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a Univ. of Arkansas Northeast Research and Extension Center, P.O. Box 48, Keiser, AR 72351
b Cotton Incorporated, 6399 Weston Parkway, Cary, NC 27513
* Corresponding author (bourland{at}uark.edu)
Two breeding lines of cotton (Gossypium hirsutum L.), designated as Arkot 9101 (Reg. no. GP-799, PI 638507) and Arkot 9108 (Reg. no. GP-800, PI 638508) were released in 2004 by the Arkansas Agricultural Experiment Station. Arkot 9101 (tested as 9101-97-09) and Arkot 9108 (tested as 9108-04-17) were developed using the generalized procedures outlined by Bourland (2004). Both lines were derived from crosses made in 1991 with a common parent, the breeding line 8110-27 from which Arkot 8110 (Bourland et al., 1997) was developed by direct selection. The breeding line 8110-27 was derived from a cross of ‘Tamcot SP21S’ (Bird, 1979) and Pee Dee 6520 (Culp and Harrel, 1979). The second parents of Arkot 9101 and Arkot 9108 were ‘H1330’ (Bourland, 1996) and MD32ne, respectively. MD32ne is a BC1F2:3 nectariless breeding line selected by W.R. Meredith, Jr., using ‘Deltapine 90’ as the recurrent parent and DES 16ne (Meredith and Bridge, 1977) as the donor parent.
Both F2 populations were advanced to the F3 without selection. Individual plants (designated as 9101-97 and 9108-04) were selected from the respective F3 generations in 1993 and evaluated as F4 progenies in 1994 and as strains in 1995 and 1996. A second cycle of selection in 1996 gave rise to 9101-97-09 and 9108-04-17, which were tested as progeny rows in 1997 and were promoted to strains in 1998.
The two strains were included in 29 replicated field tests at four Arkansas Agricultural Research Station sites in the Mississippi River Delta and compared with ‘ST474’ in 1998 to 2000 and ‘PSC 355’ in 2001 to 2003. Lint yield of each line was significantly greater than that of the check cultivar in approximately one-fourth of all tests. Averaged across all tests, lint yield of Arkot 9108 was 7% greater than yields of Arkot 9101 and the check cultivars. Yields of Arkot 9108 numerically exceeded the check cultivar in all 29 tests, while Arkot 9101 tended to yield relatively better in sites north of central Arkansas. Lint fraction, fiber length, and length uniformity of the two lines were similar to those of the check cultivars. Each line had approximately 5% stronger fiber strength and approximately 3% lower fiber elongation than the check cultivars. The micronaire values for Arkot 9108 were approximately 8% higher (coarser fiber) than the check cultivars while micronaire readings of Arkot 9101 were similar to the check cultivars.
Both lines had approximately 8% higher lint index (more lint per seed), approximately 7% higher seed index (larger seed), and produced approximately 7% more fibers per seed than the check cultivars. Compared with these check cultivars, yield production for the two lines appear 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.
Except for plant height and leaf pubescence, the two lines are morphologically similar to ST474 and PSC355. Height of each line averaged approximately 5% shorter than that of the check cultivars. Visually rated in seven tests of the 29 replicated tests, leaf pubescence of Arkot 9101 and Arkot 9108 averaged 5.2 and 3.5 based on a rating scale of 1 (smooth leaf) to 7 (very hairy) (Bourland et al., 2003).
Arkot 9101 and Arkot 9108 display good host plant resistance traits. During selection, both lines were screened for resistance to races 1, 2, 7, and 18 of Xanthomonas campestris pv. malvacearum (Smith) Dye, the causal agent of bacterial blight. Resistance to these races conveys resistance to all known U.S. races of this pathogen. In subsequent tests, neither line exhibited symptoms of bacterial blight even after field inoculations with the pathogen. In the 2001 and 2002 National Cotton Fusarium Wilt Test at Tallassee, AL, resistance of Arkot 9101 and Arkot 9108 to fusarium wilt [caused by Fusarium oxysporum Schlect. F. sp. vasinfectum (Atk.) Snyd. & Hans.] was equal to the resistant check, M-315 (Glass et al., 2001, 2002). Arkot 9101 had a lower percentage of wilted plants than M-315 each year. In field tests, both lines were at least as resistant as ST474 or PSC355 to Verticillium wilt (caused by Verticillium dahliae, Kleb.) and thrips (Thrips spp.). In 2003, both lines were more resistant to tarnished plant bug [Lygus lineolaris (Palisot de Beauvois)] than the susceptible frego-bract check, but Arkot 9101 had significantly more damaged flowers than Arkot 9108 and PSC355. In 2002 and 2003 tests, an intermediate level of resistance to root knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] was observed for Arkot 9101. In the same tests, response of Arkot 9108 to root knot nematode was similar to that of the susceptible checks ST474 and PSC355.
The combination of adaptation to the Mississippi River Delta, good fiber properties, and specific host plant resistance traits make these lines valuable to cotton breeding programs. Development of Arkot 9101 and Arkot 9108 were supported in part by funding from Cotton Incorporated. Small quantities of Arkot 9101 and Arkot 9108 seed 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, Arkot 9101 and Arkot 9108 may not be used as a recurrent parent in a breeding program.
NOTES
Accepted for publication March 31, 2005.
REFERENCES
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