Chinese cabbage (Brassica rapa ssp. pekinensis) – a valuable source of resistance to clubroot (Plasmodiophora brassicae)

Abstract

Clubroot, caused by the protozoan parasite Plasmodiophora brassicae Woronin, is one of the most damaging diseases of Brassica napus worldwide. Resistant plant material is valuable for cultivation in all areas of high incidence of the disease and intensive growth of oilseed rape. We have evaluated clubroot resistance, plant morphology and seed quality in 15 lines of an F 4 generation and selected six lines of F 5 generation of interspecific hybrids obtained from a cross between a male sterile line of B. napus 'MS8', selected from resynthesized oilseed rape (B. rapa ssp. chinensis × B. oleracea var. gemmifera) and an ecotype of B. rapa ssp. pekinensis. Clubroot resistance was evaluated using a bioassay with P 1 -P 5 pathotypes of P. brassicae (according to the classification of Somé et al. 1996). The resistance to the pathotype P 1 was successfully fixed in the F 5 generation, and improved in some lines in respect to the pathotypes P 2 -P 4 . The resistance to P 1 and the other tested pathotypes was not linked. Characterization of plant material included recent techniques of FISH and BAC-FISH with a special focus on the analysis of ribosomal DNA (rDNA) of selected individuals. Two hybrid lines combined high levels of resistance with appropriate plant morphology, good seed quality traits and a stable chromosome number and arrangement. Recent techniques of 'chromosome painting' provided good insight into chromosome organization in the hybrids obtained, and offered opportunities of further improvement of the breeding process.

Chromosome instabilities in resynthesized Brassica napus revealed by FISH

“…Uppercase letters denote the genomic origin of tagged chromosomes; Arabic numerals refer to the nomenclature of rDNA-bearing chromosomes; *Represents chromosomes A5, A6, and A9; white lines with intervals indicating recombination breakpoints. Scale bars 5 μm synthetic B. napus lines (Książczyk et al 2011;Niemann et al 2017;.…”

“…Using rDNA-FISH mapping combined with the C-genome-specific BAC probe, it is possible to recognize chromosome pairs: A1 (bearing 5S and 35S rDNA in opposite arms), A3 (bearing 35S rDNA (NOR) and 5S rDNA), A10 and C4 (bearing 5S rDNA), C7 (35S rDNA) and C8 (35S rDNA (NOR)) (Hasterok et al 2006 ; Xiong and Pires 2011 ). Additionally, this approach can reveal chromosome rearrangements between the A and C genomes in RS lines of Brassica (Szadkowski et al 2010 ; Książczyk et al 2011 ; Xiong et al 2011 ; Niemann et al 2017 ). Many studies have demonstrated genetic changes caused by homoeologous recombination between ancestral genomes (Parkin et al 1995 ; Udall et al 2005 ; Xiong et al 2011 ; Niemann et al 2017 ), which can contribute to the formation of new gene combinations and can also destabilize the karyotype (Gaeta and Pires 2010 ).…”

“…Additionally, this approach can reveal chromosome rearrangements between the A and C genomes in RS lines of Brassica (Szadkowski et al 2010 ; Książczyk et al 2011 ; Xiong et al 2011 ; Niemann et al 2017 ). Many studies have demonstrated genetic changes caused by homoeologous recombination between ancestral genomes (Parkin et al 1995 ; Udall et al 2005 ; Xiong et al 2011 ; Niemann et al 2017 ), which can contribute to the formation of new gene combinations and can also destabilize the karyotype (Gaeta and Pires 2010 ). Thus, in studying hybrid forms, it is important to verify their genetic variation, which might be detected at the chromosome level.…”

“…Populations of natural and RS B. napus exhibit chromosome instability and recombination, which changes the arrangement of rDNA loci and results in locus gain or loss (Hasterok et al 2001 , 2006 ; Niemann et al 2017 ). Maluszynska and Heslop-Harrison ( 1993 ) revealed that allopolyploid B. napus genotypes have fewer rDNA loci than the sum of the loci of their diploid ancestors; other studies confirmed this observation (Hasterok et al 2001 ; Xiong et al 2011 ).…”

In-field screening for host plant resistance to Delia radicum and Brevicoryne brassicae within selected rapeseed cultivars and new interspecific hybrids

“…In order to obtain interspecific hybrids with genetic pest resistance, paternal forms harbouring high level of resistance to B. brassicae and D. radicum were selected according to the literature data. All interspecific cross-derived lines were sister-pollinated (five plants were enclosed in one paper bag during flowering) for four generations in order to stabilize the fertility [25]. Morphotypes of plants of the F 5 -F 7 generations were compared with the parental lines, as described by Wojciechowski [26].…”