Selection for resistance to Plasmodiophora brassicae Wor. in oriental subspecies of Brassica rapa L.

Abstract

Selection for resistance to Plasmodiophora brassicae WOR. in oriental groups of Brassica rapa L. Two hundred and sixty-live cultivars of leafy, oriental bassicas were tested for resistance to 18 collections of Plasmodiophora brassicae , the causal agent of clubroot. The tests were conducted in the greenhouse at low and high level inoculum concentrations. Eleven cultivars of B. rapa pe-tsai, five cultivars of B. rapa pak-choy and three cultivars of B. rapa choy-sum consistently segregated for resistance at the lower concentration of inoculum (1000 spores/ml). All 265 cultivars were susceptible at the higher concentration (1000000 spores/ml). Three cultivars were used in pedigree and recurrent selection schemes for increased resistance. After three cycles of selling resistant individuals, significantly more resistant S3 lines were derived from each cultivar. Lines derived from two cultivars, Chinese White and PI 257236, continued to improve with each cycle of selection and demonstrated increased resistance to higher levels of inoculum (up to 100000 spores/ml) New cultivars based on intercrosses of S2 resistant individuals also had significantly better resistance than the original cultivar. After two cycles of selection in the third cultivar, PI 419007, resistance did not increase and its ST mass did not differ significantly from the original cultivar. Evidence that indicates resistance is pathotype-non-differential and offers an alternative to major gene, pathotype-differential types of resistance currently being introduced to the leafy oriental brassicas from other Brassica rapa groups.

Screening ofBrassicagermplasm for resistance toPlasmodiophora brassicaepathotypes prevalent in Canada for broadening diversity in clubroot resistance

“…The aim of this research was to explore the Brassica A-, B-and C-genome species and their amphidiploids to identify germplasm with superior resistance to clubroot disease for use in breeding oilseed Brassica crops with durable resistance to Canadian P. brassicae pathotypes. Several researchers investigated the diploid A-and C-genome species and in their amphidiploids (AACCgenome) for resistance to different P. brassicae pathotypes or races (Tjallingii 1965;Ayers and Lelacheur 1972;Toxopeus and Janssen 1975;Miller and Williams 1986;Dias et al 1993;Voorrips and Visser 1993). However, none of these studies included all diploid and amphidiploid Brassica species in order to get a comparative view on the occurrence of resistance to specific pathotypes.…”

“…On the other hand, wide genetic diversity has been reported to be present in the B-genome species B. nigra (Negi et al 2004). In the current study, of the 77 B. nigra lines 78% were found to possess a high level of resistance against five Canadian P. brassicae pathotypes.…”

Role of plant breeding in controlling soil-borne diseases

“…Some of these, with soil-borne disease as examples are: pedigree, for common root rot of wheat (46); single seed descent, for common root rot of wheat (3); backcross, for fusarium wilt of watermelon (Orton in Stakman & Harrar (57)) and for sclerotinia wilt of bean (1); recurrent selection, for clubroot of Chinese cabbage (40); interspecific hybridization, for clubroot of Brassica spp. (13); and intergeneric hybridization, for eyespot of wheat (38).…”