Abstract
Although Pythium myriotylum is a very destructive root pathogen of cocoyam, the host defense response in this plant-pathogen interaction has not been fully studied. Four cocoyam germplasm accessions were inoculated with P. myriotylum, and their induced defense responses were characterized. The induction and spatio-temporal accumulation of chitinase and b-1,3-glucanase were determined by enzymatic activity assays of crude root extracts from inoculated and non-inoculated (control) plants, sampled at 0, 2, 4, 6 and 8 days post inoculation (dpi). Furthermore, induced proteins were extracted from roots of inoculated and control tolerant (RO1054 and RO3015) and susceptible (RO2063) accessions at 8 dpi, and characterized by isoelectric focusing (IEF), sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analyses. Chitinase and b-1,3-glucanase were consistently produced in high amounts in the roots of the tolerant accession RO1054, 8 days after inoculation. SDS-PAGE and immunoblotting showed that induced chitinases (37, 35 and 33 kDa) in the tolerant cocoyams were immunologically related to PR-3a purified from barley leaves inoculated with Erysiphe graminis f. sp. hordei, and induced osmotins (42-45 kDa) were immunologically related to osmotins purified from cultured NaCl-adapted tobacco protoplasts. These results suggest that tolerance in cocoyam infected with P. myriotylum may be associated in part with the production of pathogenesis-related (PR) proteins including one hydrolytic enzyme of known antifungal activity (PR-3). Key words: b-1,3-glucanase, chitinase, cocoyam, PR protein, Pythium myriotylum, osmotin.
Highlights
In nduction and d chara acteriz zation of pathogen nesis-re elated proteins s in roots of cocoy yam
The objective of this study was to determine and characterize host-specific defense related proteins induced in cocoyam, their serological relationship to known PR proteins and if there is temporal accumulation of these PR proteins in response to P. myriotylum infection
There was a significant increase in chitinase activity in roots of all inoculated plants, compared to the controls
Summary
In nduction and d chara acteriz zation of pathogen nesis-re elated proteins s in roots of cocoy yam Four c cocoyam ge ermplasm accessions es were s were inoc culated with h P. myrio otylum, and their indu uced defens se response characterized. -1,3-glucana ase were determined d by enzyma atic activity assays of crude c root ex xtracts from m inoculated and non-in noculated (control) plants, sample ed at 0, 2, 4,, 6 and 8 day ys post inoc culation (dpi)). Furthermo ore, induced proteins were extrac cted from ro oots of inoc culated and control tolerrant 015) and sus sceptible (RO2063) accessions at a 8 dpi, and characterize ed by isoele ectric focusin ng (IEF), sod dium dodecy yl sulfate polyacrylam mide gel ele ectrophoresiis Chitinase an nd -1,3glucanase were w consisttently produc ced in high amounts a in tthe roots of tthe tolerant a accession R
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