| Saccharum officinarum L.is the largest sugar crop in China and the world,and one of the important commercial crops in southern China.However,the influence of sugarcane lodging is more and more serious with increasing cane yield.After lodging,the plant growth and sugar accumulation in stalk was seriously affected,resulting in considerable losses in cane and sugar yield,and difficulty in machine operation in the field.Using the combination progeny of sugarcane crosses with the parents from home and abroad and commercial sugarcane varieties with different lodging types as materials,this research evaluated the lodging resistance of the entries,analyzed the relationship between lodging and several biochemical parameters and microstructure,and investigated the molecular mechanism of the lodging resistance by combining with transcriptomics,in order to provide the basis for excavating the lodging resistance-related genes and breeding elite lodging resistant sugarcane varieties.The main results were as follows.1.The lodging grades and lodging resistance index of sugarcane were established.According to the lodging degree,sugarcane lodging could be divided into 3 grades that were,grade 1(complete lodging),grade 2(half lodging)and grade 3(erect).The established lodging resistance index was verified by using different sugarcane varieties(clones)with different lodging resistance.The experiments in plant and ratoon crops found the changes in lodging resistance index had the same trend,which reflecting the real lodging occurrence in the field.The erect type GT42 had a lodging resistance index of 3.0,while that was less than 1.2 complete for the lodging type GF98-296,and the valus between them for the half lodging ROC22 and GT10-2003.In both plant and ratoon crops,the height of gravity center was positively and significantly in GF98-298 than GT10-2003 and GT42 but not ROC22.The ratio of basal stem diameter to mid stem diameter in GT42 was over 1,higher than the other varieties.GF98-296 showed the lowest bending height in both plant and ratoon experients while GT42 had no bending height as it is an erect variety.GF98-296 showed the highest puncture strength.For different lodging types,the complete lodging type showed significantly higher plant height and height of gravity center but lower bending height than the other three varieties.The ratio of basal stem diameter to mid stem diameter was higher than 1 for the erect type.The lodging resistance was significantly correlated with ratio of basal stem diameter to mid stem diameter and brix.The ratio of basal stem diameter to mid stem diameter was significantly correlated with brix.The plant height was significantly correlated with single stalk weight and height of center of gravity.When the ratio of basal stem diameter to mid stem diameter was more than 1,it belonged to "tower" type,was good for lodging resistance.When the ratio was less than 1,it was easy to get lodged as it has a heavier “head” and lighter “foot”.2.The established lodging grade and lodging resistance index of sugarcane were verified by using 2030 seedlings of 30 combinations to estimate the lodging grade,basal stem diameter and mid stem diameter,and these data were good to prove the sugarcane lodging resistance ability.It was found that the brix was decreased after lodging occurred in sugarcane,the ratio of basal stem diameter to mid stem diameter was positively significantly correlated with the lodging resistance.With the lodging resistance index,the 30 combinations used in this study were divided into 3 categories,16 were found in the erect group,13 in the half lodging group,and 2 in the complete lodging group.3.It was found that the contents of lignin and hemicellulose were higher in the stem of erect plants than the lodged ones.Among them,the contents of lignin,protopectin and Si showed the highest in GT42,and the lowest in GF98-296.The content of Soluble showed the highest in GT10-2003.The nitrogen content was significantly higher in GF98-296 than other varieties.The nitrogen contents in the lodging ROC22 and the lodging GT10-2003 were significantly higher than those in their erect status.GT42 was always in the erect status and it had the highest silicon content,while GF98-296 had the lowest silicon content.There was a very significant positive correlation between calcium content and potassium content,and the crop was prone to lodging when the calcium content was high.There was a very significant negative correlation between nitrogen content and hemicellulose content,namely,sugarcane plants with higher nitrogen content would have lower hemicellulose content in the stem,which was prone to lodging.Microstructure observation found that the epidermis in stem of GT42 showed the highest degree of lignification and embolization in the tissue.In the visual field,the number of vascular bundles in stem were obviously more in GT42 than in GF98-296,the vessels and fiber lignification in vascular bundle were more developed,and the ratio of length to width of cortical cells were larger,which reflected a higher mechanical strength in the whole stem of GT42 as compared with GF98-296.In addition,the tear of the peripheral cells in GT42 stem during the sectioning process also confirmed the high degree of lignification of fiber cells and duct cells.However,the epidermal cells in stem of GF98-296 showed many layers with neat arrangement and high epidermal hardness,which is consistent with of its strong puncture strength but prone to lodging because lacking sufficient mechanical strength