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USDA-ARS, Crop Genetics and Production Unit, Delta Research Center, Stoneville, MS 38776. Mention of trade name or commercial product in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture
* Corresponding author (linghe.zeng{at}ars.usda.gov).
ABSTRACT
Species polycross (SP) cotton germplasm was developed from multiple crosses among Gossypium tetraploid species. SP156 (Reg. No. GP-903, PI 654087), SP177 (Reg. No. GP-904, PI 654088), SP179 (Reg. No. GP-905, PI 654089), SP205 (Reg. No. GP-906, PI 654090), and SP225 (Reg. No. GP-907, PI 654091) were released by the USDA-ARS for their highly desirable combinations of yield, yield components, and fiber properties. The SP lines were tested for yield and fiber quality in 2005, 2006, and 2007 at six year-locations. SP179 and SP225 averaged 1221 and 1348 kg ha–1, respectively, for yield in three years' trials compared with 1359 kg ha–1 for ‘Deltapine 555BR’. Fiber bundle strength of these two lines is 233 and 228 kN m kg–1, respectively, compared with 227 kN m kg–1 for ‘FiberMax 960B2R’ (FM960B2R). Yields of SP156, SP177, and SP205 are at least 7% higher than the average, 965 kg ha–1, of FM960B2R and ‘Phytogen 72’ (PHY72). Strength of SP156, SP177, and SP205 is 241, 238, and 236 kN m kg–1, respectively, compared with 241 kN m kg–1, the average of FM960B2R and PHY72. Span length and short fiber content in these lines are also comparable to FM960B2R and PHY72.
Abbreviations: AFIS, Automated Fiber Information System • DP555BR, ‘Deltapine 555BR’ • FM960B2R, ‘FiberMax 960B2R’ • G, genotype • L, location • PHY72, ‘Phytogen 72’ • PM2167R, ‘Paymaster 2167R’ • SP, species polycross • ST4892BR, ‘Stoneville 4892BR’ • Y, year
Cotton germplasm lines SP156 (Reg. No. GP-903, PI 654087), SP177 (Reg. No. GP-904, PI 654088), SP179 (Reg. No. GP-905, PI 654089), SP205 (Reg. No. GP-906, PI 654090), and SP225 (Reg. No. GP-907, PI 654091) were released by USDA-ARS. The species polycross (SP) germplasm was developed by crossing among Gossypium tetraploid species. The germplasm underwent 11 generations of random mating followed by 12 generations of selfing. The lines from this germplasm were tested for yield and fiber quality at six year-locations in 2005, 2006, and 2007. Five lines were released for their highly desirable combinations of yield, yield components, and fiber properties. The superior traits in these lines provide breeders opportunities to meet the needs from textile industry for fiber quality and also maintain productivity for growers.
Methods
Species polycross germplasm were initiated by P.A. Miller in 1967 at North Carolina State University, Raleigh, NC. The population was advanced by William R. Meredith, Jr. The SP germplasm were developed by crossing 12 cultivars and strains of G. hirsutum L. with four tetraploid species: G. barbadense L., G. tomentosum Nutt., G. mustelinum Watt., and G. darwinii Watt. The entries in G. hirsutum include ‘Auburn M.’, ‘Carolina Queen’ (Coker Pedigree Seed Co., Hartsville, SC), ‘Stoneville 213’ (Stoneville Pedigreed Seed Co., Stoneville, MS), ‘Deltapine Smooth Leaf’ (Delta and Pine Land Co., Scott, MS), ‘Coker 413’ (Coker Pedigree Seed Co., Hartsville, SC), ‘Deltapine 523’, ‘Stoneville 508-9117’ (Stoneville Pedigreed Seed Co., Stoneville, MS), TH149-20, PD 2165, Ga. H.T., Atlas (AxC)-261, and Mo. 61-470. The pedigrees of most of these entries are available in a report by Bowman et al. (2006). All strains except Stoneville 508-9117 have genetic background of Beasley's triple hybrid [(G. arboretum L. x G. thurberi L.) x G. hirsutum] (Miller and Rawlings, 1967). The exact strains of the four tetraploid species used in the crosses as parents and the crossing pattern are unknown. All 12 entries of G. hirsutum and the other four tetraploid species were involved in the initial crosses. Seeds of the F2 were produced in a winter nursery located in Mexico. From 1968 to 1978, the progenies were maintained by natural pollinations in a small isolated field with high bee activity near Raleigh, NC. Natural crosses in field exceeded 50% (Miller and Rawlings, 1967). Following the retirement of P.A. Miller from North Carolina State University, a small sample of seeds was forwarded to William R. Meredith, Jr. From 1979 to 2004, 2000 plants from this population were grown almost every other year at Stoneville, MS, under a predominantly self-pollinating environment. This population was maintained and advanced by harvesting one boll from each plant and bulking the harvested seeds for planting in the next generation. Until 2004, this population underwent a total of 11 generations of random mating and 12 generations of selfing. In 2004, 260 plants were randomly chosen and 15 to 20 bolls were collected from each plant. The seeds from each plant were planted as one line in 2005 in the evaluation trial.
