Page 12 - 04 Cotton SA October 2014

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Global Warming from <<< 11
associated fi bers are the basic components of
yield. Depending upon the duration, timing
and severity of the heat stress, any of these
events could be compromised resulting in
poor seed and lower yields.
Reproductive development is also hastened
as temperatures increase, i.e., the time to the
appearance of the fi rst square, fi rst fl ower and
fi rst mature open boll decrease as the average
temperature for each event increases. In
addition, the development of fl owers up the
main stem, the vertical fl owering interval, will
increases with increasing temperature. The
total number of fruiting sites produced has Studies of the eff ect of increased carbon dioxide on cotton growth and yield. Left: Controlled environment
been shown to increase approximately 50% as study in Mississippi; RIGHT: Open chamber fi eld experiment in Arizona. (From MSU.edu and ARS.USDA.gov)
the temperature increased from 30°C to 40°C.
However, boll retention decreases signifi cantly
under high temperature and is reported to be
the most heat sensitive component of cotton
yield, with enhanced abortion of squares and
young bolls at temperatures above 30°C for
both Pima and Upland cotton.
At higher temperatures, stem and leaf growth
of cotton declines, as well as shoot biomass,
accompanied by an increase in vegetative
branches and a decrease in fruiting branches.
Roots generally have a lower optimum
temperature range for growth than shoots. The Cotton fl ower showing the anthers, stigma, style, and ovary with the seeds. (From University of Georgia and
eff ects on growth from elevated temperatures Tyson Raper)
during the night may be of more importance
than during the day. High, above average, Eff ect of Water Defi cit on Cotton Plant losses are often associated with fl ooding
temperatures during the day decrease Growth events due smaller plants and reduced number
photosynthesis and carbohydrate production, of bolls being produced.
and high night temperatures will increase Global warming and climate change will
respiration and further decrease available be associated with changes in patterns In conclusion, cotton production will
carbohydrates, resulting in decreased seed of precipitation and availability of water, be impacted by future climate change.
set, reduced boll size and decreased number more frequent occurrence of extreme Although the increased photosynthesis
2
of seeds per boll, and the number of fi bers per weather events including droughts or heavy caused by the rising CO levels will promote
seed. rainfall. Water-defi cit stress has a signifi cant increased biomass production, this will not
eff ect on cotton growth and development, necessarily translate into higher yields due
Final yield has also been shown to be strongly with primary eff ects on plant structure, leaf to the negative impact higher temperatures
infl uenced by temperature in cotton and a morphology and physiological processes such have on reproductive growth. However,
negative correlation between cotton lint yield as stomatal conductance, photosynthesis and rising temperatures will lengthen the season
and high temperature was reported for the respiration. The implications are impaired available for growing cotton, permitting shifts
Mississippi Delta. Boll number and boll size, metabolic functions such as carbohydrate and in planting dates and also permitting cotton to
the basic yield components, are negatively energy production as well as carbohydrate be double-cropped behind other crops in an
impacted by high temperature. Boll retention translocation and utilization. Yield reductions expanded region. Rising temperatures may
decreases signifi cantly under high temperature. and fi ber quality compromises are inescapable also eventually promote the movement of
Cotton plants exposed to a 36/28°C day/night when water-defi cit stress or fl ooding conditions cotton production into more northern regions.
growth temperature regime have been shown override the plant’s protective mechanisms. Precipitation pattern disruptions that result in
to retain approximately 70% fewer bolls than more occurrences and increased severity of
plants grown under a 30/22°C day/night Howev er, advances are being made at the drought stress episodes could promote either
temperature regime. The number of seeds per physiological level entailing identifi cation at a shift in dryland to irrigated cotton production
boll is an important basic component of cotton the molecular level identifi cation of genes or in an abandonment of cotton production
yield and accounts for more than 80% of total involved with increased drought tolerance for on some of those aff ected acres. However,
yield variability in cotton. High temperature improved tolerant varieties. In C3 plants such cotton will have to compete for the water
stress is a major factor negatively impacting as cotton, higher concentrations of CO2 with necessary for any increased irrigated acreage.
seed development. For example, in the USA global warming, would also reduce plant’s Current research eff orts are being focused on
there was a lower average number of seeds stomatal openings and hence the loss of water 2 improving cotton varieties for increased high
per boll (23.6 seeds/boll) in a hot year (mean by transpiration. In addition, a buildup of CO temperature and drought tolerance. In short,
maximum daily temperature of 36.6°C during in the atmosphere and causes plants to provide cotton production will continue to exist as
fl owering) compared to 28 seeds/boll in a cool less evaporative cooling, thereby aff ecting climate change progresses, but will just have
year (mean maximum daily temperature of water use effi ciency. A second consequence to adapt to the altered environment like every
32.2°C. This was explained because heat stress of altered precipitation distribution patterns is other living organism. By: Professor Derrick M.
decreased seed number by compromising the potential for intermittent fl ooding events Oosterhuis; University of Arkansas, USA
ovule fertilization. to occur during the growing season. Yield

Katoen SA Cotton 12 September 2014