Evaluation of Stem Polyphenol Content as a Potential Marker for Selecting Foot-Rot-Resistant Sweet Potato (Ipomoea batatas (L.) Lam.) Hybrids

Foot rot, a disease caused by the fungal plant pathogen Diaporthe destruens, has been a major problem throughout East Asia. In major sweet-potato-producing regions, developing sweet potato cultivars that are resistant to foot rot has become an urgent priority. The possibility of selecting resistant cultivars by using polyphenols in the stems as markers was recently suggested, but this selection method has not been tested in the crossbreeding of sweet potato cultivars. In this study, we crossed the sweet potato cultivars ‘Konaishin’ and ‘Tamaakane’ (each of which is resistant to foot rot), analyzed the polyphenols in the stems of the resulting hybrid lines, and evaluated the possibility of selecting resistant lines. As a result, KT No. 7 and KT No. 8 showed similar or lower total polyphenol contents (145.9 and 112.9 mg GAE 100 g−1 FW, respectively) compared to ‘Tamaakane’ (142.2 mg GAE 100 g−1 FW). The selected line, KT No. 7, exhibited the highest resistance among the hybrids when it was directly inoculated with the foot rot pathogen using stems as test material, showing a disease severity value of 1.8, which was substantially lower than that of ‘Tamaakane’ (50.0). These results suggest that stem polyphenol content has potential as a marker for identifying promising candidates with foot rot resistance, although its predictive value may vary depending on genetic and environmental factors. This approach may help improve the efficiency of foot rot resistance screening in sweet potato breeding programs.