| Seed coating has been a key method of preventing plant diseases and insect pests. Seed coating formulation has been used widely in nonirrigated farmland,while application of seed coating special for rice in the south is severely insufficient. The main reason is that they live in different circumstances and have different demand on assistants. The rice seed coating lives in water environment, which has a high demand on water absorption resistence and pesticide persistence.The demand on water resistence of membrane agents is also higher than that used in nonirrigated farmland. Therefore, the choice of membrane agent need considering not only stability of the seed coating, water absorption and resistence but also its controlled release and persistence, which ensures the seed germinate normally. The rice blast is a kind of infectious diseases that arises in the south at the seeding stage, and the focus of present research is developing a rice seed coating agent of long-term controlled-release type in order to prevent the rice blast at the seeding stage.Aiming at rice blast control,the thesis of this paper is to accomplish water resistence and long-term controlled-release of rice seed coating agent through formula screening combined with functional modification of the polyving akohol.The following contents are main studies:A series of membrane agents special for rice seed coating were synthesized by blending polyvinyl acetate, styrene-acrylic latex and modified PVA.When the monomer ratio was1:2:1, synthesized membrane agent had a low shedding rate of3.26%,high germination rate of98.25%;Observation under optical microscope showed that porosity of membrane agent was small and breakage of membrane agents for30days in the water was low. Azoxystrobin amount after different soaking time was determined by HLPC.The retention rate of azoxystrobin after30d soaking was about30%with favorable controlled-release,which is suitable for membrane agents of the rice seed coating in the south.Through screening different dispersant, membrane agents and thickening agents, a new formula and preparation method for rice seed coating using by using azoxystrobin as active ingredients was established. The optimum formula of10%azoxystrobin seed coating was10%azoxystrobin,8%YUS-FS3000,0.12%gum,0.5%quick T,0.5%soap soil,8%membrane agents.At grinding speed of500r/min for2h, the size of the rice seed coating was less than3μm, shedding rate was less than5%, and germination rate of the seed coating reached98.25%.Toxicity test and security assess of rice seed coating showed that azoxystrobin had perfect controlling effect on rice blast with EC50value of0.0395μg/mL, and seed coating had no adverse effect on germination of rice seed. The germination power and germination rate increased respectively by0.83%and1.29%compared with CK. Meanwhile,plant heigt and dry weight increased respectively1.3cm and1.2g compared with CK. So the membrane agent of the rice seed coating can enhance seed performance and is suitable for rice seed coating agent in the south. |
