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United States Department of Agriculture

Agricultural Research Service

Title: Use of Molecular Markers to Study Host-Pathogen Co-Evolution: a Case Study of the Fungal Pathogen Phialophora Gregata

Authors
item CHEN, WEIDONG
item Grau, C - UNIVERSITY OF WISCONSIN

Submitted to: Plant Genome: Biodiversity and Evolution
Publication Type: Book / Chapter
Publication Acceptance Date: December 28, 2004
Publication Date: June 1, 2006
Citation: Chen, W., Grau, C.R. Use of molecular markers to study host-pathogen co-evolution: a case study of the fungal pathogen phialophora gregata. pp.365-383. In: A.K. Sharma and A. Sharma (eds.), Plant Genome: Biodiversity and Evolution. Science Publishers, Enfield, New Hampshire.

Interpretive Summary: Brown stem rot of adzuki bean and soybean caused by Phialophora gregata provides an ideal example to study host-pathogen co-evolution. Molecular markers were developed targeting at three different taxonomic levels to study the interaction of the pathogen with the host plants. First, molecular markers based on ITS region of nuclear rDNA were developed to differentiate the pathogen P. gregata from the co-colonizing species Plectosporium tabacium. Second, a molecular marker based on an intron near the 5' end of nuclear small subunit rDNA was used to differentiate two formae speciales of P. gregata, f. sp. adzukicola infecting adzukibean and f. sp. sojae infecting soybean. This marker could be employed to differentiate the two formae speciales without pathogenicity tests. Third, three sets of molecular markers were developed to separate isolates of P. gregata f. sp. sojae into two distinct populations (A and B) and a third population for f. sp. adzukicola. The three independent sets of molecular markers (IGS region of the nuclear rDNA, three microsatellite loci, eight anonymous DNA loci) were all correlated in identifying the two populations. Furthermore, the two genetic populations correspond to defoliating and non-defoliating pathotypes, and differential cultivar preference. This chapter documents the importance of using molecular markers in advancing our understanding of adaptation of P. gregata to host plants.

Technical Abstract: The brown stem rot pathosystem was taken as a case study using molecular markers targeted at various taxonomical levels to study host-pathogen co-evolution. A series of molecular markers have been developed for differentiation at three taxonomical levels to study the interaction of Phialophora gregata with soybean. First, molecular markers based on ITS region of nuclear rDNA were developed to differentiate the pathogen P. gregata from the co-colonizing fungus Plectosporium tabacium. Results showed that there was a negative correlation in natural occurrence between the two fungal species in soybean plants. Second, a molecular marker based on an intron near the 5' end of nuclear small subunit rDNA was used to differentiate two formae speciales of P. gregata, f. sp. adzukicola infecting adzukibean and f. sp. sojae infecting soybean. This marker could be employed to differentiate the two formae speciales without using pathogenicity tests. Third, three sets of molecular markers were developed to separate isolates of P. gregata f. sp. sojae into two distinct populations (A and B) and a third population for f. sp. adzukicola. The three independent sets of molecular markers (IGS region of the nuclear rDNA, three microsatellite loci, eight anonymous DNA loci) were all correlated in identifying the two populations. Furthermore, the two genetic populations correspond to defoliating and non-defoliating pathotypes, and differential cultivar preference. Isolates of population A preferentially infect susceptible soybean cultivars and isolates of population B preferentially infect resistant soybean cultivars. This series of molecular markers greatly helped advancing our understanding of adaptation of P. gregata to host plants.

Last Modified: 9/29/2014
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