The limitations of a cut leaf test for assessing the frost resistance of the tuber-bearing solanums

Abstract

On the basis of physiological work, a cut leaf test was developed by which the frost resistances of a range of the tuber-bearing Solanums were determined. The test, enabling the resistances of thirty cut leaves to be tested during each freeze, was so designed that any variations, which might have arisen from different levels of supercooling, were avoided. During the tests prechilled material was cooled, at a rate of 2°C/hour, to a desired temperature. At this limit the temperature was held constant until the material had been below 0°C for a period of six hours. A rapid thaw was then given and the percentage injuries of the leaves were estimated after a period of recovery. After a number of tests, at temperatures from-2 to-6°C, a numerical value, the frost killing temperature was given to each plant. The use of the test is limited, for it was shown that the resistances of a chronological series of leaves vary considerably; greatest resistance is present in the central leaves. The ranges of resistance shown by identically genetical plants is considerable; such variation might be reduced by means of controlled growth conditions. The effect of the rate of thawing upon subsequent injury was also investigated. No appreciable differences between rapidly and slowly warmed leaves were apparent, yet the latter treatment produced greater uniformity in the rise and fall of resistance as the leaf passes from youth to maturity.