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Joseph J. King and Michael J. Havey

The bulb onion (Allium cepa L.) is a diploid with an very large nuclear genome of 15300 Mbp/1C (107× arabidopsis, 16× tomato, 6× maize). We developed a low-density genetic map with morphological, RAPD, and RFLP markers to examine genome organization and to study QTL controlling phenotypically correlated bulb quality traits. A mapping population of 58 F3 families was derived from a cross of the inbreds Brigham Yellow Globe 15-23 (BYG) × Alisa Craig 43 (AC). These inbreds are distinct in solids, storability, pungency, and bulb shape. Analysis of 580 RAPD primers detected 53 (9%) polymorphisms between BYG and AC, but only 12 (2%) segregated at expected ratios among F3 families. Using probes from onion cDNA libraries and four restriction enzymes, 214 RFLPs were identified between mapping parents. A 112-point map includes 96 RFLPs, 13 RAPDs, a locus controlling complementary red bulb color, and two loci hybridizing with a clone of the enzyme alliinase (EC 4.4.1.4), which produces the flavors characteristic of Allium species. Duplicated loci were detected by ≈25% of RFLP probes and were unlinked, loosely linked (2 to 30 cM), or tightly linked (<2 cM). This frequency of duplication was comparable to species with polyploid ancestors (paleopolyploids) and was higher than that found in most true diploids. However, the distribution of duplicated loci suggests that, in contrast to whole genome duplications typical of paleopolyploids, the contemporary size and structure of the onion genome may be a product of intrachromosomal duplications (cryptopolyploidy) and subsequent structural rearrangements.

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Joseph J. King and Dennis P. Stimat

Changes in quantity and form of nitrogen used were evaluated during development of Dendranthema × grandiflora `Iridon', `Sequoia' and `Sequest' grown in hydroponic solutions containing 28 ppm NO 3 - (as Ca(NO3)2) and 28 ppm NH4 + (as(NH4)2SO4). Four plants of each cultivar were harvested every ten days over ninety days. Data were collected on plant height, leaf number, flower bud diameter, and root and shoot dry weights. Nutrient solutions were changed every ten days and sampled at days 1, 5, and 10 of each cycle. Concentrations of NO3 - and NH 4 + of nutrient solutions and dried plant tissues were determined by micro-Kjeldahl. Total tissue nitrogen was determined for `Sequoia' by macro-Kjeldahl. Depletion of nitrogen from solutions approximated a 1:1 ratio for NH4 +:NO3 - throughout the crop cycle (r = 0.96). Although the sample date × cultivar interaction was significant for both forms of nitrogen, overall patterns of nitrogen uptake were similar among cultivars. Nitrogen uptake expressed per gram of tissue dry weight was greatest in the first month of development. However, total nitrogen uptake was greatest from days 40 to 60. Developmental stages corresponding to this period are a cessation of new leaf development and flower bud diameters of approximately 1.0 cm. Nitrogen uptake decreased rapidly as flowers expanded. Correlations between morphological changes and nitrogen demands could maximize the efficiency of nitrogen applications.

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Joseph J. King and Dennis P. Stimat

Changes in quantity and form of nitrogen used were evaluated during development of Dendranthema × grandiflora `Iridon', `Sequoia' and `Sequest' grown in hydroponic solutions containing 28 ppm NO 3 - (as Ca(NO3)2) and 28 ppm NH4 + (as(NH4)2SO4). Four plants of each cultivar were harvested every ten days over ninety days. Data were collected on plant height, leaf number, flower bud diameter, and root and shoot dry weights. Nutrient solutions were changed every ten days and sampled at days 1, 5, and 10 of each cycle. Concentrations of NO3 - and NH 4 + of nutrient solutions and dried plant tissues were determined by micro-Kjeldahl. Total tissue nitrogen was determined for `Sequoia' by macro-Kjeldahl. Depletion of nitrogen from solutions approximated a 1:1 ratio for NH4 +:NO3 - throughout the crop cycle (r = 0.96). Although the sample date × cultivar interaction was significant for both forms of nitrogen, overall patterns of nitrogen uptake were similar among cultivars. Nitrogen uptake expressed per gram of tissue dry weight was greatest in the first month of development. However, total nitrogen uptake was greatest from days 40 to 60. Developmental stages corresponding to this period are a cessation of new leaf development and flower bud diameters of approximately 1.0 cm. Nitrogen uptake decreased rapidly as flowers expanded. Correlations between morphological changes and nitrogen demands could maximize the efficiency of nitrogen applications.

