| Malus toringoides (Rehd.) Hughes was collected by Wilson in western Sichuan in 1904, and Rehder described it as a variety of M. transitoria Schneid in 1915. In 1920, it was named M. toringoides (Rehd.) Hughes by Rehder M. toringoides (Rehd.) Hughes belongs to Series Kansuenses Rehd. of Malus Miller of Rosaceae in plant taxonomy. Scattered distribution of M. kansuensis Rehd and (or) M. transitoria Schneid were found in the main habitat of M. toringoides (Rehd.)Hughes. The three species overlapped each other in the weastern part of Sichang and the Southern of Gansu showed their geogeraphic affinity, and their difference in distribution showed the characteristics of geographic vicariation(vertical vicariation) and they are, therefore, called vicarious species. In this subflora forest vegetation of China-Himalagas, there were many new and old species co-existed. The morphological variations of M. toringoides (Rehd.)Hughes ranges between those of M. transitoria Schneid and M. Kansuensis Rehd. The feature of morphological variations of M. toringoides (Rehd.)Hughes looked like those of the results of introgressive hybridization.M. toringoides (Rehd.)Hughes was a facultative apomiictic species. Used as a rootstock for apple trees. M. toringoides (Rehd.)Hughes showed highly resistant to various environmental stresses and effects on the grafted trees in dwarfing, early fruiting, good productiving and improvement of fruit quality. Therefore M. toringoides (Rehd.)Hughes was considered as a very important apple germplasm resource in genus Malus. M. toringoides (Rehd.)Hughes was highly diversified in morphological characters, germplasm characteristics (such as tolerance to salt, drought, heat, cold, water-logging, and resistance to valsa mail Miyabe et Yamada, Xylaria malt Fromme), and in ecological habitats. It was one of the wild species in genus Malus which showed high resistance to various environmental stresses.Concering M. toringoides (Rehd.)Hughes there were, however, many questions, such as its origin, and the genetic background of diversity differention, still needed to be answered. Therefore,in this thesis, the M. toringoides (Rehd.JHughes, M. transitoria Schneid, M. kansuensis Rehd, M. xiaojinensis Cheng.et. Jiang, and M. maerkangensis Cheng,Zeng et. Jin were selected as experimental materials. The traditional numerical analysis, AFLP (Amplified Fragment Length Polymorphism) markers techniques, and Anderson pictodalized scatter diagrams, hybid index were used in this thesis to study on the origin and differentiation of genetic diversity of M. toringoides (Rehd.)Hughes.I The origin of M.toringoides (Rehd.)HughesYu(1974)considered that M. toringoides (Rehd.) Hughes was closely related to M. Kansuensis Rehd and that M. transitoria Schneid to M. toringoides (Rehd.) Hughes. This thought pointed out that the origin of M. toringoides (Rehd.) Hughes were probably derived from nature hybridization and hybrid between M. kansuensis Rehd and M. transitoria Schneid. According to the leaf lobe variation features of M. toringoides (Rehd.)Hughes, M. transitoria Schneid and M. Kansuensis Rehd, the lobe index and lobe-length index were used to draw 'Pictorialized scatter diagriam' . The genetic diversities of the three population of M.toringoides (Rehd.)Hughes had values intermediate between M. transitoria Schneid and M. kansuensis Rehd. Population I andII were more closely related to M. transitoria Schneid in the figure, and population III was more closely related to M. kansuensis Rehd. We found that the trends of decrease and increase of lob-length index and lob index within the population of M. toringoides (Rehd.) Hughes were the same, but the actual change of them were not completely consistent. We could pick out pairs of plants from the population which had the same lobe-length index values, but the lobe index value of one of them was much greater than that of the other. In the same way, we found pairs of plants which had same lobe index values, but the lobe-length index value of one of them was much greater than that of the other. Anderson(1953) thought that the scattered and non-random association of characters was the essential evidence for hybridization. This results showed M. toringoides (Rehd.)Hughes was originated from reciprocal cross of M. transitoria Schneid with M. kansuensis Rehd then repeatedly backcross with one of the parents resulted introgressive hybridization population.Based on the major taxonomic characters of flowers, leaves and fruit of M. transitoria Schneid and M. kansuensis Rehd, an index value for each character was decided. We supposed the total index value of M. kansuensis Rehd was zero, and those of M. transitoria Schneid was twenty, there were obviously discontinuous. M. toringoides (Rehd.)Hughes have the index values intermediate between M. transitoria Schneid and M. kansuensis Rehd. The index values of population I and II were 11.27 and 11.71.These index values are closely to M. transitoria Schneid.Both 'Pictorialized Scatter Diagram' and 'Hybrid Index Analysis' showed that the number of backcrosses of population I and II hybrid with M. transitoria Schneid were more than that with M. kansuensis Rehd, and those of population III hybrid with M kansuensis Rehd more than that with M. transitoria Schneid. Population III was seedings of M. toringoides (Rehd.)Hughes which collected from mountain hills back of the Agriculture Research Institute of Aba Autonomous Region, Maerkang, and morphological trait was more closely related to M. kansuensis