A series of experiments investigating the interactive effects of
light and temperature on vegetative
growth, earliness, fruiting, yield and fibre properties in three cultivars
of cotton, was undertaken in
growth rooms. Two constant day/night temperature regimes with a difference
of 4 °C (30/20 and
26/16·5 °C) were used throughout the growing season in combination
with two light intensities (75
and 52·5 W m−2).
The results showed that significant interactions occurred for most of
the characters studied.
Although the development of leaf area was mainly temperature-dependent,
plants at harvest had a
larger leaf area when high temperature was combined with low rather than
with high light intensity.
Leaf area was least in the low temperature–low light regime. However,
the plants grown under the
high temperature–low light combination weighed the least.
Variations in the number of nodes and internode length were largely
dependent on temperature
rather than light. Light did, however, affect the numbers of branches,
sympodia and monopodia. The
first two of these were highest in the high light–high temperature
regime and the third in the low
light–low temperature regime.
All other characters, except time to certain developmental stages and
fibre length, were reduced at
the lower light intensity. Variation in temperature modified the light
effect and vice versa, in a
character-dependent manner. More specifically, square and boll dry weights,
as well as seed cotton
yield per plant, were highest in high light combined with low temperature,
where the most and
heaviest bolls were produced. But flower production was favoured by high
light and high
temperature, suggesting increased boll retention at low temperature, especially
when combined with
low light. Low temperature and high light also maximized lint percentage.
Fibres were shortest in the high temperature–high light regime,
where fibre strength, micronaire
index and maturity ratio were at a maximum. However, the finest and the
most uniform fibres were
produced when high light was combined with low temperature.
Cultivar differences were significant mainly in leaf area and dry matter
production at flowering.