Effect of rainfall on HCN content in cassava roots

Environmental conditions can modify the cyanide content in cassava roots. A given cultivar with low cyanide could result in an increased HCN content under different environmental conditions (Dominguez et al, 1979). Regulation of HCN content by selecting climatic conditions could be used according to the end product desired. Two plant groups of the same cultivar were used to analyze the effect of rainfall distribution during plant cycle on the HCN content. Plants were produced in vitro, kept in soil for one month under controlled conditions in green houses and subsequently transferred to the field. After eight months in the field, the roots were harvested and cyanide contents were evaluated (Ikediobi et al, 1980). In Bolivar State, the rain starts in March, reaches a maximum in July and decreases until December, accumulating a total of 67.2 inches. The first group was transferred to the field in April and harvested in January. The second was transferred in June and harvested at the end of February. A significant higher value of HCN content (174 plus or minus 18 u HCN/g fresh parenchyma) was obtained in plants harvested after two months of drought as compared to those harvested in the middle of January (42 plus or minus 5 ug HCN/g fresh parenchyma). A second comparison of the effect of total rainfall was performed with other cultivar using the location described above and a different location in Cojedes State. In Cojedes the rainfall starts in March, has two maxima in July-August and October and gradually decrease until January, accumulating a total of 42.4 inches. When rains last longer, no significant effect of total rainfall on the HCN content was observed in the cultivars studied. In Bolivar State the HCN content was 69 plus or minus 15 u/g fresh parenchyma with 67.2 inches of rain while in Cojedes State was 61 plus or minus 8 u/g fresh parenchyma with 42.4 inches. These results suggest that HCN content depends more on the lasting humidity in the soil during the plant cycle than on the total rainfall. On these bases it is possible to decide the date when the plants must be transferred to field, according to the last use of the roots to be produced