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A Rapid Method for Evaluating Freezing Injury to Leaves of Cyanogenic Plants¹

Methods for simple and rapid evaluation of frost damage in plants are limited. A method to evaluate viability following freezing that is applicable to leaves of cyanogenic plants is described. The method involves the change of color of a paper disc impregnated with alkaline picrate from yellow to orange-brown, owing to reaction with hydrogen cyanide (HCN) released from injured leaves. All leaves and leaflets of birdsfoot trefoil (Lotus corniculatus L., cv. Leo) released, HCN following freezing injury and had similar LD₅₀ values. Leaves that will produce about the same amount of HCN can be obtained near the middle of a plant. Results obtained with this qualitative HCN test were similar to results obtained with existing tests of viability. The main advantages of this test are that it does not expose the plant material to an unnatural situation, and that it allows for more killing temperature measurements for a given labor investment.

Key Words: Frost hardiness • Winter hardiness • Survival index • Viability • Hydrogen cyanide • Lotus corniculatus L. • Birdsfoot trefoil

² Plant physiologist, technician, and soil scientist, respectively, Agriculture Canada, Range Research Station, Kamloops, B.C. V2B 8A9 Canada.

Received for publication November 20, 1985.