Abstract
A strategy for genetic improvement of coffee Coffea canephora plants is to aggregate through artificial crossings the characteristics of the Conilon botanical variety, such as shorter height and drought resistance, with the higher average grain size and resistance to pests and diseases of the Robusta variety. Efficiently separating the clones into these two groups with the aid of appropriate analytical procedures makes field tasks easier for professionals and, thus, allows the systematic production of intervarietal hybrids. This study verifies if the non-parametric discriminant analyzes of the k-nearest neighbors (k-NN) and k-average neighbors (k-AN) would be able to correctly classify 130 coffee clones in their botanical varieties previously designated as Conilon, Robusta and Intervarietal Hybrids populations from ten quantitative agronomic characteristics, including the processed coffee beans yield, considering the existing population genetic divergence. These characteristics were found to be good discriminatory variables and the discriminant analyzes k-NN and k-AN, based on the principle of similarity by neighborhood, classified the clones with high hit rates. The k-AN discriminant analysis was able to better discriminate intervarietal hybrids from the group clones Conilon. The results correctly reflected the genetic diversity between the botanical varieties and intervarietal hybrids of Coffea canephora, allowing us to conclude that these classification methods can assist breeders in the main task of discriminating Conilon from Robusta clones.
Highlights
In the coffee plant Coffea canephora Pierre ex Froehner, two cultivated botanical varieties stand out commercially and exhibit different characteristics (Davis et al, 2006)
Considering that breeding programs of the species Coffea canephora have focused on the exploration of promising artificial crosses between the Conilon and Robusta types, our objective was to verify if the discriminant analyzes k-nearest neighbors (k-NN) and k-average neighbors (k-AN) could classify and correctly allocate Coffea canephora clones into botanical varieties or in intervarietal hybrids, based on agronomic characteristics commonly measured in the field and considering the existing population genetic divergence
For the dataset with the three populations included, the mean (79.62%), minimum (77.69%) and maximum (81.54%) values of percentages of correct classification (Pc) by the method of the k-nearest neighbors exceeded the value of Pc (70.00% and nc = 91 clones) of the k-AN method, and reflected differences between methods in terms of the number of classification hits from ten to fifteen clones, depending on the k value adopted by the k-NN
Summary
In the coffee plant Coffea canephora Pierre ex Froehner, two cultivated botanical varieties stand out commercially and exhibit different characteristics (Davis et al, 2006). The characteristics of the Robusta botanical variety are greater vigor, erect growth, larger leaves and fruits, late maturation, less tolerance to water deficit, and greater tolerance to pests and diseases. Plants of the Conilon botanical variety have shrubby growth, early flowering, branched stems, elongated leaves, drought resistance, and greater susceptibility to diseases (Ferrão et al, 2015). The crossing of these two varieties occurs naturally, creating hybrid genotypes that can exhibit the best characteristics of each group, associated with the expression of heterosis (Charrier & Berthaud, 1988). The efficient separation of these two botanical varieties allows the systematic production of intervarietal hybrids (Rocha et al, 2015)
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