Family variation and potential for genetic gain in frost resistance of Pinus radiata

Abstract

Twenty-three Pinus radiata seed orchard clones of the New Zealand “850” series were each control-pollinated with a mix of 10 pollens to produce polycross families. The seed was sown in open nursery beds. Seedlings were potted up at six times of the year and subjected to white advective frosts in controlled-environment rooms, with up to seven frosting runs of variable severities at each time. There were significant differences (p< <0.001) between families in frost injury, such that, although there was statistically significant family × time interaction, some families were consistently more frost resistant (tolerant) than others. No association between frost resistance and growth rate was evident. Individual-tree heritability estimates for frost damage scores were around 0.3 at given times, and 0.20 over all times. Prospective gain in resistance from progeny testing over several seasons of the year, with 2:23 selection, is about 1°C. An additional gain of 0.4°C resistance appears obtainable from 1:90 selection of individuals within pair-crosses in a single frosting run. This additional (within-cross) gain might be increased to around 0.75°C, with the same culling rate but testing one ramet per seedling at each of four times of the year.