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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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Genetic transformation of cut roses may greatly facilitate cultivar improvement programs by shortening the time required to introduce new genes into elite germplasm. The biolistic process offers a very promising method for the genetic transformation of roses.

Several factors that have a significant affect on transformation efficiency were examined in an effort to optimize the biolistic process for gene transfer in roses. The factors examined were type of tissue (leaf segments, petioles, callus, etc.), bombardment distance, the number of bombardments, DNA construct and microcarrier velocity.

Two constructs of the reporter gene, β-GUS, were examined to determine which construct provided the highest level of expression. Only the construct designated pBI 426 provided β-GUS positive cells in leaf and callus tissue. This construct was used in all subsequent experiments.

Experiments to find the optimum number of bombardments and rupture disk pressure were carried out using leaf and callus tissue and 1.6 μm gold particles. The optimum number of bombardments per sample was three for leaf tissue. The optimum rupture disk pressure was 900 p.s.i. for leaf and callus tissue.

Meristems of axillary buds are being bombarded in situ on stem-bud explains. These should yield transgenic rose plantlets in 3 to 4 weeks.

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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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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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The Legislative Commission on Minnesota Resources initiated a program to develop a viable seed industry for the production of native grasses and forb. A part of this program is to measure the amount of genetic diversity among and between populations in Minnesota. This information will be used to develop strategies for the distribution of seed in land reclamation and for management of seed production to maintain the genetic diversity of commercial seed lots. Two grasses, Andropogon geradii and Schizachyrium scoparium, and two forbs, Monarda fistulosa and Liatris sp., were used in this study. Genetic diversity of populations was measured using morphological traits and isozyme analysis of 30 to 50 individuals from each of the 13 to 49 populations. Thirteen enzymes systems were examined to detect polymorphisms. Isozyme polymorphisms have been detected in Liatris populations for PGM, MDH and ACP. No isozyme polymorphisms have been detected in grass populations. Morphological characteristics were measured in a common nursery to remove genotype × environment interactions. Variation in height, number of stems and number of inflorescences were observed within and among grass populations. Liatris populations varied in leaf number, width and length and shoot dry weights.

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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

New Guinea impatiens have been growing in popularity as a potted, bedding and hanging basket plant. This growth has been due mainly to the development of new cultivars by commercial breeding programs. However, no one has investigated or reported the inheritance of simple Mendelian traits of economic importance.

A study of the genetics of six qualitative traits was undertaken to elucidate inheritance of these traits in New Guinea impatiens. The traits studied were flower color, flower size, leaf color, leaf vein color, leaf variegation and variegation of leaf margins. Thirteen genotypes were used as parents in reciprocal crosses of all possible combinations. Fourteen crosses yield sufficient seed for use in the inheritance studies. Fifty to one hundred progeny were used from each cross. Segregation of the traits of interest were observed in the F1 populations. Inheritance measures were based on the segregation pattern of the F1 progeny.

Heritabilities for traits varied widely. Genetic models based on segregation ratios will be presented for each trait. The mode of inheritance and heritabilities revealed from this study will be useful to plant breeders in developing efficient cultivar improvement strategies.

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