Resistance Variability of Arabica Coffee Genotypes (Coffea arabica L.) to Leaf Rust Disease (Hemileia vastatrix)

Coffee leaf rust disease (Hemileia vastatrix) causes large damage to Arabica coffee plantation in Asia, Africa, and America.  In Indonesia, particularly in North Sumatra, the resistance level of Arabica coffee genotypes is still unknown. The objective of this research was to determine the resistance variability of Arabica coffee genotypes to leaf rust disease and its relation to leaf morphology.  A total of 84 genotypes grown in North Sumatra were selected in November 2015 and 2016, and December 2017 using a nested design.  Data were analyzed using nested design, correlation, stepwise regression, and cluster hierarchy analysis. The result showed that the G56 genotype performed the most resistant to leaf rust disease, with a severity of 5.21%.  The severity of leaf rust disease has high genotypic variation, low heritability, and high genetic advance.  Leaf morphological ratios showed moderate to high genotypic variation and heritability.  The severity of leaf rust (y) significantly correlated with the ratio of leaf length to leaf area (x1) and the ratio of leaf length to leaf width (x2) with the equation y = 2.04 + 62.48x1 - 3.95x2, and multiple correlation coefficients R = 0.470 **. By using the leaf rust severity and the two ratios in the cluster analysis, these 84 genotypes were grouped into five clusters.  The result showed that several Arabica coffee genotypes with a high level of resistance to leaf rust disease are potential to be further developed.