Term
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Definition
| An autotetraploid with four sets of identical chromosomes. |
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Term
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Definition
| The harvestable product is the stem. A perennial plant with dioecious, bee-pollinated flowers. Crowns are produced at a crown nursery and planted in 20 cm furrows to produce perennial asparagus plants that overwinter as storage roots, and can live up to 10 years. There is no harvest until the 3rd year. In the spring, stems come up using energy reserved from the roots. After full harvest, full fern stage replenishes stores for winter. |
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Definition
| A GMO restorer gene for genetically engineered male sterility. Used when pollen production from half the hybrids is not enough for full yield. Inhibits RNase. A homozygous BB population is used as the pollinator when creating a hybrid, producing a hybrid population that is 100% fertile. |
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Definition
| An indicator of quality in asparagus. It is correlated with spear length. |
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Definition
| Have extreme inbreeding depression. Inbred lines are dwarfed. It is difficult to emasculate carrots by hand, so hybridization processes are more complex, and use male-sterility. |
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Term
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Definition
| In inbred lines, a 240:1 amplification per generation is sufficient for production to be economical. Hybridization is easy. Emasculation is a simple matter of removing the tassel. |
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Term
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Definition
| Production of asparagus crowns for transplant into fields. |
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Term
| Cytoplasmic male sterility (CMS) |
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Definition
| The most common form of male sterility used in hybrid seed production. Mutation is inherited maternally in the mitochondria. Alwasy produces sterile progeny. No Mendelian segregation is observed. Can be unstable in some plants: fertile plants arise spontaneously. |
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Term
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Definition
| Cross-pollinating and self-incompatible. |
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Term
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Definition
| All possible crosses in a population of inbred lines, or between two populations of inbred lines. |
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Term
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Definition
| A theory for heterosis. Hybridization brings together favourable alleles for many loci, leading to vigour. With this theory, it should be possible to produce an inbred line that is homozygous for all favourable alleles, thus matching any hybrid vigour. |
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Term
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Definition
P1/P2//P3/P4
A four-way cross. Used if pollen production in the male parent is also decreased by inbreeding depression. Hybrids have low uniformity and vigour. Has the worst vigour, uniformity, and cost of production of all the hybrids. This type of cross was used in 1930s, when inbred lines had economically low yields. |
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Term
| Environmentally sensitive nuclear male sterility |
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Definition
| Recessive nuclear male sterility which is only expressed under certain environmental conditions. rr plants are easily selfed under normal conditions. RR is crossed with rr under restrictive conditions, producing 100% Rr fertile hybrids. Used in 25% of rice hybrids. Includes temperature and photoperiod sensitivity. |
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Term
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Definition
| One gene blocking the expression of another. |
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Term
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Definition
| The foliar stage of asparagus, occuring after harvest. Replenishes root stores for the winter. The true leaves of asparagus plants are the scales on the spears. Most photosynthesis occurs in the feathery stems. |
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Term
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Definition
| Indicates the strength of the method based on genetic expectations. |
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Term
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Definition
| Doubled by pollination control. Shows that half-sib selection is better than mass selection. |
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Term
| General combining ability |
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Definition
| The average performance of progeny when mated with a genetically diverse population such as an open-pollinated population. |
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Term
| Genetically engineered male sterility |
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Definition
| Used if cytoplasmic male sterility is unstable, or if Rf genes are tightly linked to undesirable alleles. An RNase nuclear gene is inserted, controlled by a tapetum-specific promoter, linked to a GMO gene for herbicide resistance. The RNase kills pollen grains. A hemizygous male sterile individual is created (T/-). If crossed with a herbicide resistant pollinator, half the progeny will be sterile (T/-), and the other half will be fertile, but herbicide susceptible (-/-), they can easily be removed by applying herbicide. |
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Term
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Definition
| A family which has the same mother plant (harvested from one plant), but pollinated by a large population of pollinators. Lower variance between families than in S1 families. |
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Term
| Half-sib selection with pollination control |
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Definition