Two hundred and sixty lines from this germplasm were evaluated for yield and fiber quality at Stoneville, MS, in summer 2005 (Zeng et al., 2007). Five lines were selected from the 260 lines tested in 2005 for yield and fiber quality. These lines were further tested for yield and fiber quality in 2006 and 2007. In total, the lines were tested at six year-locations. In 2005, the germplasm lines were planted at two field locations with two replications each in Delta Research Center at Stoneville, MS. These two field sites located about 1000 m apart with soil types of Beulah fine sandy loam (coarse-loamy, mixed, active, thermic Typic Dystrochrepts) (Location 1) and Bosket fine sandy loam (fine-loamy, mixed, active, thermic Mollic Hapludalf) (Location 2). In 2006, the lines were planted at three locations at Stoneville (Locations 1, 2, and 3) with four replications each. The field site of Location 3 was located between the sites of Location 1 and Location 2 with soil type similar to that of Location 1. In 2007, the lines were planted at one location at Stoneville (Location 2) with four replications. A complete randomized block design was used in all the trials. Five cultivars as standards in the National Cotton Variety Trial, ‘Deltapine 555BG/RR’ (DP555BR; Delta and Pine Land Co.; Scott, MS), ‘FiberMax 960B2R’ (FM960B2R; Bayer Crop Sciences; Research Triangle Park, NC), ‘Phytogen 72’ (PHY72; Phytogen Seed Co., Indianapolis, IN), ‘Paymaster 2167R’ (PM2167R; Delta and Pine Land Co.), and ‘Stoneville 4892BG/RR’ (ST4892BR, Stoneville Pedigreed Seed, Stoneville, MS) were used as checks in all trials. The checks were grown with four replications at each location in all trials. In 2005, plants were grown in single-row plots, each 4.57 m long on a 1.0-m row spacing. Plant stand ranged from 25 to 70 plants plot–1. Plots were thinned to 25 to 40 plants plot–1. At harvest, 30 bolls from each plot were hand harvested and ginned using a laboratory saw gin to determine yield components. Lint samples were used to determine fiber quality. Remaining bolls from each plot were collected by hand to determine yield. In 2006 and 2007, the SP lines and cultivars were grown in single-row plots, each 9.14 m long on a 1.0-m row spacing. Standard conventional production practices were applied in the trials at all locations. At harvest, 50 bolls from each plot were hand harvested and ginned using a laboratory saw gin to measure yield components. Lint samples were used to determine fiber quality. Remaining bolls from each plot were harvested by a mechanical picker for yield measurements. Twenty grams of lint were submitted to StarLab, Knoxville, TN, for analysis of fiber quality. Fiber strength was measured by a stelometer as the force per tex required to break a bundle of fibers. Elongation was the percentage of elongation at the point of break in strength determination. Fiber span lengths were measured as the average length of the longest 50 and 2.5% of the fibers scanned, respectively. Micronaire was measured as micronaire units using the Fibronaire instrument. Fibers were also analyzed for mean short fiber content, fineness, and maturity ratio using the Automated Fiber Information System (AFIS). Short fiber content was measured as the percentage by weight of the fibers that are less than 12.7 mm. Fineness was measured as the weight per unit of length in millitex. Maturity ratio was measured as the proportion of mature fibers divided by the immature fibers. In the trials of 2006, fiber samples from only one replication at each location were analyzed for fiber properties. Fiber samples from all replications at each location were analyzed for fiber properties in the remaining trials. Leaf area was measured on the fourth fully extended leaf from the top of a plant using a Li-3100 Area Meter (LI-COR, Inc., Lincoln, NE). Plant height was measured from ground to the top of the main stem. Nodes of the first fruiting branch were counted as the node number from the cotyledon node to the node at the first fruiting branch on the main stem.
The GLM procedure of the Statistical Analysis System (Version 6; SAS Institute, Cary, NC) was used for analysis of variance on all data. A mixed model was used with genotype (G) as fixed effect and year (Y), location (L), G x Y, and G x L as random effects. Mean separation among genotypes was conducted using Waller–Duncan k-ratio procedure (Ott, 1988). The Waller–Duncan t tests were conducted only when the F tests for genotype effects were significant at p = 0.05.
