Studies On Absorption And Distribution Of Zinc And Iron In Maize And QTL Mapping Of Related Traits

Zinc?Zn?,iron?Fe?,copper?Cu?and manganese?Mn?are essential micronutrients for plant growth and development.Maize?Zea mays L.?is a sensitive crop for lack of zinc,iron and other elements.About one-third of the calcareous soil in the world show insufficient supply of micronutrients such as zinc and iron,most maizeis planted in calcareous soil in northern China.Therefore,improving the absorption and utilization efficiency of Zn,Fe and other micronutrients in maize itself can increase maize yield effectively,which is also the most economical and sustainable measure to guaranteencrop security.In this study,two inbred lines with significant differences in Zn and Fe concentrations in maize grains and their combinations F₁ wereused as test materials todetermine the concentrations of zinc and iron in different leaves?or stems?at silking stage and mature stage.Also,analysis and comparison of characteristics of absorption and distribution of zinc and iron between parental generations were conducted.Next the recombinant inbred line?RIL?which derived from a cross of 178 and P53 was selectedas the test material.Linkage mapping analysis of the concentrations of Zn,Fe,Cu and Mnwas applied for these RILs on different parts?leaf,stem and grain?and from different periods?silking and mature stage?via SNP molecular biomarkers under conditions of Zn fertilization and non-Zn fertilization in 2017 and 2018,respectively.The main effect sites were exploitedin order to provide theoretical basis for breeding the varieties with high utilization efficiency of micronutrients such as zinc and iron.The main findings were as follows:1 The concentrations of Zn and Fe in leaves and stems fromdifferent ear positions of hybrids werebetween those of their parents,and tended to the parent with high concentration of zinc-iron in grains.It can also be found that the accumulation of Zn and Fe in leaves and stems of different ear positions of hybrids showed obvious heterosis,which was significantly higher than that of their parents.The concentrations of Zn and Fe in leaves and stems of parents and hybrids increased to some extent from silking stage to mature stage.The concentration of zinc in hybrid grain tended to be higher than that of female parent,and the amount of accumulation showed heterosis,whereasthe concentration of iron in hybrid grain was between the parents,and there is tendency of the accumulation amount to the female parent can bediscovered.2 The concentrations and accumulation of Zn,Fe,Cu,Mn in leaves and stems of maize with various genotypes were different against to environmental condictions,showing continuous variation.The concentrations and accumulation of Zn,Fe,Cu,Mn in the mature stage were higher than those in the silking stage,except for the Mn concentrations and accumulation in the stem.The absorption capacity of Zn,Fe,Cu,Mn in root system remained strong after silking,and the absorbed Zn,Fe,Cu and Mn in leaves and stems werehigher than thosein grains.Zinc concentration and accumulation in stem were higher than those in leaves,while the concentrations of iron and manganese in stem were lower than those in leaves,but there was no significant difference in copper concentration and accumulation in leaves and stems.There was a significant correlation relationship among Zn,Fe,Cu and Mn concentration and accumulation in leaves,stems and grains.Same strong correlation property between the concentration of these elements and their correspondedaccumulationcan be observed.3 The linkage mapping results showed that a total of 168 QTL loci were detected for Zn,Fe,Cu and Mn concentration and accumulation in leaves,among which there were 5 co-loci and 10 closely linked loci.The physical interval variation range of single QTL was 0.57¹1.81 Mb,with an average of 5.86 Mb.The phenotypic contribution rate explained by single QTL ranged from 0.26 % to 40.16 %,with an average of 11.30 %.A total of 132 QTL loci related to the concentration and accumulation of Zn,Fe,Cu,Mn in stem were detected,including 4 co-loci and 7 closely linked loci,and the physical interval variation range of single QTL was 0.60 ³2.82 Mb,with an average of 5.63 Mb.The phenotypic contribution rate explained by single QTL ranged from 0.50 % to 35.72 %,with an average of 11.49 %.80 QTL loci related to the concentration and accumulation of Zn,Fe,Cu,Mn in grains were detected,among which there were 6 co-loci and 3 closely linked loci,and the physical interval variation range of single QTL was 0.53 ¹0.67 Mb,with an average of 5.72 Mb.The phenotypic contribution rate explained by a single QTL ranged from 0.50 % to 20.01 %,with an average of 9.62 %.Stable QTL of the same trait was also detected in several different environments,among which 17 were detected in all the leaf mapping results,6 at the silking stage and 11 at the mature stage.In all the mapping results of the stem18 stable QTLs were detected,4 at silking stage and 14 at mature stage.In all the mapping results of grain,8 stable QTLs were detected.In conclusion,the concentrations and accumulation of Zn and Fe in leaves?or stems?of maize showed heterosis or middle parent heterosis,and the concentrations and accumulation of Zn,Fe,Cu,Mn in leaves and stems of different genetic types were different under varieties environments.The concentrations and accumulation of each element in mature stage were higher than those in silking stage.Zn,Fe,Cu and Mn absorbed at later stage were retained in leaves and stems higher than in grains.QTLs related to Zn,Fe,Cu,Mn concentrations and accumulation were detected under different conditions,and there were multiple tightly linked loci in these QTL.The results of this study provide a theoretical basis for breeding varieties with high efficient utilization of micronutrients such as Zn and Fe.