| Two seasons per cycle. Doesn't give strong gain in early generations, but genetic variance is maintained for a long period. Gain may exceed that of S1 selection. Has the second best gain per cycle, after S1. |
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Term
| Half-sib selection without pollination control |
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Definition
| One season per cycle. Doesn't give strong gain in early generations, but genetic variance is maintained for a long period. Gain may exceed that of S1 selection. Has the least gain per cycle. |
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Term
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Definition
| An allele is present on one chromosome, and the entire locus is absent on the other. |
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Term
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Definition
Hybrid vigour
Increased vigour from heterozygosity. Expression of recessive traits is less likely. Some crosses produce better vigour than others. Probably caused by a mixture of all theories: dominance, overdominance, and model epistasis. First demonstrated in corn by crossing different open-pollinated populations; even this produces some amount of heterosis. |
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Term
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Definition
| Produced because they are uniform, and they display heterosis. Includes single-cross, modified single-cross, three-way, and double-cross hybrids. |
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Term
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Definition
| Creation of a pure line at the same time as back-crossing it to a cytoplasmic male steril line, decreasing the amount of time it takes to produce isonuclear lines. |
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Term
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Definition
Pure line
A fixed genetic entity. If self-pollinated it does not change. A valuable inbred line has alleles which contribute to vigour in crosses with other lines, and not necessarily vigour in itself. Recurrent selection is used to produce superior inbreds. May have severely low yields, thus producing uneconomical amounts of hybird seed. Development:
1. Formation of a segregating population
2. Inbreed the population with selection. There is no advantage to the inbred line if there is no selection. Selection is similar to the methods used for self-pollinated crops, often using pedigree method, but single-seed descent and bulk methods may be used.
3. Evaluate line performance for general and/or specific combining ability. The number of reciprocal hybrid crosses possible in a populatoin of n inbreds is (n(n - 1))/2. A test-cross is performed.
4. Evaluate lines for potential hybrids. |
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Term
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Definition
| With continued selfing, plant vigour decreases due to homozygoisty of deleterious recessive alleles. Effect varies with trait. |
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Term
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Definition
| Lines developed with the same genotype, but one has cytoplasmic male sterility. The two are crossed, and the progeny of the sterile line are all sterile. These lines may be created by back-crossing a pure line to a sterile line. The sterile parent is the donor, and the fertile parent is recurrent. Isonuclear lines can be made in parallel. |
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Term
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Definition
| Used when emasculation is not economical. Male-sterile plants produce no pollen, or pollen is non-viable. Includes petaloid mutants. It cannot self-pollinate. If inter-planted with a pollinator, it will produce progeny only of that cross. Includes nuclear and cytoplasmic male sterility. |
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Term
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Definition
| One season per cycle. Successful for selecting high heritability traits. |
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Term
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Definition
| A theory for heterosis. Favourable alleles interact to produce heterosis. More biochemical pathways are open when the individual is heterozygous. |
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Term
| Modified single-cross hybrid |
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Definition
P1/P1'//P2
A type of hybrid. Used if the female parent has insufficient seed production. P1 and P1' are different but related inbred lines, derived from the same population or cross. Some of the vigour is restored to the female parent, to enhance seed production, but minimizes segregation. Hybrids made this way are not quite as vigorous as hybrids from a single cross. Has the second best vigour, uniformity, and cost of produciton, after single-cross hybrids. |
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Term
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Definition
| A type of male steriltiy. Segregation occurs when selfing or back-crossing. May be a dominant or recessive allele. |
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Term
| Nuclear restores of fertility (Rf) |
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Definition
| A GMO dominant nuclear gene which restores male sterility in plants with cytoplasmic male sterility. S-rfrf is crossed with _-RfRf (doesn't matter if cytoplasm is fertile or sterile, it will be fertile), and it produces S-Rfrf, a fertile hybrid. Incldues the Barstar gene. Unnecessary in carrots, beets, and onions, because the seed is not the saleable product: male sterility in a commercial hybrid is acceptable. |
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Term
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Definition
| Open-pollinated varieties. Thickness of the neck is important: thick necks dry more slowly and are more susceptible to rotting in storage, which can infect other onions. Narrow-necked hybrids are uniform and rot less. |
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Term
| Oppen-pollinated (OP) population |
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Definition
| Subjected to natural selection, and genetic drift. Non-uniform. |
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Term
