Preliminary Analysis Of The Phenotype And QTL Of Maize Lodging Resistance Traits

Crop lodging tends to be associated with environmental factors such as heavy rains coinciding with wind or management factors such as poor plant distribution or high densities.The inability for a plant to stand upright can drasticall reduce harvestable yield especially for maize.Maize lodging resistance has become the most critical restriction for the dramatic increase of yield and mechanical harvesting in maize during recent decades.Maize lodging exhibited to be the complex trait and was controlled by multiple genes and it is not enough for phenotypic selection based on one trait and researches should combine multiple traits for the further genetic analysis.In this study,we used the lodging maize inbreds and lodging resistance inbreds as the materials,subsequently,the assessment of the phenotypic characteristics was implemented by measuring the stem rind penetrometer resistance and the composition,as well as by observing the stem anatomy structure using the britht-field microscopy and the scanning electron microscopy.We constructed the lodging genetic segregating population for the genetic mechanisim analysis using the molecular biology methods.Furthermore,we expected to identify quantitative trait locis(QTLs)of maize lodging and their interactions with environments and other gene,which would provide important information for characterizing and cloning these QTLs.The main results of this study were as follows:1.By the phenotypic observation of maize inbred lines in the field,we selected 8 lodging maize inbreds,3 lodging resistance inbreds,and 1 brittle inbreds as materials,and the lodging materials displayed disable to stand upright while the brittle one showed easy to break down when came across heavy rains coinciding with wind.2.Through the measurement of the stem mechanical strength of rind penetrometer resistance for the materials,the result showed that the lodging inbreds exhibited the low mechanical strength than the lodging resisrance inbreds.3.The third internodes upground from age-matched plants were used for fresh hand-cut section to observe the anatomy structure.The sections were stained with phloroglucinol and analyzed under a light microscope.The anatomy analysis revealed that the epidermis and tissues around vascular bundles were stained red with phloroglucinol in the lodging resisrance inbreds,thereby demonstrating lignification of these tissues.However,these tissues were stained only weakly in the lodging inbreds.4.For the anatomical analysis of sclerenchyma cells and cell wall thickness,we utilized the scanning electron microscopy for the phenotypic characterization.The phenotypic observation indicated that the wall thickness of sclerenchyma cells underlying the epidermis and surrounding the vascular bundles was reduced in lodging inbreds compared with the wild type.5.The stem composition was determined by HPLC,UV,and burning methods.The proportion of lignin is slightly lower in lodging materials,but the cellulose and Hemicellulose content displayed no difference between the lodging and lodging resistance inbreds.The proportion of cellulose was heavily reduced in the brittle inbred,however the hemicellulose content was greater than that in wild type.So the cellulose and lignin content in the stem was related to the lodging trait,we could select the lignin content in the stem to assess the maize lodging trait.6.We utilized the loding inbred 20790 and lodging resisrance inbred LH277 to contract F2 populations.We executed the phenotypic and genotypic analysis by using the SSR markers,Depending on the Map QTL software,we identified 25 QTLs for maize lodging,which located on chromosomes 1,2,4,5,7 and 9.The phenotypic variance explained(PVE)by the QTL ranged from 5.5 to 52.5%.To sum up,our results suggested that the lodging materials exhibited the low mechanical strength,the low lignin content and the low thickness of cell wall in the stem,which closely related to the stem mechanical strength,stem anatomy structure,and stem lignin content that could be combined to assess the maize lodging trait.Maize lodging was controlled by multiple genes licos distributed on the whole genome.It was different to the brittle trait which was controlled by one gene and difficult to identify the main QTL because of the complex genetic mechanism.This study would be the most informative for cloning QTLs in maize lodging resistance breeding and the collection of SSRs was a valuable resource for maize genomic research and improvement.