Greenhouse and Field Tests for Determining the Resistance of Onion Lines to Fusarium Basal Rot1

Abstract

A greenhouse method was developed for testing the resistance of onion lines to Fusarium basal rot. Roots of onion seedlings at the first true leaf stage were dipped in a heavy suspension of the pathogen. The seedlings were then planted in silica sand and grown at a soil temperature of 24° C. The first disease symptoms in a susceptible progeny appeared in about 10 days and continued to appear for up to 10 to 14 days thereafter. Infected seedlings died or were severely stunted in growth. Resistant seedlings exhibited no disease symptoms.Field tests were conducted on muck soil known to be heavily infested with the Fusarium organism. Counts of infected plants were taken during the growing season and at harvest time. All bulbs which did not show disease symptoms were then put in cold storage for 4 months. A considerable number of bulbs which appeared to be uninfected at harvest time showed the typical decay after storage. After storage, infected and non-infected bulbs were counted and a total per cent infected was calculated.A high positive correlation existed between greenhouse and field results.