Impact of Soybean Rust on Leaf Photosynthetic Capacity of Resistant and Susceptible Soybean Genotypes.

One measure of disease damage is to determine the percentage leaf area that is covered by disease lesions.  These lesions reduce the ability of the leaf to intercept maximum radiant energy and thereby compromise the production potential of the plant.  A biotrophic pathogen such as Soybean rust may well have impact on leaf production potential which exceeds that directly related to the amount of radiation intercepted by the leaf.   The objective of the current study was to determine the impact of Asian soybean rust on leaf production potential.  The experiment was as a randomized complete block, split-split plot study conducted in a controlled environment chamber, with three replications over time. The treatments were 1) inoculum rate (high versus zero), 2) plant resistance (resistance versus susceptible lines), and 3) lesion age (sporulating versus non sporulating). 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 did sporulate 11 days after inoculation.