No abstract

A heterozygous F1 mapping population of cacao (Theobroma cacao L.) was created and evaluated for resistance to frosty pod [caused by Moniliophthora roreri (Cif. and Par.) Evans et al.], and black pod [caused by Phytophthora 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’ × ‘UF 273’. Progeny were used to form a linkage map using 180 markers. The linkage map contained 10 linkage groups (LGs), 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, with UF 273 appearing to be the source of resistance. These alleles are being used for scoring progeny in ongoing cooperative marker‐assisted selection projects, and constitute the first QTLs identified for frosty pod resistance. Three QTLs for black pod resistance were found on LG 4, 8, and 10, with the most 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.

Oat (Avena sativa L.) β‐glucan lowers serum cholesterol in humans. Development of oat cultivars with greater groat (caryopsis) β‐glucan content would increase the nutritional and economic value of the crop. The objectives of this experiment were to evaluate the response to phenotypic selection among individual S0 plants for greater groat β‐glucan content in two genetically broad‐based populations; to compare selected experimental lines to standard check cultivars; and to estimate genetic variances and heritabilities and to test for nonadditive genetic variance for β‐glucan content. We measured groat β‐glucan contents of check cultivars and parental lines and random S0:1 lines from initial and selected generations of each population grown in field experiments in 1996 and 1997 at two Iowa locations. Mean β‐glucan content increased from 53.9 to 59.9 g kg−1 in one population, and from 63.5 to 66.0 g kg−1 in the other, following selection. Genetic variance of β‐glucan content decreased by 9 to 22% following selection, but heritability for β‐glucan content did not change significantly. Heritability estimates ranged from 0.80 to 0.85 on a line mean basis. Additive variance was the only substantial component of genetic variance. Some experimental lines had significantly greater β‐glucan content than the best check cultivars and lines. Phenotypic selection for greater groat β‐glucan content will be effective for developing cultivars with elevated β‐glucan contents.

Knowledge of genetic differences among commonly cultivated cacao clones, as well as the type of gene action involved for disease resistance, yield, quality, and horticultural traits, are essential for cacao breeders to select parental clones efficiently and effectively. This information is also critical for quantitative geneticists in designing and improving quantitative trait loci (QTL) localization strategies using breeding populations, whether they involve analysis of multiple populations crossed to one common parent or association genetic analysis. The objectives of this research were to 1) verify the genetic identity of parental cacao clones used to produce hybrids for field evaluation at the Centro Agrónomico Tropical de Investigación y Enzeñanza (CATIE), Turrialba, Costa Rica, using molecular marker analysis, and 2) estimate general and specific combining ability (GCA and SCA) of the parental clones for resistance to frosty pod (Moniliophthora roreri Cif. and Par.) and black pod [Phytophthora palmivora (Butl.) Butl.] diseases, total number of pods, vigor (as measured by trunk diameter), and measures of maturity (months to first flowering and pod production). Misidentification of cacao clones was found at three levels. Molecular marker analysis revealed that six parental clones differed in identity to supposedly identical accessions from other germplasm collections. Trees of the parental clone UF 273 consisted of two clearly different genotypes, resulting in two types of progeny, requiring separate designation for correct statistical analysis. Out-crossed progeny, presumably from foreign pollen, and selfed progeny were also found. Two of the traits measured, percent healthy pods and percent pods with frosty pod, showed predominantly additive gene action, while the traits total number of pods and trunk diameter, demonstrated regulation by both additive and nonadditive gene action. Number of months to first flowering and first fruit both showed evidence of predominant regulation by nonadditive gene effects. Crosses of two parental clones, UF 712 and UF 273 Type I, were identified as potential candidates for QTL analysis as breeding populations, given their favorable GCA estimates for frosty pod resistance and total pod production, respectively.

Commercial production of cacao in Hawaii is increasing, and this trend is expected to continue over the next several years. The increased acreages are being planted with seedlings from introduced and uncharacterized cacao populations from at least three initial introductions of cacao into the islands. Productive seedlings have been selected from a planting at Waialua, Oahu. The parents of these selections were believed to be the population at the Hawaii Agriculture Research Center (HARC) at Kunia; however, potential parental populations also exist at Univ. of Hawaii research stations at Waimanalo and Malama Ki. Using microsatellite markers, we analyzed the potential parental populations to identify the parents and determine the genetic background for 99 productive and 50 unproductive seedlings from the Waialua site. Based on 19 polymorphic microsatellite loci the parental population was identified as trees from Waimanalo and not trees from Malama Ki or Kunia. The Kunia and Malama Ki populations were very similar with low allelic diversity (A = 1.92) and low unbiased gene diversity (Hnb) of 0.311 and 0.329, respectively, and were determined to be Trinitario in type. The Waimanalo, productive seedling, and unproductive seedling populations had much higher levels of genetic diversity with Hnb of 0.699, 0.686, and 0.686, respectively, and were determined to be upper Amazon Forastero hybridized with Trinitario in type. An additional 46 microsatellite markers were amplified and analyzed in the Waimanalo parents, productive, and unproductive seedlings for a total of 65 loci. Seventeen loci contained alleles that were significantly associated with productive seedlings as determined by Armitage's trend test. Of these, 13 loci (76.4%) co-located with previously reported quantitative trait loci for productivity traits. These markers may prove useful for marker assisted selection and demonstrate the potential of association genetic studies in perennial tree crops such as cacao.