Acquired Resistance to Mefenoxam in Sensitive Isolates ofPhytophthora infestans

Abstract

The systemic fungicide mefenoxam has been important in the control of late blight disease caused by Phytophthora infestans. This phenylamide fungicide has a negative effect on the synthesis of ribosomal RNA; however, the genetic basis for inherited field resistance is still not completely clear. We recently observed that a sensitive isolate became tolerant after a single passage on mefenoxam-containing medium. Further analyses revealed that all sensitive isolates tested (in three diverse genotypes) acquired this resistance equally quickly. In contrast, isolates that were "resistant" to mefenoxam in the initial assessment (stably resistant) did not increase in resistance upon further exposure. However, there appeared to be a cost associated with acquired resistance in the initially sensitive isolates, in that isolates with acquired resistance grew more slowly on mefenoxam-free medium than did the same isolates that had never been exposed to mefenoxam. The acquired resistance of the sensitive isolates declined slightly with subsequent culturing on medium free of mefenoxam. To investigate the mechanism of acquired resistance, we employed strand-specific RNA sequencing. Many differentially expressed genes were genotype specific, but one set of genes was differentially expressed in all genotypes. Among these were several genes (a phospholipase "Pi-PLD-like-3," two ATP-binding cassette superfamily [ABC] transporters, and a mannitol dehydrogenase) that were up-regulated and whose function might contribute to a resistance phenotype.

Differentiation of Pythium spp. from vegetable crops with molecular markers and sensitivity to azoxystrobin and mefenoxam

“…Although there were no aa changes present in the RPA190 sequence of mefenoxam‐resistant isolates, the high up‐regulation of three ABC transporter genes were found in three different P. ultimum mefenoxam‐resistant isolates. This indicates that ABC transporters might be related with the efflux of mefenoxam, since similar findings of the strong activation of the same ABC transporter genes have been found in P. ultimum upon treatment with mefenoxam (more then 25‐fold), and of distinct ABC transporters in P. infestans with acquired resistance to mefenoxam (more then 30‐fold) . Overall, it seems that ATP‐binding cassette superfamily (ABC) transporters might be related with mefenoxam resistance in P. ultimum .…”

High levels of diversity and population structure in the potato late blight pathogen at the Mexico centre of origin

“…Even in the absence of sexual reproduction, P. infestans has overcome major gene host resistance introduced into potato and evolved fungicide insensitivity (Fry ; Childers et al . ; Randall et al . ).…”

“…Both mating types are now present in the United States, but sexual populations are rare and short-lived (Gavino et al 2000;Danies et al 2014). Even in the absence of sexual reproduction, P. infestans has overcome major gene host resistance introduced into potato and evolved fungicide insensitivity (Fry 2008;Childers et al 2015;Randall et al 2014).…”

Pathogen enrichment sequencing (PenSeq) enables population genomic studies in oomycetes

“…(). These neutral markers are well established worldwide and enable the rapid genotypic classification of isolates as part of population genetic studies (Widmark et al ., ; Delgado et al ., ; Fry et al ., ; Childers et al ., ; Tian et al ., ). SSR markers are useful for the study of demographic processes, and can reveal population bottlenecks and founder events, as well as patterns and rates of gene flow.…”