Submitted to: Sugar Journal
Publication Type: Abstract Only
Publication Acceptance Date: 5/8/2011
Publication Date: 6/8/2011
Citation: Zhao, D., Glynn, N.C., Glaz, B.S., Comstock, J.C., Sood, S.G. 2011. Physiological Responses of Sugarcane to Orange Rust Infection. Sugar Journal. 29.
Technical Abstract: Sugarcane orange rust, caused by Puccinia kuehnii, is a relatively new disease in the United States that substantially reduces yields in susceptible sugarcane cultivars in Florida. The objective of this study was to determine physiological responses of sugarcane to orange rust infection by quantifying effects of the disease on leaf chlorophyll level (SPAD index), net photosynthetic rate, dark respiration, stomatal conductance, intercellular CO2 concentration, and the relationships between these leaf physiological traits and rust disease ratings. Treatments included four sugarcane cultivars (CP 72-2086, CP 88-1762, CP 89-2143, and CPCL 99-4455) and two rust inoculations (not inoculated and inoculated). Spores of orange rust were collected from infected leaves of field-grown sugarcane prior to inoculation. Plants growing in pots were inoculated with these field-collected orange rust spores using a leaf whorl inoculation method at the 5-leaf stage. A disease rating was assigned weekly using a scale from 0 to 4. At the same dates of rust assessment, SPAD index and photosynthetic components of the top visible dewlap (TVD) leaves were measured. About 4 weeks after inoculation, these measurements were taken on the rust infected and uninfected portions of inoculated leaves. No significant differences were detected between the non-inoculated and inoculated plants for any physiological variable, when measurements were taken on TVD leaves or uninfected portions of inoculated leaves. However, the rust infected portions of inoculated leaves showed significant reductions in SPAD index, stomatal conductance, leaf transpiration rate, and net photosynthetic rate at disease ratings = 2. The infected leaf portions with rust ratings of 4 had 43-47% less leaf SPAD index and net photosynthetic rate compared with the non-inoculated control. The rust infected portion of the inoculated leaves had increased intercellular CO2 concentration and dark respiration rate. Although leaf SPAD index, photosynthetic rate, stomatal conductance, and transpiration rate at the rust infected portion of the leaves decreased linearly with increased rust rating, the effect of orange rust on net photosynthetic rate was much greater than that on stomatal conductance and transpiration. Reduction in leaf photosynthesis by orange rust under low light was greater than that under high light intensity. These results help improve our understanding of orange rust etiology and the physiological bases of sugarcane yield loss caused by orange rust. The quantitative relationships between orange rust ratings and photosynthesis components could be used for modeling the impact of orange rust on leaf photosynthesis and plant growth in sugarcane