ELECTRICAL IMPEDANCE RATIO TECHNIQUE FOR RAPID ASSESSMENT OF FROST DAMAGE IN PINUS RADIATA

A simple, low-frequency, impedance technique has been applied to frost damage evaluation in seedlings of Pinus radiata D. Don. Stem resistive impedance at 100 Hz was measured before and after a frost to calculate a pre- to post-frost impedance ratio (ZR). By demonstrating a relationship between ZR and the proportion of seedlings surviving a frost (with no more than 30 % needle damage) a relationship between ZR and expected survival was derived. This relationship was used to predict the number of seedlings lightly or seriously damaged in each of two separate populations of seedlings subjected to a range of frosts. Frost damage, with up to one seedling in error out of each batch of six in one population and nine in the other, was correctly assessed in 78 % and 90%, respectively, of the frosts of those populations. In frosts where more than 10 % of the seedlings were incorrectly classified the impedance ratio tended to overpredict survival. Seedlings with a ZR <0.9 had a 100 % chance of surviving, and this screening method could provide for rapid selection of material where no seedling loss is acceptable