|MOTAMAYOR, JUAN CARLOS|
|Schnell Ii, Raymond|
Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2007
Publication Date: 9/20/2007
Citation: Brown, J.S., Phillips-Mora, W., Power, E.J., Krol, C.A., Cervantesmartinez, C., Motamayor, J., Schnell II, R.J. 2007. Mapping QTL for resistance to frosty pod and black pod diseases, and for horticultural traits in Theobroma cacao L.. Crop Science. 47:1851-1858.
Interpretive Summary: Two fungal diseases have caused extensive problems in the South and Central American cacao (Theobroma cacao L.) growing areas during the last fifty years, witches’ broom (Moniliophthora perniciosa) and frosty pod (Moniliophthora roreri). A third, more ubiquitous disease, black pod (Phytophthora sp.) exists throughout the world. Though the diseases can be controlled to an extent with chemicals, it is difficult in tropical areas to do so; firstly, the presence of the causal organisms during most of the year causes the need to spray quite frequently, which becomes quite expensive, and secondly, such frequent application can cause environmental problems over time. The danger of resistance to chemicals is also present, especially with such frequent application. Hence, genetic resistance is thought to be the most promising route for obtaining long-term control of these organisms. In this experiment, a population of 256 trees from a cross of ‘Pound7’ and ‘UF273’ was analyzed with 180 molecular DNA markers. A robust genomic map was produced, artificial inoculation was used to test for frosty pod and black pod, and five related horticultural characteristics were scored. ‘Pound 7’ was found previously to have tolerance to black pod, while ‘UF273’ was found to be tolerant to frosty pod, making this cross a good complementary cross. Five quantitative trait loci (QTL) were found for frosty pod, and three QTL for black pod were found, one of which seemed to be identical over several experiments. Two QTL were found for months to jorquette formation, and one QTL each was found for average trunk diameter growth rate, and for pod color. The QTLs had high significance values for every trait, especially disease traits. We feel quite confident in using these QTLs to select for desirable progeny without observing the phenotype first. This will allow more space for progeny in the nursery for yield selection, and selection for other less heritable traits.
Technical Abstract: An F1 heterozygous mapping population of cacao (Theobroma cacao L.) was created and evaluated for resistance to frosty pod (Moniliophthora roreri [Cif. and Par.]), black pod (Phytophtora palmivora [Butl.] Butl.) and for five horticultural traits at CATIE in Turrialba, Costa Rica. The population consisted of 256 F1 progeny from the cross, ‘Pound 7’ x ‘UF 273’. Progeny were used to form a linkage map using 180 markers. The linkage map contained ten linkage groups (LG), numbered as the LG in the cacao reference map, and was used to locate putative quantitative trait loci (QTL) for resistance to the aforementioned diseases and five horticultural traits. Resistance to frosty pod was measured by internal and external pod resistance. Five QTLs for frosty pod resistance were found on three LGs, 2, 7, and 8. Resistance came primarily from ‘UF 273’, the parent noted to be more resistant, though ‘Pound 7’ contained one resistant allele. These alleles are being used for scoring progeny in ongoing cooperative marker assisted selection (MAS) projects, and constitute the first QTLs identified for frosty pod resistance. Three QTLs for black pod resistance were found on LG 3, 8, and 10, with the favorable alleles coming from ‘Pound 7’. One QTL was found on LG 4 for average trunk growth rate, and two QTLs for height of first jorquette were identified on LGs 4 and 6. One QTL each for average trunk diameter growth and pod color was found on LG 4.