2Cultivar Development in Cross-pollinated Species Compared to self-pollinated species, cross-pollinated species differ in their gene pool structure, and in the extent of genetic recombinationUnselected populations typically consist of a heterogeneous mixture of heterozygotes; as a result of outcrossing, genes are re-shuffled in every generation
3The breeder focuses more on populations, rather than individual plants, and on quantitative analysis, rather than qualitative traitsProgeny do not breed true, since the parent plant is pollinated by another plant with a different complement of alleles
4Because progeny do not breed true in cross-pollinated crops, the usual progeny testing that would be employed in self-pollinated material is much less informative.A more useful way to assess genetic potential is to examine combining ability:General combining abilitySpecific combining ability
5Combining ability: the ability of an inbred line to give characteristic performance in hybrid combinations with other lines.The progenies are tested for performance as populations and related back to parental.More precision can be obtained by using a homozygous inbred line as the pollen donor (tester line).
6General combining ability: the average or overall performance of a line in hybrid combinations (open pollinated); represents additive genetic variance and additive x additive epistasisSpecific combining ability:the performance of a line as compared to other lines when crossed with the same pollen donor (specific pollen source); represents non-additive genetic variance
7Recurrent selectionAny breeding system designed to increase the frequency of desired alleles for particular quantitatively inherited characters by repeated cycles of selectionIdentify superior genotypes for the trait under selection.Inter-mate the superior genotypes and select improved progeny.
8Population structures Self-pollinatorsmixture of homozygous linesa single homozygous lineimprove through cross, inbreed, select new superior homozygous lineCross-pollinatorsmixture of heterozygous plants (population)maintain through cross-pollination (OP)improve through selection of plants with desired genes, avoid too much inbreeding
9Progeny test vs combining ability test Self-pollinatorsevaluate pure line offspring (Measure agric. value)Cross-pollinatorsevaluate selfed offspring (if possible) No C.A.)evaluate test cross offspring (Measure combining ability)homozygous line tester (specific combining ability)heterogeneous population tester (general combining ability
10Recurrent selection principle 1. Select best plants2. Intercross selectedto form next generationPhenotypic recurrent sel.Mass selectionGenotypic recurrent sel.Evaluate offspring
11Mass selection Very simple population improvement Efficient only for high heritability traitsPopulation maintenance Remove off types First step in breeding programs
12Select good looking plants Half-sib selection1. seasonSource populationSelect good looking plantsand intercross2. seasonPlants in each offspringhave female parent incommon. They arehalf-sibsThey reveal combiningability of selected plantProgeny test of selected plants in isolation3. seasonA is lessefficient than BA. Composite seedfrom superiorprogeniesB. Composite remnantseed from plants withsuperior progenies
14Source population Cross pairs of selected plants Full sib selectionbased onpair crossesMeasures specific combining ability between selected plantsComposite remnant cross seedfrom combinations with superior progenies
15self-pollinate selected plants Source populationself-pollinate selected plantsSelection fromS1 progenyoffspring testOnly if selfingis possibleComposite remnant selfed seedfrom selected plants with superior progenies
16Formation of synthetic cultivars ClonesSource populationClone selected plantsThe selected baseclones are keptto form new Syn1seeds regularlyPolycross selectedsuperior clonesPolycross offspring evaluationThe cultivar is propagateduntil Syn2-Syn5 to obtainenough seedClones with highcombining abilityWith well combining clonesthe synthetic can be moreuniform and vigorous thantraditional OP cultivarsIntercross toform Syn1Open pollinateto form syn2
17Breeding clonally propagated species Plants are highly heterozygousOften semi-sterileOften polyploidsTwo major breeding methodsSpontaneous or induced mutations (sports)Hybridization (often between subspecies / species)
18Hybridization in clonally propagated species Clone AXClone BPotatoBegoniaOrchidsSelect best looking seedlingsEvaluate clones 1-2 seasonsMultiply and market superior clones