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Molecular comparison of natural hybrids of Phytophthora nicotianae and P. cactorum infecting loquat trees in Peru and Taiwan

     Entomology and Plant Pathology Department, University of Tennessee, Knoxville, Tennessee 37996

L.M. Aragon-Caballero
J.G. Flores-Torres

     Departamento de Fitopatologia, Universidad Nacional Agraria La Molina, Lima 12, Peru

Willem Man in ’t Veld

     Department of Mycology, Plant Protection Service, P.O. Box 9102, 6700, HC, Wageningen, the Netherlands

K.H. Lamour ¹

     Entomology and Plant Pathology Department, University of Tennessee, Knoxville, Tennessee 37996

Natural Phytophthora hybrids (P. nicotianae x P. cactorum) infecting loquat in Peru and Taiwan were characterized with AFLP (amplified fragment length polymorphism) markers, the internal transcribed spacer (ITS) region and the phenol acid carboxylase gene (Pheca) and inheritance of the mitochondrial cytochrome oxidase I gene (coxI). AFLP profiles of two Taiwanese isolates recovered in 1995 were polymorphic in ~50% of the fragments whereas five Peruvian isolates, recovered 2002–2003 and 2007, showed no genotypic variation. Sequencing analysis of the cloned ITS region resulted in the identification of sequences with high homology to either P. nicotianae (99%) or P. cactorum (97%). Direct sequence analysis of the Pheca gene revealed 13 heterozygous sites suggesting the presence of both P. nicotianae and P. cactorum genes in P. hybrids isolates. Melting analyses of coxI suggested that all seven Phytophthora hybrids inherited the mitochondrial DNA from P. nicotianae. Our results suggest that Phytophthora hybrids from Peru might have originated from a single hybridization event and that the two isolates from Taiwan might have originated through different hybridization events. The Peruvian hybrids appear to have persisted at least 3 y at three locations. Possible factors influencing the population structure of Phytophthora hybrids infecting loquat are discussed.

Key words: hybridization, mitochondrial DNA