The effect of the time and mode of application of gibberellic acid and inhibitors of gibberellin biosynthesis on the dormancy of potato tubers grown from true potato seed

Gibberellic acid (GA(3)) and inhibitors of gibberellin biosynthesis (daminozide and chlormequat chloride) were applied to the foliage of potato plants grown from true seed (TPS) either once at two stages of plant development, 40 and 60 days after transplantation (DAT), or repeatedly at 10 day intervals starting from the same growth stages. When GA(3) was applied towards the end of the vegetative cycle (either singly 60 DAT or repeatedly from the same date), it induced rapid breakage of tuber dormancy, a reduction in specific weight, a higher rate of respiration and increased weight loss during storage. Single applications of GA(3) early in the vegetative cycle (40 DAT) had no effect on the weight loss and specific weight of tubers during storage, whereas repeated foliar applications of GA(3) starting from the same stage resulted in the formation of tubers with a low specific weight and a high rate of weight loss during storage. However, the tubers from these treatments did not break dormancy uniformly, and, although in the early stages of storage they exhibited a high rate of respiration, this declined to the level of the control (no growth regulator applied). Although daminozide and chlormequat chloride did not affect the duration of tuber dormancy and had little or no effect on any of the other metabolic indicators studied, gibberellin is nevertheless implicated in dormancy breakage, and its application late in the growth cycle may be of practical value in cases where tubers are required for planting soon after harvest. Overall, tubers from TPS respond to plant growth regulator treatment in a similar way to those from plants grown from seed tubers. (c) 2007 Society of Chemical Industry.