Although cultivated SHB are typically capable of setting fruit when self-pollinated, growers commonly plant multiple cultivars to enhance cross-pollination (Williamson et al., 2015). This recommendation is based on previous research describing the benefits of cross-pollination among cultivated blueberry species. Cross-pollination has typically been associated with improved fruit set in northern highbush blueberry [V. corymbosum (Bailey, 1938; Coville, 1921; Dogterom et al., 2000; Ehlenfeldt, 2001; MacKenzie, 1997; Meader and Darrow, 1947; Miller et al., 2011; Morrow, 1943)], rabbiteye blueberry [Vaccinium virgatum (Darnell and Lyrene, 1989; El-Agamy et al., 1981; Gupton and Spiers, 1994; Meader and Darrow, 1944; Payne et al., 1989)], lowbush (Vaccinium angustifolium) and half-high blueberry (V. corymbosum × V. angustifolium hybrids) (Aalders and Hall, 1961; Harrison et al., 1994; Rabaey and Luby, 1988; Wood, 1968), and SHB (Chavez and Lyrene, 2009; El-Agamy et al., 1981; Gupton and Spiers, 1994; Lyrene, 1989). In contrast, greater fruit set in a cultivar after self-pollination compared with cross-pollination has been observed infrequently and has often been attributed to reduced compatibility with the pollen source used for cross-pollination (Ehlenfeldt, 2001; Gupton, 1984; Lang and Danka, 1991; White and Clark, 1939).
Greater fruit size and/or a shorter fruit development period with cross-pollination compared with self-pollination has been documented in northern highbush, rabbiteye, lowbush, half-high, and SHB cultivars (Chavez and Lyrene, 2009; Ehlenfeldt, 2001; Gupton, 1984; Gupton and Spiers, 1994; Lang and Danka, 1991; Lyrene, 1989; MacKenzie, 1997; Meader and Darrow, 1944, 1947; Morrow, 1943; Payne et al., 1989; Rabaey and Luby, 1988; Wood, 1968). In these studies, an increase in the number of fully developed seeds was associated with the increase in fruit size and shorter fruit development period. Supporting this association between seed number and fruit size and development period are cases where interspecific crosses have been compared with crosses that were either self- or cross-pollinated. Aalders and Hall (1961) found reduced seed set in lowbush × velvetleaf blueberry (Vaccinium myrtilloides) crosses that resulted in smaller fruit size and later ripening compared with intraspecific lowbush crosses. Similarly, Gupton and Spiers (1994) found that SHB cultivars pollinated with rabbiteye pollen had reduced fruit weight, but no significant difference in fruit development period compared with intraspecific SHB crosses. Among intraspecific northern highbush crosses, Ehlenfeldt (2001) regressed fruit size and ripening time measurements on total seed number and found the weight of ‘Rubel’ was not impacted by seed number.
The degree to which earliness and yield are improved by cross-pollination is an important consideration when forming planting recommendations for SHB. Early fruit maturity is a critical factor for the SHB industry, as growers rely on the high-value marketing period between the conclusion of southern hemisphere fresh blueberry imports and onset of harvest in traditional U.S. production regions. Therefore, current recommendations suggest including multiple cultivars for cross-pollination in all new SHB plantings. However, larger single-cultivar fields are easier to manage, particularly for some of the common cultural practices necessary for production in subtropical regions (e.g., timing and rate of hydrogen cyanamide application), and would be desirable for mechanical harvest.
The objective of this study was to compare the effects of cross- and self-pollination on fruit set, fruit size, seed number, and time to reach berry maturity among new and traditional SHB cultivars.
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Williamson, J.G., Olmstead, J.W. & Lyrene, P.M. 2015 Reproductive Growth and Development of Blueberry. 30 June 2015. <https://edis.ifas.ufl.edu/hs220>