Effects Of Pesticides On Grain Yield And Quality In Wheat And Relevant Physiological Mechanism

Pesticide residue was one of the most important factors affecting wheat hygienic and nutritional quality. Wheat plant was enriched in nutriment during flowering and grain-filling period, which might result in high incidence of diseases and pests. So fungicides and insecticides were frequently applied to control diseases and pests on wheat plants. These pesticides would inevitably affect grain yield and quality in wheat, and deposit in wheat grains, plants and field soil, causing potential or realistic harm to grain hygienic quality and field environment. So it was necessary to investigate the effects of pesticide application on grain yield and quality, and physiological mechanism in wheat so as to provide a solid base for constructing a safe wheat producing system.The experiments on avermectins, imidacloprid, chlorpyrifos and dimethoate against wheat pests were conducted on the Experimental Farm of Jiangsu Provincial Key Lab of Crop Genetics and Physiology of Yangzhou University from 2005 to 2009 to investigate the grain yield and quality in wheat, and physiological mechanism. The main results were as follows. 1. Controlling techniques of wheat aphids from heading to grain filling stageThe efficacy of avermectins, imidacloprid, chlorpyrifos and dimethoate against wheat aphids and the effects on natural enemy on weak-gluten wheat Yangmai13 plants were investigated from heading to grain-filling. The timing of pesticide application was also under investigation. The population of natural enemy fluctuated along with that of wheat aphids. All the four pesticides provided excellent efficacy over wheat aphids on weak-gluten wheat Yangmai13 plants. Compared with chlorpyrifos and dimethoate, avermectins and imidacloprid had lower killing rates against natural enemy. It was appropriate to spray pesticide only once when wheat aphids initially prevailed, corresponding to wheat growing period from heading to the 7th day after anthesis (7 DAA). These pesticides didn't produce good controlling effects on small brown planthoppers although they had good efficacy over wheat aphids.2.Effect of the pesticides on wheat grain yieldIn order to investigate the poisonous and positive effects of pesticides on weak-gluten wheat and the relationship between these two effects, the yield of the Yangmai 13 were analyzed after spraying four pesticides, avermectin, imidacloprid, chlorpyrifos and dimethoate, with different times (one, three and six) of recommended dosage of each pesticide under the condition of artificial dislodgement and inoculation of pests. Results indicated as follows. (1) Under the condition of artificial dislodgement, spraying pesticides resulted in the downtrend of grain yield, grain number per ear, 1000-grain weight, 100-superior grain weight and 100-inferior grain weight, and the declined effects were significant at the 0.05 or 0.01 probability level when 6 times of recommended dosage was applied. However, in the treatments of inoculating pests, the yield of Yangmai 13 increased significantly after spraying pesticides. (2) Of the four pesticides, avermectin and chlorpyrifos had lower poisonous effect on Yangmai 13 and produced more efficient effects on increasing grain yield than imidacloprid and dimethoate. (3) Totally, spraying pesticides had much more positive effect on increasing grain yield than poisonous effect. Under the condition of recommended dosage, the poisonous effects were so tiny that they could be neglected. The poisonous effects increased significantly when using excess pesticide, which should be paid much more attention. 3. Effect of pesticides on wheat grain qualityIn order to investigate the poison and positive effects of pesticides on weak-gluten wheat and the relationship between these two effects, the grain of the Yangmai 13 were analyzed after spraying four pesticides, avermectin, imidacloprid, chlorpyrifos and dimethoate, with different times (one, three and six) of recommended dosage of each pesticide under the condition of artificial dislodgement and inoculation of pests. Under the condition of artificial dislodgement, spraying pesticides didn't produce significant effects on protein content and amylase content of wheat, but resulted in downtrend of starch content and amylopectin content. However, in the treatments of inoculating pests, the protein content in the grain of Yangmai 13 decreased significantly at the 0.01 level of probability, the content of total starch and amylopectin increased significantly at the 0.01 level of probability. The content of amylase also increased significantly in some treatments