Principles of Plant Genetics and Breeding

554 CHAPTER 34
4 Disease resistance. Some of the major diseases of
cotton are as follows:
(a) Seedling diseases. Some of the major diseases
of cotton are caused by Fusarium spp., Pythium
spp., and Rhizoctonia solani. These soil-borne
fungi cause diseases to seedlings in wet soil,
including damping-off and seed rot. The consequence
of these diseases is reduced crop stand.
(b) Nematodes. The root-knot nematode,
Meloidogyne incognita, is a destructive pest in
some growing regions. Resistance to the disease
is quantitatively inherited.
(c) Verticillium wilt. This disease occurs widely in
the US. Some genotypes with resistance occur in
the G. barbadense species.
(d) Bacterial blight. Also called angular leaf spot,
bacterial blight (Xanthomonas malvaceaum) is
widespread throughout all cotton production
regions. Resistance to the disease is conditioned
by two or more major genes with minor or
modifier genes.
5 Insect resistance. The major insect economic insect
pests of cotton are the boll weevil and bollworm.
(a) Boll weevil. Caused by Anthonomus grandis,
this insect pest causes cotton squares to drop.
Early maturing cultivars tend to escape the pest.
Basu, A.K., and S.S. Narayanan. 1997. Cotton. In: Genetics,
cytogenetics, and breeding of crop plants, Vol. 2. Cereal
and commercial crops (Bahl, P.N., P.M. Salimath, and
A.K. Mandal, eds). Science Publishers, Inc., Enfield, NH.
Cotton Information. 2002. North Carolina Cooperative
Extension Service. North Carolina State University,
Raleigh, NC.
Jiang, C.X., T.Z. Zhang, J.J. Pan, and R.J. Kohel. 1998.
Polyploid formation created unique avenues for response to
selection in Gossypium cotton. Proc. Natl. Acad. Sci. USA
95:4419–4424.
Part A
Please answer the following questions true or false:
References and suggested reading
Outcomes assessment
1 The fruit bud of the cotton plant is called a boll.
2 New World cotton species have a genomic formula of AA.
3 The long fiber of cotton seed is called the lint.
4 The economically important species of cotton is G. barbadense.
(b) Cotton bollworms. Various lepidopteran insects
belong to this group of devastating insect pests
of cotton. These include the cotton bollworm
(Helicoverpa zea), tobacco budworm (Heliothis
virescens), and pink bollworm (Pectinophora
gossypiella). Genetic engineering procedures
have been used to address the attack by these
pests through the development of Bt cultivars.
6 Fiber quality. The quality traits of importance in the
cotton industry include fiber length, fiber strength,
and fiber fineness. Breeding objectives include
improving fiber length and uniformity for improved
spinning performance and utility of cotton. The
fiber strength determines yarn strength, while fiber
fineness affects the texture or feel of the fiber. Fiber
strength is important for the current technology of
open-end (rotor) spinning, which demands stronger
fibers.
7 Seed quality. In addition to lint, cotton is also grown
for its seed oil. A major goal in breeding seed quality
in cotton is to reduce the pigmentation that discolors
the seed oil. The use of glandless cotton cultivars
(the glands produce gossypol, a terpenoid compound
responsible for the discoloration of the seed oil) helps
to improve seed oil quality. However, glandless cultivars
are more susceptible to insect attack.
Meredith, W.R., Jr. 2005. Minimum number of genes controlling
cotton fiber strength in backcross population. Crop
Sci. 45:1114–1119.
Rahman, M., D. Hussain, and Y. Zafar. 2002. Estimation of
genetic divergence among elite cotton cultivars – genotypes
by DNA fingerprinting technology. Crop Sci. 42:2137–2144.
Stiller, W.N., J.J. Reed, G.A. Constable, and P.E. Reid. 2005.
Selection for water use efficiency traits in a cotton breeding
program: Cultivar differences. Crop Sci. 45:1107–1113.