Residue Of Pyraclostrobin And Its Effects On Physiological And Biochemical Properties Of Rice And Edible Qualities Of Polished Rice

Pyraclostrobin is a broad-spectrum strobilurin fungicide which developed by BASF corporation in Germany. Pyraclostrobin is widely used to prevent plant disease caused by ascomycetes, adelomycetes, basidiomycetes and oomycetes on fruits, vegetables, grains, peanut and other crops. At present, there is little report about dissipation and residue behavior of pyraclostrobin or effect of pyraclostrobin on crops. In this thesis, dissipation and residue behavior of pyraclostrobin and its effects on physiological and biochemical characters of rice(Oryza sativa L.) plant and rice edible quality were systematically studied after 25% pyraclostrobin missible oil was applied to the paddy fields. This study will provide a scientific basis for the safe use of pyraclostrobin in the paddy fields. The main results were summarized as follows:In this paper, a new method was developed for the residual analysis of pyraclostrob in by ultraperformance liquid chromatography-mass spectrometry(UPLC-MS/MS) in rice plant, paddy soil, paddy water, rice husk and brown rice. The pyraclostrobin residues in samples were extracted with aqueous acetonitrile, cleaned up on a Florisil column, separated on a C18 reverse phase column using aqueous methanol and methanoic acid as mobile phase, and detected with positive ionization electrospray ionization-mass spectrometry under a multiple reaction monitoring(MRM) mode. The minimum detectable amount of pyraclostrobin was 1.0×10-12 g. The minimum detectable concentrations of pyraclostrobin in rice plant, paddy soil, paddy water, brown rice and rice husk were all 0.0002mg·kg-1. For paddy straw, paddy soil, paddy water, rice husk and brown rice, the mean recoveries of the method were respectively from 87.8% to 104.1%, 88.7% to 99.1%, 93.1% to 102.1%, 86.2% to 102.5% and 84.7% to 101.0%, and the relative standard deviations were respectively from 2.9% to 9.2%, 8.5% to 11.7%, 2.8% to 5.9%, 5.8% to 8.1%, 3.7% to 4.9%. The sensitivity, accuracy and precision of this method could meet the requirements of pesticide residue analysis.The dissipation dynamics of pyraclostrobin in rice plant, paddy soil and paddy water were studied through two-year and three-place field experiments conducted in 2013 and 2014 in Heilongjiang and Jiangsu provinces and Guangxi Zhuang autonomous Region. The results showed that the dissipation behavior was fitted with first-order reaction kinetic model. In rice plant, paddy soil and paddy water, the half lives of pyraclostrobin were respectively from 5.9 days to 42.8 days, 7.4 days to 18.1 days, 0.9 days to 44.1 days.Final residues of pyraclostrobin in rice plant, paddy soil, rice husk and brown rice were studied. 25% pyraclostrobin missible oil was sprayed two or three times upon the rice in the experimental fields in Heilongjiang and Jiangsu provinces and Guangxi Zhuang Autonomous Region during the growing season for rice in 2013 and 2014. The interval between sprays was 10 days. The pesticide was respectively applied at 150 g ha-1(the lower limit of the recommended dose) and 225 g ha-1(the upper limit of the recommended dose). The final residue of pyraclostrobin in rice plant, paddy soil, rice husk and brown rice were analyzed on the 30 th, 40 th and 50 th day after the last application, respectively. The results showed that the final residue of of pyraclostrobin increased as the application dose and application times increased, or as the harvest interval decreased. The results also showed that on the 50 th day after the last application, the final residue of pyraclostrobin in rice plant was 0.113-3.805 mg kg-1, and the maximum residue in paddy soil was 3.177 mg kg-1 and the final residues in rice husk was 0.117-1.870 mg kg-1, and the final residues in brown rice was lower than 0.25 mg kg-1.The effects of pyraclostrobin on physiological and biochemical properties of rice plant were studied. 25% pyraclostrobin missible oil was sprayed one time upon the rice in the experimental field in Heilong province at the dose of 225 g ha-1(a.i.) at the part of the growing season in 2013. The results showed that compared with the control total chlorophyll content in the lives of rice sprayed pyraclostrobin decreased, and malondialdehyde(MDA) content increased. Total activity of superoxide dismutase(SOD) in the sprayed rice increased more than that in the control after spray, especially on the 7th day. Overall, peroxidase(POD) activity in the sprayed rice was lower than that in the control. Catalase activity and proline content changed wavily according to the time after spray, and the increase percentage of catalase activity in the sprayed rice over the control reached the maximum on the 10 th day.25% pyraclostrobin missible oil was sprayed two or three times upon the rice in the experimental fields in Heilongjiang and Jiangsu provinces and Guangxi Zhuang Autonomous Region during the growing season for rice in 2013. The interval between sprays was 10 days. The pesticide was respectively applied at 150 g ha-1(low concentration) and 225 g ha-1(high concentration). Protein, amylase and moisture contents and RVA(rapid viscosity analyzer) profile characteristic parameters of rice were analyzed on the 30 th, 40 th and 50 th day after the last application, respectively. The results showed that these indexes were not remarkably affected by dose of the pesticide, times of application or interval between the last application and harvest.