Collection And Evaluation Of Rhododendron Germplasm Resources In Shennongjia

Rhododendron is one of genera with the most abundant species of woody flowering plants.It is also an important plant for garden application and soil and water conservation.Shennongjia,known as the "hometown of Rhododendron",has few reports on the germplasm resources of Rhododendron.In this study,the germplasm resources of Rhododendron in Shennongjia were investigated,and the ornamental value of 11 species(including varieties)of 3 subgenera collected from Shennongjia was evaluated by analytic hierarchy process,so as to provide selection basis for their introduction and application.Based on SSR molecular marker and whole genome resequencing,the genetic diversity,phylogeny of Rhododendron were analyzed,which laid a foundation for introduction and breeding parent selection.The results of this study are as follows:(1)The evaluation system of Rhododendron was constructed by analytic hierarchy process.According to the weight,the 12 specific evaluation indexes are as follows: flower color > flower fullness > flower shape > flowering phenology >number of flowers in inflorescence > flower diameter > observation of plant appearance > aromaticity > leaf fullness > leaf size > leaf color > life form.The ornamental value scores of 11 Rhododendron collected in Shennongjia forest area range from 1.9258 to 3.9056,who are divided into three grades,grade I(> 3.61points): Rhododendron ordoxa var.faregesii、Rhododendron simsii and Rhododendron sutchuenense.Grade II(3.31 ～ 3.60 points): Rhododendron fortunei、 Rhododendron pulchrum 、 Rhododendron discolor 、 Rhododendron praeteritum 、 Rhododendron concinuum;grade III(< 3.30 points): Rhododendron hypoglaucum、Rhododendron mariesii and Rhododendron augustinii.(2)Genetic diversity and genetic structure of 11 species(including varieties)of Rhododendron in Shennongjia were analysed based on SSR molecular markers.Twelve pairs of highly polymorphic primers were selected from 35 pairs of primers for fluorescence capillary electrophoresis.The number of average alleles(Na)and Number of effective alleles(Ne)were 2.0833-14.3333 and 1.9536-9.0000 respectively.Shannon diversity index I and Nei’s expected heterozygosity(H)were 0.5827-2.2884 and 0.3704-0.8529 respectively.Observed heterozygosity(Ho)and expected heterozygosity(He)were 0.5000-0.8417 and 0.4444-0.8850 respectively.16.36%,34.55% and 49.09% of the populations were in high,medium and low degree of genetic differentiation,and the genetic variation mainly occurred within the species.Structure analysis and population principal coordinate analysis divided 11 species Rhododendron of into two clades,Rhododendron ordoxa var.faregesii was divided into one clade,and other Rhododendron were another clade.In the UPGMA tree,the Subgen.Hymenanthes gathers into one clade.Rhododendron pulchrum and Rhododendron mariesii of the Subgen.Tsutsusi gathers into one clade,and Rhododendron mariesii of the Subgen.Tsutsusi and two species of the Subgen.Rhododendron are clustered in the clade of the Subgen.Hymenanthes.(3)Based on the resequencing study,the genetic structure of 10 species(including varieties)of Rhododendron of 3 subgenera in Shennongjia was studied.According to principal coordinate analysis,Subgen.Hymenanthes.and Subgen.Tsutsusi are clustered into two clades,and Subgen.Rhododendron is clustered into one clade alone.The Structure Analysis divided 10 species of Rhododendron into 4clades and 5 species of Subgen.Hymenanthes into 2 clades.In ML phylogenetic tree,the Subgen.Hymenanthes and the Subgen.Rhododendron gather into one clade respectively,and the three species of the Subgen.Tsutsusi gather into one clade separately.The original population first differentiated into the Subgen.Tsutsusi,and the Subgen.Hymenanthes is a younger subgenus.