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| Section: General Biotechnology / Plant Biotechnology |
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Azolla
Azolla is an aquatic heterosporous fern which contains an endophytic cyanobacterium, Anabaena azollae, in its leaf cavity. The significance of Azolla as biofertilizer in rice field was realized in Vietnam. Recently, it has become very popular in China, Indonesia, Philippines, India and Bangladesh.
A total of six species of Azolla are known so far viz., A. caroliniana, A. filiculoides, A. mexicana, A. microphylla, A. nilotica, A. pinnata and A. rubra. Out of these A. pinnate is commonly found in India. The global collections of several species of Azolla are maintained at CRRI (Cuttack). Within the leaf cavity filaments of Anabaena azollae are present. Dr. P.K. Singh, at CRRI has done an outstanding work on mass cultivation of Azolla and its use as biofertilizer in rice and other crop fields.
Mass cultivation of Azolla
Microplots (20m2) are prepared in nurseries in which sufficient water (5-10 cm) is added. For good growth of Azolla, 4-20 Kg P2O5/ha is also amended. Optimum pH (8.0) and temperature (14-30°C) should be maintained. Finally, microplots are inoculated with fresh Azolla (0.5 to 0.4 Kg/ m2). An insecticide (furadon) is used to check the attack of insects. After three, week of growth mat formed by Azolla is harvested and the same microplot is inoculated with fresh Azolla to repeat the cultivation.
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Azolla mat is harvested and dried to use as green manure. There are two methods for its application in field: (a) incorporation of Azolla in soil prior to rice plantation, and (b) transplantation of rice followed by water draining and incorporation of Azolla (Singh, 1977, 1979, 1980). However, reports from the IRRI (Philippines) reveal that growing of Azolla in rice field before rice transplantation increased the yield equivalent to that obtained from 30Kg N/ha as urea or ammonium phosphate.
Moreover, Azolla shows tolerance against heavy metals viz. As, Hg, Pb, Cu, Cd, Cr, etc. It tolerates low concentration but at high levels a setback in biochemical pathways is caused. A. pinnata absorbs heavy metals into cell walls and vacuoles through evolution of specific metal resistant enzymes. Therefore, heavy metal resistant species such as A. pinnata can also be incorporated as green manure in rice field near the polluted areas where heavy metal concentration is between 0.01 and 1.5 mg/liter. Due to development of chemical industries and discharge of effluents into water bodies, heavy metal concentration is gradually increasing day by day. Industries where work of electroplanting, fertilizers, tanning, etc. are done, they act as a chief source for soil and water pollution. For example, disturbed vegetation in aquatic system around Damodar river valley in India has received a great attention. |
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Fig. 12.4. Mass cultivation of Azolla in India. |
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