Poor fruit set and suboptimum berry size are potential yield- and profit-limiting factors for southern highbush (Vaccinium corymbosum hybrids) blueberry production. Factors that commonly affect fruit set include pollinator population during bloom, weather-related factors that influence pollinator activity and pollen transfer during bloom, and freezing temperatures during or after bloom, which damage ovules and ovaries thereby inhibiting seed and fruit development. Much research over the past decade has focused on use of GA3 to overcome fruit set problems in blueberries grown in the lower southeastern United States (NeSmith, 2005). Although GA3 has increased fruit set of blueberry, there are problems regarding late ripening and reduced fruit size associated with its use.
The cytokinin compound N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) has shown some positive results in increasing fruit size and fruit set in a number of fruit crops, including table grapes (Vitis sp.), kiwifruit (Actinidia chinensis Planch and A. deliciosa), apples [Malus × domestica (Borkh.)], table olives (Olea eropaea L.), and Japanese persimmon (Diospyros khaki Thunb.) (Antognozzi et al., 1993a, 1993b; Greene, 1989, 1993; Looney, 1993; Reynolds et al., 1992; Sugiyama and Yamaki, 1995). Recently, preliminary research has shown that CPPU may also be beneficial in rabbiteye blueberry production (NeSmith, 2002; NeSmith and Adair, 2004); however, there has been no research reported on CPPU effects on southern highbush blueberries. The objective of this research was to evaluate the response of several southern highbush cultivars to applications of CPPU under greenhouse and field conditions.
Antognozzi, E., Famiani, F., Palliotti, A. & Tombesi, A. 1993a Effects of CPPU (cytokinin) on kiwifruit productivity Acta Hort. 329 150 152
Looney, N.E. 1993 Improving fruit size, appearance, and other aspects of fruit crop ‘quality’ with plant bioregulating chemicals Acta Hort. 329 120 127
NeSmith, D.S. 2002 Response of rabbiteye blueberry (Vaccinium ashei Reade) to the growth regulators CPPU and gibberellic acid HortScience 37 666 668
Reynolds, A.G., Wardle, D.A., Zurowski, C. & Looney, N.E. 1992 Phenylureas CPPU and thidiazuron affect yield components, fruit composition, and storage potential of four seedless grape selections J. Amer. Soc. Hort. Sci. 117 85 89