Influence Mechanism Of Different Rootstock Grafting On Nitrogen Efficiency Of Wax Gourd

Wax gourd（Benincasa hispida（Thunb）Cogn.）belongs to the Cucurbitaceae Wax gourd genus,an annual trailing herb,and is one of the important vagetable in our country.In production,the excessive application of nitrogen fertilizer by melon farmers is prominent,which not only affects the yield and quality,but also brings harm to the ecological environment.Improving nitrogen utilization efficiency is beneficial to solve the above problems.Grafting can improve nitrogen utilization efficiency,and proper rootstock is the key to success or failure.Therefore,it is practically significant to screen the rootstocks with high nitrogen efficiency of wax gourd and to clarify the mechanism of improving the nitrogen efficiency of wax gourd.In this study,firstly 11 kinds of rootstock materials were selected to analyze the nitrogen efficiency of grafted plants at seedling stage under normal nitrogen and low nitrogen levels,and screened out nitrogen-efficient rootstocks under different nitrogen levels.Then,using’Haizhen No.1’recommended by our research group,selecting nitrogen-efficient materials under low nitrogen levels as rootstocks and self-rooted wax gourd as a control,field verification experiments of nitrogen efficiency under two nitrogen application levels were carried out.At the same time,the transcriptome analysis of the grafted wax gourd with’Haizhen No.1’as the rootstock was carried out,to find out the mechanism by which grafting affects the nitrogen efficiency of wax gourd.Finally,the changes of morphological and physiological characteristics,dry matter accumulation and nutrient requirements of’Haizhen No.1’as the rootstock of grafted wax gourd were studied,to provide cultivation technical guidance for wax gourd production.The main findings are as follows:Firstly,with’Tiezhu 168’as the scion,11 kinds of grafted and self-rooted seedlings were hydroponically cultivated under low nitrogen(0.5 mmol·L^-1)and normal nitrogen(14.0mmol·L^-1),and determinate the plant dry matter,nitrogen content and nitrogen accumulation at seedling stage.Nitrogen efficiency of under normal nitrogen level and low nitrogen level at the seedling stage were divided into three categories by principal component analysis and cluster analysis methods.Among them:under the normal nitrogen level,’Heigan’was the high nitrogen efficiency type,’Jingxinzhen No.1’and’301’were low nitrogen efficiency types,’Haizhen No.1’,’Dongzhen No.1’,’Huangzhen No.1’,’Xuetengmu’,’Kaijia’,’Guozhen No.2’,’Jingxinzhen No.1’and’Jingxinzhen No.5’were the nitrogen intermediate-efficiency type.Under low nitrogen level,’Jingxinzhen No.1’was the nitrogen high-efficiency type,’Huangzhen No.1’and’Kaijia’were the nitrogen low-efficiency type,’Haizhen No.1’,’Dongzhen No.1’,’Xuetengmu’,’301’,’Heigan’,’Guozhen No.2’,’Jingxinzhen No.2’and’Jingxinzhen No.5’were the nitrogen intermediate-efficiency type.Secondly,through field experiments,nitrogen efficiency of self-rooted wax gourd and grafted wax gourd with’Haizhen No.1’and’Jingxinzhen No.1’as rootstocks was analyzed under 15 kg·667m^-2（N15）and 45 kg·667m^-2（N45）two nitrogen application levels.It was found that the nitrogen physiological efficiency,nitrogen use efficiency,nitrogen harvest index and nitrogen fertilizer partial productivity of self-rooted wax gourd and Haizhen 1under the N15 treatment level were significantly higher than those of Jingxinzhen No.1.There was no significant difference between the self-rooted wax gourd and the grafted wax gourd of Haizhen No.1.At the N45 level,only the nitrogen physiological efficiency of the grafted wax gourd of Jingxinzhen No.1 was significantly higher than that of the self-rooted wax gourd.This indicates that the nitrogen efficiency of Jingxinzhen No.1 grafted wax gourd is not as good as that of Haizhen No.1 grafted wax gourd under low nitrogen level.In another word,there is a difference between the nitrogen efficiency screening at the seedling stage and the field,and suggested that a two-step screening method is more suitable for nitrogen efficiency screening.There is no significant difference in yield between Jingxinzhen No.1 grafted wax gourd,so it is suggested to use’Haizhen No.1’as the material of wax gourd with high nitrogen efficiency in production.Thirdly,transcriptome analysis of the seedling leaves of Haizhen No.1 grafted wax gourd and self-rooted wax gourd under normal nitrogen and low nitrogen levels showed that,there were 1639 up-regulated and 1442 down-regulated genes in the grafted wax gourd under normal nitrogen,and 1639 up-regulated and 1442 down-regulated genes in the grafted wax gourd under low nitrogen.There were 323 up-regulated and 337 down-regulated genes;the differentially expressed genes of grafted wax gourd under normal nitrogen were more than those under low nitrogen.Differential genes are involved in multiple biological processes and signal transduction pathways.In addition,in the nitrogen metabolism pathway,the genes related to nitrite reductase and carbonic anhydrase were up-regulated;in the plant hormone signal transduction pathway,the auxin-related signal transduction pathway was significantly up-regulated,and the grafting of wax gourd significantly improve the synthesis and secretion of auxin,and promote the growth of plants.Fourthly,in production,it is recommended to use’Haizhen No.1’as the material for nitrogen high-efficiency rootstock of wax gourd,and the reduction of nitrogen fertilizer is feasible.For the reason,the growth and development characteristics of grafted winter melon with’Haizhen No.1’as rootstock were analyzed at different nitrogen application levels through field experiments.The results showed that the nutrient requirements of grafted wax gourd of the rootstock showed the rules is potassium>nitrogen>phosphorus.The demand for phosphorus was relatively more at the expansion stage of the fruit.Under different nitrogen application levels,the rootstock grafted wax gourd chlorophyll a,chlorophyll b,total chlorophyll,leaf number,vine length,and aboveground dry matter accumulation were not significantly different,indicating that the growth and development of the rootstock grafted wax gourd was not affected when the nitrogen application was reduced to 15kg·667m^-2.The dry matter mass of the stems and leaves has not decreased significantly from the early stage of flowering to the middle and late stages of fruit expansion,that is,growth center not fully transferred to fruit during reproductive growth.Therefore,it is recommended to carry out appropriate measures such as pruning,topping and topping the plant after the early flowering stage to inhibit the growth of vegetative organs at a certain extent and improve the yield of wax gourd.