Agriculture Reference
In-Depth Information
observed by adversity of climate. Elevated temperature can disrupt the
normal growth and development of plants, which ultimately affects crop
productivity.
Measures to adapt to these climate change-induced stresses are critical
for sustainable vegetable production. Until now, the scientific information
on the effect of environmental stresses on vegetables is overwhelmingly
on tomato. There is a need to do more research on how other vegetable
crops are affected by increased abiotic stresses as a direct potential threat
from climate change.
10.2
THRESHOLD LEVELS OF HEAT-STRESS
A value of daily mean temperature at which a detectable reduction in
growth begins may be referred to as threshold temperature. Upper and
lower developmental threshold temperatures specific for many plant spe-
cies have been determined through controlled laboratory and field ex-
periments. A lower developmental threshold or a base temperature is the
temperature belowwhich plant growth and development cease. Similarly,
an upper developmental threshold is the temperature abovewhich growth
and development stop. Base threshold temperatures vary with plant spe-
cies, for example, spinach (2 °C), lettuce (4.4 °C), pea (4.4 °C), French
bean (10 °C), asparagus (5.5 °C), pumpkin (13 °C), tomato (15 °C), etc.
The lower threshold temperature of cool season and temperate crops are
often lower compared to tropical crops. Upper threshold temperatures also
differ for different plant species and genotypes within species. However,
determining a consistent upper threshold temperature is difficult because
the plant behaviormay differ depending on other environmental conditions
(Miller et al., 2001). In tomato, for example, when the ambient tempera-
ture exceeds 35 °C, its seed germination, seedling and vegetative growth,
flowering and fruit set, and fruit ripening are adversely affected. For other
plant species, the higher threshold temperature may be lower or higher
than 35 °C. Legumes are particularly sensitive to heat stress at the bloom
stage; only a few days of exposure to high temperatures (30-35 °C) can
cause heavy yield losses through flower drop or pod abortion (Siddique
et al., 1999). In general, base and upper threshold temperatures vary in
plant species according to varying habitats. Hence, appraisal of threshold
