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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 9704 (Reg. No. GP-914, PI 654509) and Arkot 9706 (Reg. No. GP-915, PI 654510) are noncommercial breeding lines of cotton (Gossypium hirsutum L.) that were released by the Arkansas Agricultural Experiment Station in August 2008. Both lines were derived from 1997 crosses using one common parent, Ark 9108-04, a breeding line from which Arkot 9108 was selected. The second parent for Arkot 9704 was M331RKN. The other parent of Arkot 9706 was Arkot 8712. The lines were evaluated in 15 replicated tests in Arkansas from 2004 through 2007 and compared to check cultivars SG 105 and PSC 355. Lint yields of Arkot 9704 and Arkot 9706 were equal to the check cultivars. Yields of both lines could be attributed in part to higher lint per seed (and lint fraction) produced by fewer seed per area than either check cultivar. Arkot 9706 was earlier maturing than Arkot 9704 and the two check cultivars. Fiber properties of Arkot 9706 were very similar to PSC 355, whereas Arkot 9704 produced lower micronaire, length uniformity index, and strength than Arkot 9706 and PSC 355. Leaf pubescence and bract trichome density of Arkot 9704 were less dense than either check cultivar, whereas Arkot 9706 was similar to SG 105 for these traits. Both lines expressed resistance to bacterial blight. Arkot 9704 expressed resistance to tarnished plant bug equal to PSC 355, whereas Arkot 9706 expressed higher resistance than either check cultivar. The relative yield, maturity, and line-specific host plant resistance traits make these lines valuable to cotton breeding programs.
Abbreviations: RBTN, Regional Breeders' Testing Network
Arkot 9704 (Reg. No. GP-914, PI 654509) and Arkot 9706 (Reg. No. GP-915, PI 654510) are noncommercial breeding lines of cotton (Gossypium hirsutum L.) that were released by the Arkansas Agricultural Experiment Station in August 2008. Both Arkot 9704 and Arkot 9706 were derived from 1997 crosses (with reciprocal crosses bulked) using one common parent, Ark 9108-04, a breeding line from which Arkot 9108 (PI 638508, Bourland and Jones, 2005) was selected. The second parent for Arkot 9704 was M331RKN (PI 603045, Shepherd et al., 1996). The other parent of Arkot 9706 was Arkot 8712 (PI 626101, Bourland et al., 2005). Both lines were released as part of an ongoing effort to develop improved germplasm lines having enhanced yield, yield components, earliness, host plant resistance, and fiber properties.
Methods
Early Generation Population and Line Development
Both lines were developed using the generalized procedures 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. Two of the individual plants were designated as 9704-13 and 9706-38 and were evaluated with other progenies at Keiser and Rohwer in 2000 and 2001. Individual plant selections from the F2:F4 generation, which were grown at Keiser in 2001, were evaluated as progenies in 2002 and 2003. Two of these selections produced Arkot 9704 (tested as 9704-13-08) and Arkot 9706 (tested as 9706-38-06).
Field Test Evaluations
From 2004 through 2007, Arkot 9704 and Arkot 9706 were compared to ‘PSC 355’ (PVP 200000167) and ‘Sure-Grow 105’ (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 in 2005 through 2007, the Delta Branch Experiment Station at Clarkedale in 2004, the Judd Hill Cooperative Research Site at Judd Hill in 2005 through 2007, the Lon Mann Cotton Research Station at Marianna in 2004 through 2007, and the Southeast Branch Experiment Station at Rohwer in 2004 through 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 at the Keiser, AR, test site 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.
Both lines were also evaluated in the 2006 Regional Breeders' Testing Network (RBTN; www.cottonrbtn.com), which included agronomic field tests at 10 locations from North Carolina to Arizona.
Pest Resistance Evaluations
During selection, nurseries, and seed increases, Arkot 9704 and Arkot 9706 plants 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-month-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 by 1 m, were replicated 12 times in a RCB design and managed to encourage tarnished plant bug populations. White flowers were sequentially examined for plant bug damage, as indicated by discolored anthers, five to eight times over a 2-wk period in August of each year. 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.
