Pollination effects on fruit production of ‘Star Ruby’ grapefruit ( Citrus paradisi Macf.)

Abstract

Flowers of ‘Star Ruby’ grapefruit were hand-pollinated with ‘Valencia’ orange ( C. sinensis (L.) Osbeck), ‘Marrs’ orange, ‘Ruby Red’ grapefruit ( C. paradisi Macf.) and ‘Star Ruby’ grapefruit pollen. Flowers cross-pollinated with ‘Ruby Red’ pollen produced more fruit than did self-pollinated flowers. Flowers cross-pollinated with either ‘Marrs’ or ‘Valencia’ pollen did not produce as many fruit as ‘Ruby Red’-pollinated flowers, nor did they produce more fruit than self-pollinated or open-pollinated flowers. Few fruit were produced when ‘Star Ruby’ flowers were not hand-pollinated. Less than 0.5% of ‘Star Ruby’ pollen germinated in 15–25% sucrose solutions, whereas between 6 and 21% of the pollen from ‘Valencia’, ‘Marrs’ and ‘Ruby Red’ germinated. The number of fully-developed seeds per fruit was increased only when ‘Marrs’ pollen was used. These data show that ‘Star Ruby’ produces very little functional pollen and few functional ovules, and suggests that ‘Star Ruby’ has weak parthenocarpic ability.