The 2012 ASHS Annual Conference

Vaccinium corymbosum L. is the major contributor to the southern highbush blueberry gene pool. Anecdotal evidence describes this species’ root system as thin, fibrous roots oriented parallel to the soil surface. In contrast, Vaccinium arboreum Marsh. is a wild Vaccinium species native to the Southeastern United States that has not been extensively utilized for blueberry breeding but has been reported to have deeper and thicker roots than V. corymbosum. Here we describe the root morphology and architecture of V. arboreum (VA), V. corymbosum (VC), and an interspecific hybrid between the two species (F1) grown in a hydroponic system with high (90 μM) or low (10 μM) iron concentrations. Two-year-old clonal plants rooted from softwood cuttings were grown in a hydroponic system for 110 days before they were destructively harvested. Roots were scanned and analyzed with WinRhizo Pro 2008a. Average root diameter, total root volume, total root length and specific root length were measured. Root length was classified into different categories according to root diameter, and length in each category was expressed as percent of total root length. VC had significantly greater total root length and volume than VA. Although the F1 had significantly higher total root length than either parent, root volume was intermediate between the two. Average root diameter was similar between VC and VA, while the F1 exhibited significantly smaller root diameter. Fine roots (diameter ≤ 0.3 mm) accounted for a significantly higher percentage of root length in VA than VC, while root diameters > 0.4 mm were more abundant in VC than in VA. Root diameters in the F1 generally resembled those of VA. Iron deficiency significantly increased the abundance of very fine roots (diameter ≤ 0.1 mm) but not other root diameters. When grown in high iron concentration, the three genotypes had no significant differences in specific root length. However, when grown in low iron concentration, the F1 exhibited significantly higher specific root length than either parent.  Using specific root length as a diagnostic of the morphological response to low iron concentrations, we found that both parents responded by increasing nutrient uptake efficiency (intensive adaptation) while the F1 responded by increasing fine root biomass (extensive adaptation). These findings show that VC, VA and F1 plants of similar age have considerable differences in root morphology and that these differences are the product of genetic and environmental factors.