Project Summaries

10-663AR  Project Manager: D. C. Jones

MAINTAINING SUSTAINABILITY OF COTTON BY GENETIC IMPROVEMENT

Freddie M. Bourland, University of Arkansas

Non-replicated evaluation is conducted in early generations of materials because either a line has not yet been selected or seed are too scarce for replicated testing. Once superior advanced progeny are identified, they are promoted to strain-status and evaluated in replicated tests over multiple locations per year.  After progressing though the Advanced Strain Test, materials are either discarded or released.

Breeding line evaluations were conducted in 2012 for populations and progenies derived from crosses made in 2007 through 2012.  Materials from 2009 through 2011 crosses were evaluated as populations in 2012 with individual plant selections made from the populations derived from 2009 crosses.  Materials from 2007 and 2008 crosses were evaluated as progenies in 2012.  Detailed lists of crosses made in each year are available upon request.

The 24 crosses made in 2012 included 7 between inbred lines and 17 double crosses (intercrosses of 2011 F1's).  The single crosses made in 2012 included crossing UA48 and UA222 to superior lines identified in the Regional Breeders' Testing Network (RBTN). Also, UA48 was crossed to the obsolete cultivar 'Columbia' which was known to have superior fiber length.  Five of the double crosses were between 2011 double crosses, i.e. incorporation of four parents used in 2010.  Double crosses in cotton have been used for a number of years to assist in breaking up linkages, to increase the probability of favorable recombination of genes that might not be achieved through single crosses, and to assimilate more genes within a breeding program into one background.  Our use of double crosses also accentuates the scarcity of superior breeding material since private germplasm is generally not available.  F1 seed from each 2012 cross have been sent to Mexico for winter increase.

The F2 generation of the 24 crosses made in 2011 was evaluated at Keiser in 2012.  The 24 crosses included 16 single crosses (eight crosses of superior RBTN lines by superior Arkansas lines and eight crosses between superior Arkansas lines) and eight double crosses (intercrosses of 2010 F1's). Eight of the single crosses involved a nectariless or reduced nectaried parent. Boll samples were taken from each population in a modified single seed descent (SSD) fashion.  The modifications to SSD included collecting a boll rather than a seed from each plant, avoiding off-type plant and poorly performing plants, and taking a specific number of bolls from each population.  Bolls were only collected from nectariless plants in populations derived from crosses with a nectariless parent.

The 24 crosses (F3 generation) made in 2010 were evaluated at Keiser in 2012.  The 24 crosses included 16 single crosses (eight crosses of superior RBTN lines by superior Arkansas lines and eight crosses between superior Arkansas lines) and eight double crosses (intercrosses of 2009 F1's).  Nectariless parents were included in five of the eight double crosses.  Nectaried plants were rogued from three of the populations.  Modified SSD selection was used in each population.

The F4 generation of the 24 crosses made in 2009 were evaluated at Keiser in 2012. The 24 crosses included 14 single crosses (ten crosses of superior RBTN lines by superior Arkansas lines and four crosses between superior Arkansas lines), five crosses of a superior Arkansas line with a 2008 F1, and five double crosses (intercrosses of 2008 and 2005 F1's).  All of the crosses using an F1 and two of the single crosses had at least one nectariless parent.  Individual plants were only made from nectariless plants in these populations.  Fifty individual plants were selected from each population.  These 1200 individual plants have been ginned and fiber properties are being determined.  Once HVI fiber properties are determined, Q-score will be calculated and individual plants will be discarded if they do not possess superior fiber quality.

The 24 crosses [F5 generation progeny rows] made in 2008 were evaluated at Keiser (2-row plots) and at Judd Hill (1-row plots). The 24 crosses were all single crosses.  Ten of the single crosses include UA48 as one parent (with goal to further enhance fiber quality), and five were crosses to JAJO 4141 (with goal to develop superior nectariless lines).  Except for the five crosses to JAJO 4141, all crosses were between superior Arkansas lines.  Seed for the F5 progeny rows were from 1820 individual plants selected in 2011. Out of 780 plants selected from 10 UA48 crosses, 334 (43%) were discarded for fiber quality (using Q-score); out of 1030 plants selected from the other crosses, 516 (49%) were discarded for fiber quality.  The 2012 F5 progeny included 960 progeny and 72 check plots evaluated at two locations.

In previous years, we have determined progeny row yields by machine harvesting 1 of 2-rows at Keiser and the 1-row plots at Judd Hill.  Using these yield data, boll samples were then hand harvested from selected progenies.  In 2012, a sample of seedcotton was obtained from each plot at Keiser by placing a mesh bag over a chute from the back drum on one of the two rows.  Since the back drums pick the inside of 2-row plots, this sample should have less outcrossing than other seedcotton from other chutes.  Although the yield calculations are short the amount caught in the mesh bags, the relative amount should be about the same for all plots.   By doing this, we are 1) not rushed to make selections prior to hand picking, 2) require less labor to obtain samples, 3) not as restricted on number of selections, 4) colect harvest data from an additional row (larger plot), 5) collect samples out of field earlier than by hand picking, and 6) can use fiber data more effectively in selections.  We have encountered some mechanical problems in handling the samples and will later determine whether we will continue using this sampling strategy.

