Use of chlorophyll fluorescence to evaluate the cold acclimation and freezing tolerance of winter and spring oats

The efficiency of the excitation capture by open Photosystem II (PSII) reaction centres was measured by the F-v/F-m ratios in a collection of winter and spring oats in order to assess the effects of hardening and freezing on the functionality of PSII and also the suitability of a chlorophyll fluorescence-based method to screen oat cultivars for frost tolerance. A significant reversible decrease in F-v/F-m was found in all genotypes during acclimation to low, non-freezing temperatures. F-v/F-m analysis appears to be an attractive test for the evaluation of frost tolerance in oats, being rapid, non-invasive and capable of monitoring a trait related to a crucial stage in the acquisition of frost tolerance. It is more sensitive and precise than other standard methods and highly correlated with field-evaluated frost damage. The measurements made during recovery I or 2 days after stress when the visual symptoms are not yet expressed, were especially advantageous because of the large variability in genotype response. The r-values (close to 0.8) were reduced due to the non-standard behaviour of the winter cultivar 'Aintree'. The cold acclimation response of this genotype has been analysed in detail and the limits of artificial freezing tests are discussed.