Reducing post-harvest physiological deterioration in cassava breeding by National Root Crops Research Institute Umudike
Cassava roots are notable for their short shelf-life due to post-harvest physiological deterioration (PPD). PPD is initiated by mechanical damage, which typically occurs during harvesting and progresses from the proximal site of damage to the distal end, making the roots unpalatable within 72h. The short shelf-life severely limits marketing options by increasing losses, marketing costs, and limiting access to urban markets and processing centres. Reducing PPD of cassava roots is amongst top research priorities National Root Crops Research Institute (NRCRI) Umudike. Our main approaches NRCRI aimed at reducing Cassava PPD include conventional breeding, mutagenesis, molecular breeding and genetic engineering. Land races and exotic genotypes have been screened for delayed PPD. Limited variability was observed amongst land races in this trait. Thirty three genotype with delayed PPD at 7 days after harvesting (DAH) and 22 with delayed PPD at 14 DAH have been identified from backcross populations of Manihot walkerae. Gamma radiation was used to induce genetic variation for delayed PPD in local germplasm. Mutagenized populations were developed using in-vitro plants and OP seeds of farmer preferred varieties and land races. Few genotypes from these populations had low PPD (7DAH). Genetic mapping for PPD using genomic DNA isolated from young leaves of parental genotypes indicated that genetic factors, most likely major QTLs, were likely involved in the expression of delayed PPD in cassava. Another strategy adopted was to use the synergistic effect of over expressing nuclear encoded gene, alternative oxidase (AOX) and increased accumulation of beta carotene content in cassava roots to delay onset of PPD. Constructs carrying appropriate genes were successfully transferred into cassava and plants expressing the inserted genes have been obtained and are being evaluated appropriately. Preliminary success has been achieved in developing materials with delayed PPD. Further evaluation of these materials at different locations is necessary due to high influence of G x E interaction on the trait. Furthermore, markers for PPD are being developed, and image analysis method of assessing roots for PPD is being introduced to help straighten and fast-track the selection of genotypes with delayed PPD.
Keywords: Gamma radiation, molecular breeding, genomic breeding, genetic engineering and delayed PPD