Non-destructive sampling procedure for biochemical or gene expression studies on post-harvest physiological deterioration of cassava roots

Cassava (Manihot esculenta Crantz) roots spoil 2-3 days after harvest due to post-harvest physiological deterioration (PPD), which had remained an unsolved problem until recent reports of genetic variation for tolerance to it. PPD is a genetically active, oxidative process triggered when the harvested roots are separated from their mother plant. The short shelf life of harvested roots results in large losses and high transport and marketing costs. Recent reports on positive genetic variation for tolerance to PPD will facilitate breeding for extended shelf life of the roots and a better understanding of the biochemical and genetic events leading to PPD. However, PPD scoring is difficult and prone to large experimental errors. It is often the case that roots from the same plant can have 0 and 100% PPD score due to injuries during the harvest process, variation in dry matter content and, most likely, other variables yet to be identified. Therefore, sampling a root for biochemical or genetic studies and measuring PPD in a different root, is not a reliable approach. A device has been developed and tested for the possibility of extracting a core of root parenchyma, filling the space with melted paraffin (to reduce oxygen availability), and then one or two weeks later visually quantifying PPD in the same root. Sampling the roots did not have any significant effect on PPD suggesting that the protocol can be used for biochemical composition and gene expression studies related to the causes of PPD and the possibilities of developing tolerance to it.