P. Kakes
Cyanogenesis, i.e., the ability to produce hydrogen cyanide (HCN) under particular circumstances, is a widespread phenomenon in plants. Both direct and indirect evidence points to a primarily defensive function of cyanogenesis, but the direct evidence is limited and obtained mainly from species polymorphic for cyanogenesis. Other functions of cyanogenesis have been proposed, but these are mostly of a secondary nature. The question of whether or not to change the cyanogenic potential of existing cassava cultivars can only be addressed within the general framework of a cost-benefit analysis of chemical defense. Such an analysis requires a common yardstick to measure both cost and benefit. From an evolutionary point of view the best yardstick is fitness, but in agricultural species, yield (under specified conditions) can also be used. It is important to include all the effects of changes in cyanogenesis in a cost-benefit analysis. In this paper, the components of costs and benefits will be discussed, and a short review of the evidence for a defensive function of cyanogenesis in cassava will be presented. The data available in the scientific literature are scant and equivocal, and it is difficult to separate the effects of variation in cyanogenesis from the effects of other characters in which the cassava cultivars under study may differ.

Several methods are proposed for gathering information on the function of cyanogenesis in cassava; these include studying existing data and devising new experiments. In new experiments, the following points should be considered:

  1. Variation in cyanogenesis, herbivore resistance and yield should be studied in crosses made specifically for the purpose.
  2. Cyanoglucoside concentration and beta-glucosidase activity should be measured regularly in both leaves and starchy roots, during the course of the experiments.
  3. Herbivore activity should be controlled, and at least two different levels of herbivory should be applied.

In the absence of data it is currently impossible to give guide-lines for breeding objectives regarding cyanogenesis.

Kakes, P. (1994). THE FUNCTION OF CYANOGENESIS IN CASSAVA. Acta Hortic. 375, 79-86
DOI: 10.17660/ActaHortic.1994.375.5
Defense mechanism, chemical defense, cost-benefit analysis, herbivory

Acta Horticulturae