Genetics, Vol. 160, 949-959, March 2002, Copyright © 2002

Genetic and Physical Mapping of Avr1a in Phytophthora sojae

Terry MacGregora, Madan Bhattacharyyab, Brett Tylerc, Ravindra Bhatd, August F. Schmitthennerd, and Mark Gijzena
a Agriculture and Agri-Food Canada, London, Ontario N5V 4T3, Canada,
b Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73402,
c Department of Plant Pathology, University of California, Davis, California 95616
d Department of Agronomy, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio 44691

Corresponding author: Mark Gijzen, 1391 Sandford St., London, ON N5V 4T3, Canada., gijzenm{at}em.agr.ca (E-mail)

Communicating editor: P. J. PUKKILA

The interaction between soybean and the phytopathogenic oomycete Phytophthora sojae is controlled by host resistance (Rps) genes and pathogen avirulence (Avr) genes. We have mapped the Avr1a locus in F2 populations derived from four different P. sojae races. Four RAPD and nine AFLP markers linked to Avr1a were initially identified. Nine markers were used to compare genetic linkage maps of the Avr1a locus in two distinct F2 populations. Distorted segregation ratios favoring homozygous genotypes were noted in both crosses. Segregation analysis of all the markers in one F2 population of 90 progeny generated a map of 113.2 cM encompassing Avr1a, with one marker cosegregating with the gene. The cosegregating DNA marker was used to isolate P. sojae BAC clones and construct a physical map covering 170 kb, from which additional DNA markers were developed. Three markers occurring within the BAC contig were mapped in an enlarged population of 486 F2 progeny. Avr1a was localized to a 114-kb interval, and an average physical to genetic distance ratio of 391 kb/cM was calculated for this region. This work provides a basis for the positional cloning of Avr1a.




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