Quantitative studies on the relationship between plowing into soil of clubbed roots of preceding crops caused by Plasmodiophora brassicae and disease severity in succeeding crops

The effect of the plowing of clubbed roots of cracifers on the population of Plasmodiophora brassicae in soil was quantitatively studied by measuring the number of resting spores produced in the diseased plants. Though the mean number of resting spores per diseased plant increased with the increase of the disease severity, it remained almost identical for the disease severity classified into category 3 among host species and cultivars tested. Mean number of resting spores per diseased plant ranged from 9.3 to 10.9 (log) regardless of the value of the disease index. When the number of resting spores in soil was calculated based on these data and plant cultivation methods, the values were equivalent to 4.8-6.4 resting spores g^-1soil (log)where clubroot disease occurred severely. The value of the disease index of Chinese cabbage plants grown in the pots where clubbed roots of initially grown plants had been plowed into soil (plowing plot) was higher than that in the pots where no plants had been grown (control plot) and where the clubbed roots of initial plants had been removed (removal plot). Though the number of resting spores of P. brassicae in soil decreased by 14% of the inocoKum concentration immediately after the inoculation, the number of spores after the first cultivation in the removal plot was similar to that in the control plot. On the other hand, the number of resting spores in the plowing plot increased significantly compared with that in the control plot. The plowing of clubbed roots into soil resulted in the increase of the population of P. brassicae and disease severity of clubroot in subsequent cultivation in the field. The results corresponded to the values estimated based on the number of resting spores in soil in relation to each value of the disease index.     

大豆作为前作植物对油菜根肿病发生的影响

为了解前作大豆对后茬油菜根肿病的影响,采用大田轮作试验和实时荧光定量PCR检测法,研究大豆、白菜、油菜分别作为前作,调查后茬油菜根肿病的发生和土壤中休眠孢子含量,比较分析了不同前作的根系分泌物对休眠孢子萌发的影响,结果表明前作大豆,后茬油菜根肿病的发病率和病情指数分别为34.00%和19.26、土壤休眠孢子含量为1.45×106个/克土壤,显著低于前作为油菜、白菜和撂荒对照的相应量。大豆、油菜和白菜根系分泌物均可刺激根肿菌休眠孢子萌发。与根肿菌休眠孢子共培6 d后,大豆根系分泌物培养的休眠孢子萌发率为29.82%,显著高于白菜（15.52%）、油菜根系分泌物（14.83%）和营养液（6.48%）培养下的萌发率。据此推测,前作种植大豆,后茬油菜根肿病发生和危害减轻,原因应与大豆根系分泌物刺激根肿菌休眠孢子萌发,产生的游动孢子因缺少寄主植物而死亡,导致诱发病害的初侵染源（土壤中休眠孢子含量）减少有关。     

抗根肿病秋大白菜新品种‘CR京秋新3号’

大白菜‘CR京秋新3号’是由分子标记辅助饱和回交转育获得的抗根肿病的细胞质雄性不育系CMS84427CR和自交系832172CR配制而成的中晚熟一代杂种。生育期80 ~ 85 d,植株半直立,株高44 cm左右,开展度75 cm左右。外叶绿色,叶球直筒、叠抱,球高约34 cm,宽约18 cm,净菜质量约4 kg,净菜产量约90 t • hm-2。抗根肿病2号生理小种,抗病毒病、霜霉病。适合北方地区秋季种植。     

萝卜根肿病抗感品种间侵染过程及生理生化差异分析

根肿病是十字花科作物的重要病害之一,严重影响十字花科作物（油菜、白菜和萝卜等）的产量和品质。为探究根肿病的抗病机理,为防治十字花科根肿病进行田间早期的诊断预报提供依据,以两个抗病性不同的萝卜品种为试验材料,观察了根肿菌侵染的差异,利用qPCR技术测定了不同时间点根内根肿菌含量,并采用紫外分光光度法测定了其接种根肿菌后根部防御酶活性和可溶性糖含量。结果表明：根肿菌在两个萝卜品种中均发生根毛（初级）侵染,但是仅能在感病萝卜根中完成侵染循环,抗病萝卜没有观察到皮层（次级）侵染。推测次级游动孢子不能分化成休眠孢子囊是抗病萝卜抗病的主要原因。在接种后第25~45 d,感病萝卜根内的菌含量显著增加,抗病萝卜则相反,提示此期间是根肿菌在感病萝卜体内快速繁殖的重要时期。同时,接菌后抗病萝卜根部SOD活性、POD活性和可溶性糖含量高于感病品种,而CAT活性低于感病萝卜,表明较高的SOD、POD活性和可溶性糖含量以及较低的CAT活性对于萝卜的根肿病抗性具有重要的作用。     

