MSc

The present investigation entitled “Physiology and management of submerged weeds in the wetland rice ecosystem” aimed to identify and characterize the different submerged weed species of wetland rice ecosystem, understand their growth pattern and evolve possible management practices. The study consisted of survey, identification and morphological characterization of submerged weeds of rice ecosystem of the central zone of Kerala. The effect of environmental conditions on growth and multiplication of the most common weed, Utricularia aurea and its control were also studied.
Weed survey was conducted in ten locations each in Thrissur, Palakkad and Ernakulam districts of Kerala. Submerged weeds from the rice fields were collected along with soil and water samples from ten locations for further studies. The major submerged weeds in the rice ecosystem included hydrophytes and algal species. Seven hydrophytes and three species of algae were commonly seen in the region. The major hydrophytes were Utricularia aurea, Utricularia exoleta, Elodea canadensis, Hydrilla sp., Egeria densa, Cabomba sp. and Najas sp. while the common algal species were Spirogyra, Chara and Nitella.
The water and soil samples collected were analyzed in the laboratory for different physico-chemical properties such as pH, electrical conductivity (EC), total suspended solids (TSS), dissolved oxygen (DO), E. coli content, soil enzymes and hormones which affect growth of the rice plant. pH had the larger influence on growth of submerged weed species. Highest weed growth was observed between pH range of. 7.2 to 8.01 (neutral to alkaline). The presence of submerged weeds reduced the dissolved oxygen content of water and increased the content of TSS and E. coli, adversely affecting water quality and supply of oxygen to rice root. The presence of dissolved nitrate in the water may be a major reason for high incidence of these weeds. Soil enzymes and hormones also positively influenced their growth.
The physiological parameters such as chlorophyll content, nitrate reductase activity, indole acetic acid (IAA) and GA contents of the weeds were also studied. It was found that IAA, GA and chlorophyll promoted weed growth. High nitrate reductase was observed in Nitella. Elodea canadensis had the capacity to purify the water by reducing the TSS and improving the dissolved oxygen content.
The most common submerged weed in the rice ecosystem was Utricularia aurea and hence this weed was selected to study the effect of light, UV radiation and chemicals on growth and multiplication.
Effect of light on weed growth was studied by using different shade nets which allowed 50 per cent and 75 per cent light infiltration. Effect of UV radiation was studied by growing the plants under polyhouse cladded with mylar film which allowed zero UV and polyethylene sheet which allowed 80 per cent UV radiation. Growth and multiplication of Utricularia aurea in the open condition and different light and UV levels were compared. Zero UV and temperature in the range of 30-310C was found to be ideal for weed growth. Both high water temperature and high UV were detrimental. Growth of the weed was not altered with shading, indicating that moderate shade not affect the weed growth.
Effect of CuSO4 (1ppm, 2ppm and 3ppm), 2, 4-D (1ppm, 2ppm and 3ppm) and lime (100 ppm, 200 ppm and 300 ppm) on growth of Utricularia aurea was measured by recording the rate of degradation of the weed one month after application in pot culture study. Good control was obtained with higher concentrations of all the three chemicals tried. Three ppm of CuSO4, 2, 4-D and 300 ppm lime gave better results. Lime was found to be more effective in the control of Utricularia aurea.