Genetic control of growth, biomass allocation, and survival under drought stress in Pinus radiata D. Don seedlings

Drought is one of the critical factors limiting plant growth, and knowledge about genetic adaptation to drought is necessary to develop strategies for successful reforestation on drought-prone sites. In this study, genetic variation was investigated in 98 full- and half-sib radiata pine (Pinus radiata D. Don) families, representing Chilean coastal and interior populations, subjected to two water regimes: well-watered and drought-stressed. Assessed traits, in 5-month-old seedlings, included height (H), diameter (D), height-to-diameter ratio (HDR), dry biomass of needles (NDW), stem (SDW), roots (RDW), and total (TDW), root-to-shoot ratio (RSR), and survival (SUR). After 115 days of treatment, growth, biomass, and survival were nearly two times higher under the well-watered regime than under the stressed one. Families differed significantly in most traits, with individual tree heritabilities ranging from 0.14 for SUR to 0.63 for D in the well-watered treatment. Families from the interior showed the highest heritability for D, SDW, RDW, and TDW when grown in the water-stress treatment. The genetic correlations between treatments were moderately strong, which suggests the presence of a genotype by watering regime interaction. Most traits were strongly correlated (genetic correlations often exceeded 0.40). Compared to the first generation families from coastal sites, the third generation families from the interior sites showed an increase in SUR and RSR. Thus, potential exists to screen families at the seedling stage for drought hardiness and to identify parents from the interior sites with potential to produce a more drought-resistant breed with satisfactory growth rates and yields in dry environments.