Agriculture Reference
In-Depth Information
environment and detect individuals/lines with higher yield (Ehlers and
Hall, 1998).
Several types of morphological traits help in heat tolerance in the
conventional breeding approaches. Long root length has a good ability
to uptake water and nutrients from the soil. Short life-span helps to mini-
mize the temperature effect on plant. Hairiness provides partial shade to
cell wall and cell membrane and repels sunrays. Small size of leaf resists
evaporation due to reduction of stomata. Leaf orientation enhances the
photosynthetic activity and produces tolerance against heat stress. Leaf
glossiness and waxiness repel sunlight.
A proposed method has been detected in selection criteria during early
steps of crop growth that can be linked to heat resistance during repro-
ductive steps. In tomato, a potent positive correlation has been found be-
tween yield and fruit set under high temperature. Therefore, estimation
of germ plasma to detect sources of heat resistance has regularly been
performed by screening for fruit set under high temperature (Berry and
Rafique-Uddin, 1988). Among various other characteristics that are influ-
enced by high temperature, the nonreproductive trends involve efficiency
of photosynthesis, assimilate translocation, mesophyll tolerance, and cel-
lular membranes disorganization (Chen et al., 1982). Breeding to develop
such characteristics under high temperatures can lead to improvement of
varieties with heat resistance approaches.
Various other concerns when applying conventional breeding proto-
cols to promote heat resistant crops may arise. Detection of genetic re-
sources with heat resistance approaches is one such concern. In most of
the vegetables, for instance tomatoes and legumes, the genetic differentia-
tions within the cultivated species are restricted which necessitates the de-
tection and use of wild accessions (Foolad, 2005). Sometimes heat resis-
tance is linked to various unfavorable agronomical or horticultural traits.
In tomato, for instance, two unfavorable traits generally observed in heat
resistant lines are small fruit and limited foliar canopy (Scott et al., 1997).
The small fruit production is mostly because of improper impacts of high
temperature on the creation of auxins in the fruit and the poor canopy is
for the sake of the highly reproductive nature of the heat resistant varieties
(Scott et al., 1997).
Resistance breeding for heat stress is yet in its primitive step and less
information on breeding for heat resistance in various vegetable crops is
available. In spite of the complicatedness of heat resistance and hardships
