Host adaptation and speciation through hybridization and polyploidy in Phytophthora

Area of Science:

• Oomycete genetics and evolution
• Plant pathology
• Evolutionary biology

Background:

• Interspecific hybridization is recognized as a significant factor in the evolution of Phytophthora.
• The ecological fitness and distribution consequences of hybridization in Phytophthora remain poorly understood.
• Phytophthora clade 8b comprises cold-tolerant, plant-pathogenic oomycetes primarily affecting winter vegetables.

Purpose of the Study:

• To investigate hybridization events within Phytophthora clade 8b.
• To characterize the genetic and genomic features of hybrids.
• To explore the role of hybridization and polyploidy in the evolutionary dynamics of Phytophthora.

Main Methods:

• DNA sequencing of nuclear (ITS, Ypt1) and mitochondrial (Cox1, Nadh1) loci.
• DNA content estimation using flow cytometry.
• Cloning of nuclear gene products to detect additivity and recombination.

Main Results:

• Three distinct hybrid types were identified based on mtDNA haplotypes, involving different parental species.
• Nuclear gene analysis revealed additivity, indicative of allopolyploid hybridization followed by diploidization.
• Hybrid isolates exhibited novel host ranges and pathogenic potential, with clade 8b species showing evidence of widespread polyploidy.

Conclusions:

• Interspecific hybridization and polyploidy are likely linked phenomena in Phytophthora evolution.
• These processes contribute to the emergence of novel pathogenic traits and influence the evolutionary trajectory of the genus.
• Polyploidy appears to be a common characteristic within Phytophthora clade 8b.