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Population genetics in Orobanche species

The study of population genetics of Orobanche species is of great importance since the understanding of the variability within and between pathogenic populations is essential if selection programmes need to target sources of resistance at different areas and suitable breeding strategies need to be developed. The analysis of RAPD marker variation within and among six natural populations of Orobanche crenata Forsk. parasiting faba bean from southern Spain has shown that most of the molecular diversity was attributable to differences among individuals within a population. Further study based on ISSR markers including three O. crenata populations from Israel and three from Spain has detected the significant differentiation between these two regions. In the case of Spanish populations, diversity was attributable to differences among individuals within populations and the among-population partitioning was not significant. On the other hand, in the case of Israeli populations, the molecular differentiation among populations was significant. The patterns of RAPD variation were also analysed in 2 Orobanche foetida Poir. populations attacking cultivated crops (chickpea and faba bean) in Tunisia, and 3 populations growing on wild hosts (2 from Spain and 1 from Morocco). Tunisian populations infecting crops have shown significantly higher levels of diversity as compared with populations growing on wild hosts. Although most of the diversity was found among individuals within populations, the diversity attributable to differences among populations was also substantial while the differentiation between groups of populations growing on crops and those growing on wild host was not significant. In spite of a substantial internal variation among individuals within populations growing on crop fields, there was a significant divergence between the two hosts considered, confirming a clear host-differentiation between O. foetida populations infecting chickpea and faba bean. Current research studies include the molecular analysis of host-differentiation in O. crenata populations growing on faba bean, pea, chickpea, vetches, and grass pea and in O. gracilis populations infecting different wild host as Genista sp., Ulex sp., Onobrychis sp., Trifolium sp. etc. The further development of population genetic studies of Orobanche species will require the use of codominant marker systems as microsatellites and more extensive sampling of populations from different regions and different hosts.

Orobanche; population genetics; host-differentiation; molecular markers

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