Selection parameter in coffee breeding for leaf rust (Hemeleia vastatrix) resistance is very important. Breeders used leaf-rust severity and leaf-rust incidence as parameters of direct selection. However, scientific proof is not yet available whether leaf morphology can be used as a parameter of indirect selection. The objective of this research was to seek the possibility of leaf morphology parameter and its ratio to be used as selection criteria through analyses of genotypic and phenotypic correlations of parameter of rust disease and parameter of leaf morphology and its ratio. The result revealed that genotypes showed significant variations in leaf-rust severity (5.21–25.84%), leaf morphology, and leaf-morphology ratio. Leaf length to leaf width ratio, leaf length to leaf area ratio, and leaf width to leaf weight ratio were not affected by the environment. Leaf-rust severity performed highly significant positive genotypic and phenotypic correlations the ratio of with leaf length to leaf area. For selection criteria, leaf-rust severity could be better used rather than leaf-rust incidence and branch-rust incidence. The ratio of leaf length to leaf area could also be used as an indirect selection criterion because the ratio showed a highly significant genotypic correlation with leaf-rust severity (rGab = 0.254**). However, the ratio of leaf length to leaf area is even better chosen for selection criteria rather than leaf-rust severity because the ratio was not affected by the environment.   Keywords: fungus, Hemeleia vastatrix, indirect selection

Genetic variation is important in plant breeding. However, information on the genetic variability of Arabica coffee especially in coffee field of North Sumatra was not yet available.  Magnitude of morphological variation, genotypic variation, phenotypic variation, heritability, genetic advance, genetic correlation, and phenotypic correlation of plant vigors and yield components of 28 genotypes were evaluated using nested design.  This research showed morphological and genetic variations of the genotypes in the field. Based on the research locations as operational taxonomic unit, the genotypes were separated into three clusters. Most of the parameters had low to moderate genotypic variation, while phenotypic variation was moderate to high. Heritability and genetic advance were low, moderate, and high. Several plant vigors and yield components had a positive significant genetic and phenotypic correlation one another, and several had negative ones. Coffee berry borer infestation (CBBI) had a highly significant negative genetic correlation with leaf width (rG = -0.309**), leaf weight (rG = -0.671**), fruit diameter (rG = -0.320**), and bean length (rG = -0.175**). CBBI showed a significant positive genetic correlation with mesocarp pH (rG = 0.134*).  To reduce CBBI, selection for higher leaf weight is better. Selection on lower pH of mesocarp could be considered to decrease CBBI.Keywords: cluster analysis, genetic correlation, genetic heritability, variability

<p>Coffee leaf rust disease (<em>Hemileia vastatrix</em>) 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- 3.95x_2, 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.</p>

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The performance of Arabica coffee (Coffea arabica L.) depends on the climate, soil, pests, and elevation. Information on the performance of Arabica coffee growing in the changing climate of North Sumatra has not been available so far. To provide such information, 28 genotypes were studied. The nested design used three factors. Seven climate zones, two locations in each climate zone, and two coffee farms (genotype, G) in each location were selected. The research showed that the genotypes were highly significantly different (α = 0.01). G5, G6, and G20 produced the heaviest hundred beans. G13, G19, and G25 suffered the least coffee berry borer infestation (CBBI). The length of rainy season became the most important factor (r2 = 0.54). The CBBI (y, %) correlated significantly and negatively with the elevation (x, m) with the equation of y = 46.4 – 0.025x. The climate zones showed a significant difference (α = 0.05). The genotypes produced heavy beans also in two wet months of the rainy season and one dry month. The temperature (x, °C) was the most important factor affecting CBBI (r2 = 0.65) with the equation of y = –338.2 + 15.5x. The soil pH correlated significantly and positively with beans weight and bean width.