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a Univ. of Arkansas Division of Agriculture Northeast Research and Extension Center, P.O. Box 48, Keiser, AR 72351
b Cotton Incorporated, 6399 Weston Pkwy., Cary, NC 27513
* Corresponding author (bourland{at}uark.edu).
ABSTRACT
Arkot 9721 (Reg. No. GP-918, PI 654511) is a noncommercial breeding line of cotton (Gossypium hirsutum L.) released by the Arkansas Agricultural Experiment Station in August 2008. Arkot 9721 was derived from a 1997 cross between Arkot 8712 and Ark 8708-31-06, an advanced breeding line. Arkot 9721 was evaluated in 15 replicated tests in Arkansas from 2004 through 2007. Lint yield, lint percentage, and seed produced per area for Arkot 9721 were about 5 to 8% lower than two check cultivars when data from 2006 were excluded (due to poor seed germination of Arkot 9721). Arkot 9721 produced larger seed with an equal amount of lint per seed as the check cultivars. Maturity and plant height of Arkot 9721 were similar to ‘PSC 355’. Leaf pubescence and bract trichome density of Arkot 9721 was intermediate between the smooth-leaf and hairy-leaf check cultivars. Arkot 9721 produced significantly longer, more uniform, and finer fibers than PSC 355. Compared with check cultivars, Arkot 9721 expressed improved resistance to bacterial blight [caused by Xanthomonas campestris pv. malvacearum (Smith) Dye], equal resistance to root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood], and less resistance to Verticillium wilt (caused by Verticillium dahliae Kleb.). Resistance of Arkot 9721 to tarnished plant bug was equal to PSC 355 and greater than ‘SG 105’. The improved fiber properties in conjunction with relatively good yield, maturity, and line-specific host plant resistance traits make Arkot 9721 valuable as a breeding line to cotton breeding programs.
Arkot 9721 (Reg. No. GP-918, PI 654511) is a noncommercial breeding line of cotton (Gossypium hirsutum L.) that was released by the Arkansas Agricultural Experiment Station in August 2008. The germplasm line was derived from a 1997 cross of Arkot 8712 (PI 626101, Bourland et al., 2005) and Ark 8708-31-06. The latter is an advanced breeding line that was derived from the double cross of F1 (‘Deltapine 50’, PVP 8400154/‘Deltapine Acala 90’, PVP 8400143)//F1 (Miscot 7918/Miscot 7803-52). The germplasm lines Miscot 7918 (Bourland and White, 1989b) and Miscot 7803-52 (Bourland and White, 1989a) were developed by crossing lines from the Texas A&M Multi-Adversity Resistance Cotton Breeding program (Bird, 1982) by lines adapted to the Mississippi River Delta region. Deltapine 50 and Deltapine Acala 90 were widely grown cultivars released in the 1980s. Arkot 9721 was released as part of an ongoing effort to develop improved germplasm lines having enhanced yield, yield components, earliness, host-plant resistance, and fiber properties. In combination with good agronomic properties, the enhanced fiber quality of Arkot 9721 makes it valuable as a breeding line.
Methods
Early Generation Population and Line Development
Arkot 9721 was developed using procedures previously outlined by Bourland (2004). Within F1 populations grown at the Southeast Branch Station (Rohwer, AR) in 1998, bolls from visually superior individual plants were harvested and bulked. The F2 bulk populations were grown at the Northeast Research and Extension Center (Keiser, AR) in 1999, and superior individual plants were selected and harvested separately. A single F2 plant was designated as 9721-23, and evaluated with other progenies at Keiser and Rohwer in 2000 and 2001. Individual plant selections in 2001 from the F2:F4 generation, were evaluated as progenies in 2002 and 2003. One of these F4 derived plant selections resulted in Arkot 9721 (tested as 9721-23-08).
Field Test Evaluations
From 2004 through 2007, Arkot 9721 was compared to ‘PSC 355’ (PVP 200000167) and ‘SG 105’ (PVP 9900190) in 15 replicated field tests at five Arkansas Agricultural Research Station sites (Table 1
). Experiment station test sites included the Northeast Research and Extension Center at Keiser (2005–2007), the Delta Branch Experiment Station at Clarkedale (2004), the Judd Hill Cooperative Research Site at Judd Hill (2005–2007), the Lon Mann Cotton Research Station at Marianna (2004–2007), and the Southeast Branch Experiment Station at Rohwer (2004–2007). Since the Clarkedale and Judd Hill sites are only 42 km apart and have the same soil type, the two locations were considered the same location for analysis over years.
