Rice (Oryza sativa L.) head-rice yield (HR) is a key export and domestic quality trait whose genetic control is poorly understood. With the goal of identifying genomic regions influencing HR, quantitative-trait-locus (QTL) mapping was carried out for quality-related traits in recombinant inbred lines (RILs) derived from crosses of common parent Cypress, a high-HR US japonica cultivar, with RT0034, a low-HR indica line (129 RILs) and LaGrue, a low-HR japonica cultivar (298 RILs), grown in two US locations in 2005-2007. Early heading increased HR in the Louisiana (LA) but not the Arkansas (AR) location. Fitting QTL-mapping models to separate QTL main and QTL × environment interaction (QEI) effects and identify epistatic interactions revealed six main-effect HR QTLs in the two crosses, at four of which Cypress contributed the increasing allele. Multi-QTL models accounted for 0.36 of genetic and 0.21 of genetic × environment interaction of HR in MY1, and corresponding proportions of 0.25 and 0.37 in MY2. The greater HR advantage of Cypress in LA than in AR corresponded to a genomewide pattern of opposition of HR-increasing QTL effects by AR-specific effects, suggesting a selection strategy for improving this cultivar for AR. Treating year-location combinations as independent environments resulted in underestimation of QEI effects, evidently owing to lower variation among years within location than between location. Identification of robust HR QTLs in elite long-grain germplasm is suggested to require more detailed attention to the interaction of plant and grain development parameters with environmental conditions than has been given to date.

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Cacao (Theobroma cacao L.) is an important cash crop in tropical growing regions of the world and particularly for small cacao farmers. Over the past two decades, ‘CCN 51’ has become one of the most planted cultivars in Ecuador, mainly as a result of its high productivity and disease resistance. Intermixing of Nacional fine flavor Ecuadorian beans with beans of ‘CCN 51’ has become common practice, reducing overall bean quality and decreasing value. The primary goals of this study were to determine the genetic identity, structure, and allelic richness of ‘CCN 51’, its maternal origin and to compare ‘CCN 51’s’ agronomic characteristics against a composite group of Nacional cultivars. To investigate the complex genetic background of this cultivar, 70 simple sequence repeat loci were used. The high heterozygosity observed (56 of 70 loci) for ‘CCN 51’ is not characteristic of traditional Nacional cultivars. Comparison of agronomic characteristics between ‘CCN 51’ and several Nacional cultivars indicates significant differences in cacao dry bean weight, yield potential, production efficiency, percent healthy pods, and witches' broom [Moniliophthora perniciosa (Stahel) Aime & Phillips-Mora] disease incidence. Additionally, physical, chemical, and organoleptic characteristics suggest that ‘CCN 51’ is different from those of Nacional lineage. Based on population structure analysis, the predominant ancestries for ‘CCN 51’ are Iquitos (45.4%), Criollo (22.2%), and Amelonado (21.5%) genetic groups. A lesser proportion of its genome was accounted for by genetic groups Contamana (3.9%), Purús (2.5%), Marañon (2.1%), and Nacional (1.1%) admixtures. Results of phylogenetic analyses using the unweighted pair group method with arithmetic mean yielding high bootstrap values strongly support the relatedness of ‘CCN 51’ with Iquitos, Criollo, and Amelonado genetic groups. Moreover, seven mitochondrial simple sequence repeat loci revealed that ‘CCN 51’ maternally inherited the ‘IMC 67’ cytotype. ‘CCN 51’ constitutes a valuable cacao genetic resource that is currently used not only in its country of origin, but also in many other national breeding and selection programs worldwide.

Chemical analyses were conducted to determine the qualitative and quantitative differences in monoterpenes and sesquiterpenes in plant material from avocado trees, Persea americana Mill. (Lauraceae). The initial study analyzed plant material sampled from the trunk to the leaves through different branch diameters to quantify proximo-distal spatial differences within a tree. All trees were seedlings initiated from a single maternal tree. Two-way analysis of variance was conducted on 34 chemicals that comprised at least 3% of the total chemical content of at least one tree and/or location within a tree. There were significant interactions between genotype and location sampled for most chemicals. Parentage analysis using microsatellite molecular markers (SSR's) determined that the four trees had three fathers and that they represented two full-siblings and two half-sibling trees. Descriptive discriminant analysis found that both genotype and location within a tree could be separated based on chemical content, and that the chemical content from full-siblings tended to be more similar than chemical content from half-siblings. To further explore the relationship between genetic background and chemical content, samples were analyzed from leaf material from 20 trees that included two sets of full-sibling seedling trees, the maternal tree and the surviving paternal tree. Descriptive discriminant analysis found good separation between the two full-sibling groups, and that the separation was associated with chemistry of the parental trees. Six groups of chemicals were identified that explained the variation among the trees. We discuss the results in relation to the discrimination process used by wood-boring insects for site-selection on host trees, for tree selection among potential host trees, and the potential use of terpenoid chemical content in chemotaxonomy of avocado trees.

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