Assessment of biological and molecular variability between and within field isolates of Plasmodiophora brassicae

Plasmodiophora brassicae is an obligate biotroph that causes clubroot, one of the most damaging diseases of crucifers. Differential cultivars and random amplified polymorphic DNA markers were used to assess the extent of genetic diversity among nine single-gall populations of P. brassicae and 37 single-spore isolates (SSI) derived from four of those field samples. Isolates were classified into eight pathotypes, and each isolate was associated with a unique molecular genotype. Virulence and DNA polymorphisms were detected within and between field isolates, and among SSIs from different pathotypes, hosts and geographical origins. The relatively high level of genetic diversity among field isolates was similar to that among SSIs derived from a single-club field isolate. Molecular and pathogenicity-based classifications were not clearly correlated, but isolates belonging to pathotype P1 were clustered. Two RAPD markers were specific to pathotype P1. The finding that genetic differences can occur in P. brassicae field isolates will be an important consideration in resistance genetic studies and in choosing breeding strategies to develop durable clubroot resistance.     

气象因子对油菜根肿病发生的影响

根据安徽黄山市2008-2012年的气象资料和田间调查的病情,采用逐步回归和通径分析法,分析了气象因子与油菜根肿病发病率的关系。结果表明,9月份月均温、9月上旬降雨量和9月下旬降雨量与根肿病发病率关系最密切。建立了油菜根肿病的预测模型。     

The use of an evolutionary scheme for cauliflowers in the screening of genetic resources

Summary A hypothetical scheme is given for the evolution of the different types of cauliflower (Brassica oleracea var. botrytis L.). This has been useful in identifying sources of reduced susceptibility to cabbage root fly (Delia radicum (L.)), and may also be useful in the search for reduced susceptibility to clubroot (Plasmodiophora brassicae Woron.). It is argued that knowledge of the phylogeny of types within each crop species is of great importance in the exploitation of genetic resources.     

Transfer of resistance to race 2 of Plasmodiophora brassicae from Brassica napus to cabbage (B. Oleracea spp. Capitata). IV. A resistant 18-chromosome B1 plant and its B2 progenies

Summary The somatic karyotype and meiotic chromosome behavior were studied in an 18-chromosome B₁ plant derived from backcrossing a triploid (Brassica napus x B. oleracea ssp. capitata) F₁ hybrid to cabbage. It is considered that cabbage chromosomes no. 1 and no. 7 were substituted by two shorter B. napus chromosomes. Meiotic disturbances were more apparent during the late stages of second division. Seed fertility of this plant was largely restored in the second backcrosses with both cabbage and broccoli. 18-chromosome B₂ plants resistant to race 2 of Plasmodiophora brassicae were recovered among the progenies.Contribution no. J. 725 from the Research Station, Research Branch, Agriculture Canada, St-Jean, Québec J3B 6Z8.     

Adaptation of quinoa (Chenopodium quinoa) to Northern European agriculture: studies on developmental pattern

The inheritance of resistance to clubroot, caused by Plasmodiophora brassicae in Brassica oleracea was studied in the F₁, F₂and backcross progenies of three crosses between resistant and susceptible doubled haploid lines. Fresh weights of affected (CW) and healthy (HRW) parts of the root system were measured and R = ln((HRW+0.5)/(CW+0.5)) was used as a measure of resistance. R was shown to have a normally distributed error term with a constant standard deviation over the entire scale. Analysis of means indicated the presence of two complementary resistance genes in one of the crosses. In the other two crosses analysis of means also indicated two-locus interactions, in these cases reducing the cumulative effects of loci homozygous for resistance or for susceptibility alleles. The numbers of segregating resistance genes in these two crosses could not be determined. The presence of epistatic interactions precluded analysis of variance; therefore in this case the measurements were not more informative than the symptom grades analyzed in a previous study.R showed a high rank correlation (-0.85) with symptom grades assigned to the same plants. The results of genetic analyses of R were generally in agreement with those obtained earlier using symptom grades. Symptom grades can therefore be regarded as a reliable measure of symptom development, despite their more subjective nature.