Examination of resistance to clubroot in accessions of Brassica oleracea using a glasshouse seedling test

A glasshouse test was elaborated for assessing large numbers of seedlings ofBrassica oleracea for resistance to clubroot, a disease caused by the fungusPlasmodiophora brassicae. The method offers good control of inoculum density per plant, and requires 6–7 weeks from sowing. The results from the glasshouse test correlated well with field test results. With this method, 71 accessions ofB. oleracea reported to carry resistance to clubroot, and one susceptible control cultivar were tested with a Dutch clubroot isolate. High levels of resistance were found in several accessions of cabbage, broccoli and curly kale. F₁-populations of resistant cabbage or curly kale × susceptible cabbage were fully susceptible, indicating recessive inheritance of resistance in all cases.     

大白菜NPR家族基因鉴定及表达模式分析

为明确大白菜NPR转录辅助因子在大白菜基因组中的数量、结构和表达特点,揭示NPR在水杨酸信号途径调控大白菜生长发育过程中的作用.本研究利用拟南芥资源信息库TAIR10和芸薹属基因组网站Brassica Database鉴定大白菜基因组中的NPR家族成员,并对其蛋白和基因特性进行生物信息学分析.鉴定出大白菜基因组中包括1...     

十字花科蔬菜品种对根肿菌4号和9号小种的抗性

依据江西省内根肿病菌的生理小种类群分布,分别在婺源县4号小种区域和南昌县9号小种区域设立田间病圃,于2016年9—12月对108个十字花科蔬菜(花椰菜、包菜、萝卜、大白菜、小白菜)品种进行抗性鉴定,并随机选取其中29个品种进行人工接种鉴定。结果表明:十字花科不同种间蔬菜对根肿菌不同小种的抗性存在差异,种内品种对同一小种的抗性也存在差异;花椰菜、包菜和萝卜对9号小种均有抗性,上海黑叶五月慢、新奶白、京绿乌塌菜3个小白菜品种和京夏王、北京桔红心、京春娃2号等13个大白菜品种对9号小种有抗性;参试品种对4号小种的抗性不如对9号小种的,但仍筛选到紧花6、紧花16、松花2等10个花椰菜品种和满堂红萝卜品种可在4号小种区域种植。     

Comparison of techniques for estimation of resting spores of Plasmodiophora brassicae in soil

Clubroot (Plasmodiophora brassicae) is an important disease of canola (Brassica napus) and other brassica crops. Accurate estimation of inoculum load in soil is important for evaluating producer risk in planting a susceptible crop, but also for evaluation of management practices such as crop rotation. This study compared five molecular techniques for estimating P. brassicae resting spores in soil: quantitative polymerase chain reaction (qPCR), competitive positive internal control PCR (CPIC-PCR), propidium monoazide PCR (PMA-PCR), droplet digital PCR (ddPCR) and loop-mediated isothermal DNA amplification (LAMP). For ddPCR and LAMP, calibrations were developed using spiked soil samples. The comparison was carried out using soil samples collected from a long-term rotation study at Normandin, Québec, with replicated plots representing 0-, 1-, 2-, 3-, 5- and 6-year breaks following susceptible canola infested with clubroot. CPIC-PCR and ddPCR provided repeatable estimates of resting spore numbers in soil compared with estimates from qPCR or LAMP alone. CPIC-PCR provided the most robust measurement of spore concentration, especially in the 2 years following a crop of susceptible canola, because it corrected for effects of PCR inhibitors. PMA-PCR demonstrated that a large proportion of the DNA of P. brassicae detected in soil after the susceptible canola crop was derived from spores that were immature or otherwise not viable. Each assay provided a similar pattern of spore concentration in soil, which supported the conclusion of a previous study at this site that resting spore numbers declined rapidly in the first 2 years after a susceptible crop, but much more slowly subsequently.     

Influence of cultivar resistance and inoculum density on root hair infection of canola (Brassica napus) by Plasmodiophora brassicae

The impact of cultivar resistance and inoculum density on the incidence of primary infection of canola root hairs by Plasmodiophora brassicae, the causal agent of clubroot, was assessed by microscopy. The incidence of root hair infection in both a resistant and a susceptible cultivar increased with increasing inoculum density, but was two‐ to threefold higher in the susceptible cultivar; the relationship between root hair infection and inoculum density was also substantially stronger and more consistent in the susceptible cultivar. In the susceptible cultivar, the root hair infection rate peaked between 6 and 8 days after sowing and then declined. In the resistant cultivar, it increased over the 14‐day duration of each study. It appears that examination of root hair infection by microscopy in a bait crop of susceptible canola could serve as a useful tool for estimating P. brassicae inoculum levels in soil. In a separate trial, the relationship between inoculum density and clubroot severity, plant growth parameters, and seed yield was assessed under greenhouse conditions. Inoculum density in the susceptible genotype was strongly and positively correlated with clubroot severity and negatively correlated with plant height and seed yield. In addition, a single cropping cycle of the susceptible cultivar contributed significantly higher levels of resting spores to the soil in a greenhouse test than did a cycle of the resistant cultivar, as assessed by quantitative PCR and microscope analysis.     

