Extreme Temperature Responses, Oxidative Stress and Antioxidant Defense in Plants - Abiotic Stress: Plant Responses and Applications in Agriculture - page 183

of more enzymes, isozymes though they help in maintaining more catalytic activity to cope
with the LT stress [139].
3.7. Yield components and yield
Reproductive phase products are the key components of economic yield and hence LT stress
during the reproductive phase has significant economic and social consequences. All the
adverse effects of cold stress ultimately lower the yield of crop. Low temperature-induced
yield reduction is a common phenomenon in many crops [98, 99, 140, 141]. Low temperature
often causes flower abortion, pollen and ovule infertility, breakdown of fertilization, poor seed
filling, decreases in seed setting which ultimately reduce the grain yield [116]. In O. sativa , LTs
are responsible for 30-40% yield reduction in temperate growing areas [142]. It was observed
that about 16 and 37% yield reduction in the rice variety of BRRI dhan46 and BRRI dhan31 due
to late sowing mediated LT stress [98]. In another report, it was observed that LT stress near
about 11°C caused yield reduction in maximum genotypes and only 23 genotypes were
screened out among the 244 genotypes considering their better yielding ability under LT [99].
The reduction in yield in C. sativus L. was from 15 up to over 18% due to low soil temperature
[143]. In C. melo L., total yields decreased linearly for cold stress (21 and 32 h) which accounted
for 10% lower than normal condition [143]. Frost prevailing just after flowering can result in
yield reduction and the quality or grade loss. Premature flowering or bolting is occurred due
to LT stress which has economic importance for the Chinese cabbage industry because
advanced flower stalk development results in an unmarketable head [120]. In B. napus and B.
rapa various abnormal structures were observed like reduced diameter and extensive white
patches, white reticulation, red-brown pigmentation, folded seed, extensively shriveled seed,
etc. those are the causes for reduced market value of this crop[103].
4. Responses of perennial crops to extreme temperature
Like annual crops, perennial crops are also sensitive to extreme temperature. Fruits and nut
trees are important crop plants which often face extreme temperature stress induced damages.
Every fruit tree species has a range of optimum temperatures (Table 3) above or below which
the growth and yield markedly reduced. The mean temperatures range for optimum growth
of most tropical fruits are about 24-30°C [144, 145]. For instance, mango ( Mengifera indica ) tree
can tolerate HT up to 48°C only for a certain period of time [146], on the contrary it has only
partial tolerance to LT. In another study, Schaffer et al. [147] observed that monoembryonic
mango cultivars tend to be more LT tolerant than polyembryonic cultivars [147]. However,
several studies have shown that LT promote reproductive morphogenesis in mango. Dinesh
and Reddy [145] studied the responses of fruit trees to temperature and observed differential
responses to temperature in different fruit species. They concluded that lychee and longan
require a warm sub-tropical to tropical climate that is cool but also frost-free or with only very
slight winter frosts not below -4°C, and with high summer heat, rainfall, and humidity. In
longan, stressful temperatures of <15°C at the young fruit stage reduce fruit growth potential
and final size as reported by Young et al. [148]. Stressful LT also induces excessive fruit drop