Abstract
Clubroot, caused by Plasmodiophora brassicae Woronin, is one of the most important diseases of oilseed rape (Brassica napus L.). The rapid erosion of monogenic resistance in clubroot-resistant (CR) varieties underscores the need to diversify resistance sources controlling disease severity and traits related to pathogen fitness, such as resting spore production. The genetic control of disease index (DI) and resting spores per plant (RSP) was evaluated in a doubled haploid (DH) population consisting of 114 winter oilseed rape lines, obtained from the cross ‘Aviso’ × ‘Montego,’ inoculated with P. brassicae isolate “eH.” Linkage analysis allowed the identification of three quantitative trait loci (QTLs) controlling DI (PbBn_di_A02, PbBn_di_A04, and PbBn_di_C03). A significant decrease in DI was observed when combining effects of the three resistance alleles at these QTLs. Only one QTL, PbBn_rsp_C03, was found to control RSP, reducing resting spore production by 40%. PbBn_rsp_C03 partially overlapped with PbBn_di_C03 in a nucleotide-binding leucine-rich repeat (NLR) gene-containing region. Consideration of both DI and RSP in breeding for clubroot resistance is recommended for the long-term management of this disease.
Highlights
Clubroot, caused by the obligate parasite Plasmodiophora brassicae Woronin, is one of the most important diseases of cruciferous crops worldwide, causing significant yield and quality losses in oilseed rape and other Brassicas (Dixon, 2009)
Research on clubroot resistance has focused mainly on disease severity expressed as a disease index (DI)
Resting spore production in host genotypes has not been examined to the same extent, this is an important measurement of pathogen fitness, affecting inoculum build up in infested fields
Summary
Clubroot, caused by the obligate parasite Plasmodiophora brassicae Woronin, is one of the most important diseases of cruciferous crops worldwide, causing significant yield and quality losses in oilseed rape (canola; Brassica napus L.) and other Brassicas (Dixon, 2009). The pathogen survives in Abbreviations: CR, clubroot-resistant; dai, days after inoculation; DH, doubled haploid; DI, disease index; RSP, resting spores per plant. Four New QTLs Controlling Clubroot the soil as long-lived resting spores (Kageyama and Asano, 2009). The resting spores germinate to produce primary zoospores, which infect the host root hairs. The secondary zoospores penetrate the cortical tissue and develop into intracellular secondary plasmodia, which cleave to produce a new generation of resting spores (Kageyama and Asano, 2009). These resting spores are released back into the soil, where they serve as inoculum for future infections. As many as 1 × 1010 resting spores per g of gall tissue may be produced on a susceptible B. napus host (Hwang et al, 2013)
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