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Leaf and bracts were sampled from the Keiser, AR, tests in 2005 through 2007. Leaf pubescence was rated using the rating system established by Bourland et al. (2003). Bracts were sampled and marginal trichome density was determined using methods of Bourland and Hornbeck (2007). Leaf and bract data were analyzed by SAS v. 9.1 PROC GLM (SAS Institute, Cary, NC) with years and replications being random and entries being fixed.
Pest Resistance Evaluations
During the development of Arkot 9721, progeny and seed increase nurseries were inoculated with multiple races of Xanthomonas campestris pv. malvacearum (Smith) Dye, the causal agent of bacterial blight using field inoculation procedures described by Bird and Blank (1951). Susceptible plants were rogued from the early-generation populations and subsequent seed increases. Percentages of wilted plants associated with Verticillium wilt (caused by Verticillium dahliae Kleb.) were visually estimated in field tests at Clarkedale in 2004 and at Judd Hill in 2006.
In 2005 through 2007, response to root-knot nematode [Meloidogyne incognita (Kofoid & White) Chitwood] was evaluated in greenhouse beds filled with soil (Routon [fine-silty, mixed, active, thermic Typic Epiaqualfs]–Dundee [fine-silty, mixed, active, thermic Typic Endoaqualfs]–Crevasse [mixed, thermic Typic Udipsamments] complex) and infested with heavily galled roots. Roots of approximately 1-mo-old seedlings were evaluated for degree of galling (none, light, or heavy) of roots. An index was calculated by adding the number of seedlings with light galling (times 50) and the number with heavy galling (times 100), then dividing by the total number of seedlings. Plots were 0.6 m long by 0.3 m wide with approximately 10 plants per plot, and arranged in an RCB with three replications.
Response to tarnished plant bug [Lygus lineolaris (Palisot de Beauvois)] was determined in small plot field tests conducted at Keiser, AR, in 2005 and 2006. Single-row plots, 6 m by 1 m, were replicated 12 times in an RCB design and managed to encourage tarnished plant bug populations. White flowers were examined sequentially five to eight times over a 2-wk period in August of each year for plant bug damage, as indicated by discolored anthers. A collective measure of percentage of damaged flowers over the sequential samples was determined for each plot.
All pest resistance data collected in Arkansas, except bacterial blight data, were analyzed using SAS v. 9.1 PROC GLM (SAS Institute, Cary, NC) with years and replications as random and entries being fixed.
Characteristics
Yield and Yield Components
In 3 of 4 yr of testing, lint yields of Arkot 9721 were about 10% lower than the check cultivars (Table 1). Very low lint yields in 2006 may have been associated with poor planting seed quality. Standard germination percentage of Arkot 9721 seed used in 2006 was only 47% compared with 82% for SG 105. Arkot 9721 appeared to be similarly adapted to all four Arkansas testing sites. When compared over all locations and years, lint yield of Arkot 9721 was significantly lower than either check cultivars (Table 2
). With 2006 data excluded, lint yield of Arkot 9721 remained significantly lower than SG 105 but was equal to PSC 355.
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Morphological and Fiber Traits
Arkot 9721 was equal to PSC 355 in height but taller than SG 105 (Table 3
). As indicated by open bolls percentage, maturity of Arkot 9721 was equal to the check cultivars. Based on a rating system developed by Bourland et al. (2003), leaf pubescence of Arkot 9721 was equal to SG 105 and more glabrous than PSC 355. Marginal bract trichome density of Arkot 9721 was intermediate between the two check cultivars. All other morphological traits of the line were not distinctive from SG 105 or PSC 355.
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Pest Resistance and Heat Tolerance
During selection, Arkot 9721 was screened for resistance to multiple races of Xanthomonas campestris pv. malvacearum (Smith) Dye, the causal agent of bacterial blight. Resistance to the multiple races conveys resistance to all known U.S. races of this pathogen. Arkot 9721 exhibited resistance to bacterial blight in annually produced seed increase blocks that were inoculated with the pathogen.
Arkot 9721 exhibited higher incidence of Verticillium wilt in field tests at Clarkedale (2004) and Judd Hill (2006) than either check cultivar (Table 4 ). In greenhouse tests, Arkot 9721 was equally susceptible to root-knot nematode as SG 105 and PSC 355. In field tests conducted in 2006 and 2007, tarnished plant bug resistance of Arkot 9721 was equal to PSC 355 and greater than SG 105 and the susceptible frego-bract check.
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Small quantities of Arkot 9721 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.
Acknowledgments
Arkot 9721 was developed with financial support from Arkansas Agricultural Experiment Station and Cotton Incorporated.
Footnotes
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.
Received for publication April 30, 2009.
References
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