A field and a laboratory experiment was carried out in 1996 to evaluate the effects of gibberellic acid (GA) to break dormancy and apical dominance of potato seed tubers. A comparison between gibberellic acid spraying application on the haulm and directly on the tubers was established. Four different tuber sizes were used from each one of the Baronesa, Macaca, and Monte Bonito cultivars. The plant treatments were 0, 250, 500. 750 and 1000 g/ha of GA sprayed seven days before haulm destruction. Two GA concentrations were applied (10 and 30ppm) immediately after harvest as tuber treatment. No interactions from GA applications and cultivars, neither from GA applications and tubers sizes were observed. All the haulm treatments resulted in an increasing on the percentage of sprouted tubers and on the number of sprouts per tuber. In addition it reduced the number of days from planting to emergence. A tuber application of 30ppm of GA increased the number of sprouts per tuber by 113.6%, and increased the number of stems per square meter by 37.8%. Moreover the 30ppm application of GA reduced the length of the penod from planting to emergence. When compared with untreated control, 30ppm of GA treatment showed an increase of the total yield (13.8 %) and of the number of tubers per plot (23.2%). The yield of seed tubers was increased by 25.8% and the number of seed tubers by 27.6%. In conclusion, tuber spraying with GA increases the rate of sprouting, the number of stems and the number of produced tubers as well as the yield. Independently on the GA treatment, big seed tubers show a fast emergence of the seedling, a great number of stems and an increased height as compared to small seeds. These improve the number and the yield of tubers. Different sizes of tubers must be planted separately at an appropriate density, in order to gain a suitable stem density, and a uniform plant height, to increase the yield of commercial tubers.
potato (Solanum tuberosum L.); dormancy; gibberellic acid