The 2006 RBTN included evaluation for resistance to root-knot nematode, tobacco budworm [Heliothis virescens (F.)], and cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] at three different sites (www.cottonrbtn.com).
Characteristics
Yield and Yield Components
Lint yields of Arkot 9704 and Arkot 9706, relative to the check cultivars, were higher at the Marianna (central AR) and Rohwer (south AR) than at the two more northern locations (Table 1). The relative yields of both lines produced were lowest at Keiser. Over all locations, relative yields of Arkot 9706 tended to be higher than Arkot 9704. When compared over locations and years, yields of both lines were statistically equal to each other and to the check cultivars (Table 2
).
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Among 24 entries evaluated over all 10 RBTN locations in 2006, Arkot 9704 and Arkot 9706 produced the second- and fifth-highest lint yields, respectively. Lint yield of Arkot 9704 was statistically equal to the highest-yielding entry at every location except Tallassee, AL, Keiser, AR, and Lubbock, TX. Lint yield of Arkot 9706 was higher than SG 105 at College Station, TX, and Rocky Mountain, NC, and statistically equal to SG 105 at the other eight locations. These yields indicate that both lines are broadly adapted to varied growing conditions.
Morphological and Fiber Traits
Both Arkot 9704 and Arkot 9706 were equal to PSC 355 in height but taller than SG 105 (Table 3
). As indicated by open bolls percentage, Arkot 9704 was earlier maturing than Arkot 9706 and the check cultivars. Maturity of Arkot 9706 was equal to check cultivars.
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Fiber quality parameters of Arkot 9706 were almost identical to those of PSC 355 and differed only slightly from SG 105 (Table 3). In contrast, Arkot 9704 had lower micronaire, length uniformity index, and strength than Arkot 9706 or PSC 355. Lines that produce lower micronaire, or finer fibers, are desired in the mid-south cotton region. Fiber length of Arkot 9704, Arkot 9706, and PSC 355 produced fibers of equal length, which was shorter than that of SG 105. Fiber parameter values for Arkot 9704, Arkot 9706, and SG 105 across the 10 locations of the 2006 RBTN were in relative agreement with values found across locations and years of Arkansas tests (www.cottonrbtn.com).
Pest Resistance and Heat Tolerance
During selection, Arkot 9704 and Arkot 9706 were 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. Both lines exhibited resistance to bacterial blight in annually produced seed increase blocks that were inoculated with the pathogen.
The incidence of Verticillium wilt on the two lines in field tests at Clarkedale (2004) and Judd Hill (2005 and 2006) was equal to the check cultivars (Table 4 ). Due to earlier boll loading, early-maturing lines tend to have higher incidence of wilted plants. Although it expresses earlier maturity, Arkot 9704 had equal incidence of wilted plants and nearly equal yields as the check cultivars at the Verticillium wilt test sites (Table 1).
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Both lines were more resistant to tarnished plant bug than SG 105 and the susceptible frego-bract check in field tests conducted in 2006 and 2007 (Table 4). Damaged flowers values of PSC 355 were higher than Arkot 9706 but lower than Arkot 9704. A caged trail of the 2006 RBTN at Dallas, TX, indicated that both lines were equal to DP 393 and had more squares damaged by fleahoppers than SG 105 (www.cottonrbtn.com). At the Mississippi State, MS, site of the 2006 RBTN, lint yields of Arkot 9704 were equal to, and Arkot 9706 were higher than, SG 105 in tobacco budworm–infested plots.
Lint yield of Arkot 9704 was higher than any other entry at the Maricopa, AZ, site of the 2006 RBTN. Out of 24 entries, Arkot 9706 produced the eighth-highest yield and was equal to SG 105. High yields at this site indicate that a line may possess good heat tolerance.
Availability
Small quantities of Arkot 9704 and Arkot 9706 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 9704 and Arkot 9706 were 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 December 16, 2008.
References
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