Richard E. Widmer

Multigenic self incompatibility in hexaploid Chrysanthemum

SummaryEleven garden chrysanthemum siblings obtained through two generations of single-plant selfpollination were selfed and crossed in a complete diallel. Outcrosses to unrelated individuals were performed to test for male and female fertility. Since eleven crossing patterns were found inthe diallel, at least three genes must be assumed. Our data suggest independent gene action with intragenic dominance. One inbred, 77-AM3-3, expressed a high level of pseudo-self-compatibility (PSC) by giving some very low cross seed sets along with high self seed set. This inbred also exhibited variable PSC from season to season.

Inbreeding depression in garden and glasshouse chrysanthemums: germination and survivorship

SummarySixty-six chrysanthemum (Dendranthema grandiflora) inbred selections, noninbred cultivars and hybrids, and D. makinoi were the base populations from which up to three generations of inbreds were obtained using multiple plant descent. Each parent possessed pseudo-self compatibility (PSC), which allowed seed set following self pollination. Rapid-generation cycling (laboratory seed ripening to heart stage and subsequent embryo rescue) reduced generation time and minimized confounding maternal with zygotic inbreeding depression during post heart-stage seed development. Selection criteria were male/female fertility and PSC. Two stages of the life cycle were chosen to evaluate inbreeding depression: germination (seed development to germination) and survivorship (fertile individuals at anthesis). PSC was environmentally interactive and genotype dependent, causing variable levels of self seed set between and within populations and generations. By the end of the second generation, families from all noninbred cultivars, D. makinoi, and one F1 hybrid were eliminated from the experiment due to self incompatibility and/or inbreeding depression. Post-germination inbreeding depression was severe in several advanced inbreds. Inbred progeny of most F1 or F2 hybrids expressed less or equal amounts of inbreeding depression compared to advanced inbreds. Linear regression coefficients for either germination or survivorship on percent homozygosity were negative. Correlation coefficients between percent germination and survivorship (as a percent of seed set) were highly significant for Minnesota inbreds (r=0.67, P≤0.002) and hybrids (r=0.67, P≤0.006). The correlation coefficient was higher when percent germination and survivorship (as a percent of germinated seedlings) were compared (r=0.95, P≤0.001).

Inheritance of flower color in Dendranthema grandiflora Tzvelev. (Chrysanthemum morifolium Ramat.) using cultivars and inbreds. I: Plastid pigmentation

SummaryProgeny from controlled crosses of 28 garden chrysanthemum (Dendranthema grandiflora Tzvelev.) inbreds in various combinations as males with 3 heterozygous cultivars and 10 inbreds as females were evaluated for plastid pigmentation in a series of field and glasshouse environments. Disomic inheritance of a dominant gene, which acts to inhibit pigmentation, best explained the data. However, 1 of 8 families involving a glasshouse cultivar with colorless plastids (‘Puritan’) as female and inbreds with yellow plastids as males deviated significantly from the expected 1:1 ratio. This family consistently exhibited an excess of plants with colorless plastids. Although parent clones and cloned progeny from inbred parents were scored the same in field and glasshouse environments, reevaluation in the field of all 8 ‘Puritan’ families, first evaluated in a glasshouse environment, revealed phenotypic misclassification apparently due to environmental effects. An excess of plants with colorless plastids appeared in the glasshouse but evaluation of the same genotypes in the field resulted in an excess of plants having yellow plastids. Submerging ray florets in a hot-water bath revealed yellow plastids masked by vacuolar pigments, thus reducing chances of misclassification. The data suggest that evaluation of highly variable families in a single environment can lead to misclassification of plastid pigmentation. However, even with evaluation in 2 or more environments, certain families may exhibit an excess of plants with colorless plastids.

Evaluating self-incompatibility in Chrysanthemum: The influence of ovule number

SummaryThe impact of ovule number on seed set calculations for self-incompatible (SI) species was investigated. Diploid Chrysanthemum was chosen for this study because accurate counts of the potential number of ovules could be made. Individuals in populations of C. carinatum, C. coronarium, C. c. subsp. spatiosum, and C. segetum were crossed in complete diallels. All species exhibited similar results. Therefore, only the diallel data from C. coronarium subsp. spatiosum were presented. The seed set data with and without ovule counts were processed by SIGMAS, a computer program designed to analyze SI data. Incorporation of the actual number of ovules into seed set diallels provided the most realistic representation of values for self-incompatibility studies. Data derived from equations excluding ovule counts might lead to inaccurate genetic interpretations. Ovule counts were significant between and within genotypes for self (disc and ray florets), but not cross (ray florets only) pollinations. The disc florets in self-pollinations were found to be responsible for increasing the variability in ovule number. The statistics indicate that the disc and ray florets composed two distinct populations. At the diploid level with a single daisy flower type, the disc floret numbers were variable, whereas ray florets were relatively static. This was not the case with polyploid chrysanthemums, where both ovule populations were dynamic and interactive. The conservative nature of percent pseudo-self-compatibility (%PSC) deems it necessary to obtain an accurate measure of female fertility. Values for this could be obtained using a bulk pollination or a tester with unmatched S alleles.

Interaction among sporophytic S loci in self-incompatible garden chrysanthemums

SummaryCertain parent-progeny crosses were studied to determine whether several S loci acted independently or epistatically to produce incompatibility in garden chrysanthemums, Chrysanthemum morifoliumRamat. The ratios of compatible: incompatible crosses with the original parent, as the pollen parent, were nearly 1:3, 1:1, and 1:1 for the I1, backcross (BC), and BCF2 generations, respectively. In particular, crosses between each progeny and the original parent showed that the number of compatible crosses was much higher than expected if each S locus acted independently. Therefore, interaction must have existed among pollen S alleles from different S loci. This information was used to demonstrate a method by which garden chrysanthemums could be inbred by sib mating in successive generations.

Thin-layer chromatographic analysis of flower color phenotypes in Dendranthema grandiflorum Ramatuelle inbreds and clonal cultivars

SummaryFour glasshouse and 13 garden chrysanthemum cultivars or inbred seedlings from the color groups white, yellow, pink/purple, and orange/red/bronze were analyzed with thin-layer chromatography (TLC) for qualitative and quantitative pigment constituents. TLC confirmed the presence of eight carotenoids in yellow and bronze cultivars. Qualitative differences exised only for spots 5–8. Rf values for lutein matched those of spot 4. Flavonoid analysis of purples and bronzes revealed two anthocyanidins, one of which was cyanidin, one flavone, and two phenylpropanoids. White cultivars had four phenylpropanoids, two of which were caffeic and ferulic acids. In most cases, inbred and non-inbred cultivars within a given phenotypic class did not exhibit qualitative differences. Color analysis could be pursued at any level of inbreeding, but inheritance studies would be severely hampered using non-inbred genotypes of this hexaploid floricultural crop.

Rapid method of determining pollen incompatibility in Chrysanthemum morifolium Ramat

SummaryA classification system for predicting high, medium and low seed set from Chrysanthemum morifolium crosses was developed. Stigmas collected and preserved 8 days after pollination were examined with a binocular microscope for adhering pollen grains. Florets from compatible crosses had brown stigmas with pollen grains attached and embryo development while florets from incompatible crosses had white stigmas with no or rarely 1 or 2 pollen grains attached and no embryo development. Using this method the occurrence of seed set was predicted with 78.5% accuracy in one year and 89% in the following. This provides a method of determining the compatibility of a chrysanthemum cross without waiting the 1 to 2 months required for seed ripening.