The Genetic Structure Of Three Pairs Of Related Species Of Viola With Chasmogamous And Cleistogamous Breeding System

As an important component of biodiversity, genetic diversity is the basis of species diversity. Researches in this field can provide important information for revealing population evolutionary histories and analyzing population evolutionary potential and population future. Breeding system is the most important factor that influences population genetic structure, which determines the population gene frequencies and consequently determines the population genetic structure patterns of offspring. However, our knowledge is very limited for population genetic structure of those plant taxa with complex breeding systems such as CH/CL (chasmogamous/cleistogamous) systems. Violets have distinct breeding systems. They not only reproduce mostly with cross-breeding in chasmogamous systems companied with self-breeding, but also reproduce with complete self-breeding in cleistogamous systems. Besides these breeding systems, V. bulbosa and V. tuberifera which are endemic to the Qinghai-Tibet Plateau, can reproduce clonally through their bulbs and stolons.After broad survey in the fields, 22 wild populations were selected from 3 pairs of related species, such as V. bulbosa and V. tuberifera. Genetic diversity and population genetic structure of the 22 populations was analyzed using random amplified polymorphic DNA (RAPD) marker. The results provided useful information for better understanding of relationship between breeding systems and population genetic structure, and taxonomic status of the 3 pairs of related species with morphologic similarity at the molecular level. The results are as follows:160 individuals were amplified in the 5 populations of V. bulbosa and the 4 populations of V. tuberifera with 14 random primers. At the specie level, the percentage of polymorphic bands (PPB) , Nei's gene diversity (h) and Shannon diversity index (I) of V. bulbosa, were 85.09%, 0.2532 and 0.3848 respectively; and those of V. tuberifera were 77.67%, 0.2628 and 0.3937 respectively, so they both showed rich genetic diversity. But at the population level, V. bulbosa and V. tuberifera did not present high genetic diversity, in that the means of h and I were 0.1320 and 0.1997 respectively, and the genetic differentiation among populations were evident. The mean of Gst by POPGEGE was 49.00%, and it showed equal genetic variance among andwithin populations, which is far greater than that of the plants with cross-breeding system (Gst = 0.216) .It was found that the species without bulbs and stolons all had high genetic diversity at the specie level, and their means of percentage of polymorphic bands(PPB), Nei's gene diversity (h) and Shannon diversity index (I) , were 87.30%, 0.2734 and 0.4161, respectively; furthermore the means are 51.39%, 0.1728 and 0.2615 at the population level respectively, showing rich genetic diversity as well. The gene differentiation degree among the populations of V. monbeigii, V. variegata and V. tenuicornis was not greater than the V. bulbosa and V. tuberifera, but it was still higher than the mixed-breeding plants and more close to the self-breeding plants. Morever, clustering analyses of populations of 3 pairs of related species showed that, V. bulbosa and V. tuberifera clustered in populations respectively; spotted and unspotted taxa of V. monbeigii clustered together; V. variegata and V. tenuicornis clustered together.Based on the above studies, the conclusions are as follows: the chasmogamous/ cleistogamous (CH/CL) breeding modes of violets have great impacts on their genetic structures, and the main reason why the genetic differentiation of CL plants is far higher than that of mixed-breeding plants is that the cleistogamous plants produces a majority of seeds by self-pollination; the taxa with bulbs and stolons have greater genetic differentiation than those without them; V. bulbosa and V. tuberifera should be treated as different species, and it is reasonable that V. variegata and V. tenuicornis are classified into one specie, and the spotted and unspotted taxa of V. monbeigii do not show evident genetic differentiation.