Plant Architecture of Vaccinium Genotypes as Influenced by Soil Characteristics

Vaccinium species vary in both canopy architecture and soil adaptation. For example, canopies of southern highbush blueberry (SHB, V. corymbosum L. hybrids), rabbiteye blueberry (RE, V. virgatum Aiton.), and sparkleberry (VA, V. arboreum Marsh.) range from multi-caned shrubs to monopodial trees. Optimum organic matter content, soil pH, and drought tolerance also vary between species. This variation may reflect differences in root architecture among Vaccinium species. To assess the effects of genotype and soil on plant architecture of Vaccinium spp., we randomly selected nine seedlings from five populations and grew them in bench-top rhizotrons. The seedling populations were open-pollinated VA (G1) and controlled crosses of RE × RE (G2), SHB × VA (G3), SHB × (SHB × VA) (G4), and SHB × SHB (G5). G3 and G4 are expected to be comprised of 50% and 25% of the VA genome, respectively. Sixty days after germination, seedlings were transplanted to rhizotrons containing either sphagnum peat moss or a 3:1 mixture of sphagnum peat moss and perlite. Seedlings were destructively harvested 77 d after transplanting. Canopy architecture was determined using digital calipers and a LiCor LI3100C leaf area meter, and root architecture was determined using a scanner and WinRhizo Pro 2008a. Root-to-shoot ratio and average root diameter were similar for genotypes from different populations. Total root length, volume and surface area were greater in the G3 and G4 populations than in the others. The G2 population exhibited less root branching than the other populations. For above-ground measurements, the G5 population exhibited significantly greater number and length of first order lateral branches and a significant increase in leaf number compared to the other populations. Growth media also affected root and shoot architecture. Seedlings grown in the peat-perlite mix developed thinner root systems than seedlings grown in peat alone, as evidenced by their significantly higher specific root length and percentage of root length with diameters below 0.9 mm. Above ground, seedlings grown in sphagnum peat were denser and more leafy than seedlings grown in peat-perlite, as evidenced by their significantly greater plant height, total leaf area, and length of the main cane, and their significantly shorter internode length. These results indicate that plant architecture in Vaccinium species is influenced by interactions between genetic factors and soil characteristics. Additionally, these results suggest that RE and VA can be used as sources of different plant architecture traits in blueberry breeding.