Agriculture Reference
In-Depth Information
ABSTRACT
Moisture stress is one of the greatest environmental factors reducing yield
in arid and semiarid crops. Drought is often accompanied by relatively
high temperatures, which promote evapotranspiration, (ET) and affects
photosynthetic kinetics, thus intensifying the consequences of drought
and further reducing crop yield. About two third of the geographical area
of India receives low rainfall (less than 1000 mm), which is also charac-
terized by uneven and erratic distribution. Out of net sown area of 140
million hectares about 68% is reported to be vulnerable to drought stress
and about 50% of such vulnerable area is classified as 'severe,'where fre-
quency of drought is almost regular. Vegetables being succulent in nature,
are sensitive to drought stress, particularly during flowering to seed de-
velopment stage. Moreover, the legume vegetables, for instance cowpea,
vegetable pea, Indian beans, etc., grown in arid and semiarid regions are
generally affected by drought at the reproductive stage. Drought stress
triggers drought tolerance mechanisms involving certain morphological,
physiological and biochemical traits in vegetables, which are considered
to be adaptive in nature. These traits are investigated thoroughly to serve as
screening tools in developing drought resistance varieties with greater po-
tential to maximize use of stored soil water and increased economic yield
per unit water use. Starting from germination potential, shoot and root
architecture and root anatomy, shoot and root fresh and dry weight ratio,
total leaf area, stability to flowering processes are needed to be analyzed.
Important physiological traits such as osmotic adjustment, cell membrane
stability, (CMS), photosynthetic and transpiration rate, stomatal conduc-
tance, water use efficiency, (WUE) chlorophyll fluorescence parameters,
photosynthetic pigment content, plant canopy temperature simultaneously
with biochemical attributes including level of antioxidant enzymes, non
enzymatic antioxidant and pyridine nucleotides involve in drought toler-
ance mechanism.
9.1 INTRODUCTION
Drought may be defined as a climatic hazard, which implies the absence or
very low level of rainfall for a week, month or years, long enough to cause
moisture depletion in soil with a decline of water potential in plant tissues.
