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A Comparison of Greenhouse and Field Screening Methods for Blackleg Resistance in Doubled Haploid Lines of Brassica napus. V. K. BANSAL, Research Associate, Department of Plant Science, University of Alberta, Edmonton, AB, Canada T6G 2P5. P. D. KHARBANDA, Plant Pathologist, Alberta Environmental Centre, Vegreville, AB, Canada T9C 1T4; and G. R. STRINGAM, Professor, M. R. THIAGARAJAH, Research Associate, and J. P. TEWARI, Professor, Department of Plant Science, University of Alberta, Edmonton, AB, Canada T6G 2P5. Plant Dis. 78: 276-281. Accepted for publication 28 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0276.

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 0.82) with greenhouse disease severity data for all three growth stages. In greenhouse experiments, disease seventy data for different growth stages were also highly correlated (r 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.

Keyword(s): host resistance, Phoma lingam, stem canker