Effect Of Foliar ZnSO₄ Application Combined With Commonly Used Pesticides In The Production Of Wheat On Zn-enrichment Of Grain And Its Possible Mechanism

Dietarydeficiency of Znhas attracted worldwide attention.Wheat is one of the three major cereal food crops,and the study about Zn biofortification of its grain is important to ameliorate dietary deficiency of Zn.In the potentially Zn-deficient calcareoussoilin northern China,foliar Zn application proposed is a effectively and rapidly agronomic methodto improvethe concentration and bioavailability of Znin wheat grain.However,the limitedly usingof foliar Zn in practice is due toits no advantage reportedin increasing yield while spraying alone in this area,and the extra investment of labor and time.At present,the foliar ZnSO₄ application combined with pesticides has become the latest attempt to achieve Zn biofortification of wheat grain.Therefore,it’s necessary to explore the effect of foliar ZnSO₄application combined with pesticides on the Zn biofortification of wheat grains and its mechanisms.This study investigated the formation of Zn-pesticide complexes after mixing the ZnSO₄·7H₂O with triadimefon or imidacloprid in distilled water,and revealed the impact mechanism of foliar ZnSO₄ application combined with triadimefon or imidacloprid on Zn-enrichedofwheat grain by greenhouse experiment.Additionally,field experiment was conducted to investigate the foliar ZnSO₄ application combined with corresponding pesticides in different stages affect on the Zn quality in wholegrain and its milling fractions.The main results were obtained as below:（1）The Zn²⁺concentration and the formation of Zn-pesticide complexes after mixing the0,0.2%,0.4%and 0.6%ZnSO₄·7H₂O with triadimefon and imidacloprid respectively in waterwere explored through a laboratory analysis test.The results showed thatthe recovery of Zn in the filtrate was increased with the increase of ZnSO₄·7H₂O concentration,and the weight their filter residue was reduced,regardless of mixing ZnSO₄·7H₂O with triadimefon or imidacloprid.For the treatments of ZnSO₄·7H₂O and triadimefon mixed in water,the infrared spectrogram of their filter residue were similar to the triadimefon.But the infrared spectrogram of their filtrate showed 2 strong peaks at 1156 cm^-1 and 1106 cm^-1,and significantly reduced of the main absorption peaks at 1725 cm^-1（C=O）,1583 cm^-1 and 1489cm^-1（benzene ring）.Compared with imidacloprid,the infrared spectrogram of filter residue and filtrate in the treatments of ZnSO₄·7H₂O and imidacloprid mixed in watershowed that the main absorption peaks at 1200¹600 cm^-1 were obviously disappeared.Thus,mixing ZnSO₄·7H₂O with triadimefon or imidacloprid could not affect the Zn²⁺concentration in filtrate,and could increase the solubility of the pesticides.The water-soluble Zn-pesticide complexes were formed after mixing ZnSO₄·7H₂O with triadimefon in water.And after mixing ZnSO₄·7H₂O with imidacloprid in water,the water-soluble and water-insoluble Zn-pesticide complexes were formed.（2）A greenhouse pot experimentwas conducted to evaluatethe influences of foliar ZnSO₄（0.4%ZnSO₄·7H₂O）application combined withtriadimefon（Tr）or imidacloprid（Im）on Zn translocation and distribution in wheat.The results showed that foliar ZnSO₄ application alone or combined with pesticides（Tr or Im）significantly increased the dry weight and the total Zn concentration in grain compared with control.Compared with foliar ZnSO₄application alone,there was no significant effect of foliar ZnSO₄ application combined with pesticides on the total Zn concentration in wheat grain,but the dry weight of grain increased by more than 17%,thus the Zn content in grain were increased significantly.Meanwhile,the foliar ZnSO₄ application combined withpesticides increased the total Zn concentration and content in vegetative organs of wheat,and the increment was higher in the leaves and glumes than in the stems.In addition,the post-anthesis shoot Zn uptake and its mobilization to grain in the foliar ZnSO₄ application combined withpesticidestreatments were higher than foliar ZnSO₄ application alone.Furthermore,the soluble Zn proportion to total Znin foliar Zn application alone treatment was 60.8%,and the solubleZn proportion to total Zninthe foliar ZnSO₄ application combined withpesticides treatmentswere surpassed 70%.Accordingly,the foliar ZnSO₄ application combined withtriadimefon or imidacloprid not only did not show any adverse impact on the grain Zn response to foliar ZnSO₄ application,but also can enhance the Zn transfer to grain and thereby grain Zn accumulation by increasing Zn uptake and availability in vegetative tissues.（3）Field experiment was conducted to investigate the effect of foliar ZnSO₄（0.4%ZnSO₄·7H₂O）application combined with3 groups of pesticides in flowering/filling stage（thiophanate/imidacloprid,beta-cypermethrin/triadimefonand pyridaben/carbendazim）on Zn concentration and bioavailabilityin both wholegrain and its milling fractions.The results showed the foliar ZnSO₄ applied alone or combined with pesticides in flowering/filling stage greatly increased the Zn concentration and bioavailability in wholegrain,flour and bran.Compared with foliar ZnSO₄ application alone,foliar ZnSO₄ application combined withpesticides in flowering/filling stageincreased the Zn concentration in bran,but the Zn concentration in whole grain and flour and the Zn distribution ratio in flour did not increase significantly.The phytate concentration in flour and PA/Zn significantly decreased,whereas estimated Zn bioavailability increased in whole grain and flour in the foliar ZnSO₄ application combined with beta-cypermethrin/triadimefontreatment.The estimated Zn bioavailability increasedinflourinthefoliarZnSO₄applicationcombinedwith pyridaben/carbendazimtreatment,but there was no effect of foliar ZnSO₄ application combined with thiophanate/imidaclopridon Zn bioavailability in whole grain and its fractions.Therefore,the foliar ZnSO₄ application combined withpesticides did not show any adverse impact on Zn nutritional quality in wheat whole grain and flour Zn,relative to foliar ZnSO₄application,andcould improve Zn bioavailability,especially in foliar ZnSO₄ application combined with beta-cypermethrin/triadimefon.In summary,in terms of grain Zn biofortification,foliar ZnSO₄ application combined withpesticides would not affect the Zn-enrichment effect of wheat grain and flour in the potentially Zn-deficient calcareous soil in northern China,and it also could improve the Zn bioavailability.Therefore,foliar ZnSO₄ application combined withpesticides can be used as a simply and effectively agronomic measure to achieve Zn biofortification of wheat grain.