Evaluation of Pythium root rot and damping off resistance in the ancestral lines of North American soybean cultivars and chemical control of the active ingredient ethaboxam in seed treatments

McLachlan, Katherine Susan

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Description

Title

Evaluation of Pythium root rot and damping off resistance in the ancestral lines of North American soybean cultivars and chemical control of the active ingredient ethaboxam in seed treatments

Author(s)

McLachlan, Katherine Susan

Issue Date

2016-04-27

Director of Research (if dissertation) or Advisor (if thesis)

• Walker, David R.
• Bradley, Carl A

Committee Member(s)

Diers, Brian

Department of Study

Crop Sciences

Discipline

Crop Sciences

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Pythium ultimum var. ultimum
• soybean
• oomycete
• seed treatment

Abstract

Effects of Pythium ultimum var. ultimum and other Pythium species on the North American Ancestral Soybean Lines A trend towards planting soybean (Glycine max (L.) Merrill) earlier in the growing season has made seedling diseases more prominent. A survey of biotic causes of yield loss between 2006 and 2009 rated seedling diseases second in only to soybean cyst nematode. Pythium ultimum var. ultimum is an oomycete that favors cool wet conditions in early spring and causes seed decay, root rot, and seedling damping off. Resistance to this pathogen has yet to be reported in soybean. The objective of this study was to evaluate the response of the North American ancestral soybean lines and their first progeny to determine if the genotypes had resistance. These lines contain approximately 99% of the genes of modern North American cultivars. An Illinois isolate of P. ultimum var. ultimum was used for the screen. Fourteen of the 90 ancestral and first progeny lines were found to have varying levels of partial resistance. A subset of five lines, four resistant and one susceptible, from the ancestral screen were then screened for resistance against isolates of three different species of Pythium that were collected in Illinois: P. ultimum var. ultimum from the ancestral screen, P. irregulare, and P. sylvaticum. The results showed that the partially resistant lines conferred resistance across the three Pythium species. The results also revealed that there were different levels of aggressiveness among the isolates of the Pythium species. P. ultimum var. ultimum showed to be the most aggressive, followed by P. irregulare, then P. sylvaticum, respectively. The lines identified in both studies could provide potential sources of resistance to Pythium damping-off and root rot for modern soybean breeding programs. Effects of the active ingredient, ethaboxam, in fungicide seed treatments on stand establishment and yield of soybean in Illinois. Seed treatments are a popular management tactic for seedling diseases. The active ingredient, metalaxyl, has been on the market for over 30 years to control oomycetes, especially Pythium spp. and Phytophthora sojae. A new active ingredient, ethaboxam, has recently come to the fungicide seed market as a new management tool against oomycetes. In order to understand the effects of the new active ingredient, non-inoculated field trials were established across the state of Illinois in 2014 and 2015. Trials were placed at the University of Illinois research stations near DeKalb, Urbana, and Dixon Springs. Six fungicide seed treatments consisted of an (1) untreated control, (2) metalaxyl (Sebring 2.65ST; Valent USA Corp., Walnut Creek, CA) at 4g a.i./100kg of seed, (3) ethaboxam (Intego Solo; Valent USA Corp., Walnut Creek, CA) at 7.5g a.i./100kg of seed, (4) ethaboxam + metalaxyl at 7.5g + 2g a.i./100kg of seed, (5) ethaboxam + metalaxyl at 7.5g + 4g a.i./100kg seed, and (6) ethaboxam + metalaxyl at 7.5g + 7.5g a.i./100kg of seed. A broad spectrum fungicide of Rizolex with the active ingredient of tolclofos-methyl at 5 g a.i./100 kg of seed (Valent USA Corp., Walnut Creek, CA) was applied to all of the seed treatments except the untreated control. Plant stands from each plot were taken within three weeks of emergence, R1 root weights, shoot weights, root rot severity were collected mid-growing season and seed yield was collected at harvest. Fungicide seed treatments had a significant effect on plant stand (P=.0002), but not on yield (P=0.7466), root weigh per plot (P=0.0823), shoot weight per plot (P=0.1873), and root rot per plot (P=0.4017). The untreated control had significantly lower plant stand that the other treatments. The treatments with the varying ratios of ethaboxam to metalaxyl were not significantly different from each other, but the treatment with 7.5 g + 7.5g a.i. of ethaboxam + metalaxyl had significantly higher plant stands than the ethaboxam only treatment. Yields from each of the treatments were not significantly different from each other including the untreated control. The results show that seed treatments with ethaboxam and metalaxyl could help protect against stand loss associated with oomycetes seedling diseases.

Graduation Semester

2016-05

Type of Resource

text

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Copyright and License Information

Copyright 2016 Katherine McLachlan

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