Pythium, Phytophthora, and Phytopythium spp. associated with soybean in Minnesota, their relative aggressiveness on soybean and corn, and their sensitivity to seed treatment fungicides

L. Radmer, G. Anderson, D. M. Malvick, J. E. Kurle, A. Rendahl, A. Mallik

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

Pythium spp. cause seed decay, damping-off, and root rot in soybean and corn; however, their diversity and importance as pathogens in Minnesota are unknown. Our objectives were to identify the Pythium spp. present in Minnesota soybean fields, determine their aggressiveness on corn and soybean, and investigate their sensitivity to seed treatment fungicides. For identification, sequences obtained using internal transcribed space ITS4 and ITS1 primers were compared with reference sequences in the National Center for Biotechnology Information database. Seedling and soil samples yielded over 30 oomycete species. Aggressiveness was determined using two methods; a seed assay, which also examined temperature effects on aggressiveness, and a seedling assay. Of 21 species evaluated, seven Pythium spp. were pathogenic on both soybean and corn, reducing root growth by 20% or more while two Pythium and one Phytopythium spp. were pathogenic only on soybean. Aggressiveness of many isolates increased as temperature increased from 15°C to 25°C. The sensitivity of 10 pathogenic species to azoxystrobin, ethaboxam, mefenoxam, pyraclostrobin, or trifloxystrobin was tested. EC50 values for mefenoxam and ethaboxam were 10−2 of those to strobilurin fungicides. Pythium spp. in Minnesota are diverse and a significant cause of seedling disease on soybean and corn. Most Pythium spp. isolated in this study were more sensitive to mefenoxam and ethaboxam than to strobilurin fungicides.

Original languageEnglish (US)
Pages (from-to)62-72
Number of pages11
JournalPlant disease
Volume101
Issue number1
DOIs
StatePublished - Jan 2017

Bibliographical note

Funding Information:
We thank the research group of M. Chilvers at Michigan State University for help with selection of Pythium isolates from seedlings that were used in this study. This was part of a large collaborative effort that will be published separately. Funding for this research was provided by the Minnesota Soybean Research and Promotion Council, The North Central Soybean Research Program, the USDA National Institute of Food and Agriculture, and The Minnesota Agricultural Experiment Station.

Publisher Copyright:
© 2017 The American Phytopathological Society.

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