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Fruit Varieties Journal
(Fruit Var J)

American Pomological Society

Volume 30 Number 3 Article 3 Pages: 79-79
Year 1976 Month 7
Title: Considerations in Backcrossing Programs for Clonally Propagated Perennial Crops
Author: R.L. Anderson
Backcrossing highly selected populations to incorporqte desired genes from exotic (usually horticulturqlly inferior) parents is an important breeding method in most crop plqnt species. The classic methodology was developed for transferring simply inherited traits into seed propageted cultivars that could be readily inbred. The genetic basis for this classic system, as outlined by Harlan and Pope and by Briggs, was reviewed. It was emphasized that polygenetically inherited traits are more difficult to transfer in both seed and clonally propagated crops due to population size, linkage, and heritablikty complications.
The classic system was contrasted with what it workable in commercially clonally propagated crops pointing out that lack of inbred recurrent parents, long generation time, and in some cases, severe inbreeding depression cause complications. Selective backcrossing, wherein the transferred and recurrent parent traits are both selected in each generation, must be used where the recurrent parent is non-inbred. Even then in clonal crops the goal must not be recovery of the recurrent parent phenotype per se with the donor trait added. This is impossible to be achieved. Instead the target population is a new segregating population from which horticulturally suitable cultivars can be extracted.
Linkage is a more difficult problem in backcrossing a heterozygous recurrenty parent(s) and especially so for backcrossing polygenetically inherited traits. The use of one generation of recurrent mass selection for total horticultural acceptability was suggested after each backcross. This will increase the opportunity for recombination of donor polygenes (for the trait under transfer) with the recurrent genome. Without this recurrent mass selection process the level of performance for the donor trait will be reduced due to loss of favorable alleles.
Use of one recurrent parent cultivar per backcross cycle for 2 cycles was suggested since use of more cultivars will reduce population size and selection intensity. In the thrid backcross cycle several recurrent parent cultivars should be used simultaneously to increase total genetic variability. Several improved cultivars should result.


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