Dissertation
Dissertation > Agricultural Sciences > Crop > Cereal crops > Rice

Study on Comparing the Biology of Weedy Rice (Oryza Sativa L.) and Cultivated Rice (O.Sativa L.)

Author LiZhenBo
Tutor DongLiYao
School Nanjing Agricultural College
Course Pesticides
Keywords Weedy rice Cultivated rice Biology Germination Yield Chemical control
CLC S511
Type Master's thesis
Year 2010
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In this paper, the influence of different environmental factors on the germination of weedy rice (Oryza sativa L.) and cultivated rice from Jiangsu Province were studied; Based on the experiments conducted in fields, the differences of growth process, agronomic characterizations and seed morphology between weedy rice and cultivated rice had been investigated; Also, the influence of weedy rice on the yield and quality of cultivated rice had been investigated. Based on the results of bioassay, the possibility and effeciency of herbicide use to control weedy rice was evaluated. The results were listed as follows:Laboratory and greenhouse experiments were conducted to compare the affection of different environmental factors on the germination of weedy rice and cultivated rice. Weedy rice and cultivated rice are all germinated over a range of constant temperatures from 10 to 45 C, but germination of weedy rice is higher than cultivated rice at lower temperature (12.5 C). Weedy rice and cultivated rice were not affected by photoperiod. The optimum pH range for germination of cultivated rice was ranged from 4 to 8, but greater germination of weedy rice occurred at pH values of 3 and 10 compared with cultivated rice. Germination of weedy rice and cultivated rice seeds were all decreased accompanied with decreasing osmotic potential, and no germination occurred at a solution osmotic potential of-0.8MPa, but weedy rice had greater germination than cultivated rice at solution osmotic potential from-0.4 to-0.7MPa. Germination of weedy rice and cultivated rice were all decreased with increasing salt concentration, but weedy rice had greater germination than cultivated rice at salt concentration from 180 to 380 mM. Seedling emergence of weedy rice and cultivated rice were highest when seeds were placed on the soil surface of 0-3cm and declined with increasing of burial depth, but seedling emergence of cultivated rice was higher than that of weedy rice at 5-7cm burial depth.We screened one weedy rice sample that show strong resistance in different environmental factors. The research indicates that:under different environmental factors of 20 C, pH6 and pH8, osmotic potential-0.3 MPa, NaCl concentration 180 mM, respectively, this weedy rice sample had strong germination vigor than cultivated rice; under 20 C or different NaCl concentration, the length of radicle and plumule of weedy rice were greater than cultivated rice; Under different water potential, the length of weedy rice radicle was significantly longer than cultivated rice, but the length of weedy rice plumule was not significantly difference; under 7cm burial depth, the length of weedy rice mesocotyl was significantly longer than cultivated rice.Based on the study on agronomic characterizations of weedy rice and cultivated rice, differences were found in 32 weedy rice and 6 cultivated rice on plant height, tillering numbers, the correction green weight and dry weight of above-ground plant parts at different stages of plants vegetative growth. By plant height,91% of weedy rice were classified into a biotype of long growth period (>100d) and shorter seedling (77-100cm), and 9% are identical to indica belonging to the biotype of long growth period (>100d) and higher seedling (102-140cm).63% weedy rice samples are exhibited shorter tillering stage (60d) but more tillering numbers (19-31),31% identical to indica have longer tillering stage (100d) and fewer tillering numbers (12-26), and 6% are longer tillering stage and more tillering numbers(32-52). However, japonica is shorter tillering stage and little tillering numbers (8-13). Weedy rice’s fresh weight and dry weight of above-ground plant parts are obvious less than cultivated rice.The weedy rice (Oryza sativa L.) in Jiangsu Province intermediated in agronomy between japonica cultivar and indica cultivar. It is showed that weedy rice is short in plant height (63.32-96.62cm,75% less than 80cm), short and broad in flag leaf, long and narrow in penultimate leaf, long in panicle length (20.41-31.30cm), panicle large number of branches (11.83-14.8), short in rachis length (20.41-31.30cm) little grain number per panicle (141.56-195.51), large in tiller angle (20.5°-46.0°), much grains fall number per panicle (4.15-38.83),weak in dormancy and awn. However, the weedy rice’s seed morphology was different from cultivated rice’s. It is showed that weedy rice’s glume tenacity is darker than cultivated rice’s on color, and pericarp is red.If weedy rice seeds were mixed into cultivated rice seeds, the yield and quality of cultivated rice would be affected. In this paper, the impact of weedy rice on Nanjing 44 is studied in direct seeding rice fields. It was showed that the production of Nanjing 44 was reduced by 24%-64%, when the seed number of weedy rice is increased from30 to 150. Meanwhile, the rice quality was affected when 38%-91% weedy rice seed were mixed into the cultivated rice seeds.In order to study the effect of herbicides on weedy rice in rice fields, different types of herbicides were screened to test their toxicity on weedy rice, and their safety on cultivated rice. The results showed that no common herbicides could control weedy rice selectively, and any herbicide to which weedy rice was suspectible could also do harm to cultivated rice.

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