Variation and differentiation among and within populations of Maius toringoides Hughes revealed by morphological evidence

摘要

Malus toringoides Hughes is highly diversified in morphology, germplasm characters and ecological distributions. It is highly resistant to various environmental stresses too and, therefore, an important germplasm in genus Malus Miller. The 'pictorialized scatter diagrams' and 'hybrid index' were used to investigate the variation and differentiation among and within populations of M. toringoides. The results showed that the rich diversity in M. toringoides was derived from the introgression of it with M. transitoria or (and) M, kansuensis by facultative apomixis. The new variants produced in the introgressive hybridization were maintained by apomictic reproduction mating system, and after for million and million years evolution, the current introgressive hybridization populations of M. toringoides with much diversity and complexity were formed. The existing populations of M. toringoides are components of a hybridization complex of three species. Because of the gene recombination and increased mutation rate occurred in the fertile hybrids, the gene pool of M. toringoides has been greatly enriched. Therefore, these results give us a deep insight into the genetic mechanism of the species differentiation and high resistance of M. toringoides to various environmental stresses. Type A separated from the 2nd population is similar to M. maerkangensis and type B to M. xiaojinensis. A further investigation would have an important meaning for study on the origins of M. maerkangensis and M. xiaokingensis, and for the species formation through hybridization in genus Malus.