Metabolic diversity in sweet potato (Ipomoea batatas, Lam.) leaves and storage roots

Abstract

Sweet potato (Ipomoea batatas, Lam.) is an important root vegetable in developing countries. After its domestication in Neotropical America, human migration led to the distribution of the sweet potato plant throughout the world. Both leaf and storage root are high in compounds of nutritional value. Yet, the storage roots are of particular value due to their significant content of provitamin A (β-carotene). The breeding effort for elite sweet potato lines led to the reduction of genetic diversity and the potential to improve other traits. The focus of the present study was to assess the metabolic diversity of 27 sweet potato cultivars including landraces and improved varieties. A metabolite profiling approach was optimised for sweet potato leaf and storage root tissue and 130 metabolites identified with three different analysis platforms. The data highlighted a lack of correlation between storage root phenotype and leaf metabolism. Furthermore, the metabolic diversity of storage roots was based on the secondary metabolism, including phenylpropanoids and carotenoids. Three cultivars of three different flesh colouration (yellow, orange and purple) showed a significant difference of the primary metabolism. This data demonstrates the value of metabolite profiling to breeding programs as a means of identifying differences in phenotypes/chemotypes and characterising parental material for future pre-breeding resources.

Fig. 1. Pathway display of metabolites detected in sweet potato leaf and storage root tissue.

The colouration of the metabolites indicates where the metabolite was detected in leaf material (green), storage roots (orange) or both tissues (grey)

Fig. 2. Pigmentation profiles of leaf and storage roots.

Carotenoid content of storage root (a) and leaf (b) tissue analysed as dry weight (DW). Cultivars were grouped into phenotypes by storage root pigmentation, as displayed next to the cultivar codes. Error bars represent the standard deviation of four biological replicates

Fig. 3. Principal component analysis of metabolite composition of leaf (triangles) and storage root (circles) tissue.

The score plots show the variation in the overall metabolite composition (a, b) and the primary metabolites only (c, d). Colouration of the cultivars represents the pigmentation of the storage root as displayed in the legend

Fig. 4. Correaltion between ß-carotene, starch and sucrose content in storage roots.

Graph shows the linear regression between ß-carotene measurements and starch (a) and sucrose (b) content. Linear regression coefficient (R²) and significance of the regression are displayed for each graph