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Title: Virulence and molecular characterization of experimental isolates of the stripe rust pathogen (Puccinia striiformis) indicate somatic recombination

Author
item LEI, YU - Washington State University
item WANG, MEINAN - Washington State University
item WAN, ANMIN - Washington State University
item XIA, CHONGJING - Washington State University
item See, Deven
item MIN, ZHANG - Sichuan Agricultural University
item Chen, Xianming

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2016
Publication Date: 12/30/2016
Citation: Lei, Y., Wang, M., Wan, A., Xia, C., See, D.R., Min, Z., Chen, X. 2016. Virulence and molecular characterization of experimental isolates of the stripe rust pathogen (Puccinia striiformis) indicate somatic recombination. Phytopathology. 107:329-344.

Interpretive Summary: The stripe rust pathogen causes the disease on wheat, barley, and grasses. Natural population studies have indicated that somatic recombination plays a possible role in the pathogen variation. To determine if somatic recombination can occur, susceptible wheat or barley plants were inoculated with mixed urediniospores of paired isolates of the stripe rust fungus, and progeny isolates were selected by passing through a series of inoculations of wheat or barley genotypes and compared with the parental isolates on 18 wheat and/or 12 barley genotypes that are used to differentiate races of the wheat and stripe rust pathogens for virulence changes. The isolates were also tested with 51 simple sequence repeat and 90 single-nucleotide polymorphism markers for genotype changes. From 68 possible recombinant isolates obtained from nine combinations based on virulence tests, 66 were proven by molecular markers. Various types of recombinants were determined, including lost virulence from both virulent parental isolates, gained virulence from both avirulent isolates, combined virulences from both parents, and inherited virulence from one parent and avirulence from another. Marker data indicate that most of the recombinants were produced through chromosome re-assortment and cross-over after the hybridization of two parental isolates. This study shows that somatic recombination is a mechanism by which new variants can be generated, and the results improve the understanding of the pathogen evolution.

Technical Abstract: Puccinia striiformis causes stripe rust on wheat, barley, and grasses. Natural population studies have indicated that somatic recombination plays a possible role in the pathogen variation. To determine if somatic recombination can occur, susceptible wheat or barley plants were inoculated with mixed urediniospores of paired isolates of P. striiformis. Progeny isolates were selected by passing through a series of inoculations of wheat or barley genotypes. Potential recombinant isolates were compared with the parental isolates on the set of 18 wheat and/or 12 barley genotypes that are used to differentiate races of P. striiformis f. sp. tritici (the wheat stripe rust pathogen) and P. striiformis f. sp. hordei (the barley stripe rust pathogen), respectively, for virulence changes. They were also tested with 51 simple sequence repeat and 90 single-nucleotide polymorphism markers for genotype changes. From 68 possible recombinant isolates obtained from nine combinations of isolates based on virulence tests, 66 were proven by molecular markers. Various types of recombinants were determined, including lost virulence from both virulent parental isolates, gained virulence from both avirulent isolates, combined virulences from both parents, and inherited virulence from one parent and avirulence from another. Marker data indicate that most of the recombinants were produced through chromosome re-assortment and cross-over after the hybridization of two parental isolates. The results demonstrate that somatic recombination is a mechanism by which new variants can be generated in P. striiformis.