Use of Turnip (Brassica rapa var. rapifera) and Rutabaga (B. napus var. napobrassica) for the Improvement of Clubroot Resistance in Spring B. napus Canola

Abstract

Clubroot disease, caused by Plasmodiophora brassicae, is one of the most serious threats to spring Brassica napus canola production in Canada. Growing of clubroot-resistant cultivars is the key to control this disease. The genetic base of the Canadian spring B. napus canola for clubroot resistance genes is narrow, and a strong resistance to the newly evolved pathotypes cannot be achieved using the available resistance genes. In this study, two advanced-generation breeding populations of spring B. napus canola, a BC1F8 population derived from spring B. napus canola × B. rapa subsp. rapifera European fodder turnip accession ECD 01 interspecific cross and a doubled haloid (DH) population developed from spring B. napus canola × Canola line carrying clubroot resistance of B. napus var. napobrassica rutabaga cv. Polycross, were accessed for resistance to different pathotypes of P. brassicae. Several canola lines carrying resistance to multiple P. brassicae pathotypes including 2B, 3A and 5x (L-G1) were identified in both populations, and resistance to these pathotypes showed significant positive correlation suggesting that the genetic control of resistance to these two pathotypes might be under a similar genetic control. QTL mapping by using the DH population identified the chromosomes A03 and A08 carry clubroot resistance. In case of the A03, a genomic region located at about 32-54 cM region conferred resistance to P. brassicae pathotypes 2B, 3A, 5x (L-G1), 3H and 3D, and a region at about 210-220 cM conferred resistance to pathotypes 3H and 3D; these two genomic regions could be positioned at about 16 and 25 Mb of the physical map of A03. In case of A08, a region located at 0.0-2.35 cM contributed resistance to pathotypes 2B, 5x (L-G1), 3H and 3D, and a region located at 2.35-5.55 cM contributed resistance to pathotype 3A; these two genetic regions could be positioned at about 11-13 Mb of A08. Thus, results from this thesis research demonstrated that the turnip accession ECD 01 and rutabaga cv. Polycross carry resistance to different P. brassicae and can be used to broaden the genetic base of spring B. napus canola for resistance to clubroot disease. The knowledge of the genomic regions of A03 and A08 carrying clubroot resistance can be used in the breeding, as well as for fine-mapping of the QTL regions and map-based cloning of the clubroot resistance genes.