THE STAGES AT WHICH FROST INJURY OCCURS IN ALFALFA

Abstract

This investigation deals with the injury caused to four varieties of alfalfa (Medicago sativa L.), under freezing–thawing conditions comparable with those of Australian tableland regions.Evidence is presented to show that the intactness of cell membranes influences the magnitude of the low-frequency resistance attained in frozen tissues.Measurements of the maximum resistance attained during freezing, the proportionate drop in resistance after freezing, and the minimum resistance attained after freezing, are considered in relation to two subsequently determined criteria of injury. The results are interpreted as showing that injury occurs in tissue during freezing, in the frozen state, and during thawing.Brief comments follow concerning causes of injury at the various stages, factors responsible for hardiness, and the procedure necessary for selecting the most hardy genotype.