Efficient In Vitro Screening for Higher Soil pH Adaptability of Intersectional Hybrids in Blueberry

We tested efficient in vitro methods for screening the genotypes with higher pH tolerance using multiple shoots of intersectional hybrids between Vaccinium corymbosum 'Spartan' and V. bracteatum. The response of the four hybrid clones tested to different pH levels was clone-dependent in vitro. An apparent difference was found in the rooting rate among the hybrid clones even at higher pH levels; the rooting rates of JM4 (91%) at pH 8.0 indicated a significantly high value compared with other clones (JM1: 24%, JM2: 9%, TM3: 8%, 'Spartan': 0%). Furthermore, JM4 showed constantly high rooting rates (91% to 100%) at all pH levels with no significant differences. Similar differences in the root characters of the hybrids were also confirmed by checking the viability of roots using fluorescein diacetate (FDA)/propidium iodide (PI) staining after dipping the roots of in vitro-produced shoots in liquid medium at different pH levels for 6 hours. These results suggest that an in vitro screening method using the rooting rate of multiple shoots and the viability test of roots by FDA/PI staining as a marker could become a very useful tool for the selection of germplasm with tolerance to higher pH within a short time using small planting spaces. In addition, JM4, which showed a high rooting rate at pH 8.0, could be useful in breeding new cultivars with higher pH tolerance.