Promiscuity, fertility and survival of ITS clade 6 hybrids associated with riparian ecosystems in Western Australia
Burgess, T., Hüberli, D., White, D., Stukely, M. and Hardy, G. (2012) Promiscuity, fertility and survival of ITS clade 6 hybrids associated with riparian ecosystems in Western Australia. In: 6th International Union of Forest Research Organisations,IUFRO Working Party 7-02-09, 9 - 16 September, Córdoba, Spain.
Over the past few years several large scale Phytophthora surveys have been undertaken in Western Australia. In all cases, the ITS region of numerous isolates obtained from water or riparian soil have been unsequencable. These isolates are hybrids, all involving parental species from ITS clade 6, subclade II. Parental species are P. thermophila (T), P. fluvialis (F), P. litoralis (L), P. amnicola (A) and P. taxon stagnum (S). In most cases, two alleles were found for the nuclear genes and a single allele for the mitochondria gene, suggesting that each hybrid is a result of an independent sexual hybridization event involving two parental species with the mitochondria inherited from the maternal parent. To date the following hybrids have been characterised (maternal parent first); A‐F, A‐S, F‐S, L‐S, T‐A, T‐S and S‐F. The hybrid isolates all appear to be sterile and readily produce sporangia on soil extract, however, some of them produced unusual or aborted sporangia. The growth and colony pattern produced by the hybrids on three different agar media is similar to that of the maternal parent. These hybrids have predominantly been isolated from natural waterways but some have been isolated from the rhizosphere soil of dying plants. There is no evidence of subsequent hybridization events (back crossing or hybrids crossing with hybrids), but this cannot be ruled out at this stage. The two parental ITS alleles are combined and subsequently recombined through mitotic recombination events creating significant variation between the rDNA subunits. The fact that this occurs suggests that the hybrids are relatively stable and are able to survive without resting structures, probably through continual sporulation within riparian ecosystems. Their role in the environment remains a mystery.
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|Murdoch Affiliation:||Centre for Phytophthora Science and Management
School of Biological Sciences and Biotechnology
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