Flooding affects the development of Plasmodiophora brassicae in Arabidopsis roots during the secondary phase of infection

Clubroot, a disease of Brassicaceae species, is caused by the soilborne pathogen Plasmodiophora brassicae. High soil water content was previously described to favour the motility of zoospores and their penetration into root cells. In this study, the effect of irrigation regimes on clubroot development during the post‐invasive secondary phase of infection was investigated. Three irrigation regimes (low, standard, high) were tested on two Arabidopsis accessions, Col‐0 (susceptible) and Bur‐0, a partially resistant line. In Col‐0, clubroot symptoms and resting spore content were higher under the ‘low irrigation’ regime than the other two regimes, thus enhancing the phenotypic contrast between the two Arabidopsis accessions. Clubroot severity under high and low irrigation regimes was evaluated in near‐isogenic lines derived from a Col‐0 ×  Bur‐0 cross, to assess the effect of soil moisture on the expression of each of four quantitative trait loci (QTL) controlling partial resistance. The presence of the Bur‐0 allele at the QTL PbAt5.2 resulted in reduced severity only under low irrigation, whereas the Bur‐0 allele at QTL PbAt5.1 was associated with partial resistance only under high irrigation. QTL PbAt4 reduced the number of resting spores in infected roots, but was not associated with reduced clubroot symptoms. The results indicated that soil moisture could have consequences for the secondary phase of clubroot development, depending on plant genotype. Future genetic studies may benefit from using combinations of watering conditions during the secondary stage of infection, thus opening up the possibility of identifying genetic factors expressed under specific environmental conditions.     

盈江县高山大白菜根肿菌生理小种鉴定及抗源筛选

采用Williams鉴别系统对云南省盈江县高山大白菜产区采集的根肿菌进行鉴定,4个鉴别寄主均表现为感病,病情指数分别为21、33、28、30,说明该根肿菌为4号生理小种。采用菌土法接种盈江根肿菌,对18个抗根肿病大白菜品种进行抗性鉴定,其中6个品种发病率和病情指数均为0,对盈江根肿菌表现免疫;2个品种病情指数10,表现抗病,可以作为该病区大白菜新品种选育的抗性遗传资源。     

Inactivation of soil-borne plant pathogens during small-scale composting of crop residues

Samples of heavily infested crop residues were incorporated in static compost heaps (2.5–4.6 m³) of the Indore type. Temperature increased to 50–70°C within 6 days depending on the type of crop residues used and the location within the heap. The heat phase (>40 °C) lasted 2–3 weeks and was followed by a c. 5-months maturation phase (<40 °c).=" among=" the=" 17=" pathogens=" tested,=">Olpidium brassicae and one of the four formae speciales ofFusarium oxysporum that were tested survived composting, but also their inoculum was greatly reduced.Survival during specific phases of composting was studied by incorporation and retrieval of samples at various stages of the process.F. oxysporum f. sp.melonis was completely inactivated andO. brassicae andPlasmodiophora brassicae were almost completely inactivated during the short heat phase. The three pathogens survived the long-lasting maturation phase without loss of viability. Heat evolved during composting was found to be the most important factor involved with sanitation of crop residues. The possible involvement of fungitoxic conversion products and microbial antagonism is discussed.     

油菜根肿病菌的形态和休眠孢子的生物学特性

 【目的】比较油菜根肿病菌与十字花科蔬菜根肿病菌的形态是否存在差异。研究油菜根肿病菌休眠孢子的生物学特性，为防治油菜根肿病提供依据。【方法】应用扫描电镜观察油菜根肿病菌的形态特征和休眠孢子至管腔的形态演变过程。采用地衣红染色，观测不同根分泌物和条件对休眠孢子萌发的影响。【结果】休眠孢子近球形，有乳突，直径为1.9～4.3μm（平均3.5μm），大于甘蓝根肿菌休眠孢子（2.5μm）；透射电镜下游动孢子近球形、肾形或椭圆形，直径为1.6～3.5μm（平均2.8μm），同侧生不等长尾鞭式双鞭毛。休眠孢子萌发形成游动孢子、休止孢、休止孢再生出侵入结构管腔。休眠孢子萌发的最适温度是24℃，最适pH值是6.3，腐烂处理促进休眠孢子萌发，光抑制休眠孢子萌发，休眠孢子在过滤灭菌的根分泌物中萌发率最高为62.50％。致死温度为48℃。【结论】油菜根肿病菌与十字花科甘蓝根肿病菌休眠孢子大小有明显差异，观察到休眠孢子至管腔的过程。油菜根肿菌休眠孢子的萌发条件与该病发生条件相一致。     

枯草芽孢杆菌XF-1提取物对11种植物病原菌的抑制作用

采用盐酸和甲醇抽提法,提取了枯草芽孢杆菌XF-1(Bacillus subtilis XF-1)的抑菌物质。以该提取物处理根肿菌孢子2 d,有50%孢子活性被抑制;处理9 d后,孢子萌发相对抑制率始终保持在90%以上。提取物对三七根腐病菌、水稻纹枯病菌、禾谷镰刀菌、魔芋基腐菌、烟草赤星菌生长抑制率分别为71.97%、62.23%、60.96%、60.70%和57.92%。