Further studies on the determination of cold hardiness in Trifolium repens L. and Medicago sativa L.

Abstract

This paper deals with probe measurements of low frequency resistance (R_LF), high frequency resistance (R_HF), and resistance index (= 100 x R_LF/R_HF), for the determination of cold hardiness or the injury caused by cold treatments. Populations of white clover (Trifolium repens L.) were subjected to different periods of freezing. Discrimination between treatments could be made in terms of R_LF, R_HF, and resistance index, though discrimination in terms of R_HF is poor. The rest of the paper deals with lucerne (Medicago sativa L.). Measurements were made after a cold treatment on field plants consisting of four commercial strains and their F₁ crosses, and also on F₂ seedlings. R_LF and the resistance index appear to be equally good predictors for the recovery of strains or of individual plants from such populations. The Appendix deals with measurements on commercial (tetraploid) plants, diploids, and colchicine-produced tetraploids.