The Effect of Ethrel Application on Length of the Juvenile Phase of Apple Seedlings

A 10 year study (1998-2007) was conducted to work out a method that would allow shortening of the juvenile phase of apple seedlings in conventional apple breeding programs. The investigation was based on two separate experiments, each conducted first in high plastic tunnel and then in the field. In both experiments in the first two years, the seedlings were grown on their own roots in plastic containers (cylinders) placed in the high plastic tunnels. At the end of the second year (December), shoot tips from the seedlings were collected and grafted onto dwarfing rootstock M.9 (winter grafting). By the end of March, the grafts were planted in plastic containers and placed in the same high plastic tunnel. They were cultivated there until mid - August and then planted out to the selection field. In the first experiment, seedlings belonging to two families, ‘Ligol’ x ‘Delbard Jubile’ and ‘Linda’ x ‘Golden Delicious’ were investigated. In the second experiment, two seedling populations, ‘Free Redstar’ x ‘Melodie†and ‘Free Redstar’ x ‘Coop 38’ were tested as well. In the first experiment, nine experimental treatments were studied. They involved two growing media (peat substrate and mixture of peat substrate with compost soil 1-1), two mineral fertilizers (Osmocote Plus and Azofoska - the Polish manufactured fertilizer) and two bioregulators (Gibrescol 10 MG containing GA3 and Ethrel). In the second experiment, additionally compost soil was included. It was found that Ethrel applied twice on young apple seedlings grown in high plastic tunnel, in the first and second year of cultivation in both experiments, shortened the juvenile stage of seedlings grafted and grown on M.9 rootstock. In the first year after planting in the selection field (fourth year after seed germination), 25% of the seedlings produced flowers, and in the second year all of them flowered and produced fruits.