grafted and callused in the pipe produced a 55% of graft-take, while the plants grafted and callused in the field produced a 53% of graft-take. The humid cloth band applied around the graft-point, in all the experiments determines an increase on graft-take up to 17%. The later applying of the heating device in the field determined a 15% graft-take decrease.
Grafting and heating directly the plants in the field has determine a positive influence on growth: in fact, three months after grafting, the stem diameter and the trunk height have reached up to 10 mm and 130 cm, respectively. We conclude that by heating the graft union directly in the field and by avoiding the transplant, which it is an obligatory step in the bench grafting technique, it is possible to speed up the production cycle of walnut grafted plants.