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Joseph J. King and Dennis P. Stimart

In an attempt to analyze genetically the interaction of endogenous auxin concentration and adventitious root formation, an EMS mutagenized M2 population of Arabidopsis thaliana was screened for mutants with altered abilities to form adventitious roots. A selected recessive nuclear mutant, rooty (rty), is characterized by extreme proliferation of roots, inhibition of shoot development and other morphological alterations suggestive of auxin or ethylene effects. The rty phenotype occurs in wild type seedlings grown on auxin containing medium and relatively normal growth is stimulated in rty seedlings growing on cytokinin containing medium. Analysis by GC-MS found that endogenous IAA concentrations in rty are 2 to 17 times higher than in wild type depending on tissue type and IAA form. Dose response experiments with IAA and NAA indicated that rty does not express increased sensitivity to auxin. These data suggest that the rty phenotype is due to elevated endogenous auxin. A genetic map location for rty and possible roles for the wild type RTY gene product in regulating auxin concentration will be presented.

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Joseph J. King and Mark P. Bridgen

Presowing treatments and temperature regimes were tested to improve germination of Alstroemeria hybrids 3 to 12 months following harvest. In addition, seeds from 20 intraspecific F1 hybrids of five selections were also tested 3 to 7 or 8 to 12 weeks following harvest. Seeds were pretreated by chipping the seedcoat above the embryo, general abrasion of the entire seedcoat, or soaking 12 hours in distilled water, GA, (0.029, 0.29, 2.9 mm), or KNO3 (0.5 and 1.0 m). Pretreatments were evaluated under three environmental regimes: 8 weeks at a constant 18-25C (warm), 4 weeks at 18-25C followed by 4 weeks at 7C (warm-cold), or 4 weeks at 7C followed by 4 weeks at 18-25C (cold-warm). There was an interaction between pretreatment and environmental regime for percent germination. Germination percentages for the water soak and GA, at 0.29 or 2.9 mm were significantly higher than for the other pretreatments, but were not significantly different from one another. The warm-cold environment yielded higher germination percentages than the other environments. The time to germination was longest for the cold-warm regime. This response depended on the genotype and the age of the seed. Chemical name used: gibberellic acid (GA3).

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Joseph J. King, James M. Bradeen, and Michael J. Havey

Nuclear RFLPs were used to estimate relationships among 14 elite commercial inbreds of bulb onion (Allium cepa) from Holland, Japan, and the United States. Variability for known alleles at 75 RFLP loci and 194 polymorphic fragments revealed by 69 anonymous cDNA probes and a clone of alliinase were scored to yield genetically characterized and uncharacterized data sets, respectively. The inbred onion populations possessed more than two alleles at 20 of 43 (46%) codominant RFLP loci. Relationships among the inbreds were estimated by cluster analysis of simple-matching (genetically characterized data) and Jaccard (genetically uncharacterized data) coefficients using the unweighted pair group method and agreed with known pedigrees. RFLPs confidently distinguished among elite inbreds within and between specific market classes. RFLP profiles for virtual hybrids were computer-generated by combining gametic arrays among inbreds of the same market class and analyzed as described above. Allelic and genetically uncharacterized RFLPs confidently distinguished among these hybrids, even though heterozygosity for many markers produced a majority of monomorphic fragments. We randomly sampled decreasing numbers of RFLPs from the complete data sets and calculated simple-matching and Jaccard distances, noting the numbers of probes that were unable to distinguish any two inbreds or hybrids. As few as 10 polymorphic probe-enzyme combinations distinguished among all the inbreds and samples of 20 genetically characterized or 10 genetically uncharacterized clones distinguished all the virtual hybrids. This study demonstrated that the previously reported few RFLPs observed among open-pollinated (OP) onion populations were due to the highly heterozygous nature of the OP population.

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Joseph J. King, Lloyd A. Peterson, and Dennis P. Stimart

Ammonium and NO3 uptake from hydroponic solutions containing 1 mm each of (NH4)2SO4 and Ca(NO3)2 were measured during development of Dendranthema ×grandiflorum (Ramat.) Kitamura `Iridon', `Sequoia', and `Sequest'. Nitrogen depletion from solutions approximated a 1 NH4: 1 NO3 ratio throughout a 90-day growth cycle (r = 0.96). Although harvest date cultivar interactions were significant for both forms of N, overall patterns of N uptake were similar among cultivars. Nitrogen removal from hydroponic solutions (milligrams per plant) was greatest from days 40 to 60; however, N removal (milligrams per gram of tissue dry weight) was greatest in the first month of development and decreased steadily until day 90. From day 40 to 60, new leaf development ceased while inflorescence buds developed to ≈1.0 cm in diameter. After this time, N uptake decreased rapidly as inflorescences expanded. Correlations between morphological changes and N demand could maximize the efficiency of applied N by matching form and application timing with plant needs.

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Michael J. Havey, Joseph J. King, James M. Bradeen, and Ockyung Bark