| Rice is the economic crop with the largest planting area,the highest yield level and the highest total yield in China.Rice seed coating technology has become an effective means to improve crop adversity resistance and seedling quality,standardized and precise sowing,and control crop diseases and insect pests at the seedling stage.However,China's seed coating technology is slower than foreign development.Seed coating formulation is prone to some problems,such as poor physical stability,long film-forming time,poor sustained release,low pesticide utilization,high falling off rate,poor coating uniformity,unsafe operation,high toxicity and high residue.It is relatively easy to produce coating phytotoxicity.These problems have affected the promotion and application of seed coating technology.The film-forming agent is the most critical part of the inactive component of rice seed coating formulation,and its performance is decisive for the sustained release property,stability,safety and viscosity of seed coating formulation.It is applied to the special environment of paddy field to make film-forming agents more strict on the film-forming property,water absorption and resistance,uniformity of coating,adhesion performance and long-term controlled release.Currently,the types of film-forming agents suitable for rice seed coatings are still insufficient.This study explored the application effect of the film-forming agents?ZY904-1,ZY904-2,ZY904-3 and ZY904-5?for rice seed coating,aiming to screen out which film-forming agent and recommended addition ratio can significantly improve the sustained release property of pesticides.The study will provide a reference for the development of long-acting,sustained-release,high-efficiency and low-toxicity rice seed coating formulation.First,this study evaluates the physical and chemical properties of film-forming agents from the aspects of pH,stability,viscosity,solid content,flexibility of dry film,film-forming property,water absorption and resistance,etc.After the film-forming agents were applied to the seed coating formulation,the application performance was evaluated from the aspects of the film-forming time,fastness after initial dryness,degree of uniformity,falling off rate,indoor safety of rice coating.In this study,the bactericide azoxystrobin was used as an indicator to evaluate the sustained-release properties of film-forming agents.This study quantitatively determined retention rate of pesticides at different time points after coating with film-forming agents and then soaking seeds,aiming to evaluate the effects of different film-forming agents on the sustained release performance of active ingredients.This study explored the toxicity of treatments with film-forming agents to aquatic organisms through the acute toxicity test to zebrafish.The main research results include the following aspects:1.Physical and chemical properties test results showed that the film-forming agents ZY904-1,ZY904-2,ZY904-3 have good film-forming properties.The dried film can be removed from the slide uniformly and completely after being immersed in distilled water for half an hour,while ZY904-5 has a poor film-forming property.The solid content is an important index for the content of active ingredient of film-forming agents.The content of active ingredient of each film-forming agent decreases sequentially.The solid content was45.93%,31.46%,26.83%and 6.26%,respectively.The quality of water dissolution was low after dry films made of ZY904-1,ZY904-2,and ZY904-3 were immersed in water for 72 h.The solubility was 21.36%,16.46%and 17.56%,respectively.The film-forming agent ZY904-2 has a medium viscosity,and the dry film has good flexibility after being immersed in water.The film-forming agent ZY904-2 has low solubility and good water absorption and resistance.2.The application of performance index test results showed that the germination potential of ZY904-1 was reduced respectively by 6.08%,13.33%,15.02%compared with the uncoated control after treatment with 0.5 g,1 g and 2 g/100 g seed.When the film-forming agent ZY904-1 was treated with 2 g/100 g seed,the germination rate decreased by 3.87%compared with the control,and the other treatment germination rate and germination potential had no obvious adverse effects.There were no significant adverse effects on the growth index of rice plants?plant height,root length,above-ground dry weight and underground dry weight?after coating with different proportions of film-forming agents compared with CK and Ch.The film-forming agent is safe for the growth of rice plants.After the film-forming agents ZY904-1,ZY904-2,and ZY904-3 were coated with 0.25g,0.5 g and 1 g/100 g seed,the uniformity of coating was 95.2%-96.8%,and the falling off rate was 1.5%-2.1%.These several treatments had good fastness after initial dryness with grade++.3.Determination of retention rate of azoxystrobin by the High Performance Liquid Chromatography showed that the retention rate of azoxystrobin was significantly improved after coating with ZY904-1,ZY904-2 and ZY904-3 compared with the treatment without adding film-forming agents.When the film-forming agent ZY904-2 was coated with 0.5g/100 g seed,the retention rate of azoxystrobin was increased by 34.14%compared with the control.This treatment delayed the release rate of the pesticide significantly,indicating that it has good water resistance and sustained release properties.4.Screening out the best film-forming agent and its recommended addition ratio by combining physical and chemical properties with application performance indicators:When the film-forming agent ZY904-2 was coated with 0.5 g/100 g seed,the uniformity of coating was 95.7%,the falling off rate was 1.7%,the germination potential and germination rate increased by 1.39%and 2.82%,the plant height and root length increased by 0.52 cm and0.62 cm.The above-ground dry weight and underground dry weight increased by 0.46 g and0.33 g compared with CK.After forty days of soaking,the azoxystrobin retention rate still reached 47.26%.The anti-dissolution and leaching ability of pesticides is significantly improved.The performance of long-term controlled-release was good.Finally,the film-forming agent ZY904-2 is recommended to be added in a ratio of 0.5 g/100 g seed,which is suitable for application in the development of rice seed coating components with excellent performance.5.The results of acute toxicity test to zebrafish by the film-forming agents showed that ZY904-1,ZY904-2,ZY904-3 and ZY904-5 reached the upper limit effective concentration of LC50?96 h?100.0 mg a.i./L.The toxicity level is microtoxicity.The treatments with 0.5 g ZY904-2 and ZY904-3 have a low toxicity level.The film-forming agent is low toxic to zebrafish and has high safety. |
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