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John P. Navazio and Philipp W. Simon

Three orange-mesocarp derivatives of the xishuangbannan cucumber (Cucumis sativus L. var. xishuangbannanesis Qi et Yuan), P100, P101, and P104; and NPI (P105), an unrelated cucumber (Cucumis sativus L.) reported to have orange flesh, were selected as parents for a diallel experiment to evaluate inheritance of orange cucumber mesocarp pigment over 3 years. Visual color intensity and carotenoid content were closely related. A preponderance of additive genetic effects for cucumber mesocarp pigmentation was observed in grade size 2 fruit (immature fruit used for pickling). Both additive and nonadditive genetic effects were important in grade size 4 fruit (mature). Years and yea× genotype interactions were highly significant for pigmentation of size 2 fruit, indicating the importance of environment on the expression of pigmentation in this size class. In contrast, color development was stable among years for size 4 fruit. P104 exhibited high general combining ability (GCA) estimates for size 4 fruit pigmentation across years, while P101 had high GCA estimates for size 2 fruit. The diallel analysis illustrated high fruit carotene content of parents per se. However, most hybrid combinations of the diallel reduced carotenoid content relative to parents, indicating both dominance for low carotenoid content for both fruit sizes and lack of genetic complementation among parents to enhance fruit color. Genetic control of pigmentation in size 2 fruit appeared to be independent of that for size 4 fruit.

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Leah C. McCann and Philipp W. Simon

When stored at temperatures less than 10 °C, tubers of all cultivated potatoes exhibit cold-induced sweetening (CIS) during which starch degrades to sucrose, glucose, and fructose. Upon frying at high temperatures, the reducing sugars (Fru, Glu) interact with free amino acids via the non-enzymatic Maillard reaction to form dark-colored chips that are unacceptable to consumers. In addition, scientists recently discovered that the toxic chemical acrylamide is also produced during frying. Although storage at warmer temperatures reverses CIS and circumvents dark chip production, the probability of storage loss due to shrinkage and disease increases. Wild Solanum species form the backbone of many potato-breeding programs. In this study, we evaluated 36 different plant introductions (PI) including 20 different species, grown in Madison and Rhinelander, Wis., to identify germplasm resistant to CIS for genetic analysis. After storage for 2–3 months at 4 °C, tuber sugar and amino acid content were analyzed via HPLC and slices were fried to determine chip color. Sugar and chipping data support previous research indicating CIS resistance in S. okadae, S. raphanifolium, and S. phujera. Interestingly, some germplasm selections with high reducing sugar content produced light-colored chips, indicating exceptions to the typical correlation between reducing sugar content and chip color. Genetic bases to these exceptions are under evaluation.

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Carlos A. F. Santos and Philipp W. Simon

Markers were placed on linkage groups, ordered, and merged for two unrelated F2 populations of carrot (Daucus carota L.). Included were 277 and 242 dominant Amplified fragment-length polymorphism (AFLP) markers and 10 and eight codominant markers assigned to the nine linkage groups of Brasilia × HCM and B493 × QAL F2 populations, respectively. The merged linkage groups were based on two codominant markers and 28 conserved dominant AFLP markers (based upon sequence and size) shared by both populations. The average marker spacing was 4.8 to 5.5 cM in the four parental coupling phase maps. The average marker spacing in the six merged linkage groups was 3.75 cM with maximum gaps among linkage groups ranging from 8.0 to 19.8 cM. Gaps of a similar size were observed with the linkage coupling phase maps of the parents, indicating that linkage group integration did not double the bias which comes with repulsion phase mapping. Three out of nine linkage groups of carrot were not merged due to the absence of common markers. The six merged linkage groups incorporated similar numbers of AFLP fragments from the four parents, further indicating no significant increase in bias expected with repulsion phase linkage. While other studies have merged linkage maps with shared AFLPs of similar size, this is the first report to use shared AFLPs with highly conserved sequence to merge linkage maps in carrot. The genome coverage in this study is suitable to apply quantitative trait locus analysis and to construct a cross-validated consensus map of carrot, which is an important step toward an integrated map of carrot.

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B.S. Vivek and Philipp W. Simon

Current classifications of the genus Daucus are based on morphological and anatomical characteristics. We have used single to low copy nuclear restriction fragment length polymorphisms (nRFLPs) to describe the phylogeny and relationships of eight Daucus species including cultivated carrot (D. carota L.). Parsimony analysis of 247 characters (DNA fragments from 58 probe-enzyme combinations) yielded a tree in which accessions were grouped into three major clades and phenetic analysis using Jaccard's coefficient yielded two major clusters. The phylogenetic relationships from the nuclear RFLP data generally agreed with an earlier morphological classification. Resolution and placement of D. guttatus and D. muricatus were not consistent with the morphological classifications. Molecular variation among carrot inbreds was large.

