Evaluation and utilisation of cacao (Theobroma cacao L.) germplasm at the International Cocoa Genebank, Trinidad |
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| Authors: | AD Iwaro FL Bekele DR Butler |
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| Institution: | (1) Cocoa Research Unit, The University of The West Indies, St. Augustine, Trinidad and Tobago, West Indies |
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| Abstract: | The aim of this study was to identify promising genotypes in the International Cocoa Gene bank, Trinidad (ICG,T) for use in
cacao breeding. Subsets of the germ plasm 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 (For astero, Refractario and Trinitario), Trinitario had the
highest percentage of genotypes (36.9%) with large bean weight (> 1.2 g), while For astero 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, inten 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 podrot. 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 podrot 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 corecollections would be justified.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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| Keywords: | bean number bean weight characterisation disease resistance genetic improvement pod index Phytophthora pod rot selection |
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