A comprehensive evaluation of the quality of two-year-old sweet cherry seedlings

Abstract：【Objective】The purpose of this study was to determine the key quality indexes of two-yearold sweet cherry seedlings with different scion-rootstock combinations, including 8 morphological indexes and 18 physiological indexes, in order to provide the references for quality classification sweet cherry seedlings.【Methods】Four rootstock-scion combinations were used as the materials in this research. The scion varieties were'Meizao'grafted on rootstocks of'Daqingye''Yingzhenwang''Gisela 6'and'Colt'. The 26 morphological and physiological indexes of the sweet cherry seedlings were analyzed and compared. The survival rate and growth of seedlings at the early stage of planting were also recorded. According to these data, we evaluated the comprehensive quality of the seedlings using principal components analysis.【Results】There were some differences in seedling height, seedling diameter and rootstock length. The seedling height and seedling diameter of'Gisela 6'and'Daqingye'were more than 180 cm and 1.85 cm, respectively. The rootstock length of'Daqingye'and'Yingzhenwang'were 11.55-15.91 cm;'Gisela 6'rootstock length was 9.00-10.20 cm;'Colt'7.36-8.19 cm. There were some differences in root length, root surface area, average diameter, root volume and root tip number. The root length of'Daqingye'grade I was 1 067.2 cm;'Gisela 6'grade I root surface area, root volume and root tip number were the largest, being 682.2 cm2, 47.6 cm3 and 4 141.7, respectively. The average root diameter of'Yingzhenwang'grade Ⅰ was 2.9 mm. There were some differenc-es in stem water content and root water content. Water content in the stem of'Daqingye', 'Yingzhenwang'and'Colt'were higher than in the root. The stem water content of the same rootstock was in a descending order of grade Ⅰ> grade Ⅱ> grade Ⅲ. There was no significant difference in root water content among different grades. The difference in the content of nitrogen in the stem and the root of different grades was not significant, but stem had a significantly lower nitrogen content than the root. The phosphorus content in the stem and root of the four rootstocks decreased significantly from grade I to grade III. The content of phosphorus in the stem was significantly lower than in the root. At 120 days of storage, the root activity of the four rootstocks, grade Ⅰ, Ⅱ and Ⅲ significantly reduced compared to day 0. Among them, the root activity of the'Gisela 6'grade I seedlings was 158.6 μg·g-1·h-1 and the highest, and it maintained the highest at 120 days of storage. After 120 days of storage, the root activity of'Yingzhenwang'seedlings decreased greatly, and the decrease in grade Ⅰ, Ⅱ and Ⅲ seedlings was all above 70%. Soluble sugar content in the stem was higher than that of the root, while the starch content in the root was higher than in the stem. Soluble sugar content in the stem and the starch content in the stem and root followed a decreasing order of grade Ⅰ >grade Ⅱ >grade Ⅲ within the same rootstock. Principal component analysis was applied to evaluate the comprehensive quality of the 12 grades of cherry seedlings. The contribution rates of the first 5 principal components were 42.583%, 17.487%, 15.362%, 8.599% and 6.113%, respectively, and the cumulative contribution rate reached 90.145%.PRIN 1 was mainly determined by 7 variables, including root activity, root volume, root surface area, root tip number, seedling diameter, root length and seedling height. The load values were 0.965, 0.924, 0.907, 0.894, 0.849, 0.817 and 0.816, respectively, and all of them were positively correlated with seedlings quality. Factor analysis, principal component analysis and regression method can reflect the quality of different grades of the cherry seedlings from many aspects. The quality rank order of the cherry seedlings was'Gisela 6'grade Ⅰ, 'Daqingye'grade Ⅰ, 'Yingzhenwang'grade Ⅰ, 'Gisela 6'gradeⅡ, 'Colt'grade Ⅰ, 'Yingzhenwang'grade Ⅱ, 'Daqingye'grade Ⅱ, 'Gisela 6'grade Ⅲ, 'Yingzhenwang'grade Ⅲ, 'Daqingye'grade Ⅲ, 'Colt'grade Ⅱ, and'Colt'grade Ⅲ. 30 days after the seedlings were planted, the survival rate of grade Ⅰ seedlings was above 92%, of which the highest survival rate of 100% was found in'Gisela 6'grade Ⅰ seedlings, while the survival rate of grade Ⅲ seedlings was below 90%, of which the lowest survival rate of'Yingzhenwang'seedlings was 82%. At 210 days after seedlings were planted, there were great differences in the number, length and diameter of the branches. The 3 indexes of the four rootstocks were the best in grade I seedlings. Compared with gradeⅢ seedlings, the number, length and diameter branches in grade Ⅰ seedlings of'Gisela 6'increased by 150%, 50.9% and 166.1% respectively. The number of branched in grade Ⅰ seedlings was higher than that of grade Ⅱ and grade Ⅲ seedlings. The growth of grade Ⅰ and grade Ⅱ seedlings was significantly higher than that of grade Ⅲ【Conclusion】The key indexes of the quality of the two-year-old sweet cherry seedlings included root activity, root volume, root surface area, root tip number, seedling diameter, root length and seedling height. The growth and survival rate of sweet cherry seedlings was closely related to the quality of the seedlings in the first year.