Arkansas Agricultural Experiment Station, University of Arkansas Division of Agriculture
Dale Bumpers College of Agricultural, Food and Life Sciences

A newsletter for faculty, staff and students

July-August 2005 • Vol. 31, No. 4

Notice of Release of Three Arkot S23 Germplasm Lines of Cotton

The Arkansas Agricultural Experiment Station announces the release of three noncommercial breeding lines of cotton, Gossypium hirsutum L., designated Arkot S23-1, Arkot S23-2, and Arkot S23-4.  The primary breeding objective associated with these lines was to develop near-commercial lines from a non-traditional germplasm source. 

The three lines were derived from a mixed population of germplasm developed by J. M. Stewart. A synthetic allotetraploid was made by hybridization of G.  arboreum A2-026 and G. armourianum followed by doubling of the chromosome number with colchicine.  The synthetic allotetraploid was crossed with G. hirsutum ‘Hancock’ and the trispecies hybrid was self-pollinated.  Various morphological selections and open-pollinated bulk populations were grown for eight generations in a genetic nursery at Fayetteville, AR (area with high outcrossing).  During the 8-year period the nursery contained other cultivars of G. hirsutum, multiple selections from the trispecies hybrid, and other interspecific hybrid combinations, especially involving G. herbaceum.  Genetic diversity within a line was maintained each year by bulk harvesting a boll from each plant without selection. Beginning in 1995 seeds from nine lines derived from the original trispecies hybrid were bulked, and one-cycle of mass selection was performed on an isolated population at the Main Experiment Station at Fayetteville, AR. A second-cycle was employed in a planting at Southeast Branch Station at Rohwer, AR (area with low outcrossing) in 1996.  Bolls were only harvested from plants possessing plant stature, fruiting, and lint color characteristics consistent with commercially grown cotton.  Forty individual plants (designated at S1 through S40) were selected from the segregating population at Rohwer in 1997, and evaluated as progeny rows at two Delta locations in 1998.   Nineteen of the 40 were selected and grown as advanced progeny in 1999 and 2000.   In 2000, 54 individual plant selections were made from four (S03, S08, S21 and S23) of the progeny.  Arkot S23-1, Arkot S23-2, and Arkot S23-4 were three of the 15 plants selected from the S23 progeny. 

The three lines were included in nine replicated field tests from 2002 through 2004 at four Arkansas Agricultural Research Station sites in the Mississippi River Delta and compared to ‘PSC 355' and ‘SG 105'.  Over all tests, lint yields of the three Arkot S23 lines were intermediate between the two check cultivars.  All three lines tended to have higher lint fraction, superior yield components (higher lint index, fewer seed per area), but poorer fiber quality (higher micronaire readings, shorter fiber length, lower fiber length uniformity, and weaker fiber strength) than the two checks.

Yield and fiber traits of Arkot S23-2 and Arkot S23-4 were highly similar.   Both tended to have higher lint fraction, shorter plant height, lower seed index, higher lint index, more fibers per seed, shorter fiber length, lower length uniformity, and weaker fiber strength than Arkot S23-1.  Seed index and fibers per seed of Arkot S23-1 were similar to the two check cultivars.  In contrast, Arkot S23-2 and Arkot S23-4 had lower seed index and more fibers per seed than the check cultivars. 

Yield component traits of Arkot S23-2 and Arkot S23-4 included a relatively high lint index, high number of fibers per seed, and small seed index.  Compared with the check cultivars, yield production of Arkot S23-2 and Arkot S23-4 appears to be relatively more dependent on increased lint per seed than on increased number of seed per area.  According to Lewis et al. (2000), this combination of yield components should contribute to more stable yield production.

Plant heights of Arkot S23-2 and Arkot S23-4 tended to be similar to the check cultivars, while Arkot S23-1 tended to be taller than the other lines.  Open boll ratings in 2003 and 2004 indicated that Arkot S23-2 and Arkot S23-4 were earlier maturing than the check cultivars.  Over three tests, leaves of Arkot S23-2 (rating = 4.2) were more hirsute than leaves of Arkot S23-1 (rating = 2.7) and Arkot S23-4 (rating = 2.8), based on a rating scale of 1 (smooth leaf) to 7 (very hairy) (Bourland et al., 2003).  Arkot S23-1 displays yellow pollen, while the other two lines have cream pollen.

In 2004, the three lines were more resistant to tarnished plant bug (Lygus lineolaris (Palisot de Beauvois)) than the susceptible frego-bract check and equal to the check cultivars.  In a 2004 greenhouse study, all three lines were more resistant to Rhizoctonia solani Kuehn (a major seedling disease pathogen) than SG 105.

The three Arkot S23 lines provide an untraditional breeding material, which expresses good yielding ability.  Yield components of the lines tended to be superior to the cultivar checks, but fiber quality traits are less desirable than the cultivar checks. Development of the two lines was supported in part by funding from Cotton Incorporated.  Small quantities of Arkot S23-1, Arkot S23-2, and Arkot S23-4 may be obtained for breeding purposes from F.M. Bourland, P.O. Box 48, Northeast Research and Extension Center, Keiser, AR 72351.  Unless specifically approved by the Arkansas Agricultural Experiment Station, the lines may not be used as recurrent parents in a breeding program.

                                                                   References

Bourland, F. M., J. M. Hornbeck, A. B. McFall, and, S. D. Calhoun.  2003.  A rating system for leaf pubescence of cotton.  J. Cotton Sci. 7:8-15.

Lewis, H., L. May, and F. Bourland.  2000.  Cotton yield components and yield stability. pp. 532-536. In Proc. Beltwide Cotton Conf., San Antonio, TX.  4-8 Jan. 2000.  Natl. Cotton Counc. Am., Memphis, TN.