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  • Author or Editor: Mark S. Strefeler x
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The influence of temperature and genotype on plant height, internode length, and morphological development of 20 cultivars of Pelargonium ×hortorum Bailey were determined by growing plants under one of three day–night temperature regimes (18/18C, 18/24C, and 24/18C). Temperature regime influenced internode length and plant height regardless of plant genotype. Internode length and plant height increased as the day–night temperature differential (DIF) increased from –6 to 6C. Average internode length increased from 5.3 ± 0.2 mm for –6C DIF to 6.3 ± 0.2 mm for +6C DIF. Genotypes differed for average internode length (4.2 to 8.7 mm) and plant height (54 to 95 mm). Node count increased as average daily temperature (ADT) increased. Node counts were 11.2 at 18/18C (ADT = 18), 11.9 at 24/18C (ADT = 20.3), and 12.1 at 18/24C (ADT = 21.8). Genotype × temperature interactions were not significant for the recorded traits. This study demonstrates that DIF is an effective height control strategy, regardless of geranium genotype, and that DIF combined with the selection of genetically short cultivars may eliminate the need for chemical height control in the commercial production of geraniums.

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Four heat-tolerant (`Celebration Cherry Red', `Celebration Rose', `Lasting Impressions Shadow', and `Paradise Moorea') and three non-heat-tolerant (`Lasting Impressions Twilight', `Danziger Blues', and `Pure Beauty Prepona') cultivars were identified using a Weighted Base Selection Index. These cultivars were used as parents in a full diallel crossing block with reciprocals and selfs. Progeny from five parents (25 crosses) were evaluated for heat tolerance. Four floral (fl ower number, flower diameter, flower bud number, and floral dry weight) and five vegetative characteristics (visual rating, leaf size rating, vegetative dry weight, branch number, and node number) were evaluated with emphasis placed on continued flowering under long-term heat stress. In addition, progeny from all seven parents (49 crosses) were evaluated for inheritance of adaxial leaf color, abaxial leaf color, vein color, and flower color. Significant differences were found in each data category (P < 0.001) with the exception of node number, which was not significant. Flower number varied from 0 to 2, flower diameter varied from 0 to 41 mm, floral dry weight varied from 14 to 105 mg, bud number varied from 0 to 12, branch number varied from 5 to 15, and vegetative dry weight varied from 220 to 607 mg. General and specific combining abilities of the parents were evaluated as was heritability. It was found that the four heat-tolerant cultivars had higher general combining abilities. Heat tolerance has low heritability and is controlled by many genes.

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Three drought-tolerant and four drought-susceptible breeding lines from the Univ. of Minnesota's New Guinea impatiens breeding program were crossed in all combinations (reciprocals and selfs) using a complete diallel crossing scheme. Progeny of each cross were grown using standard cultural practices and data was taken on the morphological traits shown to be related to drought tolerance in previous studies. Data was taken on leaf thickness, leaf width, leaf length, leaf area, and leaf dry weight. From these data the leaf length:width ratio and leaf dry weight/unit area (g·cm–2) were calculated. Mean squares for general and specific combining ability were estimated using Griffing's Model 1, Method 4. Differences between crosses were highly significant (P < 0.001) for all traits examined. Means squares for specific (SCA) and general (GCA) combining ability were significant indicating that both additive and non-additive gene effects are important in the inheritance patterns of these characters. For all traits, GCA was greater than SCA indicating that the additive component had the greatest influence on gain from selection for these traits. These findings agree with other estimates of GCA and SCA for these characters in other crops species. The importance of non-additive effects (SCA) on inheritance of these traits explains why we were able to make rapid improvement in drought tolerance in New Guinea impatiens and the role of additive effects (GCA) on drought tolerance indicates that we can continue to make substantial progress improving drought tolerance in New Guinea impatiens. The impact of these findings on strategies to improve drought tolerance in New Guinea impatiens will be discussed in this presentation.

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Six commercial cultivars (Anna, Aurore, Danhill, Danlight, Melanie, and Thelca), one drought-tolerant cultivar (Orangeade), nine breeding selections, and one check genotype of Impatiens hawkeri Bull were evaluated for differences in drought tolerance based on water loss and time to wilt. The six commercially available cultivars had significantly higher mean water loss than the breeding selections and `Orangeade'. These cultivars wilted in 5.11 days vs. 7.33 for `Orangeade' and 9.10 for the breeding selections. These results suggests that sufficient variability exists in New Guinea impatiens germplasm for the reduction of water loss to improve drought tolerance. Regression analysis revealed that total transpirational water loss 96 h after withholding water was an excellent predictor of the time to wilting (a simple measure of drought tolerance) after water was withheld (R 2 = 0.95). Thus, a simple, efficient, and objective method for selection of drought-tolerant genotypes has been developed for New Guinea impatiens. A comparison of offspring to parental genotypes showed that, after only one cycle of selection, water loss was significantly reduced by more than 30%. These results suggest that there is sufficient genetic variability present for the development of more drought-tolerant cultivars.