Characteristics
The SP germplasm is a unique population with exotic genes from all tetraploid species in Gossypium as well as contribution of genes from diverse cultivars and strains in G. hirsutum. Another unique feature of SP germplasm was the numerous generations of random mating during development of the germplasm. Introgression of exotic genes from wild species in Gossypium into upland cotton has been limited due to restricted recombination in the interspecific hybrids (Paterson et al., 1990; Jiang et al., 2000) and linkage drag (Zhong et al., 2002). In the original evaluation of the 260 SP lines, there was a negative genetic correlation (r = –0.28) between lint yield and fiber bundle strength (Zeng et al., 2007). A similar relationship (r = –0.35) between these two traits was also reported in an intermated population (Miller and Rawlings, 1967). Random mating for 11 generations may have increased introgression of exotic genes from wild tetraploid species into G. hirsutum and further reduced the negative association between yield and fiber quality. The reduction of the negative association between lint yield and fiber strength from –0.35 in the study of Miller and Rawlings (1967) to –0.28 in SP germplasm (Zeng et al., 2007) provided evidence for this hypothesis. Dramatic genotypic variation of yield and fiber quality in this population was reported in the previous evaluation of 260 SP lines (Zeng et al., 2007). Desirable combinations of yield, yield components, and fiber properties were identified for the 5 SP lines in the trials in 2005, 2006, and 2007. Twelve generations of selfing are sufficient to allow a high degree of homozygosity within lines. A high degree of uniformity within rows was visually observed in field.
In the trials for the five SP lines and the checks at six year-locations, significant (p < 0.01) genotypic differences were observed for all traits except fineness and maturity ratio among the SP lines and the standard cultivars (Table 1 ). Mean squares of G x Y were generally larger than those of G x L but smaller than those of G. For the traits with significant genotypic differences, mean squares of genotype were 1.8 to 10.3 times that of G x Y (Table 1). Yield and fiber data for SP lines and check cultivars are given in Table 2 . The yields of SP179 and SP225 were 1221 kg ha–1 and 1348 kg ha–1, respectively, compared with the yield, 1359 kg ha–1, for the high-yielding cultivar DP555BR. Fiber bundle strength of these two lines, 233 kN m kg–1 for SP179 and 228 kN m kg–1 for SP225, was comparable to the strength, 227 kN m kg–1, for the high fiber quality cultivar FM960B2R. Elongation of SP179 (6.59%) and SP225 (6.52%) was significantly (p < 0.05) higher than the elongation for FM960B2R (5.17%). Short fiber content for SP179 (4.97%) and SP225 (4.95%) was at least 8% less than that for FM960B2R. Fineness of SP179 (170 mtex) was similar to that of FM960B2R (168 mtex). However, the maturity ratio (0.95) for SP179 was 4.4% higher than that (0.91) for FM960B2R. In addition, SP225 is comparable to FM960B2R in micronaire and 50% span length. Yields of SP156, SP177, and SP205 are at least 7% higher than the average, 965 kg ha–1, for high fiber quality cultivars FM960B2R and PHY72. Fiber properties of these lines are similar to the averages of FM960B2R and PHY72, 6.33% of elongation, 241 kN m kg–1 of strength, 14.4 mm of 50% span length, 29.9 mm of 2.5% span length, and 4.90% short fiber content, respectively. Although fineness of SP156 and SP205 is at least 7% coarser than that of FM960B2R, maturity ratio in these two SP lines is 6% greater than FM960B2R. Generally, lint percent is negatively associated with the other yield components in most SP lines and cultivars. Although lint percent was negatively correlated with seed weight (r = –0.56) as previously reported in SP germplasm (Zeng et al., 2007), the combination of these two yield components in SP225 is unique compared to those in cultivars. Lint percent of SP225 (39.5%) is significantly (p < 0.05) higher than that in all cultivars, while seed weight of SP225 (107 mg seed–1) is also significantly (p < 0.05) higher than that in all cultivars except FM960B2R.
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In summary, the selected five SP lines have desirable combinations of lint yield, yield components, and fiber properties. The superior traits in these lines provide cotton breeders opportunities to further genetically improve lint yield and fiber quality in upland cotton.
Availability
A limited quantity of seeds (100 seeds) of these germplasm lines can be obtained from the corresponding author. We ask that appropriate recognition of the source be given if it is used in the successful development of a new cultivar.
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 June 16, 2008.
References
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