A RAPID METHOD FOR MEASURING FREEZING RESISTANCE IN CROP PLANTS

The objective of this study was to develop a technique based on chloro phyll fluorescence to assess freezing injury and resistance of leaves. Optimization was done with faba bean leaves and applicability to othe r crops was examined at winter and spring with types of barley, oats, rape and faba beans. Selected leaves from young hardened beans were su bjected to standardized freezing tests with different minimum temperat ures (T-min) and fluorescence was monitored. After a dark period basic fluorescence (F-0) was induced by 0.2 mu mol m(-2) s(-1) pulsed red l ight and maximum fluorescence (F-m) was assayed at different light int ensities. 1500 mu mol m(-2) s(-1) rendered to give the maximum possibl e output of Fm and best differentiation of differently damaged leaves by F-v = F-m-F-0. Leaf temperature during measurement and during a sho rt storage (less than or equal to 2 h) should be kept at about 0 degre es C to avoid biases between differently damaged leaves. The measuring spot on the leaf must be standardized since fluorescence response dif fered at the tip and base of a leaflet, but not between the two leafle ts of a faba bean leaf. The applicability of F-vr (ratio of F-v of str essed to unstressed leaves) as a measure of resistance was demonstrate d by comparison of winter hardiness of cultivars with freezing resista nce calculated from the relationship of F-vr and the T-min used in fre ezing tests.