Analyses on Progenitor Donors of the Cultivated Allotetraploid Cottons Revealed by GISH

GISH (Genomic i n situ hybridization) of the mitotic metaphase chromosomes of two cultivated tetraploid cotton (AD) 1 ( G. hirsutum ) and (AD) 2 ( G. barbadense ) with all 3 diploid A cotton gDNA(genomic DNA) as probes, blocking with ssDNA(salmon sperm DNA) respectively. The hybridization signals were dected distribute in the A sub-genome chromosomes of (AD) 1 and (AD) 2 , besides, three pairs of crimson signals were also detected only with the A 1-a gDNA probe. which were named GISH-NORs. GISH of (AD) 1 and (AD) 2 with all 13 diploid D cotton gDNA as probes, blocking with ssDNA respectively, except the D 6 ( G.gossypiodies ) gDNA probe generated the hybridization signals in all the chromosomes of (AD) 1 and (AD) 2 , the other 12 diploid D gDNA probes only generated the signals on the D sub-genome chromosomes of (AD) 1 and (AD) 2 , the D6 gDNA probe was very specifical.And three pairs of strong GISH-NORs were detected with all 13 diploid D genome species gDNA probes, the intensity of their GISH-NORs were much brighter than the A 1-a gDNA probe. These results visually confirmed the amphidiploid origin of the allotetraploid cotton species. DA (distinguishing ability ) values of each gDNA probe generated were calculated basing on the above GISH rsults.It showed that the DA value of A 1-a gDNA probe was the biggest in all 3 diploid A genomes both in (AD) 1 and (AD) 2 GISH, and this indicated that A 1-a genome was most likely to be the A sub-genome progenitor donor of (AD) 1 and (AD) 2 , while the D 3-d ( G. davidsonii ) and D 5 ( G. raimondii ) genome species were most likely to be the D sub-genome progenitor donor of (AD) 1 , and (AD) 2 respectively. And this further confirmed that tetraploid cottons are polyphyletic.