Registration of Arkot 9406ne, Arkot 9605ne, and Arkot 9631ne, Three Nectariless Germplasm Lines of Cotton

Three noncommercial, nectariless breeding lines of cotton (Gossypium hirsutum L.) designated Arkot 9406ne (Reg. no. GP-863, PI 641704), Arkot 9605ne (Reg. no. GP-864, PI 641705), and Arkot 9631ne (Reg. no. GP-865, PI 641706) were released by the Arkansas Agricultural Experiment Station in 2005. The lines were developed using the generalized procedures outlined by Bourland (2004), and resulted from crossing three nectaried lines developed in the University of Arkansas cotton breeding program with three nectariless lines developed by other breeding programs. Jenkins and Wilson (1996) reviewed articles indicating that the absence of nectaries on leaves and flowers confer resistance to tarnished plant bug (Lygus lineolaris Palisot de Beauvois). Arkot 9406ne was derived from a 1994 cross between La. 850082FN (Calhoun et al., 1994) and Ark 8726–22–01, a high glanding (possessing gossypol glands in calyx lobes) breeding line developed from the cross of La. HG-063 (Jones et al., 1988) by Miscot 8506 (Bourland et al., 1997a). Within F2 populations grown at Southeast Branch Station at Rohwer, AR, in 1996, bolls from visually superior individual plants were harvested and bulked. Plants derived from F3 seeds were selected using general procedures of Bird (1982) to produce seeds for F4 progeny rows grown in 1997. A progeny designated as 9406–15 was among the ones promoted and tested in replicated strain tests in 1998 and 1999. Individual plant selections from the F6 generation of 9405–15 were evaluated as progenies in 2000. One of these selections was Arkot 9406ne (tested as 9406–15–04). Arkot 9406ne was evaluated in replicated strain tests in Arkansas (15 tests), Georgia (2 tests), and Mississippi (2 tests) from 2001 through 2004. The replicated tests included ‘PSC 355’ and ‘SG 105’ as checks. Arkot 9605ne was derived from a 1996 cross between Ark 8604–01–13 and NLBG8PD23S-1–93, a nectariless breeding line developed at Texas A&MUniversity. Ark 8604–01–13 is a breeding line developed from a cross of Miscot 7918 (Bourland and White, 1989a) and Miscot 7803–52 (Bourland and White, 1989b). Arkot 9631ne was derived from a 1996 cross between Arkot 8110 (Bourland et al., 1997b) and MD51ne (Meredith, 1993). Individual plants were selected from the respective F2 populations grown at the Northeast Research and Extension Center at Keiser, AR in 1998. Seed from individual plant selections were evaluated as progenies (designated as 9605–17 and 9631–19) in 1999, 2000, and 2001 at Keiser and Rohwer. Seed from a second cycle of individual plant selections (made from the F5 generation of these two progenies grown at Keiser in 2001) were evaluated in 2002. Two of these selections produced Arkot 9605ne (tested as 9605–17–06) and Arkot 9631ne (tested as 9631–18–07). The two lines were compared to PSC 355 and SG 105 in replicated strain tests in Arkansas (7 tests), Georgia (1 test), and Mississippi (2 tests) in 2003 and 2004. Lint yields of Arkot 9406ne were equal to, or greater than, yields of at least one check cultivar in each of the 19 tests conducted in Arkansas, Georgia, and Mississippi. Over all tests, Arkot 9406ne yielded 95% as much as SG 105. Within Arkansas test sites, Arkot 9406ne yielded relatively higher in northern sites than in central and southern sites. In contrast, Arkot 9406ne yielded numerically greater than SG 105 and PSC 355 in the two 2004 tests conducted near Leland, MS, which suggests that it may also be adapted to certain south delta locations. Lint yields of Arkot 9631ne (over the 10 sites in 2003 and 2004) were similar to yields of Arkot 9406ne and about 12% greater than yields of Arkot 9605ne. Lint fraction, plant height, and fiber properties (except for lower fiber elongation) of the three nectariless lines were within 5% of values for SG 105. Compared to SG 105, Arkot 9406ne andArkot 9605ne produced fewer seed per area (7 and 16%, respectively) and more fibers per seed (6 and 7%, respectively). In contrast, Arkot 9631ne produced similar seed per area and 7% fewer fibers per seed than SG 105. According to Lewis et al. (2000), the combination of yield components associated with Arkot 9406ne and Arkot 9605ne should contribute to more stable yield production. Open boll ratings in 2004 indicated that Arkot 9605ne and Arkot 9631ne reached maturity significantly earlier than did Arkot 9406ne and the check cultivars. Leaf pubescence of the lines was visually rated based on a rating scale of 1 (smooth leaf) to 7 (very hairy) (Bourland et al., 2003). Arkot 9406ne and Arkot 9605ne both displayed an average leaf pubescence rating of 1.0, while leaf pubescence of Arkot 9631ne (rating of 1.9) was equal to SG 105. In 2004, marginal bract trichome density of the three nectariless lines was similar to SG 105 and significantly less than PSC 355. Bract size (circumference and length) of each of the three lines was statistically equal to PSC 355 and significantly less than SG 105. The three nectariless lines have displayed some degree of resistance to tarnished plant bug and certain diseases. As indicated by fewer damaged flowers in a 2004 field test, all three lines were significantly more resistant to tarnished plant bug than SG 105. In a 2004 greenhouse test, the three lines were equal to SG 105 in resistance to seedling disease (caused by Rhizoctonia solani Kühn). In the 2002 National Cotton FusariumWilt Test at Tallassee, AL, response of Arkot 9406ne to Fusarium wilt [caused by Fusarium oxysporum Schlect. f. sp. vasinfectum (Atk.) Snyd. & Hans.] was equal to the resistant check (Glass et al., 2002). During selection, the three lines were screened for resistance to multiple races ofXanthomonas campestris pv. malvacearum (Smith) Dye, the causal agent of bacterial blight. Resistance to the multiple races conveys resistance to all knownU.S. races of this pathogen. In subsequent tests, neither line exhibited symptoms of bacterial blight even after field inoculations with the pathogen. The combinations of yield adaptation, fiber properties, and specific host plant resistance traits along with the nectariless trait make these lines valuable to cotton breeding programs. Development of the three lines was supported in part by funding from Cotton Incorporated. Small quantities of Arkot 9406ne, Arkot 9605ne, and Arkot 9631ne seed may be obtained for breeding purposes from the corresponding author. Unless specifically approved by the Arkansas Agricultural Experiment Station, the lines may not be used as recurrent parents in a breeding program.