Comprehensive Evaluation of Low Temperature and Salt Tolerance in Grafted and Rootstock Seedlings Combined with Yield and Quality of Grafted Tomato

Environmental stress, especially in the form of low temperatures and salinity, has becomethe main limiting factor affecting the yield and quality of tomatoes in greenhouse production in China. Grafting, as an effective and sustainable strategy for improving plant stress tolerance, is closely related to rootstock properties and scion affinity. Here, 15 commercial rootstock genotypes were collected to investigate the differences in low temperatures and salt tolerance of rootstocks and grafted tomato seedlings in parallel, as well as well as the effect of grafting on the yield and quality of tomato. The results indicated that there were differences among rootstocks, and the resistance of grafted seedlings mainly depended on the characteristics of the rootstocks. We also found that the resistance of grafted seedlings was affected by the affinity between the scion and rootstock. Genotypes 6, 7, 11, and 14 showed advantages over the other genotypes in seedling growth, based on the fresh weight of the plants, the seedling index, and the root-shoot ratio. Genotypes 2, 7, 11, and 14 had greater total root lengths and higher numbers of root tips than other genotypes. These results showed that the significant increase in growth in the grafted tomato seedlings might have been attributable to the vigorous roots of the rootstocks. Genotypes 4, 7, 11, and 13 showed advantages with respect to low temperature stress, whereas genotypes 7, 11, 12, and 13 showed advantages with respect to salt stress. The salt tolerance of grafted tomato seedlings was influenced by both scion affinity and rootstock characteristics and was decreased by grafting. The highest yields were obtained from the grafted plants of genotypes 7 and 11, whose yields were 17.2% and 14.6% higher, respectively, than those of the control group. The rootstock genotype did not affect the fruit quality parameters, such as soluble protein content, titratable acidity, and total soluble solids content, and in most cases, the lycopene and ascorbic acid contents of the fruit increased. After considering the results pertaining to the stress tolerance of rootstocks in combination with fruit yield and quality, genotypes 7 and 11 were selected as potentially suitable tomato rootstock varieties for further large-scale applications. These results provide a new perspective for the study of rootstock characteristics and an important reference for grafted tomato cultivation in greenhouse production.