Cotton Breeding for Fiber Quality Improvement - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 207

Table 10.4 Comparison of the 2012 base HVI fiber quality properties for marketing in Australia
and the USA

Base
USA

Base
AUS

Breeding
goal Target trait Comments

Fiber length
(mm)

26.9 29.0 29.0 Also high uniformity and low short fiber

index. Premium length is 32 mm

>

Fiber strength
(g/tex)

26.0 27.0 28.0 Also high elongation. Premium strength

is 34 g/tex

>

Micronaire 3.5-4.9 3.5-4.9 3.8-4.5 Linear density 155-180 μ g/m; fiber

maturity ratio 0.85-1.00; premium
micronaire range is 3.8-4.2

ensure that they will be fit for purpose for spinning and textile manufacture,
minimum acceptable fiber parameters (base levels) are set, below which crops
can attract a penalty or discount on the standard price when marketed. Table 10.4
shows the base levels for three main fiber quality traits in the USA and Australia for
G. hirsutum cotton. While most commercial breeding is currently directed at
enhancing yield and at least consistently meeting base fiber quality, there is a
case to be made to continually push that target to embrace significantly higher
quality and develop premium fiber cultivars that attract higher prices.
There are price premiums available to growers who produce fiber strength and
length in excess of the base level and with intermediate micronaire, but premiums
are not always enough to compensate for yield loss. Breeding for improved fiber
quality is, therefore, only beneficial if yield is maintained or simultaneously
improved and most commercial breeding programs adopt this strategy of placing
fiber quality behind yield, but try to advance both.

Molecular Approaches to Yield and Quality Enhancement

Biotechnology has clearly provided powerful tools for the improvement of cotton
as evidenced by the rapid and widespread adoption of insect- and herbicide-tolerant
GM cultivars over the last two decades. Several fiber characteristics such as yield,
fineness, strength, and length are also objectives for improvement, and there are a
number of genes and gene networks that have been suggested as potential targets
for genetic modification. Cotton fibers are single hyper-elongated cells arising from
the epidermal cells of the outer integument layer of the seed coat. The synchronous
growth of thousands of terminally differentiated single-celled fibers per ovule [ 72 ]
is characterized by four overlapping developmental stages, namely, fiber initiation,
primary elongation, secondary cell wall (SCW) synthesis, and maturation
[ 73 ]. Fiber initiation begins on the day before anthesis, although fertilization
must occur for elongation to begin in earnest [ 74 ]. This initiation phase determines
the number of ovule epidermal cells that will differentiate into fiber cells and