Effect of surfactants and fungicides on clubroot (Plasmodiophora brassicae) of brassicas

Two formulations of the surfactant sodium dioctyl sulphosuccinate (Aerosol OT, Monawet MO70), one of alkyl phenyl ethylene oxide (Agral) and three fungicides (PP192, dichlorophen and a thiabendazole/iodophor complex -Byatran) were tested in field trials for control of clubroot (Plasmodiophora brassicae) on cabbage in 1988 and 1989. A standard mercurous chloride treatment (pre-sowing compost incorporation) was included in all experiments. Plants were raised in 64 cm³ blocks (1988) or 15 cm³ free-fill cells (1989). Mercurous chloride reduced disease severity and increased yield in both years. Byatran was ineffective. The surfactants and dichlorophen, applied as pre-planting soaks to the plant-raising compost, restricted disease development and increased yield in 1988 but not in 1989. A similar treatment with PP192 restricted disease severity and enhanced yield in both years. Pouring the surfactants and dichlorophen into the planting hole was more effective than using them to soak the compost. In 1989 pour treatments with Agral and a combined soak/pour treatment with dichlorophen reduced disease severity and increased yields by 250% and 97% respectively; compost treatment with PP192 gave a 150% increase.     

The occurrence of free and bound cytokinins in clubroots and Plasmodiophora brassicae infected turnip tissue cultures

This paper deals with the quantitative determination of free and bound cytokinins in clubroot tissue and in Plasmodiophora brassicae Woron, infected Brassica campestris L. callus tissue. The fractions were separated in a butanol soluble fraction containing the free cytokinins such as zeatin and zeatin riboside and a water soluble fraction containing the bound cytokinins. The butanol fraction was extensively purified and analysed by high pressure liquid chromatography (HPLC). The butanol fraction contained cytokinins which cochromatographed with zeatin and zeatin riboside and not with dihydrozeatin. Zeatin and zeatin riboside were quantitatively determined by HPLC. Recovery of the cytokinins varied between 30–50%. Clubs contained 50–160 ng zeatin and 210–300 ng zeatin riboside per g dry weight. Callus tissue contained 133 ng zeatin and 169 ng zeatin riboside per g dry weight. Clubs, callus as well as healthy tissue contain large amounts of bound cytokinins. Upon treatment of the water soluble fraction first with alkaline phosphatase and then with β-glucosidase biologically active fractions were found which coeluted with zeatin and zeatin riboside on Sephadex LH₂₀ in 20% ethanol. Evidence is presented for a novel cytokinin in the water soluble fraction which yields free zeatin and glucose-6-phosphate after treatment with β-glucosidase.     

Transcriptional profiling identifies critical steps of cell cycle reprogramming necessary for Plasmodiophora brassicae‐driven gall formation in Arabidopsis

Plasmodiophora brassicae is a soil‐borne biotroph whose life cycle involves reprogramming host developmental processes leading to the formation of galls on its underground parts. Formation of such structures involves modification of the host cell cycle leading initially to hyperplasia, increasing the number of cells to be invaded, followed by overgrowth of cells colonised by the pathogen. Here we show that P. brassicae infection stimulates formation of the E2Fa/RBR1 complex and upregulation of MYB3R1, MYB3R4 and A‐ and B‐type cyclin expression. These factors were previously described as important regulators of the G2?M cell cycle checkpoint. As a consequence of this manipulation, a large population of host hypocotyl cells are delayed in cell cycle exit and maintained in the proliferative state. We also report that, during further maturation of galls, enlargement of host cells invaded by the pathogen involves endoreduplication leading to increased ploidy levels. This study characterises two aspects of the cell cycle reprogramming efforts of P. brassicae: systemic, related to the disturbance of host hypocotyl developmental programs by preventing cell cycle exit; and local, related to the stimulation of cell enlargement via increased endocycle activity.     

Infection of Chinese cabbage by Plasmodiophora brassicae leads to a stimulation of plant growth: impacts on cell wall metabolism and hormone balance

The importance of plant hormones in clubroot infection has long been recognized. The morphological changes, such as cell division and cell elongation leading to gall formation are triggered in the early stages of infection. We analysed cell expansion by localizing Xyloglucan endoTransglucosylase/Hydrolase (XTH)-action and screened the endogenous concentrations of several classes of phytohormones by mass spectrometry in the early stages of Plasmodiophora brassicae infection in Chinese cabbage (Brassica rapa spp. pekinensis). Infected plants showed a general transient growth promotion early in infection. Furthermore a clear XTH action was visible in the epidermal layer of infected roots. Complex changes in the endogenous phytohormone profile were observed. Initially infection resulted in an increased total auxin pool. The auxin increase, together with an increased XTH action, results in wall loosening and consequently cell expansion. When the first secondary plasmodia are formed, thirteen days after infection (DAI), can be considered a switch point in phytohormone metabolism. Twenty-one DAI the plasmodia might act as a plant hormone sink resulting in a reduction in the active cytokinin pool and a lower indole-3-acetic acid content in the infected plants.     

