Comparative Evaluation of Physiological Post-Harvest Root Deterioration of 25 Cassava Accessions: Hydroxycoumarin Fluorescent Accumulation Vs Visual Analysis

Cassava (Manihot esculenta) is the most important root crop in the tropics and is consumed by 500 million people daily. Due to its drought tolerance, ability to grow in poor soils, and resistance to herbivory cassava is well suited for cultivation by subsistence farmers particularly in Africa. However its use and expansion is constrained by rapid physiological post harvest deterioration (PPD), which often starts within 24 hours after harvest, renders the root unpalatable and affects the crop’s economics value significantly. PPD is a complex process that involved changes in metabolic process and accumulation of secondary metabolites. Those metabolites include hydroxycoumarins, such as scopoletin, esculin and scopolin. The quantification of their emitted florescent has been proposal as an objective tool to evaluate PPD response in cassava. Traditionally, the evaluation of PPD has been performed by more subjective method based on the analysis of deterioration visually. Here we present data on the use of a standard visual methodology in comparison to an image analysis of hydroxycoumarins florescent accumulation. Ten month old storage roots from the Puerto Rican cassava germplasm which comprise of 25 accessions from Africa, Caribbean, Central America and South America, grown in ‘coto’ soil in the Northwest Puerto Rico were analyzed for PPD. After five days of storage at room temperature, six 0.2-0.5mm transversal sections at 15%, 30%, 45%, 60%, 75% and 90% of total length from the proximal end were cut and analyzed using the two methodologies. Our findings suggest that there was no correlation (r = 0.14) between the florescent accumulation of hydroxycoumarins and the visual symptoms five days after harvest. We concluded that the accumulation of hydroxycoumarins is not a reliable marker for evaluation of PPD response. Furthermore we were able to identify the accessions with high- and low-levels of PPD in the Puerto Rican cassava germplasm based on visual symptoms.