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

     ¹ University of Tennessee, Knoxville, TN, 37996, United States of America
² Departamento de Fitopatologia, Universidad Nacional Agraria La Molina, Lima, Peru
³ Departamento de Fitopatologia, Universidad Nacional Agraria La Molina, Lima, Lima, Peru
⁴ Mycology, Plant Protection Service, 15 Geertjesweg, Wageningen, Gelderland, 6700 HC, Netherlands
⁵ Entomology and Plant Pathology, The University of Tennessee, Rm 205 Ellington Plant Science, 2431 Joe Johnson Drive, Knoxville, Tennessee, 37996, United States of America

Natural Phytophthora hybrids (P. nicotianae x P. cactorum) infecting loquat in Peru and Taiwan were characterized using 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 in 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% homology) or P. cactorum (97% homology). 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 may have originated from a single hybridization event and that the two isolates from Taiwan may have originated through different hybridization events. The Peruvian hybrids appear to have persisted over at least three years at three separate locations. Possible factors influencing the population structure of Phytophthora hybrids infecting loquat are discussed.Key words: hybridization, mitochondrial inheritance.

Key words: hybridization, mitochondrial DNA