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United States Department of Agriculture

Agricultural Research Service

Research Project: SOYBEAN DISEASE AND PEST MANAGEMENT Title: Culturing Phakopsora pachyrhizi on detached leaves and Urediniospore survival at different temperatures and relative humidities

Authors
item Twizeyimana, M -
item Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2010
Publication Date: December 1, 2010
Repository URL: http://hdl.handle.net/10113/46327
Citation: Twizeyimana, M., Hartman, G.L. 2010. Culturing Phakopsora pachyrhizi on detached leaves and Urediniospore survival at different temperatures and relative humidities. Plant Disease. 94:1453-1460.

Interpretive Summary: Soybean rust, caused by the obligate fungal pathogen Phakopsora pachyrhizi, is one of the most serious foliar diseases of soybean worldwide. To successfully isolate, culture and multiply the pathogen, a detached-leaf assay previously developed was reevaluated; and in a separate study, the effect of temperature and relative humidity (RH) on soybean rust urediniospore survival was evaluated. The detached-leaf assay using agar medium amended with 6-benzylaminopurine performed better in retarding leaf chlorosis than filter paper alone. Temperature and RH played significant roles in survival of urediniospores as measured by germination rates. For example, urediniospores maintained at room temperature survived for 18 days when kept on infected leaves and up to 30 days when pre-dehydrated for 12 hours. Improvement in P. pachyrhizi cultural techniques and understanding of urediniospore survival will enhance our knowledge of the pathogen biology, the host-plant relationship, and conditions that favor the infection, development, and survival of the pathogen. This information will be useful to plant pathologists, epidemiologists, and other scientists interested in the biology of the soybean rust pathogen.

Technical Abstract: Soybean rust, caused by the obligate fungal pathogen Phakopsora pachyrhizi, is one of the most serious foliar diseases of soybean worldwide. To successfully isolate, culture and multiply the pathogen, a detached-leaf assay previously developed was reevaluated; and in a separate study, the effect of temperature and relative humidity (RH) on soybean rust urediniospore survival was evaluated. Three susceptible soybean genotypes, Williams 82, TGx 1485-1D and Taki Hime, and two genotypes with resistance genes, PI 462312 (Rpp3) and PI 459025B (Rpp4), were used in the detached leaf assay; only Williams 82 was used for urediniospore survival. The detached-leaf assay using agar medium amended with 6-benzylaminopurine (BAP) performed better in retarding leaf chlorosis than filter paper alone. Among the three susceptible genotypes, detached leaves of Williams 82 had the lowest level of leaf chlorosis, and often allowed for the highest urediniospore production and germination rate. Temperature and RH played significant roles in survival of urediniospores as measured by germination rates. For example, urediniospores maintained at room temperature (23-24 C at 55-60% RH) survived for 18 days when kept on infected leaves and up to 30 days when dehydrated for 12 hours before being placed in cryovials. In the RH experiment, urediniospores harvested from infected leaf pieces maintained at 85% RH (23-24 C) had highest germination and longevity. Improvement in P. pachyrhizi cultural techniques and understanding of urediniospore survival will enhance our knowledge of the pathogen biology, the host-plant relationship, and conditions that favor the infection, development, and survival of the pathogen.

Last Modified: 12/21/2014
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