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Evaluation of Round-Up Ready Soybean Cultivars for Resistance to Xanthomonas
axonopodis pv. glycines
L. D. Goradia1, S.L. Daniel1, and G. L.
Hartman2
1Department of Biological Sciences, Eastern Illinois University Charleston, IL
2University
of Illinois at Urbana-Champaign, IL
Introduction
Bacterial pustule is caused by the bacterium Xanthomonas axonopodis pv.
glycines.
It is most prevalent in soybean growing areas, especially in countries like
Australia, China, India, Japan, Korea, Sudan and the United States. X.
axonopodis pv. glycines is a gram negative, aerobic rod shaped
bacterium.
Bacterial Pustule occurs primarily on the foliage of soybeans. The first
symptoms are small, yellow-green spots with reddish-brown centers on the upper
leaf surface . In later stages
dried, broken remnants of pustule may be seen on small necrotic areas bordered
by narrow yellow halos.
A very high level of resistance to bacterial pustule disease is conferred by a
recessive gene designated rxp, originally found in soybean cultivar CNS.
Objective
The
objective of this study was to screen Round-up®
ready soybean cultivars for resistance to X. axonopodis pv.
glycines.
Methods
Round-up® ready soybean cultivars
(525) were grown in the greenhouse for 14-20 days in universal soil mix. Plants
were sprayed with X. axonopodis pv. glycines inoculum. The culture
was grown in Potato dextrose broth at 25oC for 8h. The inoculum size
was adjusted to 108 viable cells/mI. The first trifoliates were damaged by a
perforation needle. Inoculation was done by spraying the inoculum using an
atomizer attached to compressed air-line. Results were recorded after 7 days by counting the number of pustules on
heavily infected trifoliate leaves (Figure 2).
The susceptible varieties were tested again and the experiment was duplicated.
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Figure
2. Heavily infected trifoliate leaf.
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Results
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Of the 525 Round-up® ready soybean
cultivars screened, 152 cultivars (~28%) were found to be susceptible to X.
axonopodis pv. glycines and formed pustule.
Under standard greenhouse conditions, the average number of pustules per plant
was 43 and 18 for susceptible control (P1 520.733) the resistant control
(Williams 82), respectively
When the 152 susceptible cultivars were tested again, 66 were found to be highly
susceptible, based on the observation that these cultivars averaged more
pustules per plant than the susceptible control
(Table1).
Table 1. Highly susceptible cultivars.
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Forty-one (41) cultivars were found to be moderately susceptible based on the
observation that the average number of pustules per plant fell between the range
of susceptible and resistant controls (Table2).
Forty-four (44) cultivars were found to be less susceptible, based on the
observation that these cultivars averaged less pustules per plant than the
resistant control (Table 3).
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Table 2. Moderately susceptible cultivars
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Table
3. Less susceptible cultivars
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Conclusions
These results suggest that resistance is not being maintained in commercial
soybean cultivars which may lead to an increased incidence of bacterial pustule
in the field, thus impacting soybean yields. Further research calls for
detecting if the rxp gene is inserted in these soybean cultivars.
References
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Hartman, G.L. et. al., ed. 1999. Compendium ot Soybean Diseases. APS Press.
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Hartwig, E.E and S.G. Lehman. Agron Journal. 43:226-229. 1951.
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Oh,
C., S. Heu, and Yong-Chul Choi. Plant Pathol. J. 15(1):57-61. 1999.
Acknowledgement
I
would like to thank Dr. Hartmari for the facilities and Ron Warsaw for his help
in acquiring seeds and The Lewis Hanford Tiffany Botany Graduate Research Fund
for funding.
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