Identification and Characterization of Low-Nitrogen-Tolerant Potato Germplasm Resources

Screening potato germplasm for low nitrogen (LN) tolerance is essential for improving nitrogen use efficiency and agricultural sustainability. A set of 156 potato genotypes from diverse sources—including the International Potato Center (CIP), the National Potato Germplasm Repository (CAAS), and varieties and lines bred by the Qinghai Academy of Agriculture and Forestry Sciences—was evaluated under optimal (60 mmol·L−1) and low (3 mmol·L−1) nitrogen conditions using tissue culture. Nine traits related to growth, nitrogen accumulation, and nitrogen use efficiency were measured. Under LN stress, nitrogen physiological efficiency (NPE), uptake efficiency (NUpE), and utilization efficiency (NUE) increased, while most growth-related traits declined. Considerable variation was observed in fresh weight (FW), dry weight (DW), nitrogen accumulation (NA), and NUE, with coefficients of variation ranging from 0.38 to 0.40 under LN and 0.17 to 0.42 under ON. Principal component analysis identified NA and NUpE as the primary contributors to phenotypic variation. Based on comprehensive D-values from cluster analysis, the genotypes were classified into five tolerance groups: Type I—(strong low-nitrogen tolerant (13 accessions); Type II—low-nitrogen tolerant (66 accessions); Type III—moderate low-nitrogen tolerant (36 accessions); Type IV—low-nitrogen sensitive (24 accessions); and Type V—highly low-nitrogen sensitive (17 accessions). Physiological validation revealed two distinct adaptive strategies: a nitrogen conservation strategy (Type I), characterized by high NA and nitrogen content (NC) alongside moderate physiological efficiency, and an efficiency-driven compensation strategy (Types II, IV, and V), marked by low NA and NC but high physiological efficiency. The congruence between multivariate clustering and subsequent physiological measurements confirms that this classification effectively captures genotypic differences in low nitrogen tolerance. Thirteen highly LN-tolerant genotypes—including PIMPERNEL, Favorita, and Spunta—were identified as promising genetic resources for breeding nitrogen-efficient potato cultivars. This tissue culture-based screening method provides a practical tool for evaluating nitrogen tolerance in plants and supports sustainable potato production under limited nitrogen availability.