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ARS Home » Southeast Area » Miami, Florida » Subtropical Horticulture Research » Research » Publications at this Location » Publication #196592
Title: PRELIMINARY QTL MAPPING RESULTS TO FROSTY POD AND HORTICULTURAL TRAITS

Author
item Brown, James
item Schnell Ii, Raymond
item POWER, EMILIO - FORMER ARS EMPLOYEE
item KROL, CHERYL - FORMER ARS EMPLOYEE
item PHILLIPS-MORA, WILBERT - CATIE
item Cervantesmartinez, Cuauhtemoc

Submitted to: Proceedings of the XVth International Cacao Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/15/2006
Publication Date: 10/10/2006
Citation: Brown, J.S., Schnell Ii, R.J., Power, E.J., Krol, C., Phillips-Mora, W., Cervantesmartinez, C. Preliminary qtl mapping results to frosty pod and horticultural traits. Proceedings of the XVth International Cacao Conference.

Interpretive Summary: In this report, the first three quantitative trait loci (QTL) were clearly associated with resistance to Frosty Pod disease of cacao [Moniliophthora roreri (Cif. and Par.)]. Data were also taken in this cross for horticultural traits of interest using 256 F1 progeny of the single cross ‘Pound 7’ x ‘UF273’: months to first flower and fruit, months to first jorquette, average trunk growth rate, and pod color. The cross was made, grown, and evaluated by CATIE, Turriaba, Costa Rica, and fragment analysis was performed in Miami, FL, at the USDA-ARS,SHRS. One-hundred eighty microsatellite markers were used for analyzing the progeny, and software from Kyazma®, Wageningen, NL, (JoinMap® and MapQTL®) were used for map construction and locating QTL, respectively. Resistance to Frosty Pod disease was measured two ways: by internal infection and external infection. Five QTL for Frosty Pod resistance were found, two on LG2 for internal and external resistance at the same location, one on LG7 for external resistance, and two on LG10 for external and internal resistance on LG10, again, for internal and external resistance at the same location. The total amount of phenotypic variance accounted for by external infection was approximately 20% and for internal infection was approximately 18%. One QTL was found on LG4 for average trunk growth rate, one QTL on LG6 for months to first fruit, and two QTL for first jorquette height were identified on LG4 and LG6, respectively. Parental contribution for these traits will be discussed in the presentation. Log Likelihood (LOD) values for frosty pod resistance QTLs were comfortably beyond the threshold, and the differential contribution of alleles was clear, even though this can be a complex matter in a heterozygous F1 map. We plan to use these alleles for scoring progeny in ongoing cooperative marker assisted selection (MAS) projects. These are the first known QTL identified for frosty pod resistance.

Technical Abstract: A mapping population was made and evaluated for resistance and horticultural traits at CATIE, Turrialba, Costa Rica, consisting of 256 F1 progeny from a cross between ‘Pound 7’ x ‘UF 273’. Progeny were used to form a linkage map using 180 markers. It was discovered that two different types of one parent, ‘UF 273’, had been used in creating the progeny, Type I for 185 trees, and Type II for 71 trees. Only 22 loci differed between the types, and usually did not differ for both loci. Alleles that differed at these loci in Type II progeny from Type I progeny were replaced by missing loci, to allow both groups of progeny to be used for mapping, giving a far superior map than with the Type I group alone. The linkage map was then used to map putative quantitative trait loci (QTL) for resistance to frosty pod (Moniliophthora roreri [Cif. and Par.]), to black pod [Phytophthora palmivora (Butl.) Butl.], and for horticultural traits of interest: months to first flower and fruit, months to first jorquette, average trunk growth rate, and pod color. JoinMap® 3.0 and MapQTL®15.0 software were used for linkage map construction and QTL mapping, respectively. Resistance to frosty pod was measured two ways, by external pod resistance and by internal pod resistance. Five QTL for frosty pod resistance were found: two on LG2 for internal and external resistance at the same location, one on LG7 for external resistance, and two on LG10 for external and internal resistance, again, at the same location. The total amount of phenotypic variance accounted for by external infection was approximately 20% and for internal infection was approximately 18%. Allelic contribution for resistance for these QTL came from primarily from ‘UF 273’, the parent that was expected to be the more resistant parent, though ‘Pound 7’ did contain some alleles that were more resistant than one of the two alleles from ‘UF273’. The resistance QTL on LG10 was adjacent to Resistance Gene Homologue 4 (RGH4) and RGH5 when this QTL was located on the combined map of two crosses; (‘Sca6’ x ‘ICS1’)-F2 generation, mapped together with the linkage map produced from this cross. One QTL was found on LG4 for average trunk growth rate, one QTL on LG6 for months to first fruit, and two QTL for first jorquette height were identified on LG4 and LG6, respectively. Parental contribution for these traits will be discussed in the presentation. Phenotypic scoring for black pod resistance was not completed at the time of this analysis, and will be presented later. Log Likelihood (LOD) values for frosty pod resistance QTLs were comfortably beyond the threshold, and the differential contribution of alleles was clear, even though this can be a complex matter in a heterozygous F1 map. We plan to use these alleles for scoring progeny in ongoing cooperative marker assisted selection (MAS) projects. These are the first known QTL identified for frosty pod resistance.