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Evidence of spontaneous hybridization between two partially sympatric species of Chaenomeles, C. cathayensis and C. speciosa, has been obtained through analysis of offspring families from these two species, as well as from two presumed interspecific hybrid populations. A combination of different methods was applied. Analysis of diagnostic RAPD markers and of chloroplast DNA haplotypes supported the notion of spontaneous hybridization, and suggested that there has been symmetrical, rather than unidirectional, introgression between C. cathayensis and C. speciosa. RAPDs and morphological characters revealed concordant patterns of genetic relatedness among the studied offspring families. Some putative hybrid families had mainly intermediate characters, whereas others appeared to be later generation hybrids as they were genetically and phenotypically rather similar to families that appeared to represent pure species. The RAPD-based proportion of between-family variability was considerably higher in the putatively hybridogenous populations than in populations of the pure species. Within-family gene diversity estimates ranged from C. speciosa (max. Hj = 0.235) to C. cathayensis (min. Hj = 0.094) with the presumed hybrid families taking intermediate values. [ABSTRACT FROM AUTHOR]

RAPD and isozyme analyses based on numerous markers have been used for the first time to investigate patterns of phenetic and genetic differentiation among and within nine wild populations of the genus Chaenomeles represented by the species C. japonica, C. speciosa, C. cathayensis and C. thibetica. Highly significant correlations were found between the two different marker systems for both phenetic distances and gene diversity estimates. In agreement with previous studies on cultivated Chaenomeles material, C. japonica was clearly differentiated from C. speciosa and C. cathayensis. The recently recognised species C. thibetica appeared to be rather closely related to C. cathayensis. Populations of C. japonica and C. speciosa were considerably more diverse than populations of C. cathayensis and C. thibetica. Correspondingly, most of the total variability could be attributed to the within-population differentiation in the case of C. japonica and C. speciosa, and to the between-population differentiation in the case of C. cathayensis. Differences in mating systems among the species can be suggested as a possible explanation of the results. A discordant pattern was found between RAPDs and isozymes in the analyses of population structure within C. japonica. This may be explained by a higher proportion of non-neutral markers for isozymes than for RAPDs. This finding also shows the importance of using multiple molecular marker systems in studies of population structure. [ABSTRACT FROM AUTHOR]