Evaluation of the mite-fungus association responsible for the yellowing in the Welsh onion Allium fistulosum

Abstract

Under field, greenhouse and laboratory conditions, the study evaluated the mite-fungus-yellowing association in the Welsh onion Allium fistulosum, in recently established and mature crops, in the localities of San Francisco and Alianza (Pasto, Colombia), located at 2650 m elevation, with a temperature of 12°C and an average annual rainfall of 1100 mm annual. In recently established crops, the incidence of yellowing was 11.0% and 14.2%, respectively, with no difference between localities. Similarly, there were no significant difference between localities for the mature crop, with an incidence of 38.4% and 43.40%, respectively. In the sampling at each locality two kinds of mites were found which are responsible for the yellowing of onion, Rhizoglyphus echinophus and Rhizoglyphus vincatus (Acari: Acaridae), being R. echinopus with the greatest percentage of affected plants (56.7%). The fungi responsible for the damage to the onion crops were: Phoma sp., Botrytis sp., Gliocladium and Fusarium oxysporum. In the greenhouse the greatest percentage of affected plants had F. oxysporum (43.3%) and the complex F. oxysporum and Phoma sp. (40.0%). The association of the mite R. echinopus and the fungus F. oxysporum, produced the greatest percentage of affected plants (80.0%). Moreover, R. echinopus was found to present the most descendents when in the presence of F. oxysporum (78 individuals in 72 hours).