Variation in Root System Architecture and Lead Accumulation in Sweetpotato (Ipomoea batatas L.) Cultivars Bayou Belle and Beauregard

The primary objective of this work was to generate species-specific information about root system architecture (RSA) adaptations to simulated natural levels of lead (Pb) during the establishment phase and onset of storage root formation in sweetpotato. In two separate experiments repeated two times, sweetpotato cultivars Bayou Belle (BB) and Beauregard (BX) were grown on sand substrate and provided with 0.5X Hoagland’s nutrient solution with varying levels of Pb: 0, 10, 20, and 30 mg·L −1 . All experiments were arranged in randomized complete block design (RCBD) with four replications. In the first experiment, entire root systems were sampled at 5, 10, and 15 days to represent key adventitious root (AR) developmental stages. The cultivars displayed variation in RSA attributes. Cultivar BB consistently exhibited higher lateral root (LR) number and greater root length than BX under all treatment levels. In contrast, BX main root length (MRL) treated with 10 mg·L −1 Pb increased 83%, 21%, and 15% relative to the untreated controls at 5, 10, and 15 days, respectively. A second experiment was conducted to collect storage root samples at 50 days. Storage root length, width, and length-to-width ratio did not vary with Pb levels in both cultivars. However, there was a cultivar-specific variation in storage root Pb accumulation across Pb treatments. The cultivar BB did not exhibit variation in storage root Pb accumulation across Pb treatment levels. In contrast, the cultivar BX demonstrated a 200- and 300-fold Pb accumulation at 20 and 30 mg·L −1 Pb treatment levels relative to the untreated BX control plants and significantly higher relative to BB storage roots grown at similar levels. Results are consistent with the hypothesis that increased root mass is associated with low accumulation of Pb. This study provides the first documented evidence of sweetpotato RSA responses to Pb at concentrations commonly found in agricultural soils. The findings corroborate evidence from model systems and well-characterized species of genotype-specific variability in RSA adaptation to Pb presence. Linking RSA responses to Pb tolerance will support crop improvement efforts to develop cultivars with reduced Pb accumulation.