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Vol.
22, No. 19
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Research
Report
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August
2001
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Primitive Cotton
Germplasm:
Yield and Fiber Traits for 16 Day-Neutral
Accessions
Printable
PDF version (6 pages)
Jack
C. McCarty, Jr., and Johnie N. Jenkins
Abstract
Improvement
of cotton, Gossypium hirsutum L., requires genetic resources
that may extend from primitive or exotic species to commonly
grown cultivars. The introduction of desirable traits from
germplasm sources to adapted cultivars is an ongoing
process. The cotton collection of primitive accessions
contains a wealth of genetic variability; however, many of
the accessions are photoperiodic. The photoperiod response
and failure to flower and set fruit under the long-day
regime of the temperate-zone growing seasons is a major
hurdle to the use of most primitive cotton germplasm.
Accessions have been converted to day-neutrality using a
backcross breeding approach. Useful genetic variability has
been measured in the day-neutral lines for agronomic and
fiber traits. The day-neutral accessions are now available
for use in breeding programs for cultivar development and to
expand genetic variability.
Introduction
Cotton,
Gossypium spp., is an important crop that is grown in
warmer climates throughout the world. It is grown primarily
for lint fibers, which are used in the textile industry.
Oil, meal, seed hulls, and linters are also important cotton
products. Research efforts are essential for cotton to
remain a viable competitive renewable agricultural
resource.
Cotton
breeding and research have resulted in vast improvements in
yield and fiber quality. To improve agronomic and fiber
traits, plant breeders must identify sources of genetic
variability for the trait of interest. Sources of genetic
variability may be cultivars commonly grown by farmers or
they may be found in wild or exotic species.
Cotton
germplasm collection trips have resulted in a storehouse of
genetic diversity. The primitive accessions in the
Gossypium collection currently number almost 2,500 as
a result of collection trips during the last 50 years
(Anonymous, 1974; Percival, 1987; Anonymous 1997). The
primitive accessions are part of the U.S. National Cotton
Germplasm Collection, which is maintained by USDA-ARS in
cooperation with Texas A&M University in College
Station, Texas. As accessions were added to the collection,
they were routinely assigned a number with a “T”
prefix, which has been referred to as the Texas number.
Today the “T” accession number is the one most
frequently used by researchers to refer to the primitive
cottons. A plant inventory (PI) number has recently been
assigned to all accessions in the collection.
Genetic
variability has been found for many traits in the collection
of primitive accessions of G. hirsutum L. This
genetic variability has not been extensively used because
most of the primitive accessions require short days to
initiate flowers and produce fruit. Because of this
flowering response to day length, their genes are not
readily available for incorporation in cotton-breeding
programs.
A
program has been in place to incorporate day-neutral genes
in the primitive accessions. McCarty and Jenkins (1992,
1993) presented data for 79 day-neutral accessions. This
report presents data for 16 additional accessions, which
have been converted to day-neutral flowering
types.
Materials and
Methods
The
day-neutral (DN) lines were developed by crossing short-day
primitive accessions as male parents to ‘Deltapine
16’ (day-neutral donor parent) at a Cotton Winter
Nursery located at Tecoman, Colima, Mexico. The F1
generation was self-pollinated at the Winter Nursery, and
the F2 generation was grown at Mississippi State University,
where segregation for flowering response occurred. One plant
that set fruit at a low node and continues to fruit was
selected from each F2 population. The F3 progeny from this
plant was backcrossed to the accession at the Winter
Nursery. The same procedure was followed for each backcross
generation. Equal numbers of open-pollinated bolls were
harvested from each BC4F2 plant that set fruit, and the seed
were bulked for each population to provide seed for increase
and testing. Except for selection for day-neutrality after
each backcross cycle, no other selection pressure is
applied. The procedure for developing DN lines was described
in detail by McCarty, et al. (1979).
Day-neutral
BC4F5 lines of 16 primitive accessions of cotton and four
commercial cultivars were grown and evaluated in field plots
at Mississippi State University’s Plant Science
Research Center from 1997 through 1999. The 1998 test was
not carried to completion due to extreme insect pressure,
which severely impacted plant growth, yield, and quality.
The commercial cultivars were chosen to represent currently
grown cottons and included ‘Deltapine 50’ (DPL
50), ‘Deltapine 5415’ (DP 5415), ‘Sure-Grow
125’ (SG 125), and ‘Sure-Grow 501’ (SG 501).