inside the stem.4.Among the four sugarcane varieties tested,the cellulose content in root was the highest in GT42.The hemicellulose content in root was the highest in ROC22.The lignin content in root of GT42 was higher than GT10-2003.The root activity of the four tested varieties was negatively correlated with the contents of cellulose and hemicellulose,and the hemicellulose content was positively correlated with cellulose content.During growth,the cellulose and hemicellulose content in root of different varieties showed a falling and then a rising from July to August,and showed a decline in September.In contrast,the change of lignin content in root was more varied in different varieties,and GT42 showed a decline first and then increase,GF98-296 showed an increase first and then decline,ROC22 showed a decline trend all the time,and GT10-2003 showed the same trend as cellulose.The root activity in different varieties were basically consistent,namely,which showed decline first,then increase from August,and decline again from September.The variety GF98-296 showed higher root activity than the other three varieties.Morphological observation found that GT42 had the largest root amount,followed by GF98-296 and ROC22,and GT10-2003 had the smallest root amount.In the root system of G42,there were many new roots,which were thick,hard and high tough.The roots of GT98-296 and GT10-2003 were thin,with poor toughness and easy to be broken.The data of the root phenotypic characteristic of the two lodging sugarcane types were consistent with the biochemical index analysis.The xylem vessel in root was more developed in GT42 than GF98-296,which was in consistent with its high lignin content in root.In addition,the number of epidermal cell layers and cortical cells in the root of GT42 were neatly arranged,and the cell walls of cortical and pericycle parenchymal cells were thicker,which would have more stability of roots as compared with GF98-296.5.For the first time,transcriptome analysis were done by using the sugarcane varieties(strains)with different lodging states,and the average output of raw reads per sample was 93.2 Mb.After filtering,the average clean reads per sample was 88.6 Mb,and the average amount of data were 12.9 Gb(giga pair bases).A total of 232.1 Gb data were obtained,and Q20 and Q30 reads accounted for 97.6% and 92.9%,respectively.Meanwhile,a total of 706533 transcripts were obtained with a total length of 511.2 M and an average length of 723.48 BP and N50 1055 bp.According to the KEGG results,phenylpropane-like compounds and hormone signal transmission were simultaneously concentrated in three sets of differential transcripts and the difference of phenylpropane-like compounds and plant hormone transmission may be the common characteristics of all lodging properties.Zeatin may be related to the semi-lodging.MAPK and flavonoid-related metabolism,which might be related to lodging.According to GO's cellular component,the cell components concentrated differentially and jointly in three groups including cell walls,which should be the key components related to lodging.Compared with the characteristic of erection,some of the transcription factors of MYB family were upregulated while some others downregulated simultaneously in the lodging type.MYB transcription factors play an important role in the occurrence of lodging.From the metabolic level analysis,the upright character was related to lignin,cellulose and hemicellulose,and the contents of which needed to reach a certain level.The content of lignin in the plants of upright character was rather high,which played a decisive role in stem support.Therefore,the content of lignin must be analyzed before any lodging state could be analyzed.According to the enrichment results,the lodging and cross character was due to the insufficient synthesis of lignin,and the occurrence of the semi-lodging character was due to the stable lignin content,but the content of cellulose and hemicellulose did not reach the appropriate level.Lignin,cellulose and hemicellulose had their own equilibrium proportions in plants.Under the premise of stable lignin,the changes of proportion of cellulose and hemicellulose synthesis were the main reason for the occurrence of various lodging characters.Through the cluster analysis of the expressed genes,23 genes related to lignin synthesis and 28 genes related to cellulose synthesis were finally obtained.6.According to the data analysis,GT42 had high lignin content,a large number of vascular bundles with obvious lignification,a high mechanization degree of stem,belonging to a "tower" type.The root lignin content of GT42 was high,and the epidermal layer cells and cortical cells of the root were arranged in order.In addition,its cortical and columnar parenchyma cells had thicker cell walls,so the root was good at holding the plant.The xylem duct of its roots is well-developed,and water and minerals could be quickly transported to the above-ground part,which meaned that the whole plant had a very stable growth potential.GT42 was typical sugarcane variety resistant to lodging from the aspect of stem structure,physicochemical properties and microstructure.The stem lignin content of GF98-296 was low,and the number of vascular bundles in the stem was small,the degree of lignification was low,the mechanization degree of stem was low,and the stem also belongs to the "small foot" type.The typical representative of severe lodging as its root lignification degree was low,and its xylem duct was not strong. |
PDF Full Text Request