IN VITRO COLCHICINE TREATMENTS ON STRAWBERRY (FRAGARIA X ANANASSA DUCH) SHOOTS

In vitro shoots of four octoploid cultivars ('Addie', 'Etna', 'Gea', 'Savio') were treated with colchicine to induce chromosome doubling. Treatments with four colchicine concentrations (250, 500, 2500 and 5000 ppm) for periods of 5 or 9 days were conducted by keeping the proliferating cultures in vitro in a liquid medium.

The highest concentration was lethal, 'Addie' alone recording a 10% survival rate. At 2500 ppm the mortality rate was 100 % for 'Gea' and ranged from 50 to 83 % for the other cultivars over 5 days' treatment. Increasing the period to 9 days had no effect on 'Etna' and 'Savio' but caused 100 % mortality in Addie. At lower concentrations phytotoxicity was negligible.

Treated shoots were subjected to 3 proliferation subcultures before rooting; after acclimatization plants were transferred to the field. A two year field survey of plant and fruit morphological traits, as well as the recording of crop data was carried out at flowering and fruiting. The negative variations (mainly fruit malformations) observed were found to increase with increasing treatment dose and period, depending on cultivar 'Addie' was the most susceptible. Plants showing variations were selected for cloning and testing in new field trials while genetic changes are to be determined by chromosome counting.