After determining seedcotton yields, 578 of the 960 progeny were discarded.  Since the machine harvested seedcotton samples were trashy, they were processed through a burr and stick extractor prior to ginning.  Once fiber data are obtained, about 200-250 progeny will be selected for evaluation as advanced progeny in 2013.

The F6 advanced progenies from the 24 crosses made in 2007 were evaluated at Keiser (4-row plots), Marianna (2-row plots) and Rohwer (2-row plots).  Seedcotton yields were obtained from 2-rows at each site.  The additional 2-rows at Keiser were used to harvest seedcotton for seed increase.  To ensure better seed quality, all advanced progenies were harvested for seed increase, ginned and stored until selections could be made for seedcotton yield and fiber quality.  All of the lines have been ginned and a fiber sample was taken from each one. 

The 24 crosses made in 2007 included 12 single conventional crosses - eight crosses of superior Arkansas lines by superior lines from other programs (two JAJO nectariless lines and DX25105N) and four crosses between superior Arkansas lines. The other 12 crosses were single crosses involving one transgenic line (derived from Arkansas lines).  Transgenic crosses of transformed (Bt2 and/or Roundup-Ready Flex) into advanced Arkot lines have been made in an effort to improve materials via forward crossings.  Selection from crosses between frego bract (highly susceptible to tarnished plant bug) and RF lines and with advanced conventional lines have been advanced with the goal of developing a frego bract RF and conventional lines that might possibly be used as a tarnished plant bug monitor or trap crop.  This possibility is being studied in project 06-878.  Additional transgenic crosses have attempted to insert B2RF genes into advanced high gossypol and nectariless lines.  However, transgenic breeding involves more time and effort than is available in our program, and is now being restricted to special interest crosses. 

After harvesting the plots, 74 and 12 of the conventional and transgenic advanced progeny, respectively, have been saved.  The 74 conventional progeny include 29 nectariless, 14 okra leaf, 2 okra & nectariless, and 29 normal leaf & nectaried progenies.  The 12 transgenic progeny include 8 Frego-bract, 3 nectariless, and 1 red leaf line – all crossed with B2RF.  Once fiber data are obtained, superior advanced progenies will be promoted to strain status.

Eight strain tests of 120 strains (72 Preliminary, 18 New, 18 Advanced, 4 transgenic, and 8 RKN strains) were evaluated in 2012.  All samples have been ginned and yield data calculated.  At present, fiber data have not been received from the fiber laboratory.  When completed, tables (over locations and single locations) for each test will be available upon request. 

The 28 crosses made in 2006 included 18 single conventional crosses - 10 crosses of superior Arkansas lines by superior lines from other programs (LA887, DP393 and DX25105N) and eight crosses between superior Arkansas lines. All crosses having DP393 as a parent were dropped since DP393 is a patented variety.  From the conventional crosses, 72 lines were evaluated as Preliminary Strains in 2012.  Of the 72, 29 had DX25105N as one parent, and three had LA887 as one parent, and 40 were from crosses of two superior Arkansas lines. 

The lowest performance of the strains compared to the check cultivars was at Rohwer.  Hurricane Isaac caused a large amount of rainfall to occur on these plots just as bolls were beginning to open.  Consequently, early maturing lines were proportionally more affected than other lines – causing severe boll rots and loss of cotton.  Harvesting of the plots at Rohwer was delayed until late October due to rainfall and mechanical problems.  Of the 72 Preliminary Strains, 36 and 51 yielded more than DP393 and UA48, respectively, over all locations – which indicate that progress in yielding ability is being achieved.  Once fiber data is returned on these tests, 18 of these 72 lines will be chosen and evaluated as New Strains in 2013.

The other 10 crosses made in 2006 were single crosses involving one transgenic line (derived from Arkansas lines) with a selected Arkansas line or a Frego bract line.  The two crosses with a Frego bract line were made to develop a line that could be used as a trap crop (in conjunction with project 06-868).  Four transgenic lines, two RF frego bract and two B2RF normal bract lines, were evaluated as Preliminary Strains in 2012.  As expected, the two frego bract lines were the lowest yielding – 76% of DP0912B2RF over four locations.  At present, the benefit of using frego bract trap crop for tarnished plant bugs has not been established.  The two B2RF normal bract strains yielded 96% of DP0912B2RF. 

The 28 crosses made in 2005 included 18 single conventional crosses - six crosses of superior Arkansas lines by superior lines from other programs (MD09ne, JAJO1145ne, JAJO8067ne sub-okra, and DP393) and 12 crosses between superior Arkansas lines. Nine of these 18 crosses included a nectariless parent and seven included a high glanding parent.  Our 2012 New Strain Test include 8 lines derived from crosses with a nectariless parent and 8 lines derived from crosses with a high glanding parent. The other two lines in the 2012 New Strain Test were selected for resistance to root-knot nematode.

