The Impact Of Mechanical Harvesting On Amount And Germination Of Underground Bud Bank In Ratoon Sugarcane

Mechanical harvesting is an effective way for saving costs in sugarcane production,however,very little sugarcane is mechanically harvested in China,and cane yield decline in mechanically harvested ratoon crop is one of the major restrictions affecting the popularization of mechanical harvesting.Owning to the geographical complexity in sugarcane area and relatively small farmers for sugarcane production,small-scale mechanical harvesting?SMH?could be suitable for the production status.At present,rare literature on agronomic research for SMH is available.Underground bud bank?UBB?is essential for the cane yield in ratoon crops?RCs?.The impact of harvesting treatment,cultivar and treatment by cultivar interaction?GT?on UBB and their germination/sprouting,and traits that are relative to UBB include soil compaction,stool damage,gap,tons of cane per hectare?TCH?and TCH components were studied through field experiments lasted 1 plant crop?PC?and 3 RCs.Field experiments were conducted using split-plot design,harvesting treatments,i.e.,manual harvesting?MH?and SMH were treated as main factor plots,and five sugarcane cultivars ROC22,GT32,YZ05-51,FN39 and YT93-159 were treated as subplot factor.In addition,bud response to soil compaction was studied at endogenous hormone and RNA-seq levels through simulating the stress in pot trials.1.SMH had significant adverse impact on plant height,height uniformity,millable stalks and juice purity,but no significant impact was observed for single stalk weight,sugar content and fiber content.The TCH under SMH decreased by 5.84%and 15.64%as compared with MH in first ratoon crop?FR?and second ratoon crop?SR?,respectively.With increased RCs,ratoon ability?RA?of 5 tested cultivars tended to decline regardless of harvesting difference,and obviously sharp cane yield decline in SMH was observed,the RA ranged 75.8%-101.14%and 60.16%-90.43%for MH and SMH,respectively.Judged by TCH in RCs and RA,ROC22,YZ05-51 and GT32 were much more suitable for SMH than the other two cultivars.The significant GT interaction for height uniformity in maturing stage and millable stalks suggested clonal selection trials for SMH be conducted under management by SMH.2.As compared with MH,soil compaction,stool damage and gap were significantly greater under SMH.Significant correlations between stool damage and gap were observed in SR and third ratoon crop?TR?.Extremely significant?P<0.001?correlation between gap and TCH was observed in SMH rather than MH.Highly significant?P<0.01?correlation between stool damage and TCH was observed in SR under SMH rather than MH.With increased RCs,UBB in both treatments were in contrary trends,which increased under MH,while declined under SMH;millable stalk in previous crop was significantly correlated with UBB,and the amount of UBB and their germination were significantly correlated with both number of seedlings and TCH,indicating that the number of seedlings and TCH in ratoon crop relied much more heavily on the germination of UBB under SMH.As compared with MH,bud per stool in TR,UBB in SR and TR,numbers of seedlings in April and May in three RCs,were significantly lower in SMH.For cultivar GT32,YZ05-51 and ROC22,there was no significant difference between treatments for the number of seedlings in May.Even UBB in RCs was 7 to 15 times the number of bud used for establishing the PC,the increased gap made uneven distribution of UBB for RCs,therefore,cultivation practices allow input of UBB for gap may relief the ratoon cane decline under SMH;the existing of significant GT interaction for stool damage,gap,number of seedlings in April suggested the clonal selection trials aiming at developing cultivar for SMH be conducted under management by SMH.3.The cellulose contents in bottom stalk were significantly greater in SMH,for hemicellulose content and lignin content,significant treatment difference were observed merely at SR,the hemicellulose content under MH was significantly greater than SMH,and the lignin content was significantly lower in MH;Obvious difference between section of stalk was observed,cellulose and lignin contents in bottom stalk were negatively correlated with stool damage,and hemicellulose content was positively correlated with stool damage.Among all the correlations,the highest negative correlations?r=0.939?were observed between lignin contents and stool damage,and the correlations were significantly in both RCs.The results suggested that lignin contents in bottom stalk could be a potential indirect selection parameter for stool damage under SMH.4.Significant differences between treatment,cultivar and GT for ZR,IAA,ABA,GA₃,IAA/ZR and AG₃/ABA were observed,so the regulation of endogenous hormones in UBB differed in the tested cultivars when they encountered soil compaction stress.Obvious differences for correlations in the contents of endogenous hormones between treatments were observed.Significant correlations between ZR and ABA,IAA and IAA/ZR,ABA and IAA/ZR,IAA/ZR and GA₃/ABA were found merely under SMH rather than MH.Moreover,the IAA and ABA contents,IAA/ZR in UBB were significantly correlated?negatively?to the germination of UBB,IAA and IAA/ZR were significantly correlated?negatively?to the sprouting in May under SMH,however,these correlations were not significant under MH.Among 5 sugarcane cultivars,the response of endogenous hormones in YZ05-51 was much greater.Significant positive correlation was observed between contents of ZR and ABA,and significant negative correlation was observed between ZR and GA₃/ABA.Among all the endogenous hormones and two ratios,the contents of ZR and ABA,and GA₃/ABA significant regulated bud length,bud width,and bud length during short soil compaction stress?2 d-6 d?in sugarcane cultivar YZ05-51.Cultivation practices that removal of soil compaction on UBB immediately may relief the adverse impact of SMH on RCs.5.The buds of sugarcane cultivar YZ05-51 were treated with 3 levels of soil compaction,9 samples consisted of 3 from each level of treatment were collected on the 5^thday after planting,and were used for RNA-seq.After removal of the invalid data,a total of 96.63 Gb data were obtained.After analysis,we identified 7 differentially expressed genes profiles.With the increase of soil compaction,4 of them were of upward trend,while 2 of them were of downward trend.The profiles containing upward trend genes were named as Cluster 1,and the profiles containing downward trend genes were named as Cluster 2.There were 9,574 and5,141 differential expression unigenes in Cluster 1 and Cluster 2,respectively.To understand the gene expression interactions between Cluster 1 and Cluster 2,the genes significantly enriched in the pathways metabolism and membrane trafficking were further analyzed,and we found 36 genes of Cluster 1 enriched in metabolic pathway and 11 genes of Cluster 2enriched in endocytosis.They could be the candidate genes for further research on germination under soil compaction in sugarcane.