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Title:   Author  item
                                            ZHONG, MING - MISSISSIPPI STATE UNIVitem
                                            McCarty, Jackitem
                                            Jenkins, Johnieitem
                                            Saha, Sukumar
  Submitted to: Crop Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 2/2/2002
                                    Publication  Date: 6/1/2002
                                    Citation: Zhong, M., McCarty Jr, J.C., Jenkins, J.N., Saha, S. 2002. Assessment of day-neutral backcross populations of cotton using AFLP markers. Journal of Cotton Science. 6:97-103.Interpretive Summary: Primitive cotton germplasm is a valuable source of genes, but these are underutilized because most will not flower in the temperate zone where most of the cotton breeding occurs.  It is possible to introduce flowering genes into these accessions by crossing them with a temperate zone cultivar and selecting flowering genes in the  segregating generation.  With backcrossing to the accession parent the expectation is that more of the accession genome will be introduced into the selected plants in each backcross.  In theory after four backcrosses the flowering plants should contain most of the accession genome but will flower.  We used four generations of backcrosssed, selected flowering plants and compared their similarity to the non- flowering parent and the temperate zone flowering parent.  Only a few flowering plants were used as parents in each generation of  backcrossing.  We found that most of the AFLP molecular markers from the non-flowering parent were not recovered; however, most of the molecular markers from the flowering parent were recovered. This indicates that large blocks of linked genes stayed together.  This research showed that blocks of genes stay together during backcrossing in cotton and that selecting for flowering types recovered much of the flowering cultivar parent genome.  This principle should encourage the use of this diverse germplasm to breed improved cotton cultivars.
                                Technical Abstract: Accessions in the cotton, Gossypium hirsutum L., germplasm collection represent an underutilized resource.  Most will not flower in the temperate zone. In the F2 generation of a cross between a photoperiodic accession and a cultivar, day-neutral plants can be selected.  Four generations of backcrossing and selection with the  accession as recurrent parent should theoretically produce day-neutral plants genetically similar to the accession parent. We evaluated five populations (F6, BC1F6, BC2F6, BC3F6, BC4F6) of day neutral plants derived from crossing and backcrossing accessions T 78, T 174, T 326, and T 1149 as recurrent parents, respectively, with  Deltapine 16'. Genetic distances were determined using 43 AFLP primer combinations that produced 251 polymorphic AFLP markers among the five parents and a range of 91 to 129 polymorphic markers within each of the 20  populations.  Among the 20 backcross populations the recovery of markers from accession parents varied from 27 to 92% and DPL 16 was from 71 to 91%.  Genetic distance among the populations ranged from 0.35-0.75 from the accession parents and from 0.16-0.38 from the DPL 16 parent.  In successive backcross generations the day-neutral selection did not generally increase in genetic similarity to the recurrent accession parent.  Many AFLP markers seemed to stay together as linked blocks and were selected with the day-neutral phenotype.


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