Induction and characterization of pathogenesis-related proteins in roots of cocoyam (Xanthosoma sagittifolium [L] Schott) infected with Pythium myriotylum

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.

The Battle for a Sustainable Food Supply

Since the time that Homo sapiens took up farming, a battle has been waged against pests and diseases which can cause significant losses in crop yield and threaten a sustainable food supply. Initially, early control techniques included religious practices or folk magic, hand removal of weeds and insects, and “chemical” techniques such as smokes, easily available minerals, oils and plant extracts known to have pesticidal activity. But it was not until the early twentieth century that real progress was made when a large number of compounds became available for testing as pesticides due to the upsurge in organic chemistry. The period after the 1940s saw the introduction of important families of chemicals, such as the phenoxy acid herbicides, the organochlorine insecticides and the dithiocarbamate fungicides. The introduction of new pesticides led to significant yield increases, but concern arose over their possible negative effects on human health and the environment. In time, resistance started to occur, making these pesticides less effective. This led agrochemical companies putting in place research looking for new modes of action and giving less toxic and more environmentally friendly products. These research programmes gave rise to new pesticide families, such as the sulfonylurea herbicides, the strobilurin fungicides and the neonicotinoid insecticide classes