Characterizing soybean rust resistance in Glycine tomentella and effect of temperature and a fungicide on Phakopsora pachyrhizi uredinia production of urediniospores

Soybean rust (Phakopsora pachyrhizi H. Syd. & Syd.) causes significant economic losses in yield in many soybean-growing areas worldwide. Since most if not all commercial soybean cultivars are susceptible, research continues to search and characterize resistance. Perennial Glycine species have many useful traits including rust resistance that if transferred to soybean may provide many economic benefits. In this study, four F2 populations of G. tomentella derived from crossing a rust susceptible (PI 441011) with four rust resistant accessions (441008, 483218, 509501, and 583970) were evaluated for rust resistance. About 100 F2 individuals per population and parents were inoculated with P. pachyrhizi under controlled greenhouse conditions. Rust resistance was assessed on a qualitative scale based on lesion color and sporulation of uredinia. Segregation analysis of F2 populations indicated several genetic models explained the inheritance of resistance based on how the data were interpreted; the models included one dominant gene and two dominant genes. The rust resistance gene or genes in these four accessions of G. tomentella may represent unique resistance to P. pachyrhizi not found in soybean. Survival and production of urediniospores of P. pachyrhizi depends on its hosts, the environment, and exposure to fungicides. In this study, uredinia in infected leaves were washed, incubated at different temperatures and fungicide concentrations, and evaluated for re-sporulation and germination of urediniospores. There was a significant (P < 0.05) temperature effect on uredinia production of urediniospores and their germination. Uredinia produced the most urediniospores at 15 and 20°C and the least at 30 and 35°C. Germination rate of urediniospores was 84% when produced from uredinia incubated at 20°C, which was the highest compared to the other temperatures. When urediniospores of 15 isolates were exposed to varying concentrations of azoxystrobin, the effective concentration 50 values ranged from 0.01 to 0.40 ppm with an isolate from Arkansas having a significantly (P < 0.05) higher value than the other isolates. Detached inoculated leaflets incubated on azoxystrobin amended agar immediately or up to 6 days after inoculation had significantly (P < 0.05) lower leaf area affected and number of sporulating uredinia than inoculated leaves that were not incubated with the fungicide treatment for 6, 9, 12 and 15 d after inoculation. The results show that temperatures and a fungicide play a significant role in uredinia production of urediniospores and their germination. This information could have significant implications to the epidemiology of soybean rust as it relates to inoculum density.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2010

Author dc:creator

• Chang, Sungyul

Contributors dc:contributor

• Hartman, Glen L.

• soybean rust
• Glycine tomentella
• uredina
• urediniospres
• Phakopsora pachyrhizi

Statement dc:rights

• Copyright 2010 Sungyul Chang

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/16904

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/16904