Two types of field hand crosses (pairwise touching-neighbor and a full 5 × 5 diallel, Griffing's Model 2, Method 3) were performed in combination with genetic similarity estimations of mating partners using expressed sequence tag–polymerase chain reaction molecular markers to elucidate genetic factors underlying yield variations among clones (genotypes) of lowbush blueberry (Vaccinium angustifolium) in two managed fields in Maine. Genetic similarity values for touching pairs ranged from 0.308 to 0.765. Based on pairwise touching-neighbor crosses, no evidence was found for yield being affected by genetic similarity. However, self-fertility of clones was a significant positive predictor of outcross yields. The calculation of lethal equivalents, derived from selfing to outcross ratios, showed a large range in genetic load among clones and a higher average load than that previously reported in the related highbush blueberry (V. corymbosum). The diallel experiment revealed significant general and specific combining ability for all three post-pollination yield traits measured (proportion fruit set, mean mature seed per pollination, and mean berry weight per pollination). Narrow-sense heritability estimates for all three yield traits were moderately high (h2 = 0.58, 0.46, and 0.56, respectively). It is concluded that phenotypically screening for self-compatible clone yield attributes could be useful in identifying germplasm candidates for breeding and propagation.
Little is known of the genetic structure and variability of wild fields, or of the dramatic differences in yield among clones (genetic individuals), of lowbush blueberry (Vaccinium angustifolium Ait.), Maine's most economically important fruit crop. Express sequence tag-polymerase chain reaction (EST-PCR) markers that were originally developed for genetic mapping purposes in highbush blueberry (Vaccinium corymbosum L.) are shown here to be valuable for genetic fingerprinting and relationship studies in the related species, V. angustifolium. As part of an interspecific genetic relationship study, 14 genotypes, including at least two specimens of each of four closely related Vaccinium L. species (V. pallidum Ait., V. corymbosum, V. boreale Hall & Aald., and V. myrtilloides Michx.) and the only four pedigreed cultivars of V. angustifolium, grouped out as expected in a genetic similarity dendrogram (matrix “r” correlation = 0.91). This work is ultimately aimed at using these markers in exploring how genetic relationship affects yield among proximal and distant breeding individuals via controlled field hand crosses. To help address this issue, a separate group of six individuals of V. angustifolium from two managed fields were also genotyped using the EST-PCR markers. The markers were very effective at intraspecific discrimination of individuals within the same field.