Drought-adaptive Grouping of Black Pepper (Piper nigrum L.) Genotypes Using Hierarchical Clustering on Principal Components (HCPC)

Abstract

Aims: Application of Hierarchical Clustering on Principal Components (HCPC) to identify drought-tolerant genotypes of black pepper (Piper nigrum L.) based on important morpho-physiological characteristics. Study Design: Field observation supported by multivariate statistical analysis (HCPC) for genotype classification. Place and Duration of Study: The investigation was conducted across major black pepper-growing regions of Kerala, India, part of the Western Ghats. Trait measurements were performed during the peak summer drought period (March–May 2023) of the study year under in situ farmer-field conditions. Methodology: In the present study, sixty-two black pepper genotypes were evaluated for various key morpho-physiological characteristics such as specific leaf area (SLA), relative water content (RWC), leaf thickness, stomatal density, epicuticular wax content, leaf area, leaf angle, leaf length, leaf width, petiole length, number of nodes per lateral branch and lateral branch length. HCPC was employed to classify the genotypes into clusters. The pattern of genotype groupings was further visualized through factor maps (2D & 3D). Results: HCPC classified the 62 genotypes into two significant clusters: Cluster 1, containing drought-resilient genotypes (e.g., G-38, G-61, G-25, G-36, G-50, G-56), showed significantly higher leaf thickness, wax deposition and RWC (v values: leaf thickness = 5.97; wax = 6.21; RWC = 6.20). Cluster 2, comprising drought-susceptible genotypes (e.g., G-60, G-1, G-12, G-55, G-27), exhibited higher SLA (v = 6.01) and stomatal density (v = 6.33). HCPC factor maps confirmed strong separation between clusters along Dim1 (34.9%) and Dim2 (24.6%). Conclusion: HCPC effectively differentiated the drought-tolerant and drought-sensitive black pepper genotypes based on morpho-physiological adaptation. Leaf thickness, epicuticular wax and RWC showed the most positive indicators of drought tolerance, while high SLA and stomatal density were characteristic features of susceptibility. The identified drought-resilient genotypes can be used as promising candidates for climate-smart breeding and targeted conservation programs.