Characterization of Phytophthora hybrids from ITS clade 6 associated with riparian ecosystems in South Africa and Australia

• Published in: Fungal biology 2013-05, Vol.117 (5), p.329-347
• Main Authors: Nagel, Jan H., Gryzenhout, Marieka, Slippers, Bernard, Wingfield, Michael J., Hardy, Giles E.St.J., Stukely, Michael J.C., Burgess, Treena I.
• Format: Article
• Language: English
• Subjects: Amnicola; Australia; coxI; cytochrome-c oxidase; DNA, Intergenic - genetics; DNA, Mitochondrial - genetics; Ecosystem; ecosystems; Evolution; Freshwater; genes; host range; hybrids; internal transcribed spacers; Interspecific hybridization; loci; Molecular Sequence Data; parents; pathogenicity; Phylogeny; Phytophthora; Phytophthora - classification; Phytophthora - genetics; Phytophthora - growth & development; Phytophthora - isolation & purification; plant health; Recombination; rivers; soil; South Africa; surveys
• ISSN: 1878-6146; 1878-6162
• DOI: 10.1016/j.funbio.2013.03.004

Surveys of Australian and South African rivers revealed numerous Phytophthora isolates residing in clade 6 of the genus, with internal transcribed spacer (ITS) gene regions that were either highly polymorphic or unsequenceable. These isolates were suspected to be hybrids. Three nuclear loci, the ITS region, two single copy loci (antisilencing factor (ASF) and G protein alpha subunit (GPA)), and one mitochondrial locus (cytochrome oxidase c subunit I (coxI)) were amplified and sequenced to test this hypothesis. Abundant recombination within the ITS region was observed. This, combined with phylogenetic comparisons of the other three loci, confirmed the presence of four different hybrid types involving the three described parent species Phytophthora amnicola, Phytophthora thermophila, and Phytophthora taxon PgChlamydo. In all cases, only a single coxI allele was detected, suggesting that hybrids arose from sexual recombination. All the hybrid isolates were sterile in culture and all their physiological traits tended to resemble those of the maternal parents. Nothing is known regarding their host range or pathogenicity. Nonetheless, as several isolates from Western Australia were obtained from the rhizosphere soil of dying plants, they should be regarded as potential threats to plant health. The frequent occurrence of the hybrids and their parent species in Australia strongly suggests an Australian origin and a subsequent introduction into South Africa. •Four novel Phytophthora hybrids were discovered from Australia and South Africa.•Abundant recombination was detected within the ITS rDNA locus.•Three known species from Clade 6 were identified as the parents of these hybrids.•Hybrid isolates were sterile in laboratory mating tests.