A method for rapid and homogenous initiation of post-harvest physiological deterioration in cassava storage roots identifies Indonesian cultivars with improved shelf-life performance

Abstract

Cassava is the most cultivated and consumed root crop in the world. One of the major constraints to the cassava value chain is the short shelf life of cassava storage roots which is primarily due to the so-called post-harvest physiological deterioration (PPD). The identification of natural sources of PPD tolerance represents a key approach to mitigating PPD losses by generating farmer- and industry-preferred cassava cultivars with prolonged shelf life. In the present study, a PPD assessment method was developed to screen for PPD tolerance in the cassava germplasm. The proposed PPD assessment method displayed a reduced rate of microbial infection and allowed a rapid and homogenous development of typical PPD symptoms in the cassava storage roots. We successfully used the PPD assessment method in combination with an image-based PPD scoring method to identify and characterize PPD tolerance in 28 cassava cultivars from the Indonesian cassava germplasm. Our analysis showed a significant and positive correlation between PPD score and dry matter content (r = 0.589-0.664, p-value < 0.001). Analysis of additional root parameters showed a significant and positive correlation between PPD scores at 2 days post-harvest (dph) and root length (r = 0.388, p-value < 0.05). Our analysis identified at least 4 cultivars displaying a significantly delayed onset of PPD symptoms as compared to the other selected cultivars. The availability of cassava cultivars contrasting for tolerance to PPD will be particularly instrumental to understanding the molecular mechanisms associated with delayed PPD in cassava roots.

Keywords: Cassava germplasm; PPD assessment.

Fig. 1

(1) Illustration of PPD initiation by using standard and longitudinal cut methods; (2) Illustration of sampling used for DMC and HCN content measurements. A detailed description of the methods is provided in Material and Methods as well as Supplementary Methods

Fig. 2

The percentage of microbial contamination in nine cassava cultivars was assessed by longitudinal cut and standard methods at 7 and 14 dph. Asterisk (* and **) shows significance level at 5% and 1% respectively, determined by student t-test between the two methods at the same time point

Fig. 3

PPD development of nine cassava cultivars assessed by longitudinal cut and standard methods at 2 and 4 dph

Fig. 4

PPD symptoms in selected Indonesian cassava cultivars during the 7 day time course (dph = days post-harvesting)

Fig. 5

PPD scores of eight selected cassava cultivars. Statistical analysis using one-way ANOVA and LSD post hoc test at each time point (p < 0.05)

Fig. 6

Correlation between PPD score at 4 dph and percentage of dry matter content (%DMC) in 28 cassava cultivars

Fig. 7

PCA of the twenty-eight cassava cultivars for dimensions 1 and 2. Left: plot of variables, solid arrows represent traits used for computation, dotted arrows (PPD at 0, 2, 4, and 7 dph) represent supplemental traits. Right: Plot of individuals, circle, square and triangle respectively represent delayed, intermediate and early PPD.