A COMPARISON OF GREENHOUSE AND FIELD SCREENING METHODS FOR BLACKLEG RESISTANCE IN DOUBLED HAPLOID LINES OF BRASSICA-NAPUS

A group of 87 doubled haploid (DH) lines of canola (Brassica napus) were screened for blackleg resistance in the greenhouse at three plant growth stages: cotyledon, true leaf, and adult plant. Disease severity data were calculated on 33 DH lines, which were subsequently screened in field experiments over 2 yr along with parental lines and controls. The inoculum level used in field experiments was the same as that used in greenhouse screening. Blackleg disease severity and disease incidence on field-grown lines were highly correlated (r greater-than-or-equal-to 0.82) with greenhouse disease severity data for all three growth stages. In greenhouse experiments, disease severity data for different growth stages were also highly correlated (r greater-than-or-equal-to 0.83). Inoculation of DH seedlings at the cotyledon stage in the greenhouse was a reliable method for evaluating blackleg resistance. Disease severity and disease incidence in field experiments also were highly correlated (r = 0.996), suggesting that disease incidence may be used as an estimator of disease severity in field surveys.