Vaccinium section Cyanococcus (Ericaceae) consists of diploid, tetraploid, and hexaploid species (Camp, 1945). Except for one diploid species, Vaccinium myrtilloides, whose native range extends from Nova Scotia to Vancouver Island and southwestern British Colombia, all species in the section are native to eastern North America (Vander Kloet, 1988). The species in section Cyanococcus are closely related. Homoploid interspecific crosses are easy to make, and thousands of vigorous, fertile seedlings can be obtained. Tetraploid blueberry cultivars have been produced by interspecific crosses in section Cyanococcus, followed by recurrent selection for desirable horticultural characteristics and clonal propagation of the best seedlings (Coville, 1937; Ballington et al., 1996).
A strong triploid block makes it hard to cross diploid and tetraploid species within the section, but tetraploid plants of the diploid species, produced with colchicine (Dweikat and Lyrene, 1991; Perry and Lyrene, 1984), can readily be crossed with the tetraploid species, and the resulting hybrids are vigorous and fertile.
Unreduced gametes also can enable the production of fertile tetraploid hybrids from crosses between diploid and tetraploid species in section Cyanococcus (Lyrene and Ballington, 1986; Lyrene et al., 2003; Sharpe and Darrow, 1959). The frequency of unreduced gametes is low in Vaccinium, and varies widely both among and within species (Chavez and Lyrene, 2009; Megalos and Ballington, 1988; Ortiz et al., 1992).
V. elliottii, a diploid highbush species, is locally abundant on acid, sandy, and sandy-clay soils in the southeastern United States from north Florida to east Texas and as far north as North Carolina. Although Vander Kloet (1980) lumped V. elliottii with other highbush blueberries under the name Vaccinium corymbosum, most regional biologists who have taken into consideration range, plant abundance, morphology, phenology, ecology, and crossing behavior, consider V. elliottii a distinct species (Camp, 1945; Uttal, 1987; Ward, 1974). V. elliottii was easily distinguishable by simple sequence repeat analysis from diploid Vaccinium fuscatum, the highbush species it most closely resembles (Bassil et al., 2018).
V. elliottii has been used to a limited extent in blueberry breeding programs in North Carolina and Florida. The intent has been to obtain cultivars that incorporate the ability of V. elliottii to grow on drought-prone upland soils that have low organic-matter content (Lyrene, 1997; Lyrene and Sherman, 1980). V. corymbosum, the principal species used in domesticating highbush blueberry, occurs naturally on high-organic soils having poorly drained subsoils, and is poorly adapted to uplands. V. elliottii plants flower early and require relatively few days between flowering and fruit ripening. The berries ripen very early in the spring. V. elliottii berries are small, approximately the size of berries harvested commercially from Vaccinium angustifolium in Maine and eastern Canada, but are juicy, fragrant, and have small seeds. In architecture, the plants are upright, and typically form compact colonies 2 to 4 m tall, with canes that range from stiffly upright on some plants to rather weeping on others. The leaves are small and deciduous. The flowers are small and differ from other highbush blueberries by having a short style, with the stigma normally located well inside the corolla tube (Lyrene, 1994).
A highbush blueberry cultivar, Carteret, which has V. elliottii in its pedigree, was released by North Carolina State University in 2009 (Ballington and Rooks, 2009). In the late 1970s, crosses were made at the University of Florida between low-chill Florida highbush cultivars and V. elliottii plants propagated from forests in southwest Alabama and northeast Florida. Two cultivars with V. elliottii in their pedigrees, Snowchaser and Kestrel, were eventually released by the Florida blueberry breeding program. Both ripen early and produce berries that have pleasant, aromatic flavors. The success of these cultivars resulted in renewed interest in using V. elliottii as a parent in the Florida blueberry breeding program.
In 2014, 175 seeds were obtained by pollinating 4301 emasculated flowers on 19 tetraploid highbush cultivars with pollen bulked from ≈30 different V. elliottii genotypes that had been propagated as cuttings from native populations in southwest Alabama (Lyrene, 2014). From these seeds, 55 plants were grown to the age of flowering. The purpose of this paper was to describe the ploidy, phenotypes, pollen fertility, and crossing behavior of plants from these and similar crosses.
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