|Schnell Ii, Raymond|
Submitted to: Proceedings of Ingenic Workshop
Publication Type: Proceedings
Publication Acceptance Date: 10/8/2002
Publication Date: N/A
Technical Abstract: Theobroma cacao is an important tropical tree crop whose seeds are used to produce cocoa and chocolate. The genetic diversity of the most widely planted cultivars may be quite low. Thus, the potential for crop loss due to disease is a real concern to cocoa producers. For example, cocoa production in Brazil has been drastically reduced due to infection with witches' broom (Crinipellis perniciosa). Breeding of tree crops for disease resistance requires large populations segregating for disease resistance and an effective assay. If trees can not be assayed until they produce pods, this could delay assay for up to five years. Thus, molecular markers are sought that could speed the selection and propagation of disease resistant cultivars. A normal genetic approach to this problem would be to screen hundreds of genetic markers (RFLP, SSR, allozymes, AFLP) for segregation with the desired phenotype. We are proposing a shortcut to the normal genetic approach by looking for resistance gene homologues (RGH). RGH have been identified for many plant species by using degenerate PCR primers designed to a highly conserved region of the nucleotide binding site of plant resistance genes. The RGH map to the same location as known resistance genes in Arabidopsis and lettuce. Because resistance genes are often physically clustered in plants, cacao RGH may prove to be useful genetic markers which will show a stronger linkage to the disease resistance phenotype.