Screening, Biochemical, and Molecular Characterization of Postharvest Physiological Deterioration in Cassava Varieties

Abstract

Post-harvest physiological deterioration (PPD) is a significant challenge in the storage of cassava roots. The shelf life of cassava roots ranges from 24 to 72 hours, which reduces their economic value. PPD is characterized by blue/black to brown vascular streaking and the release of reactive oxygen species. Breeding efforts aimed at improving PPD resistance are hindered by limited information on the genetic diversity of different shelf-life types and cassava's natural heterozygosity. This study aimed to identify cassava varieties with delayed PPD. Twenty varieties were assessed and evaluated changes in metabolite content and gene expression during storage. Cassava varieties were planted at Kenyatta University's Plant Transformation Laboratory. After maturity, After maturity visual scoring and imaged based scoring to assess PPD at 0, 3, 5, 8, and 11 days post-harvest. Spectrophotometry was utilized to measure the levels of phenolic compounds, flavonoids, carotenoids, and anthocyanins in the stored roots. Additionally, expression of PPD related genes was monitored PAL, APX-2, APX-3, and AP using RT-PCR in both tolerant and susceptible varieties. The study's results demonstrated significant differences in PPD responses among the cultivars. Notably, the varieties NASE18 and KCA0013 exhibited a delayed onset of PPD symptoms, whereas TZ130 and Tajirika were more susceptible. Furthermore, the phenolic and flavonoid content were higher in KCA0013 and NASE18, while the carotenoid levels reached their peak in MM96/7151. Interestingly, the anthocyanin content significantly increased in the susceptible variety TZ130. The PPD-tolerant varieties showed elevated levels of PAL, AP, and APX-3 expression, while the expression of APX-2 was higher in the PPD-susceptible varieties. This study identifies promising cassava genotypes for breeding by highlighting the distinct biochemical and molecular profiles associated with PPD tolerance.