SHORTENING DORMANCY OF SEED POTATOES BY A HAULM APPLICATION OF GIBBERELLIC-ACID AND STORAGE-TEMPERATURE REGIMES

In three experiments with cvs Diamaiit (short dormancy) and Desiree (long dormancy), the effect of a haulm application of gibberellic acid (GA) on the dormancy of seed potatoes harvested immature was investigated. Several storage temperature regimes were imposed to examine the interaction between GA and storage temperature. The storage regimes included 18 and 28 C continuously, hot pre-treatments of different duration (different periods at 28 C and subsequently 18 C) and a cold pre-treatment (20 days at 2 C and subsequently 18 C). A foliar spray of 375-750 g GA/ha 3-6 days before haulm killing shortened dormancy, and minimally induced sprouting before harvest. The magnitude of the GA effect depended on the cultivar and storage temperature regime. Compared to untreated tubers stored at 18 C, dormancy was shortened by about 40 days by a GA application and storage at 18 C (Diamant) or by about 90 days by a GA application and storage at 28 C (Desiree).