of inoculating pests. Spraying pesticides significantly decreased the incidence of wheat aphids and increased grain quality. No significant effects were found among the four pesticides.Imidacloprid, chlorpyrifos and dimethoate were used to explore the suitable timing of pesticides in producing system of weak-gluten wheat for good-quality, high-efficiency and edible-safety. The protein content was declined and the starch content was improved. The RVA parameters were improved, and flour percentage and degree of softening were improved highly. Development time, stability time and valorimeter value were declined. But extensograph parameters were no observably changed. Furthermore, spraying pesticides at the stage from heading to the 7th day after anthesis was much more advantage of the forming of grain quality of Yangmai13: The protein content was lower, and the starch content was higher. The development time and stability time were shorter, and degree of softening was higher.4 Effect of spraying pesticides on photosynthetic parameters of flag leaves in wheatThe effects of spraying pesticides on photosynthetic parameters of flag leaves in winter wheat were investigated. Two winter wheat (Triticum aestivum L.) cultivars, a weak-gluten wheat cultivar, Yangmai13, and a strong-gluten wheat cultivar, Yannong19, were respectively sprayed with four widely-used pesticides, avermectin, imidacloprid, chlorpyrifos and dimethoate, with 1, 3 and 6 times of recommended dosage of each pesticide at the end of anthesis stage in no-pest treatments. The chlorophyll content (SPAD readings), net photosynthetic rate and chlorophyll fluorescence related parameters of flag leaves were measured after spraying pesticides, and were found change significantly with increase of the pesticide concentration. Imidacloprid and dimethoate produced more significant effects on these measured traits than the other two pesticides, avermectin and chlorpyrifos. The weak-gluten Yangmai13 was found more tolerant to pesticides than the strong-gluten Yannong19. Under spraying pesticides conditions, the low Pn of flag leaves is related to decreasedφPSⅡand qP, and the declined grain yield. After spraying pesticide, the activity of SOD changed, the content of MDA were increased, while the activity of POD and CAT presented declining trend. The varying range of the activity of CAT and the content of MDA were relatively large, suggesting their sensitivity to pesticide. The activity of SOD declined in the treatments of spraying six times of dosage of chlorpyrifos and imidacloprid, implying its sensitivity to the concentration of pesticide. Imidacloprid and dimethoate produced the greatest impact on the activity of the wheat antioxidant enzymes and lipid peroxidation, followed by chlorpyrifos and avermectin, while the avermectin and imidacloprid had longer duration than the other two pesticides. Compared with the high-gluten wheat cultivar Yannong19, the weak-gluten wheat cultivar Yangmai13 was more adaptable to the pesticides.5. The safety evaluation of pesticide residue in wheatTwo wheat (Triticum aestivum L.) cultivars, a weak-gluten cultivar Yangmai13 and a strong-gluten cultivar Yannong19, were respectively sprayed with four widely-used pesticides, avermectin, imidacloprid, chlorpyrifos and dimethoate, with 1, 3 and 6 times of recommended dosage of each pesticide at the end of anthesis stage. The residue of pesticides remained in different parts of wheat plants at maturing stage and in soil were measured to evaluate the effects of these pesticides on the safety of wheat producing system. Residue was not detected in the tested parts of wheat plant when spraying different dosage of avermectin, while tiny residue was found in bran and glumes when spraying imidacloprid with different dosage, and spraying chlorpyrifos and dimethoate with recommended dosage. The remains of pesticides in soil and all tested parts of wheat plants (except flour) were detected when excess dosage of chlorpyrifos and dimethoate were applied, and these remains exceeded the level of national standard when 6 times of recommended dosage of dimethoate was applied. Chlorpyrifos and dimethoate remained mainly in bran and glumes, and a little in soil. There existed dosage effects of pesticide remained in soil and different part of wheat. Under the same dosage, the remains of pesticide were detected more in the soil and different parts of Yannong19 than those in Yangmai13. It is recommended that avermectin and imidacloprid should be used in wheat producing system for pollution-free and special-purpose, the application of chlorpyrifos should be prudent, and the application of dimethoate should be avoided.