Study on diversity and sex determination of Actinidia valvata

Abstract: 【Objective】Actinidia species are native to China, which provide rich germplasm resources for rootstock breeding. Kiwifruit is one of the most successful wild fruit trees domesticated in the 20th century and is increasingly popular among consumers because of its unique taste and high vitamin content. Grafting is an asexual plant propagation technique that combines desired traits from both rootstock and scion. This technique has been used extensively in fruit crops. The current kiwifruit industry relies on a few rootstock cultivars from seedlings of Actinidia chinensis and A. deliciosa. The rootstocks selected from A. valvata are much more tolerant to waterlogging stress than those from A. deliciosa, and are commonly used in kiwifruit production. However, supposed consistent clonal rootstocks of A. valvata accessions are mixed and their genetic backgrounds are various. The genetic diversity analysis of plant germplasm resources could lay a solid foundation for kiwifruit breeding and utilization. To clarify the relationship among different A. valvata accessions, the diversity of 62 A. valvata accessions was analyzed using seven microsatellite DNA markers and 36 phenotypic traits. The plant sex determination for cultivars and accessions within species is the first step towards the correct classification of kiwifruit germplasm. The present study used sex- related DNA markers to identify plant gender at its juvenile stage and these plants could be maintained as male and female plant populations separately. The performance of male individuals of A. valvata rootstock is found better than the female ones in kiwifruit production. The aim of this study was to identify plant genders of these 62 accessions with sex- related DNA markers for better utilization of the male A. valvata germplasm.【Methods】The sixty-two A. val-vata accessions were used as materials. The diversity of these studied accessions was evaluated based on their phenotypic characters and genotypes of seven Simple Repeat Sequence (SSR). The sex-related DNA markers were used to identify plant gender, and 34 flower-related attributes were evaluated to verify genotyping results.【Results】Among all the 36 phenotypic traits, except for the lenticel color (grayish white), leaf texture (membranous), leaf tip shape (caudiform), flatness of leaf surface blade (green), flatness of leaf pubescence (none), petal shape (ovate), the main color of the interior of the petal (white), clutch condition base of the petal (reunion), calyx color (green), female style posture (oblique growth), style color (ivory), female ovary shape (bottle), male filament color (white), anther shape (oblong), anther color (yellow), petal color gradient(none), the remaining 20 traits showed different degrees of phenotypic variation, of them 16 traits were descriptive traits and 10 traits were quantitative traits. There were 25 various types for 10 descriptive traits, according to the characteristics of shoots and leaves, these 62 accessions could be clustered into five groups. The first group had the most diverse twig and leaf traits, and the petioles were mostly purple red. The second group only had one individual-- A11 and its internode length and annual branch thickness were lower than the average of all individuals. The internode length of the annual branches of the individuals in third group was higher than the average of the all samples, and the thickness of the annual branches was lower than the average of the all samples and the leaf shape was oval. The leaf length of the fourth group was higher than the average of the all samples. The fifth group only had two individuals, A43 and A27. The internode length of the annual branches in this group was the largest among the all samples, and the thickness of the annual branches was higher than the average of the all samples. The color of the annual branches was grayish brown, the pores were all elliptical, the leaf shape was oval, the leaf edge was all wavy, the leaf base was all circular, the petiole length was lower than the average of the all samples, the petiole color was all greenish yellow, and the leaf length was higher than the average of the all samples. The used seven SSR markers amplified a total of 69 alleles, with an average number of alleles 9.86 on each marker locus, the effective alleles were 2-18, the average polymorphism information content (PIC) was 0.626, and the average observed heterozygosity (Ho) and expected heterozygosity (He) values was 0.994 and 0.686, respectively. According to the SSR marker polymorphism, the 62 individuals could be clustered into four groups. The gender-related markers had identified 18 female plants and 43 male plants; the 34 individuals of flowering had been identified, 13 individuals were female plants and 21 individuals were male plants, while result of the gender-related marker identification showed that there were 9 female individuals and 25 male ones. The consistency between the morphological sex determination and the sexrelated DNA marker identification was 79.14% .【Conclusion】A total of 62 accessions of A. valvata showed abundant phenotypic diversity, especially for twig and leaf traits. Combined with plant phenotypic characters and DNA marker genotypes could effectively characterize the A. valvata germplasm, which could provide tools and materials for further breeding clonal male A. valvata rootstock.