Cotton Breeding for Fiber Quality Improvement - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 203

per plant or unit planted area [ 44 ]. The proportion of lint removed from seed cotton
is the lint fraction and is positively correlated with yield. It has provided an indirect
and cost-effective way to breed for improved yield potential [ 45 , 46 ], with increases
of approximately 10 % over the past 60 years [ 47 ]. However, lint fraction can also
be negatively correlated with seed size, potentially reducing seedling vigor [ 48 , 49 ].
There can also be an interaction between breeding and management, with
modern cultivars being more responsive to improved agronomy than older cultivars
[ 50 ]. Yield improvement in national datasets with lint yield

1,000 kg/ha are more
likely to have larger contributions of breeding to yield improvement than low
yielding systems, but a common result is for breeding to contribute approximately
50 % of yield improvement, with management contributing the rest [ 51 ]. Disease
resistance has also been important in protecting yield [ 52 ].
As noted in the Introduction, cotton has been one of the pioneer crops introduc-
ing transgenic or GM traits for insect and herbicide resistance, reducing cotton's
environmental footprint [ 53 ]. Since the original introduction of Monsanto's
Bollgard ® insect resistant trait in 1995, the area has grown rapidly, and approxi-
mately 80 % of global cotton area in 2012 was transgenic [ 54 ]. In Australia, GM
insect resistance has been shown to give an 80 % reduction in insecticide use
compared with conventional cotton [ 55 ]. Likewise, a glyphosate resistance trait
can reduce the need for residual herbicides by 50 % [ 55 ] and makes weed control
relatively reliable and simple for growers.

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Fiber Quality

In the last 50 years, giant strides have been made in plant breeding to improve fiber
quality. In fact, the definitions of preferred levels of fiber quality properties are
constantly moving as spinners demand improvements to facilitate faster spinning
and weaving (reflected in base quality, discussed in section “ Current trait targets
and breeding goals ”). Figure 10.3 shows progress in the decade up to 2010 with
fiber length, strength, and micronaire in the USA, China, India, and Australia. Note
values for each fiber property are averages of a wide range of cotton with different
management, climate, and cultivar (China reached up to 579 cultivars in 2008 [ 56 ]).
For example, for an average national micronaire of 4.3, there will typically be about
10 % of the cotton with micronaire less than 3.5 and 10 % greater than 5. In all these
countries, there has been a conscious decision by the cotton industry and breeders to
improve fiber quality to meet market demands.
Although there was little progress and even some decreases in fiber length and
strength in US cotton from the 1940s to 1980s [ 57 ], individual breeding programs
have demonstrated improvements in fiber length and strength through time (e.g.,
Bassett and Hyer [ 58 ] in California; Zhang et al. [ 59 ] in New Mexico). Since that
time, there have been gradual improvements in length of 0.08 mm per year and
strength of 0.1 g/tex per year [ 60 ].