Salt tolerance seedlings derived from putative hybrid pines (Pinus × densi-thunbergii): Possibility of candidate materials for coastal forest restoration

Japanese black pine (Pinus thunbergii) is tolerant against salty wind but susceptible to pinewood nematodes, whereas Japanese red pine (Pinus densifora) is more resistant against pinewood nematodes than P. thunbergii but weaker against salty wind. To produce materials with high resistance against pinewood nematodes and high tolerance against salty wind, we focused on seedlings derived from putative hybrid clones (Pinus X densi-thunbergii). In this study, we investigated the nuclear DNA genome composition of two putative hybrid clones. Using a PCR-RFLP method for analyzing chloroplast DNA, we subsequently identified the paternal species of progenies of two putative hybrids. Branches and potted seedlings from the progenies of P. densifora, P. thunbergii, and the hybrids were immersed in seawater. We harvested the needles from them and measured the potential maximal PS II quantum yield (F_v/F_m). We also dried some needle samples and used inductively coupled plasma mass spectrometry (ICP-MS) to determine Na concentrations. Nuclear DNA analysis of the putative hybrid clones revealed that they were Fl hybrids (P. × densi-thunbergii). Chloroplast DNA analysis revealed that progenies of the hybrid clones were sired by P. densiflora. Those progenies were significantly more salt tolerant than P. densiflora. Moreover, the Na concentration of needles of hybrid clones was lower than those of P. densifora. Our results suggest that the progenies of hybrids are potential candidates for plantation in coastal pine forests, due to high resistance against pinewood-nematode and high tolerance against salt water.