This research deals with the viability study of using stem cuttings with three different diameters, related to three different positions in the cassava plant (Manihot esculenta Crantz), and evaluating the effects of such stem cuttings on the emergence, velocity, number and weight of tuberous roots per plant and yield of three cassava cultivars. The field research was conducted in Piracicaba, SP, Brazil, during two years, from September 23, 1980 to July 23, 1981, and September 1, 1981 to July 20, 1982. The mature and healthy stem cuttings were obtained from 12 month old plants of the Mantiqueira, Jaçanã and Pirassununga cultivars. These cuttings (20 cm long) were divided into three diameter size classes: 2.6 ± .2 cm, 2.0 ± .2 cm and 1.4 ± .2 cm, representing stem cuttings taken from the main stem, the primary and the secondary ramification of the mother plants, respectively. The experimental design was a 3 x 3 factorial in randomized blocks with nine treatments in five blocks. The following conclusions are based on the results obtained: 1. The stem cutting vigor is more significantly shown in the stage of plant emergence. 2. Refering to the initial phases of the development, stem cuttings with 2.0 ± .2 cm or 2.6 ± .2 cm of diameters are prefered. 3. A smaller number of tuberous root yield per plant is compensated by a major tuberous root weight. 4. Neither stem cutting diameter nor stem cutting position influenced on root production per area. 5. The three cultivars used in the experiment showed a high root yield, and the cultivar Mantiqueira was the most productive.
cassava vegetative propagation; stem cutting quality