Agriculture Reference
In-Depth Information
of assimilates stored in vegetative plant parts both together contribute to grain yield [62].
Sometimes under HT, it happens that the sink activity lost due to the earlier panicle senescence
where the source activity still exists as the leaf senescence does not occurs [63, 64]. In those
cases, grain filling was terminated earlier than complete leaf senescence. Kim et al. [64]
reported that consistently HT increased the rates of grain filling, fraction of DM partitioning
to panicle and leaf senescence while it reduced the durations of them under the temperature
regime of 24.4 and 21.9°C in temperate variety of
O. sativa
. There is a positive contribution of
the delayed leaf senescence to grain filling and yield of crop. There are various reasons for loss
of sink activity at HT which may result from a decline of translocation ability or loss of activity
of starch synthesis-related enzymes. The sucrose synthase activity of rice grain has been
observed to be positively correlated with grain sink strength and starch accumulation [65, 66].
Another reason for decreased grain filling duration of rice under HT is reduction of cell size
on the dorsal side close to the vascular bundles [67]. In a pot experiments with 4
Arachis
hypogaea
genotypes varying in heat tolerance were grown at either 28/22 or 38/22°C from 21 to
90 d after planting (DAP). High temperature reduced total dry weight by 20 to 35%, seed
harvest index by 0 to 65%, and seed dry weight by 23 to 78% [68]. There are several reports
regarding HT induced declines in shoot DM, relative growth rate and net assimilation rate in
Z. mays
,
Pennisetum glaucum
and
Saccarum officinarum
[37, 69]. In the medicinal plant
Panax
quinquefolius
L., partitioning of DM to roots in the cool greenhouse and in the field was 73%,
whereas it was 62.5% in the heated greenhouses [70].
2.7. Reproductive development
It is notable that reproductive development of plants is more sensitive to HT because plant
fertility is considerably reduced as temperatures increase [71]. For heat-sensitive plants such
as tomato, no fruit set occurs at day/night temperatures of 35/23°C [72]. Studies on common
bean [73], and peach [74] showed that elevated temperatures during flower development can
markedly reduce the fruit set. The decrease in the fruit set has generally been attributed to low
pollen viability and germinability at HT in crop species such as tomato [75] and groundnut
[76]. Porch and Jahn [77] reported that
Phaseolus vulgaris
exposed to pre-anthesis heat stress
resulted in pollen and anther development abnormalities. In soybean, pollen viability was
lower at day/night temperature conditions of 37/27°C than at 27/27°C which resulted in a lower
pod setting [78]. High temperatures inhibit flower differentiation and development, and result
in smaller ovaries in pistillate and bisexual flowers [22].
The diurnal variation of temperature is also important for reproductive growth and develop‐
ment. Spikelet fertility of rice is sensitive to night temperature, where the degree of sensitivity
depends upon the developmental stage of the spikelet [79]. Later, Peng et al. [80] observed a
strong negative linear relationship between the number of fertile spikelets and increase in night
temperatures. Ledesma et al. [81] examined the effect of two day/night temperature regimes
(30/25°C and 23/18°C) on fruit set and fruit growth in two strawberry cultivars (Nyoho and
Toyonoka). It was recorded that high day/night temperature of 30/25°C reduced the number
of inflorescences, flowers, and fruits in both cultivars compared with control (23/18°C). The
percentage of fruit set in Nyoho was not significantly different between the two temperature
Search WWH ::
Custom Search