School of Environmental and Evolutionary Biology, University of St Andrews, St Andrews, Fife KY16 9TH, UK; and.
Am J Bot. 1999 Dec;86(12):1776-85.
Rhododendron (Ericaceae) is a large genus in which barriers to hybridization are especially weak, but many species are maintained in sympatry. Hybridization among four species of Rhododendron subsect. Pontica, which occur in sympatry in Turkey, was investigated. Material of R. ponticum, R. smirnovii, R. ungernii, and R. caucasicum and their putative hybrids was collected from the wild. Based on morphology, chloroplast DNA and nuclear ribosomal DNA restriction fragment length polymorphism (RFLP) profiles, each accession was identified as a species or hybrid combination. Five of the six possible hybrid combinations among the four species were detected. Rhododendron ponticum × R. smirnovii was represented by a single individual and R. caucasicum × R. smirnovii by one small group of hybrid plants. The combinations R. ponticum × R. ungernii and R. ungernii × R. smirnovii showed evidence of frequent backcrossing, while R. ponticum × R. caucasicum appeared unusual in that an intermediate hybrid type was abundant, whereas hybrids with phenotypes approaching either parent were rare. Possible explanations of this latter situation are discussed. The results suggest that natural hybridization among Rhododendron species is common and that ecological factors are important in maintaining integrity when species occur in sympatry.
杜鹃（杜鹃花科）是一个大属，其杂交障碍特别弱，但许多物种在同域共存。本研究调查了土耳其同域分布的 4 种杜鹃花亚属 Pontica 种间杂交的情况。从野外采集了 R. ponticum、R. smirnovii、R. ungernii 和 R. caucasicum 及其可能的杂种的材料。基于形态学、叶绿体 DNA 和核核糖体 DNA 限制片段长度多态性（RFLP）图谱，每个采集样本都被鉴定为一个物种或杂种组合。在这 4 个物种的 6 种可能的杂交组合中，检测到了 5 种。Rhododendron ponticum×R. smirnovii 仅代表一个个体，R. caucasicum×R. smirnovii 仅代表一小群杂种植物。R. ponticum×R. ungernii 和 R. ungernii×R. smirnovii 表现出频繁回交的证据，而 R. ponticum×R. caucasicum 则不同寻常，因为中间杂种类型丰富，而接近任一亲本的杂种却很少。讨论了后一种情况的可能解释。研究结果表明，杜鹃属种间的自然杂交很常见，当物种在同域共存时，生态因素对于保持物种的完整性非常重要。
