ARS | Publication request: DISCORDANT RELATIONSHIPS BETWEEN RACES AND RAPD BANDING PATTERNS IN PHYTOPHTHORA SOJAE ISOLATES

Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 6, 1998
Publication Date: N/A

Interpretive Summary: Identification of pathogen races requires complex and time-consuming experiments involving large numbers of control plants and pathogens. The ability to determine the identity of a pathogen quickly and cheaply would help breeders develop pest management strategies. The authors evaluated 55 fungal pathogen samples collected from the Midwest using molecular DNA markers. They were able to distinguish some pathogens into four distinct groups using these markers. Although some races of the pathogen could be distinguished using these approaches, no clear relationship between race and site of collection were seen. This means that pathogens are easily disbursed by farming practices but that some races of the pathogens can be easily identified. These results provide a means by which pathogens can be quickly identified and planting strategies involving different disease resistant plants can be tested.

Technical Abstract: Fifty-five Phytophthora sojae isolates were collected from soil samples and diseased soybean plants from Illinois, Indiana, Iowa, and Minnesota in 1994 and 1995. Races for the isolates were classified and these isolates were used to determine the relationship between race and RAPD banding patterns. DNA of eight P. sojae isolates identified as races 1, 3, 4, 5, 7, 8, 13 and d25 was initially amplified with 230 primers (220 Operon decanucleotide primers and 10 designed primers) to screen for polymorphisms. Sixteen Operon decanucleotide primers amplified 75 fragments, of which 23 were highly repeatable. The 16 informative primers were used to study 47 other isolates. Based on the 23 RAPD markers, a data matrix of dissimilarity was generated using PAUP 3.1.1. and a dendrogram depicting the relatedness of 55 P. sojae isolates was constructed using UPGMA (unweighted pair-group arithmetic mean). The P. sojae isolates clustered into four distinct groups. Group I included 13, ten, and five isolates of races 3, 4, and 25, respectively, and two unclassified isolates (7009IAITM and 7011IAITM). Group II included 13, three, and two isolates of races 1, 8, and 13, respectively, and one unclassified isolate (4406MNITM). Group III included two isolates of race 5 and one unclassified isolate (4609INITM), and group IV included two isolates of race 7 and one unclassified isolate (4606INITM). Nine race I isolates, three race 8 isolates, and two race 13 isolates showed identical RAPD banding patterns. Six race 3 isolates from Iowa and Minnesota also shared the same RAPD banding patterns as six race 4 isolates from Illinois, Iowa, and Minnesota. No relationship between RAPD banding patterns and the geographic distribution of the isolates was found.