Search Results
You are looking at 31 - 40 of 49 items for
- Author or Editor: Edward J. Ryder x
Genes for flowering time appear to be relatively common in lettuce and other Lactuca species. These include previously described major genes Ef-1 an Ef-2, other genes of discrete effect and genes acting in a quantitative manner. Our goals in studying the flowering time phenomenon are: 1)describe the inheritance of the traits, 2) establish their relationship to each other, and 3) elucidate their evolutionary significance.
The PI 175735 (L. serriola) is an accession with narrow leaves, spines and anthocyanin. Its flowering time is daylength related; it is early flowering under long days and late flowering under short days. It was crossed with the late flowering line C-2-1-1, which is homozygous for both late alleles in the Ef system. The F1 is late under short days and early under long days. The F2 population and F3 families were grown under long day conditions in the greenhouse, Segregation in the F2 was 3 early: 1 late. Among F3 families from early plants, segregation was 1 homozygous early: 2 segregating. Within segregating families, the ratio was again 3:1. The evidence suggests a single gene with earliness dominant.
Genes for flowering time appear to be relatively common in lettuce and other Lactuca species. These include previously described major genes Ef-1 an Ef-2, other genes of discrete effect and genes acting in a quantitative manner. Our goals in studying the flowering time phenomenon are: 1)describe the inheritance of the traits, 2) establish their relationship to each other, and 3) elucidate their evolutionary significance.
The PI 175735 (L. serriola) is an accession with narrow leaves, spines and anthocyanin. Its flowering time is daylength related; it is early flowering under long days and late flowering under short days. It was crossed with the late flowering line C-2-1-1, which is homozygous for both late alleles in the Ef system. The F1 is late under short days and early under long days. The F2 population and F3 families were grown under long day conditions in the greenhouse, Segregation in the F2 was 3 early: 1 late. Among F3 families from early plants, segregation was 1 homozygous early: 2 segregating. Within segregating families, the ratio was again 3:1. The evidence suggests a single gene with earliness dominant.
Abstract
The similar titles of Namkoong’s paper and this one invite comparison, not so much for their similarity as for the differences in sampling rationale. The main difference is in the nature of the populations that are being sampled. The population in the field is usually far away. Further, it is of unknown size and its genetic makeup and complexity can only be guessed.
Screening for lettuce (Lactuca sativa L.) big-vein resistance in the F2 generation is highly inefficient. Efficiency improves in the F3 and following generations with continued inbreeding. Traits useful in ascertaining resistance are 0% of plants showing symptoms and percentage of plants showing symptoms at a given date. Breeding lines identified as resistant in greenhouse screening have proved resistant under field conditions. Forty-nine cultivars have been identified in preliminary testing as potentially resistant. Of these, 11 have been confirmed as resistant in greenhouse and field tests.
Big vein is a disease of lettuce; symptoms include vein clearing and delayed head formation. Big vein virus is vectored by a fungus that inhabits lettuce roots. We developed a greenhouse screening procedure to evaluate cultivars and breeding materials for resistance, which is relative and based on the proportion of plants in a population that show no symptoms at an arbitrary time after inoculation. We have screened 744 cultivars in preliminary tests. Of these, 49 showed promise for resistance. Eleven of the promising cultivars showed consistent resistance in replicated greenhouse and field trials. In breeding populations, reaction of single plants is not as reliable an indicator of resistance as the reaction of plant groups. Therefore, F3 families are more useful than the F2 for screening. Field test rankings of materials selected with this method are consistent with greenhouse evaluations.
Big vein is an economically damaging disease of lettuce (Lactuca sativa L.) incited by Mirafiori lettuce big vein virus, which is vectored by the soil-borne fungus Olpidium brassicae (Woronin) P.A. Dang. Resistance to this disease is needed because no feasible cultural control methods have been identified. Partial resistance is available within cultivated lettuce and is expressed as delayed appearance of symptoms in combination with a reduced percentage of symptomatic plants. Complete resistance has been identified only in accessions of L. virosa L., an incongruent wild relative of lettuce. Resistance from L. virosa has not been introgressed into lettuce. The objective of this research was to determine whether big vein resistance from L. virosa can be introgressed into lettuce. Progenies of backcross (BC) hybrids between L. virosa and L. sativa cultivars were greenhouse tested for big vein resistance over four generations of self-pollination. Selected plants from resistant BC families were used as parents to create BC2 progeny from crosses with high partial-resistant cultivars, intermediate partial-resistant cultivars, and susceptible cultivars to test for the presence of transgressive segregants. Experiments were conducted in the greenhouse by infecting seedlings with O. brassicae zoospores collected from big vein symptomatic plants. Plots were evaluated for area under the disease progress curve and the percentage of symptomatic plants; asymptomatic plants from resistant families were retained in every generation. Complete resistance to big vein was not recovered, and may be the result of insufficient sampling of BCF2 progeny or linkage between resistance alleles and alleles causing incongruity. Variation for partial resistance was observed in all BC generations, and transgressive segregants were identified among BC2 families from crosses using partially resistant and susceptible parents. This research suggests that L. virosa contains alleles that confer partial resistance to big vein when introgressed into an L. sativa background, and these alleles are distinct from those present in partially resistant lettuce cultivars. Alternative breeding strategies should be pursued to introgress complete resistance from L. virosa into cultivated lettuce.