Effect of root rot and stem canker caused by Leptosphaeria maculans on yield of Brassica napus and measures for control in the field
S. J. Sprague A , J. A. Kirkegaard A C , B. J. Howlett B and J. Graham AA CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
B School of Botany, The University of Melbourne, Parkville, Vic. 3010, Australia.
C Corresponding author. Email: john.kirkegaard@csiro.au
Crop and Pasture Science 61(1) 50-58 https://doi.org/10.1071/CP09195
Submitted: 3 July 2009 Accepted: 14 September 2009 Published: 17 December 2009
Abstract
Leptosphaeria maculans causes blackleg of Brassica napus (canola), manifesting in symptoms including leaf lesions, stem canker, and root rot. Root rot is an extension of the stem canker phase of the disease resulting from foliar infection; however, the role of root rot in grain yield loss has not been investigated. Field experiments were conducted in south-eastern Australia to determine the efficacy of fungicides and host resistance to stem canker for the control of root rot, along with the association between root rot severity and grain yield. Fungicides applied as a seed dressing (fluquinconazole) or coated on fertiliser (flutriafol) reduced root rot severity by 16 and 41%, respectively. Root rot severity was 78% less in a B. napus cultivar with an Australian Blackleg Rating (ABR) of 9.0 (highly resistant to stem canker) than in a moderately resistant cultivar (ABR 5.5), and was also reduced in Brassica species with good resistance to stem canker. Root rot caused little or no additional reduction in yield or harvest index of individual B. napus plants above that caused by stem canker. Individual upright plants with greater than 80% of the stem cross-section blackened had significantly reduced seed yield; however, this was influenced by rainfall during the grain-filling period. This study shows that current management strategies for stem canker caused by L. maculans also control root rot in B. napus, as although the symptoms in roots are severe, these symptoms have no additional effect on yield.
Additional keywords: disease severity, oilseed rape, Phoma lingam, phoma stem canker.
Acknowledgments
We thank Neil Wratten and Trent Potter for sowing field trials, Steve Marcroft and John Graham for assistance with disease assessments, and Peter Hamblin for management and harvest of field trials in New South Wales. I thank Rana Munns for providing advice in reviewing the manuscript. Funding for S. Sprague was provided by the Australian Grains Research and Development Corporation.
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