Phenotypic Markers for Resistance to Alternaria Black Spot in Pomegranate Germplasm: Unveiling the Role of Acidity and Pigmentation

Black Spot disease, caused by Alternaria alternata, is a significant pathological challenge in pomegranate cultivation. This study evaluated the natural resistance of 37 pomegranate accessions from the Newe Ya'ar germplasm collection during early fruit development (2024-2025) to A. alternata, causing black spot disease on pomegranate. Fruits were inoculated with spore suspension (106 spores/ml) and scored for disease severity. While initial univariate analyses (Pearson/Spearman) failed to show significant linear correlations between disease severity and historical physiological traits (pH, sugar percentage, peel, and aril color), multivariate Principal Component Analysis (PCA) and K-means clustering revealed a distinct phenotypic structure explaining 56.8% of the variance. The analysis classified the varieties into three clusters: Highly Susceptible, Susceptible, and Resistant. The results indicate that while light pigmentation is associated with high susceptibility, low juice pH serves as the primary discriminator for resistant among pigmented varieties. These results suggest that fruit juice pH may serve as a useful resistance associated marker in pomegranate.