Genetic diversity and comprehensive evaluation of phenotypic traits in 73 germplasm resources of cultivated strawberries grown in Hubei province

Abstract: 【Objective】The purpose of this study is to explore the genetic diversity of cultivated strawberry germplasms from China, Japan and Korea (JapKor), Europe and America (Europe) and identify excellent germplasms by comprehensively screening phenotypic traits, including morphological traits, yield, and fruit quality, which will lay the foundation for the molecular improvement and genetic mapping of important agronomic traits in cultivated strawberry.【Methods】Based on strawberry germplasm resource descriptors, 58 phenotypic traits were systematically investigated, including plant height, plant architecture, leaf traits, flower traits, runner, fruit and other related traits. Then, the coefficient of variation as well as the Shannon's diversity index (H’) were calculated for each trait to estimate genetic diversity. Next, the Pearson correlation analysis, the principal component analysis as well as the compre-hensive evaluation value D were calculated by using the SPSS, SIMCA and R software.【Results】 Among all 58 phenotypic traits, except for petiole color (olivine), calyx color (green), blade margin serrated (sharp), lobular number (three), flower sex (hermaphrodite flower), petal shape (round), degree of concavity of calyx center(concave), the remaining 51 traits showed different degrees of phenotypic variation, of which 34 traits were descriptive traits and 17 traits were quantitative traits. There were 115 variation types for 34 descriptive traits, and 3.38 variation types for each descriptive trait. The Shannon’ s diversity index H’ranged from 0.24 to 1.49, with an average score of 0.85. The coefficient of variation of the 17 quantitative traits ranged from 10.31% to 60.65% and the Shannon’s diversity index ranged from 1.68 to 2.92. Genetic diversity analysis showed that strawberry germplasm resources showed rich phenotypic variation. Furthermore, fruit traits showed more phenotypic variation than nonfruit traits because the average Shannon’s diversity index H’was 1.05 and 0.61 for fruit traits and nonfruit traits, respectively. The Shannon's diversity index H’was the highest for fruit flavor (1.49), followed by flesh color, whose H’was 1.46. The third highest attribute was 1.35, which corresponded to pulp texture and pulp color. The average fruit weight, fruit longitudinal diameter and fruit transverse diameter were 14.34 g, 35.38 mm and 29.21 mm, respectively. The correlation coefficients among traits ranged from -0.70 to 0.95, the plant height and petiole length were extremely significantly and positively correlated, with a correlation coefficient of 0.95. Petiole length was negatively correlated with plant architecture and the lowest correlation coefficient was -0.70. In addition, 17 quantitative traits were positively correlated with each other, i.e., plant height, canopy diameter, leaf length, leaf width, length/ width ratio, petiole length, petiole diameter, number of compound leaves, leaf thickness, pedicel length, pedicel diameter, flower numbers, flower diameter, plant architecture, fruit weight, fruit longitudinal diameter and fruit transverse diameter. Leaf length/width ratio was significantly correlated with leaf shape, and trichome density of the upper leaf surface was significantly correlated with that of the lower leaf surface and leaf texture, respectively. Principal component analysis transformed 51 phenotypic traits into 15 comprehensive factors, with a cumulative contribution rate of 78.14%. The contribution rates of the first three principal components were 15.92%, 8.82% and 7.76%, respectively. The loadings of the first principal components were plant height, canopy diameter, plant architecture and other traits representing growth vigor. The loadings of the second principal components featured fruit quality, like flesh color and pulp texture. The loadings of the third principal components were flower numbers, fruit weight, fruit longitudinal diameter and fruit transverse diameter representing fruit yield. The results of principal components also illustrated that strawberry resources of China and JapKor had very similar phenotypic traits and belonged to the Asian group, while the other germplasms belonged to the Europe group, indicating that the germplasms had more phenotypic variations between the Asia group and Europe group. Germplasm resources were divided into three categories according to the comprehensive evaluation value D: excellent, medium and poor. A total of seven excellent germplasms were identified, 4 of which were from China, namely Ganlu, Ningfeng, Miaoxiang 7 and 07-D-5. Three were from JapKor including Kaorino, Benihoppe and TouKun. These excellent germplasms exhibited higher plant height, bigger canopy diameter, heavier fruit weight, bigger fruit longitudinal and transverse diameters than the other medium and poor germplasms. Among them,‘Kaorino’showed the largest fruit longitudinal and transverse diameters and TouKun had the most flower numbers. In summary, these excellent strawberry germplasms have good plant vigor and fruit yield, and have potential for breeding and theoretical research.【Conclusion】A total of 73 cultivated strawberries grown in Hubei province showed abundant phenotypic diversity, especially for fruit traits. Strawberries from different geographical ori-gins were clustered into different groups in principal component analysis based on phenotypic data. There may be more phenotypic variances between the Asia group and Europe group. Finally, seven excellent strawberry germplasms were screened out through the comprehensive evaluation index D, which can be used as breeding parents and materials for theoretical research.