Gardunia, Brian Wayne (2006-12). Introgression from Gossypium mustelinum and G. tomentosum into upland cotton, G. hirusutum. Doctoral Dissertation.
To increase genetic diversity with elite upland cotton, introgression populations
with wild species of cotton, Gossypium mustelinum and G. tomentosum, were created.
To accomplish this objective, F1, F2, BC1F1, and BC1F2 generations were developed
along with random mating populations (BC1rm1 and BC1rm2) and grown in a
randomized complete block design with four replications in College Station, Texas
during 2003 and 2004, and in Mexico during 2005 for G. mustelinum introgression
populations. These generations were tested with microsatellite markers from
chromosome 11 in order to measure the effects of selection and recombination. Later
generations (BC2F1, BC2rm1, BC2F2, BC3F1, BC3rm1 and BC3F2) and composite
generations were evaluated in a randomized complete block design with four replications
during 2004 and 2005 for agronomic properties.
Introgression barriers for G. mustelinum were found to include daylength
sensitivity and hybrid breakdown, which was only apparent in Mexico. Backcross
generations had improved fiber quality. Random mating populations did not have
increased variance and means differed little from BC1F1 levels. Microsatellite markers showed decreased frequency of G. mustelinum alleles and decreasing heterozygosity, but
no increase in map distances in random mating populations. Upper-half mean length and
upper quartile length by weight were highly heritable, as measured with parent-offspring
regression. Most other agronomic traits had moderate heritabilities. Composite
generations were found to be favorable for selection and breeding.
For G. tomentosum populations, hybrid breakdown was also a problem with low
yields for F2 and BC1F2 generations, but day length sensitivity was not. Little or no
increase in variance was found in random mating populations when compared to BC1F1
levels. G. tomentosum populations did not show improvements in fiber length as seen in
G. mustelinum populations, but did have increased strength in BC1F1 and F1
generations over TM-1. Mapping distances increased in the random mating populations
for G. tomentosum, and the frequency of alien alleles did not decrease in random mating
populations. Generation means approached recurrent parental values for most traits
within three backcrosses. Composite generations were found to be the most useful for
breeding and selection.