Interspecific Hybridization In Armeniaca And The Origin Of A.hongpingensis

Natural hybridization occurs frequently in angiosperms and is one of the driving forces for speciation and evolution.Some natural hybrids have been found in Armeniaca Mill.,bringing difficulty and confusion to the genus’ taxonomy.Among Armeniaca,A.hongpingensis Yu et Li is a narrowly-distributed species that has been recored only in the Shennongjia Forest Region.Some scholars speculat that it may be a natural hybrid of A.vulgaris Lam.and A.mume Sieb.based on morphological similarity,and some believe that it is a variant of A.mume according to morphological studies.Other related morphological studies have shown that it is an independent species and has a closer relationgship with A.mume compared with A.vulgaris.However,there has not systematical study on its taxonomic status and its genetic relationship with related species of Armeniaca.This article dealt with the aspects of morphology(including macroscopic features and micromorphology),reproduction biology and molecular systematics to explore the origin of A.hongpingensis and its genetic relationship with several species of Armeniaca.Main results are summarized as follows:Comparison of morphological characteristics:For A.hongpingensis,A.mume,A.mume Sieb.var.bungo Makino and A.vulgaris,16 qualitative characters and 23 quantitative characters were compared.There were 27 characters of A.hongpingensis were significantly different from A.mume and A.vulgaris.And there were significant differences between A.hongpingensis and A.mume var.bungo of 24 traits.For Leaf and pollen micromorphology comparison:Scanning electron microscopy was used toscan the leaves and pollens of A.hongpingensis,A.mume,A.mume var.bungo and A.vulgaris.The results showed that the four species of leaf epidermal cell shape,stomatal apparatus type,pollen morphology,and outer wall ornamentation and appendages were similar;there were significant differences in the distribution and density of indumentum,size of epidermal cells,stomata size and pollen size between A.hongpingensis,A.mume,A.mume var.bungo and A.vulgaris.Overall,it was preliminarily determined that A.hongpingensis were clearly different from them in morphology.Breeding Biology research:This study selected the A.mume and A.vulgaris cultivated in Yangling of Shaanxi to conduct research on reproductive biology and obtained the following results:1.there was a short overlapping flowering period between A.mume and A.vulgaris.2.there was a detectable pollen flow between A.mume and A.vulgaris.3.Both A.mume and A.vulgaris were used as a paternal and maternal pollination test respectively bearing fruits,indicating that the reproductive segregation between the two species is weak.Flowering overlap and weak reproductive isolation provided theoretical possibilities of natural hybrid between A.mume and A.vulgaris.Molecular Biology research:In this study,the phylogenetic relationship between A.hongpingensis and other Armeniaca species was investigated,using individuals and seedlings of A.hongpingensis and individuals of five other Armeniaca species(A.vulgaris,A.mume,A.mume var.bungo,et al.).Two nuclear genes(ITS and SBEI)and two chloroplast genes(matK and ycf1b)were sequenced to reconstruct molecular phylogenetic tree.MatK,ycf1b and SBEI were also used to reconstruct haplotype network.Phylogenetic analyses of both nuclear and chloroplast genes showed that the individuals and seedlings of A.hongpingensis grouped together with high bootstrap values(99/79.71/81),independent of other Armeniaca species.And the difference lied in the location of A.mume and A.sibirica Lam.,but both showed that the A.holosericea(Batal.)Kost.,A.mandshurica(Maxim.)Skv.,A.mume var.bungo and A.vulgaris had a closer phylogenetic position with A.hongpingensis than A.mume.The Bayesian consistent tree based on ITS sequences showed that most individual and seedling clones of A.hongpingensis grouped in two single clades with high bootstrap values(0.82,0.97);the other few individual clones clustered with A.vulgaris and A.mume var.bungo individuals;and no clones clustered with individuals of A.mume.On SBEI and ycf1b loci,haplotypes of A.vulgaris,A.mume and A.holosericea were not detected in A.hongpingensis;while on matK locus,only the haplotypes of A.vulgaris were detected in a few(2/9)seedlings of A.hongpingensis.These results suggested that A.hongpingensis was likely to be an independent species rather than a natural hybrid of A.vulgaris and A.mume and had a closer genetic relationship as well as detectable gene flow with A.vulgaris.And it had a closer relationgship with A.holosericea,A.mandshurica and A.mume var.bungo.By summarizing the results derived from the morphological,reproductive biological and molecular phylogenetics studies,it can be concluded that although there existed a possibility of hybridization between A.vulgaris and A.mume,A.hongpingensis wasn’t a hybrid of A.vulgaris and A.mume which should be regarded an an independent species,and the relationship between A.hongpingensis and A.vulgaris was closer than that between A.hongpingensis and A.mume.Also A.hongpingensis had closer kinships with A.holosericea,A.mandshurica and A.mume var.bungo and a distant relationship with A.mume and A.sibirica.