A list of the strains in the 2012 Advanced Strain Test with their backgrounds and previous testing are available from the author.  The 2012 Advanced Strain Test included eight strains that were also in the 2011 Advanced Strain Test and 10 strains from the 2011 New Strain Test.  All 18 strains were from single crosses made in 2003 and 2004.  Five of the 2003 crosses were between an Arkansas line and a commercial line and two were between superior Arkansas lines.  One additional line (M222-07) was selected from a segregating population of a cross made at the Delta Center of the Mississippi Agricultural and Forestry Experiment Station. 

Entries in the Advanced Strain Test tended to yield better with respect to the two check cultivars than strains in the other tests.  Over locations, 13 of the 18 Advanced Strains produced yields higher than DP393.  Relative to DP393, the strains performed best at Judd Hill (16 of 18 > DP393) and poorest at Marianna (8 of 18 > DP393).

The eight strains (2003 crosses and M222-07) have been evaluated for four years in replicated tests in Arkansas.  Two of the lines were included in the 2011 RBTN test. Over all locations and years, these lines have average 2 to 13% greater yield than the average of the check cultivars.   The highest yielding lines have been 0316-36, M222-07, and 0306-08. Among the 27 entries in the 2011 RBTN, 0316-36 and M222-07 produced the 6th and 23th highest yields over 13 locations.  Lint yields of 0316-36 were among the top 10 at each location except in the Alabama, Georgia, Tennessee, and Arizona tests.  Among these eight strains, most had fiber quality (Q-score) similar to DP393.  One line, 0309-31, has produced higher Q-scores but has averaged only 2% higher yield than DP393.  Fiber quality of the lines in the RBTN test was similar to DP393. 

Among the 10 strains from 2004 crosses, three are nectariless and two are high glanding. Seven of these 10 strains were included in regional tests, but these data are not yet available.  All 10 strains have yielded more than the average of check cultivars.  The highest three yielding strains are neither nectariless or high glanding.  Q-score over replicated tests (2 years) of these 10 strains range from 63 to 72.

Host plant resistance and morphological parameters for the Advanced Strains are available. All but one strain is resistant to bacterial blight and those tested are more resistant to Fusarium wilt than the susceptible check.  The three nectariless strains showed some, but not high, resistance to tarnished plant bug.  The strains differ with respect to pubescence on leaves, stems and bracts.

A special test of strains selected for resistance to root-knot nematode was evaluated at four Arkansas locations in 2012.  The test included eight strains and two check cultivars (DP393 and LA887).  The eight strains were derived from crosses to a RKN resistant line, and were selected by "survival of the fitness" technique in greenhouse planting (07-108 report).

Novel selection criteria used in this program include marginal bract trichome density, yield components, and Q-score.  Details on the development of these criteria are included in 07-108 ("Development of cotton breeding techniques and germplasm to enhance cotton yield and quality") report.  Lines with lower bract trichome density than smooth-leaf checks have been identified and advanced.  Data from 2012 suggest that improvement in yield and yield components is being achieved.  Combining high yield and high fiber quality traits into lines continues to be elusive – particularly in nectariless lines.  Lines will continue to be selected with emphasis on those that produce good yields by improvement of lint per seed (without producing very large seed) rather than increase seed per area.  Attention is being given to "fiber density" (estimated number of fibers per seed divided by estimated seed surface area).  The use of these novel selection criteria seem to be producing lines which have a wider adaptation than lines previously produced in this program.

Progress continues to be made in developing improved resistance to multiple pests as sequential evaluation of materials for multiple pest and stresses has been incorporated into the breeding program.  Most selected materials were resistant to bacterial blight, a disease that became a major concern in Arkansas in 2011 and 2012.  Strains are also evaluated for resistance to seed deterioration (using hot water technique), resistance to Verticillium wilt (by performance and wilt symptoms at Judd Hill), seedling disease (using greenhouse inoculation technique), and tarnished plant bugs (using "dirty flower" technique at Keiser).  Lines from selected backgrounds are selected and evaluated for resistance to root knot nematode in the greenhouse.  Advanced materials were being evaluated for resistance to Fusarium wilt.  Additional evaluation of agronomic performance for advanced materials is being conducted in regional tests.                           

A total of 43 germplasm lines and 3 cultivars have been released from this program since 2004.  These lines possess varying expressions of host plant resistance, fiber quality and agronomic characteristic.  Some of the lines have excelled in most parameters and are being considered for transgenic trait introgression. Most of the lines lack top performance in one or more areas, and thus are primarily useful as breeding lines.  Materials have been widely distributed to both public and private breeding programs.

Data for the three germplasm lines (0206-21, 0219-11, and 0222-15) are being summarized.  These lines were evaluated as strains in replicated tests from 2008-2011 and are being considered for release.  In additional, some of the Advanced Strains (from 2003 crosses) will likely be released in 2013.

 

Project Year: 2012
 

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