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Definition
| A theory for heterosis. Heterozygosity is important for vigour. Different co-dominant alleles may be present, and heterozygosity gives the plant more flexibility to adapt to the environment. |
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Term
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Definition
| Mutant plants which produce petals instead of stamens. They are male-sterile. |
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Term
| Photoperiod sensitive nuclear male sterility |
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Definition
| Male sterility only expressed in long photoperiods. |
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Term
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Definition
| Pickling cucumbers can be grown in the greenhouse. The fruit is immature when harvested, so yield may be measured early on. |
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Term
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Definition
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Term
| Reciprocal recurrent selection |
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Definition
| Recurrent selection for specific combining ability with another population of inbred lines. Selection occurs simultaneously in both populations, and each is used as a tester for the other. Use OP populations which produce heterosis when crossed. Yield of hybrids increases with selection, but yield of the inbred population may not. |
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Term
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Definition
| Useful for increasing the frequencies of favourable alleles in populations. Used to produce superior inbred lines. The seed from selfing is used in the next generation. |
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Term
| Recurrent selection for general combining ability |
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Definition
| Plants are simultaneously selfed and test-crossed to a tester line. Lines which produce the best progeny are selected. The seed from selfing is used in the next generation. |
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Term
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Definition
| The plant is selfed. Variability between families is maximized. |
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Term
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Definition
| Three seasons per cycle. Requires more labour than other methods, in some crops more than others. High early gains come at the expense of decreasing genetic variance faster than in half-sib selection: limits the maximum improvement. Lines can be traced back to individual plants. A lower selection pressure leads to a lower starting mean, but improves maximum gain. Has the best gain per cycle. |
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Term
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Definition
| 50% of heterozygosity is lost with each generation. After about 5 generations, uniform inbred lines are developed. Families are numbered S1, S2, S3 ... |
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Term
| Sex determination in asparagus |
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Definition
mm = female
Mm = male
MM = supermale |
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Term
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Definition
| An example of when heterozygosity is an advantage in humans. People who are heterozyous for the gene for sickle-cell anemia (thus do not have the disease), have some resistance to malaria. |
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Term
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Definition
P1/P2
A type of hybrid. Result from crossing two inbred lines. Has the best vigour, uniformity, and cost of production of all hybrid types. Became popular in the 1950s when the yield of inbred lines had improved to an economic threshold. |
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Term
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Definition
MM asparagus plants
Produced using tissue culture, or from rare male perfect flowers. When crossed with female asparagus plants, they produce all-male hybrids. By the 1980s, this was common practice. |
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Term
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Definition
| The layer of cells on the inside of the anther. Nourishes developing pollen grains. |
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Term
| Temperature sensitive male sterility |
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Definition
| Male sterility expressed only in high temperatures. |
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Term
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Definition
| Used in selection for general combining ability. Genetically diverse. May be an open-pollinated population. In reciprocal recurrent selection it is the other population being bred. |
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Term
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Definition
| A cross performed to determine the combining ability of an inbred line. |
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Term
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Definition
P1/P2//P3
A type of hybrid. Used if the female parent has severely insufficient seed production. Commonly used in carrots. Results in segregation. Hybrids are less uniform than single-cross or modified single-cross, and have less vigour, since alleles are diluted. Has the thrid best vigour, uniformity, and cost of production, after single-cross and modified single-cross hybrids. |
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Term
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Definition
| An open-pollinated cultivar of asparagus grown before the 1980s. |
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Term
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Definition
| Asparagus which was not exposed to light. Does not produce chlorophyll. |
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Term
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Definition
| Allows one cycle to be completed in a year. Gain per cycle becomes gain per year. |
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