Submitted to: National Soybean Rust Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/2006
Publication Date: 8/2/2006
Citation: Twizeyimana, M., Bandyopadhyay, R., Ojiambo, P., Pauls, C., Hartman, G.L. 2006. A detached leaf method to evaluate soybean for resistance to rust. National Soybean Rust Symposium. Paper No. 41. Available at: http//plantmanagementnetwork.org/infocenter/topic/soybeanrust/2006/posters/41.asp.
Technical Abstract: The potential of Asian soybean rust to cause severe yield losses makes it the most serious soybean disease worldwide. The causal agent, Phakopsora pachyrhizi, is an obligate parasite and a highly variable pathogen. Host plant resistance may offer the most practical solution to the disease. Rapid methods to evaluate host resistance and pathogen variability need to be developed to hasten progress in developing rust-resistant cultivars. The objective of our research was to develop a detached leaf method to evaluate soybeans for resistance to rust. We optimized the following components of the method: concentration of hormones to retard senescence of detached leaves, leaf age, and spore concentrations for inoculation. Pieces of detached leaves from 3 to 4-week-old plants of 14 lines were placed on 1% agar amended with 10 µg/g kinetin and could be used for resistance evaluation when inoculated with 1 million spores per ml. Leaves remained green for nearly 30 days at 22ºC. Fourteen lines with varying resistance levels were evaluated for days to lesion appearance, days to pustule formation, days to pustule eruption, lesion number, lesion length, lesion type, number of pustules and spores per pustule. Parallel experiments were completed in the field, using detached leaf, and greenhouse screening. Pearson correlation coefficients were highly significant between detached leaf and greenhouse for various disease evaluation parameters (r = 0.86 to 0.99; P < 0.01), and between detached leaf and field screening for plant reaction (r = 1.0) and sporulation (r = 0.82; P < 0.01) across genotypes. The detached leaf assay is a rapid method to screen soybean for rust resistance and maintain pure cultures of P. pachyrhizi.