Gibberellic Acid 4+7 Influences Shoot Growth of Seedling Pecan and Bitternut Hickory

Shoot development of seedling hickories is slow, limiting their success as viable crops using standard growing techniques. Because hickories are predominantly propagated by seed, we questioned whether gibberellic acid (GA) could be used on seedlings to overcome slow shoot development during juvenility. Treatments of one-year-old seedlings of bitternut hickory [Carya cordiformis (Wangenh.) K. Koch], pignut hickory [C. glabra (Mill.) Sweet], pecan [C. illinoinensis (Wangenh.) K. Koch], kingnut hickory [C. laciniosa (F. Michx.) Loud.], shagbark hickory [C. ovata (Mill.) K. Koch], and mockernut hickory [C. tomentosa (Lam.) Nutt.] began at bud break by applying a solution of 500 ppm GA4+7 dissolved in 95% ethanol directly to apical buds or stem tissue at three-day intervals for 27 days. After 160 days, neither treatment affected caliper of any taxon, although species differences were observed. Compared to nontreated control plants, treatment of buds resulted in a 234% and 144% increase in shoot height of bitternut hickory and pecan, respectively. In a second experiment, the same treatments were implemented on seedlings of bitternut hickory shortly after germination. Only shoot height and dry weight were affected (increased) by application of GA4+7. This study indicates plant growth regulators could be effective at increasing shoot extension of some hickories. Chemicals used in this study: Gibberellic acid 4+7 (GA4+7). Species used in this study: bitternut hickory [Carya cordiformis (Wangenh.) K. Koch]; pignut hickory [C. glabra (Mill.) Sweet]; pecan [C. illinoinensis (Wangenh.) K. Koch]; kingnut hickory [C. laciniosa (F. Michx.) Loudon]; shagbark hickory [C. ovata (Mill.) K. Koch]; and mockernut hickory [C. tomentosa (Lam.) Nutt.].