MSc

The study entitled ‘Characterization and management of weedy rice (Oryza sativa f spontanea)’ was carried out as four separate experiments conducted at COA, Vellayani and farmers’ fields of Nemom block during 2014-16. The main objectives of the study were morpho-physiological and agronomic characterization of weedy rice morphotypes of Kerala; formulation of a management strategy and assessment of crop weed interference under elevated carbon dioxide concentration.
Experiment I. ‘Morpho-physiological and agronomic characterization of weedy rice morphotypes’ was conducted as pot culture laid out in completely randomized design with eight weedy rice morphotypes collected from major rice tracts of Kerala (Trivandrum, Kuttanad, Kole lands, Palakkad, Kozhikode and Ezhome). Morphological characterization of weedy rice morphotypes using morphometric descriptors and its comparison with cultivated varieties revealed that during initial stages most of the weedy rice morphotype possess similar morphological characteristics as the cultivated varieties. Physiological characterization of weedy rice morphotypes revealed no significant variation in chlorophyll content, total soluble protein and stomatal characteristics with cultivated rice varieties. However, root growth in terms of volume and dry weight was significantly higher for most of the morphotypes collected from Trivandrum, Kuttanad, Palakkad, and Ezhome.
Earliness in 50% flowering was observed in all the weedy rice morphotypes compared to cultivated rice. Sterility of weedy rice morphotypes were significantly higher (17.77 to 32.79%) compared to cultivated rice varieties (9.23 to 12.85%). All the weedy rice morphotypes collected showed a prominence in awn length ranging from 2.37 to 9.23 cm. An average grain and straw yield of 4.89 and 16.14 g plant-1 and 1000 grain weight of 20.42 g was recorded by weedy rice morphotypes. Shattering percentage expressed as grain threshebility was significantly high for weedy rice morphotypes ranging from 29.73 to 46.32%. The seeds of weedy rice recorded wide variation in longevity ranging from 4.96 to 15 months which is an indication of variable seed dormancy.
Experiment II. ‘Management of weedy rice by enhancing rice competitiveness’ was undertaken as micro plot study by raising cultivated rice and most common weedy rice morphotype and maintaining a standard weedy rice population of 7 plants m-2. To enhance rice competitiveness, three levels of seed rates viz., 100,120 and 140 kg ha-1 in combination with three types of priming techniques, i.e., without priming, hydropriming and hardening (2.5 % KCl) were included.Among the treatments, seed rate of 100 kg ha-1 along with hydropriming(T2) recorded significantly higher number of grains per panicle (120.02), grain yield (4.44 t ha-1) and straw yield (6.71 t ha-1) which was on par with T5 (120 kg ha-1 + hydropriming).
Confirmatory trial at farmers’ field revealed that seed rates of 100 kg ha-1 or 120 kg ha-1 along with hydropriming (T2& T5) resulted in superior yield attributes inrice viz., number of grains per panicle, grain and straw yield ha-1.Weedy rice count m-2 and dry weight were significantly lower under these treatments. T2 (100 kg+ hydropriming) along with T5 (120 kg+ hydropriming) turned out to be the most economic treatment with a B:C ratio of 1.68 and 1.64 respectively.
Experiment III. ‘Effect of elevated CO2 concentration on growth of rice and weedy rice’, was undertaken as pot study under elevated CO2 concentration of 500 ppm in Open Top Chamber (Chamber A) and in ambient conditions (Chamber B and open field). The most common morphotype of weedy rice and two cultivated rice varieties (Jyothi and Uma) were selected for the study. Significant variations in vegetative (no of tillers, leaf area index and leaf area duration) as well as yield attributes and yield (no. of grain panicle-1, grain yield plant-1) were observed under elevated CO2 levels in all these three systems. Higher grain yield per plant was recorded by weedy rice in Chamber A with an elevated CO2 level (1.73 times higher than open condition), followed by Chamber B (recorded 1.19 times more than open condition). However, the extent of response varied among the cultivars under varying atmospheric situations with Uma showing a greater percentage increase in grain yield (51.4% in Chamber A and 40% in Chamber B) followed by weedy rice (42.3% in Chamber A and 16% in Chamber B).
The study revealed significant variation among the weedy rice morphotypes. Cultivated rice and weedy rice exhibited morphological similarity during initial stages of growth. Seed rate of 100 kg ha-1 with hydropriming can be recommended as the most effective and economic management strategy for weedy rice. The response of weedy rice to elevated CO2 was more compared to cultivated rice varieties.