| Watermelon(Citrullus lanatus)is extremely sensitive to low temperature,is a typical thermophilic and heat resistant plant,facilities in northern China anti-season of watermelon,chilling injury occurs frequently,it reduces the watermelon production also influenced the benefits of fruit farmer,the application of grafting technology makes this problem greatly improved,the screening of low temperature resistant rootstocks and low temperature resistant grafting combinations is the key to improve the low temperature tolerance of grafted watermelon seedlings,therefore,it is of great significance to screen the cold-resistant rootstocks and cold-resistant grafting combinations and explore the physiological basis of tolerance in grafted watermelon seedlings.In this experiment,27 watermelon rootstocks were used as materials,the low temperature tolerance of watermelon rootstocks in germination stage was evaluated,establishing a low temperature tolerance evaluation system for watermelon rootstocks and screening rootstocks with different tolerance in germination stage,then the screened rootstocks were used as the materials,own-rooted seedlings were used as the control,the physiological response of grafted rootstocks with different tolerance to low temperature stress was studied,and the most low temperature resistant grafting combination was screened,finally,the screened grafting combination was used as the material,own-rooted seedlings were used as the control,exploring the physiological mechanism of abscisic acid(ABA)in improving the tolerance of watermelon seedlings in grafting.The specific results were as follows:1.28? was used as the control,the rootstock seeds were treated at 15? for 10 d.Results showed that low temperature could delay the start of seeds germination time and reduce different watermelon root stock seeds germination rate,germination potential,germination index,radicle length and vigor index,in addition,the low temperature tolerance of different watermelon rootstock seeds was significantly different,pumpkin rootstock seeds had the highest tolerance,followed by gourd rootstock seeds,watermelon rootstock seeds had the weakest tolerance;The principal component analysis,cluster analysis and stepwise regression analysis were used to evaluate the low temperature tolerance of 27 watermelon rootstocks at germination stage,a low temperature tolerance evaluation system for watermelon rootstock seeds was established,four rootstocks with great differences in low temperature resistance at germination stage were screened out,the strong low temperature resistant varieties were LFCX and JXZ9,the low temperature sensitive varieties were JXZ1 and ZS,among them,LFCX,JXZ9 and ZS were pumpkin rootstocks,JXZ1 was gourd rootstock.2.The watermelon variety 'JX2' was used as scion,LFCX,JXZ9,JXZ1 and ZS with greatly different resistance in germination stage were screened as rootstocks,four grafting combinations were obtained after grafted,the own-rooted seedling 'JX2' was used as the control,it was cultured at 28?/18?(day/night)until the three-true-leaf stage,the seedlings were respectively moved to an artificial climate chamber at 15?/6? and 28?/18? for 7 d,then they were recovered for 3 d at 28?/18?,the physiological and biochemical indexes such as relative conductivity,proline(Pro),malondialdehyde(MDA),soluble sugar(SS),soluble protein(SP),photosynthetic parameters and chlorophyll fluorescence parameters were sampled and measured at 0,1,3,5,7 and 10 d after treatment(Growth indexes such as plant height,stem thickness,overground dry fresh weight,underground dry fresh weight and root morphology were measured on 7 d after treatment).The results showed that under low temperature stress,the aboveground and underground growth of each treatment were inhibited,the permeability of cytoplasm membrane,the degree of membrane lipid peroxidation and the content of osmotic regulatory substances were increased,and the photosynthesis were decreased,however,the degree of low temperature stress affected the grafted seedlings less than the own-rooted seedlings,among them,the grafting seedlings of pumpkin rootstock were the least affected by the low temperature stress,the grafting seedlings of gourd rootstock were the second,the own-rooted seedlings were the largest,and the LFCX grafting combination of pumpkin rootstock had the strongest resistance to low temperature.3.The LFCX grafting combination was used as treatment,the own-rooted seedling 'JX2' was used as the control,low temperature treatment was conducted at 10? for 72 h,5 m M of ABA biosynthesis inhibitor sodium tungstate solution was sprayed 1 day before low temperature stess,the relative conductivity,MDA,Pro and ABA contents in leaves were measured at 0,6,12,24,48 and 72 h after treatment,the gene expression in ABA synthesis and signal transduction pathays at critical time points was measured.The results showed that the growth of each treatment was obviously inhibited during the low temperature stress,and the relative conductivity and MDA content of each treatment showed an increasing trend,the unsprayed sodium tungstate grafted seedlings increase the least;The Pro content of other treatments also showed an increasing trend during low temperature stress except the own-rooted seedlings sprayed with sodium tungstate,grafted seedlings without sodium tungstate showed the highest increase;The ABA content in each treatment showed an increasing trend during the low temperature stress,and the ABA content and gene expression in the synthesis and signal transduction pathays of the unsprayed tungstate grafted seedlings were always higher than other treatments,it was suggested that grafting under low temperature stress may enhance ABA content in leaves by inducing the expression of ABA synthesis genes Cla009779,Cla005404,Cla019578 and positive regulatory genes Cla008802,Cla006604,Cla018017,Cla004235,Cla008760,Cla020180,Cla015990,Cla003005,Cla020167 in signal transduction pathays,in the last,the low temperature resistance of watermelon seedlings was improved. |
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