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Richard H. Ozminkowski Jr. and Pablo Jourdan

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was synthesized by sexual and somatic interspecific hybridizations from the same parent plants to compare the two methods of combining genomes and assess the genetic consequences of bypassing the gametophytic phase before hybrid formation. Highly heterozygous species parents were first produced by intraspecific hybridization between two subspecies each of B. oleracea and B. rapa. Leaf tissue from young plants of both parental species served as a source of protoplasts for fusion; the same plants were later used for crosses. Seventy-two somatic hybrids were produced using a polyethylene glycol-mediated fusion protocol and 27 sexual hybrids were obtained by embryo rescue. Somatic hybrids were produced between one B. oleracea and two sibling B. rapa plants. Sexual hybrids were successfully produced with only one of the two B. rapa siblings. Hybrids were identified by morphology, isozyme patterns, and total DNA content. Although fertile allotetraploid somatic hybrids were obtained within 7 months after seeding parent lines, >1 year was required to produce fertile sexual hybrids.

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Richard H. Ozminkowski Jr. and Pablo Jourdan

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was resynthesized by somatic and sexual hybridization. Seventy-two interspecific somatic (R0) hybrids and 27 sexual (F1) hybrids were produced from the same parent plants. R0 and F1 hybrids displayed morphology that was intermediate to the species parents, but B. rapa characteristics tended to predominate. R0 hybrids with nuclear DNA content equivalent to natural B. napus were uniform for nuclear-encoded traits, whereas allotetraploid F1 hybrids were variable for traits such as morphology, flower color, and seed production. Chloroplast restriction fragment length polymorphisms (RFLPs) showed unequal segregation in the R0 population favoring the chloroplasts of B. rapa; two of the 58 R0 hybrids tested had only the B. oleracea marker and 10 contained markers of both parents. Mitochondrial RFLPs showed a similar bias among the 56 R0 hybrids tested; only four plants showed B. oleracea markers exclusively, and the remaining plants were evenly distributed between having only B. rapa markers or having combinations from both species. In contrast, sexual hybrids displayed only maternal organelle markers.

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Richard H. Ozminkowski Jr., Robert H. Moll, and Randolph G. Gardner

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Richard H. Ozminkowski Jr., Randolph G. Gardner, Warren R. Henderson, and Robert H. Moll

Two inbred lines of fresh-market tomato (Lycopersicon esculentum Mill.), NC 20G-1 and NC 53G-1, both exhibiting prostrate growth habit (PGH), were crossed with the upright growth habit cultivar Piedmont and advanced to the F2 generation. Plants of each F2 population were grown without plant support on black plastic and subjectively rated in field plots for PGH. Extreme upright and prostrate plants were chosen from each F2 population for harvest. Mean comparisons between plants of extreme upright and prostrate habit showed increased total and marketable yields from plants with a prostrate habit. Decay and groundscarring of fruit were less in prostrate than in normally upright plants; the percentage of misshapen fruit was similar in both. The PGH character may be useful in increasing total and marketable yield of ground-culture tomatoes.

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Richard H. Ozminkowski Jr., Randolph G. Gardner, Robert H. Moll, and Warren R. Henderson

Prostrate growth habit (PGH) in tomato (Lycopersicon esculentum Mill.) lines derived from breeding material developed at the Agriculture Canada Research Station, Beaverlodge, Alberta, was the subject of a quantitative inheritance study. Plants with PGH have an increased lateral branch angle, relative to upright plants, and crown-set fruit supported above the soil surface making hand harvest easier. Genetic parameters were estimated in two families (20G and 53G), each containing PGH and upright-habit parental lines, F1, F2, and backcrosses to each parent. Field-grown plants were subjectively rated twice during the growing season. Broad-sense heritability of PGH in family 20G was estimated to be 0.65 and 0.71 for ratings of plant growth habit 6 and 9 weeks after transplanting, respectively, and 0.71 and 0.68 for those of family 53G. Narrow-sense heritability was estimated to be 0.83 and 1.05 for the two ratings in the 20G family and 0.77 and 0.78 in the 53G family. F1 and F2 means were not different from mid-parent values. The genetic variance was entirely additive and expression was influenced by the environment. The data did not support the hypothesis that PGH was controlled by a single gene.