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Chromosomal Deletion in Isolates of Phytophthora infestans Correlates with Virulence on R3, R10, and R11 Potato Lines

December 2001 , Volume 14 , Number  12
Pages  1,444 - 1,452

Theo van der Lee , Antonino Testa , John van 't Klooster , Grardy van den Berg-Velthuis , and Francine Govers

Laboratory of Phytopathology, Wageningen University, Graduate School Experimental Plant Sciences, The Netherlands

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Accepted 12 August 2001.

In Phytophthora infestans, a cluster of three dominant avirulence genes is located on the distal part of linkage group VIII. In a mapping population from a cross between two Dutch field isolates, probe M5.1, derived from an amplified fragment length polymorphism (AFLP) marker linked to the Avr3-Avr10-Avr11 cluster, hybridized only to DNA from the parent and F1 progeny that is avirulent on potato lines carrying the R3, R10, and R11 resistance gene. In the virulent parent and the virulent progeny, no M5.1 homologue was detected, demonstrating a deletion on that part of linkage group VIII. P. infestans is diploid, so the avirulent strains must be hemizygous for the region concerned. A similar situation was found in another mapping population from two Mexican strains. The deletion was also found to occur in many field isolates. In a large set of unique isolates collected in The Netherlands from 1980 to 1991, 37% had no M5.1 homologue and the deletion correlated strongly with gain of virulence on potato lines carrying R3, R10, and R11. Also, in some old isolates that belong to a single clonal lineage (US-1) and are thus highly homogenous, deletions at the M5.1 locus were detected, indicating that this region is unstable.

Additional keywords: late blight, oomycetes, plant pathogen.

© 2001 The American Phytopathological Society