Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2003
Publication Date: August 1, 2003
Citation: Stringer, S.J., Marshall, D.A., Sampson, B.J. 2003. Response of muscadine grape (vitis rotundifolia michx) to the growth regulators cppu andgibberillic acid. Hortscience. vol.38(5) pp.698-699 Technical Abstract: Experiments were conducted during 2001 and 2002 at McNeil, MS, with muscadine grapes to determine how combinations of the growth regulators GA3 and CPPU affected fruit set and berry size in six insect-pollinated and pollinator-excluded, mature, field- grown pistillate cultivars including 'Black Beauty', 'Fry', 'Higgins', 'Hunt', 'Summit' and 'Sweet Jenny'. In 2001, GA3 was applied to flower clusters pre-bloom and was followed by applications of CPPU applied at 50% bloom alone or again when fruit had developed to a size of 6-8 mm. The GA3 concentration was 20 mg.L-1 and the CPPU concentrations were either 6 mg.L-1 or 12 mg.L-1. A control treatment without either growth regulator was also included. In 2002, GA3 (20 mg. L-1) was applied either alone (pre-bloom) or in conjunction with single applications of either 12 or 24 20 mg.L-1 CPPU at 6-8 mm berry size. CPPU was also applied alone at these same use rates and application timing and a control treatment without growth regulators was also included. Results of the 2001 study showed significant variation among cultivars in response to the growth regulator treatments. Positive responses occurred in pollinator-excluded flower clusters of 'Black Beauty', 'Summit' and especially 'Sweet Jenny' which set 38% fruit that were 92% seedless. However, the fruit size of these pollinator-excluded cultivars fruit size was reduced significantly. In 2002, the responses of these same three cultivars to insect pollinated vs. insect pollinator-excluded treatments, in conjunction with growth regulators (20 mg-L-1 GA3 applied pre-bloom alone, or followed by 12 mg-L-1 CPPU applied at 70-80% bloom), were evaluated. Fruit-set in the insect pollinator-excluded treatments in conjunction with the use of either growth regulator treatment was greater than in the non-excluded treatments and was greatest with 'Sweet Jenny'. The highest percentage of seedless fruit (66 %) occurred with 'Black Beauty'. However fruit size was again smaller with all cultivars where insect pollinators were excluded. In another 2002 study involving the self-fertile cultivar 'Fry Seedless', GA3 (20 mg. L-1) was applied alone at pre-bloom; and CPPU (either 12 or 24 mg. L-1) was applied alone at 70-80% bloom, or at these same timings in conjunction with a pre-bloom application of GA3 (20 mg. L-1). Results showed that these combinations of GA3 and CPPU increased fruit set by greater than 100% and fruit size by up to 40% over that observed in the untreated control. These results suggest that combinations of the growth regulators GA3 and CPPU may be useful for increasing fruit set in muscadine grapes and for developing seedless fruit. Further work is required to elucidate the effects of cultivars, use rates and application timing. Chemical names used: N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU); gibberillic acid (GA3).