Multivariate Analyses of Climate-Resilient Traits for in situ Conservation of Black Pepper (Piper nigrum L.) Diversity in Kerala, India

Abstract

Aims: This study is undertaken for the comprehensive multivariate assessment of drought-adaptive morpho-physiological diversity in black pepper landraces from Kerala. Study Design: Survey-based evaluation of morpho-physiological traits at natural drought stress. Place and Duration of Study: The investigation was carried out over major black pepper-growing regions of Kerala, India—the main centre of diversity for P. nigrum, situated in the southern Western Ghats. The trait measurements were recorded in situ under farmer-field conditions during the peak drought period of the study year (March–May 2023 & 2024). Methodology: A total of 62 black pepper genotypes collected from diverse agro-ecological units of Kerala were evaluated for key morphophysiological traits, including specific leaf area, relative water content, leaf thickness, stomatal density, epicuticular wax content, and other leaf morphological features. Variability in traits was quantified by the coefficient of variation, and inter-genotypic differences were assessed to capture the adaptive responses to moisture deficit. Hierarchical cluster analysis, heatmap-based grouping and Principle Component Analysis (PCA) were performed to resolve genetic groupings and identify drought-resilient genotypes. The PCA loading and cos² values were used to determine which traits contributed most strongly to the overall variance. Results: The highest variability was observed for specific leaf area, with a coefficient of variation (CV) of 0.55, while relative water content exhibited the lowest variability, with a CV of 0.03. Strong inter-genotypic differentiation in epicuticular wax deposition and stomatal density reflects varied adaptive strategies to drought. Hierarchical clustering grouped the genotypes into two major groups, while heatmap clustering identified 42 drought-tolerant genotypes characterized by reduced specific leaf area, lower stomatal density, increased leaf thickness, and enhanced epicuticular wax content. PCA extracted three principal components which explained 71.81% of the total variance; PC1 represented key physiological drought-adaptive traits. Nine genotypes, namely G-44, G-61, G-38, G-50, G-56, G-32, G-54, G-36, and G-48, recorded high cos² values (>0.75) and clustered with thick leaves with high wax content and low specific leaf area, thus confirming superior drought resilience. Conclusion: Leaf thickness, epicuticular wax deposition and high relative water content emerged as the strongest positive indicators of drought tolerance, whereas high specific leaf area and increased stomatal density signified susceptibility. This study underlines substantial unused adaptive diversity in the black pepper germplasm of Kerala and supplies basic information necessary for focused on-farm conservation, climate-resilient breeding and long-term management of genetic resources.