Evaluation and utilisation of cacao (Theobroma cacao L.) germplasm at the International Cocoa Genebank, Trinidad
Authors: Iwaro A.D.; Bekele F.L.; Butler D.R.
Source: Euphytica, Volume 130, Number 2, 2003 , pp. 207-221(15)
The aim of this study was to identify promising genotypes in the International Cocoa Genebank, Trinidad (ICG,T) for use in cacao breeding. Subsets of the germplasm collection were evaluated for bean number, bean weight, pod index (581 genotypes) and resistance to Phytophthora pod rot (500 genotypes). Among three groups of cacao assessed (Forastero, Refractario and Trinitario), Trinitario had the highest percentage of genotypes (36.9%) with large bean weight (> 1.2 g), while Forastero possessed the highest proportion of genotypes (22.6%) with a large number of beans (> 45). The ICS population had the highest percentage (44.1%) of genotypes with heavy beans, and IMC the highest percentage of genotypes with large bean number (68.6%). A low, but significant negative correlation (r = 0.19, p 0.001) between bean number and bean weight suggests that an increase in bean number may repress an increase in bean weight and vice versa. However, in ten genotypes good values of bean weight and number were combined demonstrating that selection for both large bean number and bean weight is possible. The highest percentage (28.1%) of genotypes with low pod index (< 20.1) was observed in the Trinitario group (mainly ICS). The Forastero group had the highest percentage of Phytophthora resistant accessions (18.0%). The PA population had the highest proportion of resistant (24.0%) and moderately resistant (38.0%) genotypes. Sixty-five and 99 genotypes were categorised with large bean weight and high bean number, respectively, and 60 genotypes were found with a low pod index. Seventy-eight genotypes were identified with resistance to Phytophthora pod rot. A significant relationship was observed between resistance to Phytophthora pod rot (measured as the frequency of localised lesions) and bean number (r = 0.45, p 0.001) showing that the two traits may complement each other. The combination of low to intermediate pod index with moderate to high resistance to Phytophthora pod rot was found in 87 genotypes, 12 of which were also reported to have resistance to witches' broom disease. These genotypes are of high potential value in cacao breeding and their inclusion in working and core collections would be justified.
Document Type: Research article
Publication date: 2003-01-01