Unilateral cross compatibility in Vaccinium elliottii x V. arboreum, an intersectional blueberry hybrid

Vaccinium elliottii Chapmn., a diploid blueberry in Vaccinium section Cyanococcus, was crossed with V. arboreum Marsh, a diploid blueberry in section Batodendron. The goal was to produce hybrids that could be used to incorporate traits from these species into tetraploid southern highbush cultivars. The crosses were made reciprocally using two clones of each species. A recessive seedling marker gene for anthocyanin-free cotyledons in the V. elliottii clones used as female parents permitted the testing of mentor pollination. For the mentor pollinations, V. elliottii plants that were homozygous for the recessive marker allele were pollinated with a small amount of viable V. elliottii pollen carrying the recessive marker mixed with a large amount of V. arboreum pollen carrying the dominant marker. Thousands of intersectional hybrid seedlings were obtained when V. elliottii was the seed parent, both with and without mentor pollination, but no hybrids were obtained from 2735 flowers pollinated in the reciprocal crosses. The seeds that gave rise to hybrid embryos were smaller than normal V. elliottii seeds, but germinated well. Hybrid seedlings grew slowly at first, but eventually produced some vigorous plants in the field, although many plants remained much smaller than normal seedlings of the two parental species. Some of the hybrids produced numerous flowers during the 6 years they were observed in the field, but even with many diploid, tetraploid, and hexaploid section Cyanococcus blueberry plants growing nearby that could have provided pollen for their flowers, the hybrids produced no viable seed.