Characterization of oomycete species causing soybean diseases in Illinois and management applications

Phytophthora root and stem rot (PRR) and seedling diseases caused by oomycetes, are two of the most important yield limitations for soybean production in the US Midwest. Several species of Phytophthora and Pythium cause PRR and seedlings diseases, respectively. PRR is managed using cultivars with single resistance genes (Rps genes) in combination with seed treatments. In addition to Rps genes, cultivars with quantitative resistance or partial resistance are available for PRR management. The objective of this thesis is to develop precision management techniques for soybean diseases caused by oomycetes. Field experiments were conducted to evaluate resistant lines combined with an ethaboxam and metalaxyl seed treatment for PRR management. Experiments were conducted in three Illinois locations in 2017. Experiments were repeated in 2018 in one location in Urbana and one location in Iowa. The seed treatment protected stands in all locations in both years, but significant yield increases were only observed in high disease pressure environments. Both resistant and susceptible cultivars benefited from the seed treatment. For the second objective, soil samples and symptomatic plants were collected from 40 counties in Illinois to characterize the population of oomycetes in the state. Pythium ultimum var. ultimum (42%) was the most abundant species, followed by Ph. sojae (7%) and Ph. sansomeana (4%). In addition, ten more Pythium species were identified. Virulence of all Phytophthora spp. isolates was evaluated by inoculating 12 soybean differentials with known Rps genes. Sixteen pathotypes were identified among the Ph. sojae isolates, and no pathotypes were identified for Ph. sansomeana. The aggressiveness and fungicide sensitivity of the isolates was also evaluated. Aggressiveness assays were performed in the greenhouse for Phytophtora spp. isolates, and a petri plate assay was used to assess the aggressiveness of Pythium isolates. Ph. sojae was more aggressive compared to Ph. sansomeana. Py. ultimun var. ultimum, Py. ultimun var. sporangium, Py. irregulare and Py. aphanidermatum were the most aggressive Pythium species to soybean. Both Phytophthora spp. were sensitive to metalaxyl, mefenoxam, azoxystrobin, and ethaboxam. There were Pythium isolates insensitive to azoxystrobin and ethaboxam.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2021

Author dc:creator

• Cerritos Garcia, Daniel Guillermo

Contributors dc:contributor

• Mideros, Santiago X
• Diers, Brian W
• Kleczewski , Nathan M

• oomycetes, Phytophthora sojae
• Phytophthora sansomeana
• seed treatments
• pathotype
• Pythium
• aggressiveness

Statement dc:rights

• Copyright 2021 Daniel Cerritos Garcia

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/110449

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/110449