| Melons are widely grown in China and often face problems such as crop succession barriers and soil-borne diseases over many years of cultivation.Grafting can effectively overcome crop succession barriers while enhancing disease resistance,abiotic stresses,and yield of melons.Graft healing is a key aspect of grafted seedling production,temperature is a decisive factor affecting the graft healing.In production,low temperature at night leads to slow graft healing,longer healing period and more difficult management.The mechanism of the effect of temperature on graft healing has been less investigated.Therefore,in this study,thin-skinned melon ’Mignon’ was used as scion and pumpkin variety ’Deli 2’ was used as rootstock,and grafting was carried out by the common root-breaking paste method of grafting machine to investigate the effect of different night temperatures(28℃/28℃,28℃/18℃,day/night temperature)on the healing process.The effect of different night temperatures(28℃/28℃/,28℃//18℃,day/night temperature)on the healing process was investigated,and the material changes during the grafting healing period under different night temperature conditions were analyzed,and the effect of exogenous material treatment on the grafting healing process under low night temperature conditions was initially investigated,in order to provide a theoretical basis for the establishment of efficient healing technology and technical support for the promotion and application of mechanized grafting.The main research results are as follows:1.Vascular tissue paraffin sectioning of melon grafted seedlings treated with night temperature 28°C and 18°C revealed that the period of healing tissue differentiation and vascular tissue reattachment were advanced in the night temperature 28°C treatment.The xylem was connected at 3 d after grafting and reached 94.44% at 6 d for the night temperature 28℃ treatment.In the night temperature of 18°C treatment,the bast began to connect at 4 d after grafting and reached 90.00 % at 8 d.Graft adhesion at night temperature 28°C was significantly higher than that at night temperature 18°C during 2 d-5 d after grafting.At 1 d-2 d after grafting,the growth hormone(IAA)and cytokinin(CTK)contents at the rootstock and scion joints increased more in the night temperature 28°C treatment than in the night temperature 18°C treatment,and the gibberellin(GA)content increased more only at the rootstock joints than in the night temperature 18°C treatment.The fresh weight of scion stem and leaves,dry weight of scion stem and leaves,fresh weight of rootstock roots,dry weight of rootstock roots,number of scion leaves and leaf area of scion were all significantly higher in the night temperature28℃ than in the night temperature 18℃ treatment,and the absolute growth rate of stem thickness after grafting was significantly higher in the night temperature 28℃than in the night temperature 18℃ treatment.2.Sucrose,algose,inositol,glucose,D-fructose,cottonseed sugar,maltose,tyrosine,leucine,L-asparagine,ornithine and L-citrulline contents were significantly up-regulated at the grafting interface of the scion treated with night temperature 28℃compared with that of the scion treated with night temperature 18℃.The peak sucrose,alginose and cottonseed sugar contents were all earlier in the night temperature 28°C treatment than in the night temperature 18°C treatment,and the increases in glucose,fructose,inositol tyrosine,leucine,L-asparagine,ornithine and L-citrulline contents were significantly higher than in the night temperature 18°C treatment.KEGG enrichment analysis revealed that biosynthesis of secondary metabolites(ko01110),galactose metabolism(ko00052)),starch and sucrose metabolism(ko00500),ABC transporter protein(ko02010),amino acid biosynthesis(ko01230),amyl-t RNA biosynthesis(ko00970),2-oxocarboxylic acid metabolism(ko01210),cyanogenic amino acid metabolism(ko00460),citric acid cycle(TCA cycle)(ko00020),and glyoxylate and dicarboxylic acid metabolism(ko00630)were significantly enriched.3.The xylem and phloem connectivity during grafting was observed by spraying exogenous hormones and sugars on the grafted bodies at a night temperature of 18°C.It was found that: spraying 0.5 mg/L IAA or 10 mg/L KT promoted the xylem connectivity rate of melon grafting,and spraying 0.5% glucose promoted the phloem connectivity rate of melon grafting.Compared with the CK treatment,the xylem connectivity rate increased by 236% at 5 d after grafting with 0.5 mg/L IAA.The xylem connectivity rate increased by 11.54% and 56.52% for 10 mg/L KT at 6 d after grafting.The rate of phloem connectivity and xylem connectivity increased by94.12% and 117.24%,respectively,at 4 d after grafting with 0.5% glucose.The ratio of 0.5 mg/L IAA and 10 mg/L KT was 1:1,which significantly promoted the grafting and healing phloem and xylem connectivity of melon,and the phloem connectivity rate and xylem connectivity rate increased by 42.99% and 246.5%,respectively,5days after grafting.The proportions of 0.5 mg/L IAA,10 mg/L KT and 0.5% glucose were 1:1:1,which significantly promoted the grafting and healing phloem and xylem connectivity of melon,and the phloem connectivity rate and xylem connectivity rate increased by 55.77% and 173.00%,respectively,5 days after grafting. |
