Gibberellic acid (GA4 7) and the cytokinin 6-benzyladenine (6-BA) are used during bloom and fruit set to reduce russeting and improve typiness of select apple cultivars. The gibberellin synthesis inhibitor prohexadione-calcium (P-Ca) is used at the same developmental stage to reduce vegetative growth and susceptibility to fireblight. The use of GA4 7/6-BA for enhancing the typiness of Gala apples and the interaction of GA4 7/6-BA and P-Ca was investigated in a 2-yr experiment on mature Royal Gala/Bud 9 trees. Six treatments were imposed: (i) untreated control; (ii) 5.5 mg L-1 of GA4 7 and 6-BA; (iii) 11 mg L-1 of GA4 7 and 6-BA; (iv) 21 mg L-1 of GA4 7 and 6-BA; (v) 123 mg L-1 P-Ca; and (vi) a tank mixture of 21 mg L-1 GA4 7/6-BA and 123 mg L-1 P-Ca. Trees treated with P-Ca had 21%–45% less growth than the untreated trees or trees treated with GA4 7/6-BA. In one of two years, the addition of GA4 7 and 6-BA tank-mixed with P-Ca reduced the efficacy of P-Ca on shoot growth. GA4 7/6-BA decreased soluble solids and fruit firmness in 1 yr, suggesting a delay in fruit maturity. P-Ca alone reduced scarf skin by 7%–10%; however, this effect was negated when combined with GA4 7 6-BA in one of the two years. GA4 7 6-BA increased fruit typiness and length to diameter ratios.
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