Rehd. Therefore, it was also indicated that the diversity of M. toringoides (Rehd.)Hughes can be inherited its progeny by apomixes.In this thesis, we studied the origin of M. toringoides (Rehd.)Hughes applying AFLP. The bands of six pairs of AFLP primers in M. toringoides (Rehd.)Hughes, M. transitoria Schneid and M. kansuensis Rehd were recorded three types: 1) the bands were obtained both in M. transitoria Schneid and M. kansuensis Rehd, 2) the bands were obtained both in M. toringoides (Rehd.)Hughes and M. transitoria Schneid (orM. Kansuensis Rehd), and 3) the bands were obtained only in M. toringoides (Rehd.)Hughes. The analysis indicated that the AFLP bands of M. toringoides (Rehd.)Hughes were from part of added the bands of M. transitoria Schneid to those of M. kansuensis Rehd, and these bands was not from their ancestor. Smith conssidered that the bands of presumptive hybrid were from added or part of added that two parents, then it was hybrid. AFLP bands of M. transitoria Schneid and M. Kansuensis Rehd had different frequencies in different variation types of M toringoides (Rehd.)Hughes. It showed that M toringoides (Rehd.)Hughes was different from generation of backcross with their parents. These results verified in molecular level that M fori/!go/des(Rehd.)Hughes was a complex hybridization of M. toringoides (Rehd.)Hughes, M. transitoria Schneid and M. Kansuensis Rehd.From the phenotype to the genetype, we can safely draw a conclusion that M. toringoides (Rehd.)Hughes was originated from reciprocal cross of M. transitoria Schneid with M. kansuensis Rehd.2 The genetic diversity of M. toringoides (Rehd.)HughesFrom the phenotype to the genetype, M. toringoides (Rehd.)Hughes have rich diversity coefficient of variation(CV) of leaves varied between 9.67% and 34.64%, and the CV values of flowers and fruit were less than those of leaves. The CV of flowers morphological trait were between 4.76% and 5.46%, and those of fruit were between 6.80% and 8.73%. There were three types of stomatal apparatus in leaves: 1) anomocytic type, 2) anisocytic type, and 3) amphianisocytic type. The CV of stomatal density were 14.19%, and those of chloroplastid were 23.11%. In addition to triploid and tetraploid M.toringoides (Rehd.)Hughes, the mixed triplody andtetraploidy was also found in the species.1008 bands were obtained with 14 pairs of AFLP primers based on 30 individual of populationlll, and among them 891(88.39%) were polymorphic with an average of 63.7 bands for per AFLP primer. The ratio of polymorphic varied from 35.81% to 80.59% with an average of 54.74%. The Nei gene diversity index was 0.4389, and Shannon's information index was 0.6262, These number indicted that there were rich diversity in molecular.The genetic diversity of species was also influenced by their status of classification, distribution range, leaf form, propagate system and spread mechanism of seed. Among them, the propagate system was the most important factor. Being a facultative apomictic species, on the one hand, M. toringoides (Rehd.)Hughes was introgressive hybridization with M. transitoria Schneid and (or) M. kansuenses Rehd in a way of facultative apomixes. On the other hand, the new genetic variants produced via introgressive hybridization were maintained through apomicitic reproduction mating system after million and million years of evolution. The current introgressive hybridization population of M. toringoides (Rehd.)Hughes with much diversity and complexity were formed. The existing populations of M. toringoides (Rehd.)Hughes were results of a complex hybridization of the three species. Because of the gene recombination and increased mutation rate occurred in the fertile hybrids. The gene pool of M. toringoides (Rehd.)Hughes has been greatly enriched. Therefore, these give us a deep insight into the genetic mechanism of the species differentiation and high resistances of M. toringoides (Rehd.)Hughes to various environmental stresses.3 The intraspecies differentiation of M. toringoides (Rehd.)Hughes. and the formation of species novaThat were not only diploid, triploid, and tetrploid M. toringoides (Rehd.)Hughes but also mixed tri-tetraploidy facultative apomictic plants in the species, suggested that M. toringoides (Rehd.)Hughes was possibly under differentiation^ single plant which was similar to M xiaojinensis Cheng.et. Jiang and M. maerkangensis Cheng.Zeng et. Jin was found in population III, this indicated the origin of M. xiaojinensis Cheng.et. Jiang and M. maerkangensis Cheng,Zeng et. Jin.The analysis of AFLP bands showed that M. xiaojinensis Cheng.et. Jiang and M. maerkangensis Cheng,Zeng et. Jin.were interspecific hybrid, which was developed through crossing certain generation of M toringoides (Rehd.)Hughes with M. kansuensis Rehd after million and million years of evolution. M. xiaojinensis Cheng.et. Jiang and M. maerkangensis Cheng,Zeng et. Jin were obviously different from M. toringoides (Rehd.)Hughes and M. kansuensis Rehd in morphological character, cytological character and molecular character. They have independentdistribution range and apomixes, and they were recognizable classified group of self-reproducing. Stace considered that if a hybrid was a independent and recognizable self-reproducing unit, in fact it was a individual species. For this reason, M. xiaojinensis Cheng.et. Jiang and M. maerkangensis Cheng,Zeng et. Jin were individual species, and they be long to Ser. kansuenses (Rehed)Rehed. |
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