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Fifty-three commercial New Guinea Impatiens cultivars (Impatiens hawkeri Bull.) from six different breeding series were tested for level of heat tolerance. Five floral (flower number, flower length, flower width, floral dry weight, and flower bud number) and five vegetative characteristics (leaf dry weight, stem dry weight, total dry weight, number of nodes, and number of branches) were evaluated with emphasis placed on continued flowering under long term heat stress. Significant differences among cultivars were found in each data category (P ≤ .0001). Flower number varied from 0 to 6, flower length varied from 10 to 51 mm, flower width varied from 10 to 47 mm, floral dry weight varied from 0 to 0.5 g, and flower bud number varied from 0 to 14. Four heat tolerant (Celebration Cherry Red, Celebration Rose, Lasting Impressions Shadow, and Paradise Moorea) and three nonheattolerant (Lasting Impressions Twilight, Danziger Blues, and Pure Beauty Prepona) cultivars were identified using a Weighted Base Selection Index. These cultivars were used as parents in a full diallel crossing block with reciprocals and selfs. One hundred seedlings from each of 49 crosses were evaluated for heat tolerance. General and specific combining abilities of the parents were evaluated as was heritability. It was found that the four heat tolerant cultivars had higher general combining abilities. Heat tolerance has low heritability and is controlled by many genes. Superior genotypes were identified (selection intensity of 0.05) and retained for further evaluation and breeding efforts.

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Six commercial cultivars (Anna, Aurore, Danhill, Danlight, Melanie, and Thelca), one drought tolerant cultivar (Orangeade), nine breeding selections, and one check genotype of Impatiens hawkeri Bull were evaluated for differences in drought tolerance based on water loss and time to wilt. The six commercially available cultivars had significantly higher mean water loss than the breeding selections and `Orangeade'. These cultivars wilted in 5.11 vs. 7.33 days for `Orangeade' and 9.10 days for the breeding selections. These results suggest that sufficient variability exists in New Guinea impatiens germplasm for the reduction of water loss to improve drought tolerance. Regression analysis revealed that total transpirational water loss 96 hours after withholding water was an excellent predictor of the time to wilting (a simple measure of drought tolerance) after water was withheld (R2 = 0.95). Thus, a simple, efficient and objective method for selection of drought tolerant genotypes has been developed for New Guinea impatiens. A comparison of offspring to parental genotypes showed that after only one cycle of selection, water loss was significantly reduced by >30%. These results suggest that there is sufficient genetic variability present for the development of more drought tolerant cultivars.

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Abstract

Six selection indices (Smith-Hazel, desired gain, simple-weighted, rank summation, Elston's weight-free, and Baker's standard deviation) were compared to determine the effectiveness of each in identifying superior families for improving 8 fruit yield and quality traits in 3 fresh-market cucumber populations differing in genetic diversity (elite, medium-base, and wide-base). The rank summation, Elston's weight-free, and Baker's standard deviation indices were constructed with 5 traits as well as with the full 8 traits to determine whether measurement of fewer traits would suffice. The Smith-Hazel and desired gain indices were constructed using 5 traits only, since the 8-trait indices had problems with trait colinearity. The effectiveness of the indices was measured by calculating selection differentials for each index. In the elite population, the Smith-Hazel index produced negative selection differentials for all 8 traits studied. In the medium-base and wide-base populations, the Smith-Hazel index had positive differentials, but the desired gain index had negative differentials for the 8 traits studied. The simple-weighted, rank-summation, Elston's weight-free, and Baker's standard deviation indices all had positive selection differentials for the traits of interest in all 3 populations. The best index was the rank summation for 5 traits, since it had the highest overall selection differential of those measured and was easiest to calculate.

Open Access

Abstract

Variance components for 3 fruit yield and 5 fruit quality traits in 3 cucumber (Cucumis sativus L.) populations were estimated using a North Carolina Design I analysis. Three populations were studied (elite, medium base, and wide base), having been formed by intercrossing lines to produce 3 levels of genetic diversity. Families were evaluated in 1.5 × 1.5 m plots using once-over harvest at the stage of 15% oversized fruits. Heritabilities based on full-sib family selection for fruit yield ranged from 0.03 to 0.25, and for the fruit quality traits 0.00 to 0.30. The wide base population would be best for long-term selection for the traits studied, because it had the highest predicted means for all traits except percentage of culls, fruit shape, and overall performance after 15 cycles of full-sib family selection.

Open Access

Our objective was to determine whether repeated applications of 2-chloroethylphosphonic acid (ethephon) + gibberellic acid (GA3) to stock chrysanthemum plants that are day-neutral for flower bud initiation would increase the number of quality cuttings. Across five cultivars, there were no significant differences between controls and plants receiving 250 ppm ethephon in the total number of cuttings per plant. The percentage of cuttings with crown buds was greater for cuttings from controls than for ethephon-treated plants. Applying 500 ppm ethephon significantly reduced the number of cuttings. We conclude that chrysanthemum clones day-neutral for flower bud initiation and development with low long-day leaf number could be selected to form a 4 to 5 week production group.

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The study was designed to provide information on the inheritance of certain characters important to drought tolerance in New Guinea impatiens. Seven genotypes, three were drought tolerant and four drought susceptible, were crossed in a full diallel with selfs. Drought tolerance of parents was estimated using stomatal conductance. At least 55 seedlings per cross were grown in the greenhouse for 2 months and evaluated for drought tolerance. Leaf fresh weight (LFW) leaf area (LA), leaf length (LL), leaf width (LW), and leaf thickness (LT) were measured using 10 leaves from each plant (parents plus progeny). From these measurements, we calculated LFW/LA and LL/LW. Stomatal conductance was measured on parents plus progeny of three crosses (drought tolerant × drought tolerant, drought tolerant × drought susceptible and drought susceptible × drought susceptible). Heritabilities and nonadditive and additive genetic variance for each trait were determined. All characters were significantly different between families. LFW/LA and LT was positively correlated with drought tolerance. The heritabilities for these traits were high, indicating that these characters can be used for selecting for drought tolerance in New Guinea impatiens and that rapid progress can be and was made in improving drought tolerance in New Guinea impatiens.

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