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Dario J. Chavez and José X. Chaparro

Citrus kinokuni ‘Mukaku kishu’ PI539530 and its progeny were studied to identify random amplified polymorphic DNA (RAPD) primers associated with seedlessness. Ninety-one F1 [(Robinson op) × C. kinokuni] individuals showed a 1:1 segregation ratio between seedless and seeded phenotypes with seedless as a single dominant gene. Bulked segregant analysis was used to identify markers associated with the seedless locus. Eighteen RAPD primers were mapped into a partial linkage group (≈55.8 cM length) with four RAPD primers flanking the seedless locus: OPAI11-0.8 at 8.7 cM, OPAJ19-1.0 at 8.4 cM, OPM06r-0.85 at 4.3 cM, and OPAJ04r-0.6 at 6.4 cM. The identification of molecular markers linked to C. kinokuni Fs seedless locus constitutes an important and major tool for citrus breeding and selection.

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Dennis J. Werner and Jose X. Chaparro

Genetic interaction of the pillar (PI) and weeping (WE) growth habit genotypes was investigated in peach [Prunus persica (L.) Batsch]. Data from F2, BC1P1, and BC1P2 families showed that PI (brbr) was epistatic to the expression of WE (plpl). A unique growth habit not previously described in peach, and referred to as arching (AR), was recovered in the F2 family. Arching trees showed an upright phenotype similar to Brbr heterozygotes, but had a distinct curvature in the developing shoots. Progeny testing of AR trees revealed their genotype is Brbrplpl.

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Jose X. Chaparro, Ronald R. Sederoff, and Dennis J. Werner

Total cellular DNA has been extracted from leaves and\or seed of Prunus dulcis, P. persica, P. mira, P. davidiana, P. persica subsp. ferganensis, and P. triloba. Chloroplast restriction fragments have been visualized by Southern blot analysis using heterologous probes from a petunia chloroplast library. Analysis of preliminary data separates the species into three groups. The first contains P. dulcis, P. mira, and P. davidiana; the second P. kansuensis, P. persica, and P. persica subsp. ferganensis; and the third P. triloba.

PCR amplification using oligos for cytosolic glyceraldehyde-3-phosphate dehydrogenase yields genomic fragments approximately 1kb in size from P. dulcis and P. triloba. Sequence analysis will be performed to determine species relationships at the gene level.

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Michael A. Creller, Jose X. Chaparro, and Dennis J. Werner

Inheritance of the blood flesh (red-violet mesocarp) trait in peach [Prunus persica (L.) Batsch] was investigated. `Harrow Blood' fruit began accumulation of anthocyanin about 40 days after anthesis. The blood-fleshed trait was associated with the red-veined leaf phenotype in `Harrow Blood' and its self progeny. An approximate segregation ratio of 3:1 (red vein:green vein) was observed in a population generated by selfing `Harrow Blood'. All 112 F1 progeny from a cross of `Harrow Blood' × `Rutgers Red Leaf'-2n produced wild-type fruit. Phenotypic segregation for red leaf:green leaf deviated from the expected 3:1 ratio in two of three F2 families derived from these F1's. More red leaf segregants were observed than expected. Bed-veined, green-leafed progeny comprised about 25% of the green-leafed seedlings in the F2. Examination of fruit on a limited number of F2 segregants revealed the presence of red-leafed, blood-fleshed individual. Preliminary results suggest that the blood trait may be controlled by two loci. The red-vein phenotype was associated with reduced tree height in self progeny of `Harrow Blood'.

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Marilyn Rivera-Hernández, Linda Wessel-Beaver, and José X. Chaparro

Squash and pumpkins (Cucurbita sp.) are important contributors of beta-carotene to the diet. Consumers of tropical pumpkin and butternut squash (both C. moschata Duchesne) prefer a deep orange mesocarp color. Color intensity is related to carotene content. Among the five domesticated Cucurbita species, C. moschata and C. argyrosperma Huber have a close relationship. In crosses between these two species, fertile F1 plants can be easily obtained when using C. argyrosperma as the female parent. This research studied the relationship between and within C. moschata and C. argyrosperma by sequencing three genes in the carotenoid biosynthesis pathway and generating gene trees. Genotypes used in the study differed in flesh color from very pale yellow to dark orange. In some cases, haplotypes were associated with a particular mesocarp color. Further study of these types of associations may improve our understanding of color development in Cucurbita. The frequency of single nucleotide polymorphisms (SNPs) in the sequenced fragments was low. There were more SNPs and more heterozygotes among C. moschata accessions than among C. argyrosperma accessions. Haplotypes of the outgroups (C. ficifolia C.D. Bouché and C. maxima Duchesne) were always distinct from C. moschata and C. argyrosperma. These later species had both distinct haplotypes and shared haplotypes. Haplotypes shared among species tended to be maintained in the same branch of the phylogenetic tree, suggesting either gene flow between the species or a common ancestral gene. Both explanations suggest a close genetic and evolutionary relationship between C. moschata and C. argyrosperma.

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Jose X. Chaparro, Patrick J. Conner, and Thomas G. Beckman

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Thomas G. Beckman, Jose X. Chaparro, and Wayne B. Sherman

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Omar Carrillo-Mendoza, Wayne B. Sherman, and José X. Chaparro

Trees without excessive branching are desirable for the reduction of pruning costs. Genetic diversity for less twiggy genotypes exists in peach and a branching index was developed for evaluation and selection of genotypes with reduced branching. The index is based on the number of total first-order branches and the number of second-order, third-order, and fourth-order branches measured on three randomly selected first-order branches. Index values were highly correlated (r 2 ≈0.7) with the total number of branches over two growing seasons and served as a good predictor of branching patterns observed in the third growing season. Thus, the developed branching index is a useful tool in peach breeding, allowing for the early selection of trees with more desirable tree architecture.

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Omar Carrillo-Mendoza, José X. Chaparro, and Jeffrey Williamson

Tree size and branching control has gained importance as labor and pruning costs have increased. In addition, the occurrence of blind nodes is a critical factor that affects peach tree architecture and productivity in subtropical climates. Seven backcross families segregating for branching and blind nodes were developed using ‘Flordaguard’ peach × P. kansuensis or ‘Tardy Nonpareil’ almond F1s backcrossed to ‘AP00-30WBS’, ‘UFSharp’, or ‘UF97-47’ peach selections and evaluated for branching index and blind node frequency during the winters of 2010 and 2011. P. kansuensis backcrosses presented increased branching and lower blind node incidence, whereas almond backcrosses presented less branching and higher blind node incidence, resembling the P. kansuensis and almond F1 parents, respectively. There was also broad variability for branching and blind nodes within the P. kansuensis and ‘Tardy Nonpareil’ almond backcross families influenced by the peach parents that were used to generate the backcross populations. The moderate heritability and year-to-year correlation for these traits indicate that they are affected by the environment, but selection for reduced branching and lower blind node incidence is feasible.

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Thomas G. Beckman, Jose X. Chaparro, and Patrick J. Conner