Effects Of Dense Planting On Photosynthetic Electron Transport In Ear Leaves Of Maize And QTL Mapping Of Related Parameters

As a high-yield grain crop in China,maize is also an important feed source for animal husbandry.Increasing planting density is one of the main ways to increase field yield of maize.Planting density determines the absorption of light and heat,which affects the plant structure,growth and development pattern,and then affects carbohydrate accumulation.Increasing planting density will cause maize plant leaves to shade each other,which will inevitably reduce leaf photosynthesis.Some studies have shown that increasing maize planting density led to a decrease of relative chlorophyll content and net photosynthetic rate of leaves and the increase of leaf area index.However,comprehensive information on the effect of planting density on linear electron transport in maize photosynthesis is still lacking.The instantaneous chlorophyll fluorescence parameter can quantitatively reflect the electron transport process in the photoreaction.Mapping QTLs for instantaneous chlorophyll fluorescence parameters and yield related traits is of great significance for high light-efficiency breeding.In this study,we measured prompt chlorophyll a fluorescence,delayed chlorophyll a fluorescence and modulated light reflectance curves at 820 nm simultaneously to study the effect of planting density on linear electron transport in maize photoreaction.Then,a recombinant inbred lines(RIL)populaiton and a chromosomal fragment substitution lines(CSSSL)population were used to map QTLs related to prompt chlorophyll a fluorescence parameters(ABS/CSo,TRo/CSo,ETo/CSo,DIo/CSo,RC/CSo,ETo/TRo,and PIcs)and yield traits(line grain number,ear rows,ear length,ear coarse,and hundred grain weight)in two field planting environments.The main findings are as follows:1、The amplitude of instantaneous chlorophyll fluorescence curve decreased with the increase of planting density.Positive J-step and G-bands appeared after standardized treatment of each stage of instantaneous chlorophyll fluorescence curve O-J-I-P.The prompt chlorophyll fluorescence parameters PIABS,RC/CSO,TRO/ABS,ETO/TRO,and REO/ETO gradually decreased with the increase of planting density,while ABS/RC and N gradually increased.With the increase of planting density,the lowest point of the 820 nm light reflection curve was gradually raised,and both the descending and ascending slopes of the curve were gradually reduced.With the increase of planting density,the I1 and I2 points of the delayed chlorophyll a fluorescence curve decreased gradually,while the fitting parameters L1 and L2 of the attenuation curve decreased.After standardization of the delayed chlorophyll a fluorescence curve D0-I1,it was found that I2/I1 increased.These results indicate that the increase of planting density decreased the activity of PSII reaction center,blocked the electron transport process from QA to QB,reduced PSI donor-side electron transport capacity and decreased the oxidation and reduction activities of PSI.The effect of high planting density on PSII was greater than PSI activity.2.A total of 186 recombinant inbred lines(RIL)were obtained by using maize inbred line YS501 and LCD-1 as the parents.A gentic map containing 2624 bins were constructed,with a total genetic distance of 2569.89 cM,a marker density of 1.02 cM,and a marker distance of 0.98 cM.QTL mapping analysis using the the RIL population revealed four stablely-expressed QTLs for prompt chlorophyll a fluorescence parameters in two environments,namely qRET2-1 related to ETO/TRO,qRAC3-1 related to ABS/CSO,qRTC3-1 related to TRO/CSO and qREC2-2 related to ETO/CSO,and 16 QTLs for yield-related traits in E1 environment.3、One hundred and fifty-three chromosome segment substitution lines(CSSLs)constructied using LCD-1 as donor parent and YS501 as receptor parent were used to map QTL for prompt chlorophyll a fluorescence parameters and yield traits.A total of 16 QTLs loci related to prompt chlorophyll a fluorescence parameters were detected in two field planting environments.Twenty-three QTL loci associated with yield traits were detected in a single field planting environment.