Abstract
Coffee leaf rust (Hemileia vastatrix) caused large damage on Arabica coffee in Asia, Africa, and America. The resistant genotypes released to farmers in Brazil were developed from the existing cultivars. However, the cultivars of Arabica coffee existing in North Sumatra Province of Indonesia is not yet researched to find resistant genotypes. The goal of this reseach was to determine variability of coffee leaf rust and leaf morphology. In total of 84 genotypes growing in this Province were selected using nested design. Data was analyzed using nested design, correlation, stepwise regression, and hierarchical cluster analysis. This research revealed leaf rust severity had high genotypic variation, low heritability, and high genetic adveance. Ratios of leaf morhology showed moderate to high genotypic variation and heritabilities. Leaf rust severity (y) significantly correlated with both ratio of leaf length with leaf area (x1) and ratio of leaf length with leaf width (x2) with equation y = 2,04 + 62,48x1 3,95x2 with coefficient of multiple correlation R = 0,470**. By using leaf rust severity and these two ratios in cluster analysis, one cluster comprised 18 genotypes with medium leaf rust severity. It could be concluded that resistant genotypes of Arabica coffee might be possible to develop from the existing cultivars. Leaf rust severity might not be used as selection parameter in breeding for leaf rust resistance.