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3

The impact of soybean rust on leaf photosynthetic rate: The role of lesion age and resistance genes

Presenter: Elena Prior(1)

Other authors and affiliations: Brenda Kennedy(1), Don Hershman(2), Joe Omielan(1), Claudia V. Godoy(3), Roger Boerma(4), Saratha Kumudini(1). (1)University of Kentucky, Plant & Soil Sciences, Lexington, KY 40546-0312, U.S.A.; (2)University of Kentucky, Plant Pathology, Princeton, KY 42445, U.S.A.; (3)Embrapa - Soja, Londrina, Brazil; (4)University of Georgia, Crop & Soil Sciences, Athens, GA 30602, U.S.A.

Asian soybean rust causes leaf injury and accelerated defoliation. The disease lesions reduce the ability of the leaf to intercept radiant energy and thereby compromises the production potential of the plant. Although there are many studies on the role of defoliation on soybean yield, there is a paucity of information on the role of leaf lesions on plant productivity and how this may differ based on the age of the lesion and plant resistance. The objective of the current study was to determine the impact of Asian soybean rust on leaf production potential. The experiment was conducted as a randomized complete block design with treatments arranged in split-split plots under a controlled environment chamber and was replicated three times. The treatments were (i) inoculum rate (high versus zero), (ii) plant resistance (resistance versus susceptible lines), and (iii) lesion age (sporulating versus nonsporulating). Photosynthesis measurements were taken at the pre- and post-sporulating stages. The leaf area over which photosynthesis measurements were taken was marked and then photographed. These digital images were processed to estimate disease severity as a proportion of the leaf surface. Both resistant and susceptible lines formed lesions. The resistant lines formed red-brown lesions and did not sporulate; the sensitive line formed tan lesions and sporulated 11 days after inoculation. The susceptible line formed a greater number of lesions that covered a greater proportion of the leaf surface than did the resistant line. The sporulating lesions had a greater negative impact on photosynthetic activity than did the nonsporulating lesions.

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