Biomedical Engineering Reference
In-Depth Information
genomics age, it is being revisited as a potentially valuable resource in functional
genomics and may have applied uses in breeding when combined with next-
generation sequencing (NGS) technologies. Chemical and radiation mutation can
be used to saturate the genome, screened for mutations in specific target genes and
can be isolated and phenotyped. Such TILLING (Targeting Induced Local Lesions
in Genomes) [
43
] or TILLING by sequencing approaches, particularly in poly-
ploids like cotton, should allow the development of specific gene knockout plants
with agronomic potential because of their modified metabolism or biochemistry
from loss of that particular gene function. As this is non-GM, it may overcome
some of the cost and regulatory hurdles faced by a GM approach such as using gene
silencing of the same pathways.
Major Breeding Achievements to Date
The process of domestication and conversion of cotton to an annual were obviously
the first steps in enhancing lint yield by man. It was a major step in changing a
tropical-subtropical perennial shrub with relatively poor fiber and low productivity
into a temperate annual crop with fiber suited for textile production. There have
been many significant achievements in cotton breeding since the first deliberate
attempts to apply crossing and selection to improve performance. Tolerance to
pests, diseases, and adverse environmental conditions all contribute to protecting
yield and quality but are not covered here in detail as they do not directly enhance
yield potential or fiber quality.
Fiber Yield
Being morphologically indeterminate, cotton does not stop growing vegetatively to
start reproductive growth and thus requires a relatively long growing season to
maximize yield. This indeterminacy, while it allows the crop to compensate for
damage or fruit loss throughout the season by producing more fruits, can also
extend the growing season and increase production costs. Cotton breeders have
addressed this by targeting crop earliness. Early or short-season genotypes are
considered more determinate when compared with late-season (indeterminate)
genotypes; they flower rapidly, and the length of time to boll opening is reduced.
This is advantageous for milder climates and has been the major aid in breeding for
regional adaptation. To a degree, earliness can reduce loss from insects and diseases
and minimize inputs such as fertilizer or irrigation. However, utilizing the fullest
growing season maximizes yield potential in cotton, so optimizing season length,
productivity, and costs is a challenge for agronomy and breeding.
Yield is a complex trait and can be broken down into a number of components:
the weight of fibers per seed, the number of seeds per boll, and the number of bolls
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