Genetic diversity for physiological deterioration in cassava roots

Cassava roots are characterized by rapid post-harvest deterioration (PHD). Improving root storability could expand cassava markets. The objectives of this work were to assess the available genetic variability among a group of elite cassava clones in different ecosystems and to select parental material for future studies. The evaluation was conducted at three experimental sites in Colombia (Palmira, Villavicencio and Media Luna). Non-damaged roots were evaluated each day between the second and eighth day after harvest (DAH). For each root the extremes were cut to get a 14-cm piece. The distal part was covered with plastic, and percentage deterioration was evaluated in each of the seven transversal sections (2 cm). Root to root variability was relatively large, and depended on the clone being evaluated and the site. The majority of the clones evaluated at Media Luna and Villavicencio showed a linear trend when relating PHD to DAH, whereas at Palmira about half of the varieties adjusted to a quadratic model. Genetic variability on the last day of evaluation (8 DAH) accounted for 52 per cent of the total observed variability, indicating the possibility of genetic progress in a selection programme. Clones with high levels of deterioration (CM 3306-4 and CM 5253-4) will be crossed with those presenting reduced levels (CM 4484-2 and MCOL 1505) to build up genetic stocks to study intrinsic biochemical process responsible for PHD. The clone MCOL 2215 presented differential performance across evaluation sites, and represents a valuable material studying environmental effects on PHD.