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Northeast Research and Extension Center, P.O. Box 48, Keiser, AR 72351
* Corresponding author (bourland{at}uark.edu)
Two cotton (Gossypium hirsutum L.) germplasm lines, designated Arkot 8710 (Reg. no. GP-741, PI 628635) and Arkot 8717 (Reg. no. GP-742, PI 628636), were developed by the Arkansas Agricultural Experiment Station and released in 2001. Arkot 8710 and Arkot 8717 possess agronomic, fiber quality, and host-plant resistance traits that make them valuable as breeding lines.
Both lines were developed from double crosses completed in 1987. Arkot 8710 originated from crossing the F1 of ‘Deltapine 50’/Miscot T8-27 (Bourland and Bridge, 1988) by the F1 of DES 237-7 (Bridge, 1987)/Miscot 7824 (Bourland and White, 1992). Arkot 8717 originated from crossing the F1 of ‘DES 119’ (Bridge, 1986)/Miscot 7803-52 (Bourland and White, 1989) by the F1 of Miscot T8-27 (Bourland and Bridge, 1988)/8007-6, a sister line of Miscot 8006 (Bourland et al., 1993).
Arkot 8710 (tested as 8710-45-17) was derived from an F3 individual plant selection (8710-45) made in 1990, with a second cycle of selection made from the F8 generation in 1995. The second cycle selection was evaluated as a progeny row in 1996 and as a line in replicated tests from 1997 through 2000. Arkot 8717 (tested as 8717-17-12) was derived from an F3 individual plant selection (8717-17) made in 1990, with a second cycle of selection made from the F6 generation in 1993. The second cycle selection was evaluated as a progeny row in 1994 and as a line in replicated tests from 1995 through 2000. Procedures of Bird (1982), modified to permit selection for lateral root development, were used in the first cycle of selection for both lines. Second cycle selections were based on visual performance of individual plants and corresponding progeny rows.
In 10 tests from 1997 to 2000 at four Arkansas Agricultural Experiment Station sites in the Mississippi River Delta, lint yields and maturity of Arkot 8710 were equal to ‘Stoneville 474’. Arkot 8710 had shorter plant height (94 vs. 111 cm), lower lint percentage (39.0 vs. 41.8%), finer micronaire reading (4.85 vs. 5.08 units), and weaker fiber strength (264 vs. 277 kN m kg-1) than Stoneville 474. Leaf pubescence of Arkot 8710 is classed as "lightly hairy," being less dense and shorter than Stoneville 474.
Arkot 8717 was compared with either DES 119 or Stoneville 474 at four Arkansas Agricultural Experiment Station sites in the Mississippi River Delta from 1995 to 2000. Average lint yields of Arkot 8717 were 11% more than DES 119 in eight tests conducted in 1996 and 1997, but were 7% less than Stoneville 474 in nine tests conducted in 1995, 1999, and 2000. Compared with Stoneville 474, Arkot 8717 had lower lint fraction (38.0% vs. 41.2%), similar micronaire reading, but fibers were 5% longer and 9% stronger. Arkot 8717 is morphologically indistinguishable from Arkot 8710.
During selection, Arkot 8710 and Arkot 8717 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 has exhibited symptoms of bacterial blight even after field inoculations with the pathogen. In the presence of intense thrips, Frankliniella spp., pressure in 2000, both lines yielded significantly more fiber and had less relative plant injury than Stoneville 474. With less thrips pressure, differences were not significant in 1999. Both lines had significantly lower incidence of Verticillium wilt (caused by Verticillium dahliae Klebahn) than Stoneville 474 at Clarkedale in 1999.
The specific adaptation, fiber properties, and host plant resistance traits of Arkot 8710 and Arkot 8717 should make them valuable as breeding lines. Small quantities of Arkot 8710 and Arkot 8717 seed may be obtained for breeding purposes from the corresponding author.
Development of these lines was supported in part by funding from Cotton Incorporated.
NOTES
Accepted for publication January 31, 2002.
REFERENCES
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