<!--[if !supportLists]--> 1. <!--[endif]--> Abstract The work presented here is a review of cyanide in cassava. The presence of the two cyanogenic glycosides (linamarin and lotaustralin), in cassava, which on enzymatic hydrolysis leads to the production of hydrogen cyanide, is a major factor limiting cassava use as food or feed. Linamarin accounts for more than 80% of the cassava cyanogenic glucosides. It is a β -glucoside of acetone cyanohydrin and ethyl-methyl-ketone-cyanohydrin. Cassava varieties are often categorized as either sweet or bitter, signifying the absence or presence of toxic levels of cyanogenic glucosides, respectively. The so-called sweet (actually not bitter) cultivars can produce as little as 20 milligrams of C yanide (CN) per kilogram of fresh roots, whereas bitter ones may produce more than 50 times as much (1 g/kg). Cassava grown during drought are especially high in these toxins. In addition, Cyanide is a chemical defense developed to cope with a huge diversity of unfavorable biotic conditions in the field. These glycosides and cyanogenic glycosides liberate cyanide , which, blocking cytochrome c oxidase (responsible for muscle and brain function) and NIS, is poisonous to parasites and herbivores but does not affect the plant cells. A lot of factors affect the level of cyanogenic glycosides in cassava. Many processing methods that reduce c yanide levels in cassava products have been developed. <!--[if !supportLists]--> 2. <!--[endif]--> Keywords: Cassava; Cyanogenic; Hydroxynitrite; Linamarin

In spite of diligent efforts by National Root Crops Research Institute (NRCRI) Umudike and International Institute of Tropical Agriculture (IITA) to make Nigeria the largest producer of cassava in the world, the adoption rate of elite cultivars by farmers is about 40% and that is unacceptable. In addition, all cassava cultivars presently grown in Nigeria are low in essential minerals, vitamins, and protein content, and high in cyanogenic content. Cassava with yellow roots contains elevated levels of β-carotene (pro-vitamin A), an essential nutrient, but they are not commonly grown in Nigeria. Because farmers select cultivars based on multiple criteria, participatory rural appraisal and selection are essential for a successful adoption of new improved varieties. A participatory rural appraisal (PRA) and sensory evaluation were conducted in Abia, Imo, and Ebonyi states of Nigeria to assess farmers’ preferences for pro-vitamin A cassava. Some of the farmer-preferred traits included high yield, early maturity, tolerance to pests and diseases, sweetness, high amount of dry matter (DM) content, easy peeling, marketable roots, and roots that keep long in the ground without decaying. High pro-vitamin A cassava cultivars TMS 01-1368, TMS 05-1636, and TMS 05-0473 were better than farmers’ cultivar NR 8082, because of their color, high premium price, nutritional value, texture, among others, and were selected for adoption.

Controlled crosses and selection of promising cassava genotypes were carried out at Cassava Breeding Programme of National Root Crops Research Institute (NRCRI), Umudike, Nigeria, in 2010. A 3 x 3 North Carolina mating design was used to generate nine F1 population. Out of 7,044 seeds expected from all the pollinated flowers, only 1,102 seeds (15.6%) were harvested. Majority of the pollinated flowers did not develop into fruits due to abortion that happened shortly after pollination. Family TMS 98-0002 x TMS 05-0473 (B3) had the highest seed abortion rate of 75.5% whereas family TMS 98-0505 x TMS 01-1368 (B7) had the lowest seed abortion rate of 25.3%. Seeds generated from viability test were sown in pots and maintained for 28 days in the screen house. Seed germination ranged from 15.5 to 80.9% with a mean of 43.19%. The emerged seedlings were hardened and transplanted to the field alongside their parents. Four hundred and sixty four progeny survived and were evaluated 12 months after planting (MAP). There were very high levels of variability in the segregating F1 progeny for all the traits studied that will be useful for cassava breeding in Nigeria. Subsequent evaluations of promising clones have reached advanced stage for release to farmers in Nigeria. Key words: Cassava, botanical seed, germination, pollination, variation.