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Meryem Ipek, Ahmet Ipek, Douglas Senalik, and Philipp W. Simon

Production of a visible flower stalk, or bolting, has been used as a major trait to categorize garlic (Allium sativum L.) clones. Analysis of mitochondrial genome variation with polymerase chain reaction (PCR) revealed differences between bolting and nonbolting clones of garlic. Screening 333 garlic accessions from diverse geographic origins revealed a 1403-bp mitochondrial DNA marker associated with bolting that the authors call “Bolt Marker” (BltM). Bolt Marker did not amplify in any of the 131 nonbolting clones, whereas amplification of this marker was observed in 127 of 130 (97.7%) garlic clones that bolted completely in Wisconsin. Seventy-two garlic clones bolted incompletely (clones in which some but not all of the plants bolted), and this marker was not amplified in 69 (95.8%) of these clones. Because of the significant association of BltM with bolting, this PCR-based marker can be used to discriminate complete-bolting garlic clones reliably from nonbolting and incomplete-bolting ones. Sequence characterization of this marker revealed that BltM is a chimera involving both mitochondrial and chloroplast DNA. The DNA sequences including and flanking both the 5′ and 3′ ends of this marker are consistent with an ≈4.8-kbp chloroplast DNA fragment having been inserted into the mitochondrial genome downstream from the mitochondrial cox3 gene. Sequence alignment of the chloroplast genes in this chimeric region with the homologous sequences in GenBank indicate the presence of deletions, insertions, and single nucleotide polymorphisms in the coding sequences, resulting in putative, incomplete open reading frames or frame shift mutations. Hence, the authors speculate that this insertion may have occurred long ago in the evolution of garlic.

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Jack E. Staub, Philipp W. Simon, and Hugo E. Cuevas

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Barbara Michalik, Philipp W. Simon, and Warren H. Gabelman

Four methods for screening carrot (Daucus carota L.) germplasm for resistance to bacterial soft rot were compared. There were differences in resistance among strains, with most severe damage caused by Erwinia carotovora pv. carotovora SR 394 (L.R. Jones) Holland and Erwinia carotovora pv. atroseptica SR 159 (van Hall) Jennison. Inoculation of cross-sectional root slices with bacteria applied in suspension-soaked paper disks produced the most consistent response. The severity of disease damage was proportional to bacterial suspension concentration. With the development of a standard screening method, it may be possible for breeders to breed carrots with reduced susceptibility to soft rot.

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Mary Ruth McDonald, Kevin Vander Kooi, and Philipp Simon

Cavity spot of carrot, caused by several species of Pythium, is endemic in many carrot production areas of the world, including the Holland/Bradford Marsh region of Ontario, Canada. Field trials were conducted from 2002–04 to determine if carrots with different pigments varied in susceptibility to the disease. Carrots from the USDA breeding program at the University of Wisconsin were seeded in muck soil (pH 6.4, 60% organic matter) on 28, 30, and 27 May, harvested 22, 22, and 23 Oct., and assessed for disease on 5, 8, and 10 Dec. 2002, 2003, and 2004, respectively. The carrots were white (W 105-7), yellow (W 102-1), dark orange (W 101-23), red (W 104-3), and purple (W 106-3). Cultivar `Cellobunch' was included in 2003 and 2004. Twenty-five carrots of each of four replicate plots were assessed in 2002 and 2003, and 50 carrots were assessed in 2004, for disease incidence and severity [disease severity index (DSI), based on the size of the largest lesion per carrot]. Disease incidence was moderate in 2002 and 2003 (34%, 33%), and high in 2004 (60%). Consistent differences in susceptibility to cavity spot were identified over the three years of trials. The purple carrot had the lowest incidence (12%) and severity (7 DSI) of cavity spot, followed by the dark orange carrot (39%, 22 DSI) as compared to the susceptible yellow carrot (58%, 41 DSI). There was no difference in disease reaction between the yellow and white carrots. `Cellobunch' had the same reaction as the dark orange carrot. Studies are needed to determine whether the pigments themselves cause differences in the disease response.

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Pablo Cavagnaro, Douglas Senalik, Claudio Galmarini, and Philipp Simon

Allium plants possess organosulfur compounds and carbohydrates that provide unique flavor and health-enhancing properties. In previous studies of onion F3 families, significant phenotypic and genetic correlations have been reported between pungency, in vitro antiplatelet activity (IVAA), and soluble solids content (SSC); although in other studies SSC and pungency have not always been correlated. In this study we analyzed SSC, pungency, garlic-induced in vitro antiplatelet activity and the content of three predominant thiosulfinates in bulbs from two garlic families obtained from unrelated self-pollinated plants. A strong positive correlation was observed between pungency and IVAA for both sample sets, indicating that it will be difficult to develop garlic populations with low pungency and high IVAA. Allicin was the most abundant thiosulfinate and its content was positively correlated with pungency and IVAA (r= 0.70 and 0.74, respectively). The thiosulfinates AllS(O)SPropenyl and AllS(O)SMe were also positively correlated with pungency and IVAA. When compared with IVAA, AllS(O)SMe had higher r values than AllS(O)SPropenyl (0.88 and 0.50, respectively). These differences could reflect differential platelet anti-aggregatory properties of different thiosulfinates. SSC was not correlated with IVAA, pungency, or thiosulfinates content, suggesting that soluble solids in garlic can be independently selected.