Freeze‐testing youngPicea abiesplants

Abstract

Data from three independent experiments with young plants of Norway spruce were used in a methodological study of freezing tests. Frost hardiness was induced both in a phytotron and in a nursery. It was found that frost hardiness developed quickly in both environments; the frost damage decreased from 4–7% per day at a given test temperature. A large between‐ and within‐room variation in frost hardiness was obtained in the phytotron. Needle damage assessment data showed a large deviation from the normal distribution. A transformation of the data providing both normalization and homogenization of variances was possible. The plants were phenotypically grouped in different needle damage classes and mean values of growth and bud‐set were calculated for each of the classes. Mean plant height before tests and bud‐set were both strongly correlated to needle damage. Severely damaged plants were tallest, but the plants became tall because of late bud‐set. Severe needle damage had a negative influence on the growth after tests in one of the experiments. The ranking was stable between experimental entries comparing ‐10 with ‐20°C tests. The correlation between mean needle damage and actual survival after tests was high. Classification of visual symptoms on needles is a good method for estimating freezing injury in Norway spruce.