The DN
lines and cultivars were grown in single-row plots (40 feet
long, 38-inch row spacing). The experimental design was a
randomized complete block with four replicates. The soil
type was a Leeper silty clay loam (fine, montmorillionitic,
nonacid, thermic Vertic Haplaquepts). Field plots were
maintained with standard culture practices.
Seed
cotton yield was determined by mechanical harvest. A 25-boll
sample was hand-harvested from each plot before mechanical
picking. Boll samples were weighed and ginned on a
laboratory 10-saw gin to determine boll weight (grams of
seed cotton per boll), lint percentage, and seed index
(weight of 100 seeds). Lint samples were sent to Starlab,
Inc., in Knoxville, Tennessee, for determination of
micronaire, elongation (E1), fiber tenacity (FT), 2.5% span
length (2.5% SL), and 50% span length (50% SL).
Data
for all traits were subjected to analysis of variance. Means
were separated according to Fisher’s protected least
significant difference (LSD).
Results and
Discussion
Collection
and evaluation information for the cotton accessions is
presented in Tables 1-3. Most of the data in these tables
have been published previously (Anonymous, 1974; Percival,
1987) and are accessible through the USDA’s Germplasm
Resources Information Network (GRIN) database
(http://www.ars-grin.gov). However, it is useful to repeat
the data here to compare the primitive accessions with the
day-neutral backcross derived lines. A wide range of
variability exists in the primitive accessions for the
characteristics that have been evaluated.
Agronomic
and fiber data for 1997 and 1999 are presented in Tables 4
and 5. The day-neutral lines produced bolls that tended to
be smaller and seeds that were larger than the commercial
cultivars in the test. Deltapine 5415 produced the smallest
seeds among the cultivars, which is one of its
characteristics. Lint percentage for the cultivars was in
the high 30s, while that for most of the day-neutral lines
was in the low 30s. This difference was consistent for both
years of testing. Most of the day-neutral lines produced
seed cotton yields that were significantly lower than the
cultivars. As expected, lint yields were low for the
day-neutral lines because they had low lint percentages.
Most
day-neutral lines produced fibers significantly shorter than
those produced by cultivars. Fiber micronaire values tended
to be higher, while fiber strength tended to be similar to
the cultivars evaluated. T-242 DN tended to produce stronger
fibers than the cultivars during both years of
testing.
The
converted primitive accessions are useful for the diverse
germplasm they contain. Researchers looking for new traits
can now exploit the day-neutral lines. These lines can also
be used to expand the genetic base of cotton.
Summary
The
primitive accessions in the U.S. Cotton Collection are a
valuable source of genes for diversity and crop improvement.
Converting their flowering habit to day-neutrality will
facilitate their use. Sixteen day-neutral germplasm lines
have been developed, evaluated, and made available for use
in cotton improvement programs.
References
Anonymous.
1974. The regional collection of Gossypium germplasm.
USDA Report ARS-H-2. U.S. Government Printing Office,
Washington, D.C.
Anonymous.
1997. Preservation and utilization of germplasm in cotton.
Southern Cooperative Series Bulletin No. 386.
McCarty,
J.C., J.N. Jenkins, W.L. Parrott, and R.G. Creech. 1979.
The conversion of photoperiodic primitive race stocks of
cotton to day-neutral stocks. Mississippi Agricultural and
Forestry Experiment Station Research Report Vol. 4, no.
19.
McCarty,
J.C., and J.N. Jenkins. 1992. Cotton germplasm:
Characteristics of 79 day-neutral primitive race accessions.
Mississippi Agricultural and Forestry Experiment Station
Technical Bulletin 184.
McCarty,
J.C., and J.N. Jenkins. 1993. Registration of 79
day-neutral primitive cotton germplasm lines. Crop
Sci. 33:351.
Percival,
A.E. 1987. The national collection of Gossypium
germplasm. Southern Cooperative Series Bulletin No.
321.
McCarty
is a research agronomist and Jenkins is a research
geneticist with the USDA-ARS Crop Science Research
Laboratory at Mississippi State University. This project was
supported by USDA-ARS in cooperation with the Mississippi
Agricultural and Forestry Experiment Station. For more
information, contact McCarty by telephone at (662) 320-7389
or by e-mail jcm@ra.msstate.edu.
Mention
of a trademark or proprietary product does not constitute a
guarantee or warranty of the product by the Mississippi
Agricultural and Forestry Experiment Station and does not
imply its approval to the exclusion of other products that
also may be suitable.
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