根际微生态调控白菜根肿病发生的机制研究进展

白菜根肿病是由芸薹根肿菌(Plasmodiophora brassicae Woron)引起的一种常见土传病害,主要危害白菜的根部。根际是土壤-植物-微生物相互作用最活跃的关键微域,根际微生态系统中的微生物失衡是导致土传病害的重要因素,深入探究根际微生态与土传病害互作机制,有利于从根际微生物、抑病物质和功能代谢等方面挖掘防控土传病害安全高效的方法。本文综述了根际微生态与白菜根肿病的发生机制关系,从该病害的危害、发生的根际微生态机制及生防菌防治研究等方面综合分析了根际微生物调控白菜根肿病发生的机制,以期为白菜根肿病防控、促进土壤健康和维持根际微生态系统稳定提供理论依据。     

Transcriptome Analysis Identifies Plasmodiophora brassicae Secondary Infection Effector Candidates

Plasmodiophora brassicae (Wor.) is an obligate intracellular plant pathogen affecting Brassicas worldwide. Identification of effector proteins is key to understanding the interaction between P. brassicae and its susceptible host plants. To date, there is very little information available on putative effector proteins secreted by P. brassicae during a secondary infection of susceptible host plants, resulting in root gall production. A bioinformatics pipeline approach to RNA‐Seq data from Arabidopsis thaliana (L.) Heynh. root tissues at 17, 20, and 24 d postinoculation (dpi) identified 32 small secreted P. brassicae proteins (SSPbPs) that were highly expressed over this secondary infection time frame. Functional signal peptides were confirmed for 31 of the SSPbPs, supporting the accuracy of the pipeline designed to identify secreted proteins. Expression profiles at 0, 2, 5, 7, 14, 21, and 28 dpi verified the involvement of some of the SSPbPs in secondary infection. For seven of the SSPbPs, a functional domain was identified using Blast2GO and 3D structure analysis and domain functionality was confirmed for SSPbP22, a kinase localized to the cytoplasm and nucleus.     

抗根肿病大白菜的花药培养

大白菜是中国北方的重要蔬菜之一,根肿病是危害大白菜生产世界性病害,利用花药培养可以大大加速抗根肿病大白菜杂交育种工作的进程。对33份抗根肿病大白菜品种(品系)进行花药培养,有24个品种诱导出胚,品种诱导率为72.7%,以东方皇冠×C11的诱导率最高,为1.86胚/蕾。对大部分基因型来说,在培养基中添加0.4 g/L谷氨酰胺的诱导效果最好。研究还发现生长在温室中的供体植株更容易诱导出胚状体。变绿的子叶型胚转到B5+0.2 mg/L BA+0.1 mg/L NAA+0.1%活性炭的胚分化培养基上可诱导生芽。     

根肿病胁迫下外源SA对不结球白菜抗性诱导和生理生化的影响

以不结球白菜‘新矮青’为试验材料,采用菌土接种法接种根肿病菌,研究不同浓度(0.2~0.8mmol·L~(-1))的外源水杨酸(SA)对根肿病胁迫下不结球白菜植株抗性诱导和感病植株生长的影响,以及植株叶片和根系中防御酶系统的变化规律,探讨外源SA对防治不结球白菜根肿病的可行性。结果显示:(1)根肿病显著影响不结球白菜的生长,加剧植物的膜脂过氧化程度;适宜浓度的外源SA能不同程度地缓解不结球白菜所受根肿病的侵害,并以0.6mmol·L~(-1) SA处理效果最好。(2)外源SA显著降低了根肿病的发病率和病情指数,提高了抗根肿病的诱抗效果,并缓解感病对不结球白菜的生长抑制,显著促进感病植株的生长。(3)外源SA提高了不结球白菜叶片和根系中的超氧化物歧化酶(SOD)、过氧化物酶(POD)和抗坏血酸-过氧化物酶(APX)的抗氧化酶活性,以及多酚氧化酶(PPO)、苯丙氨酸解氨酶(PAL)、谷胱甘肽还原酶(GR)的防御酶活性;显著降低了植株叶片和根系中的MDA、H2O2含量及O-·2产生速率。研究表明,外源SA诱导不结球白菜对根肿病的抗性,缓解根肿病的伤害,且具有剂量效应,以根部灌施0.6mmol·L~(-1)SA的效果最好;在根肿病的胁迫下,SA可提高不结球白菜植株抗氧化酶和防御酶的活性,增强渗透调节能力和细胞活性氧清除能力,降低根肿病对植株的伤害,从而促进生长。     

Selection for resistance to clubroot (Plasmodiophora brassicae) in marrowstem kale (Brassica oleracea var. acephala L.)

Ninety-six cultivars of Brassica oleracea were screened for clubroot resistance in a seedling test using two populations of Plasmodiophora brassicae. The most resistant cultivars were kales. Sixteen resistant marrowstem kale cultivars of diverse geographical origin were used to start a selection programme for clubroot resistance. Four generations of selection, involving single plants, half-sib and full-sib families, reduced a disease index averaged over six clubroot populations from 41.2 to 12.5. This was lower than the most resistant cultivar in the original population, cv. Mixti 28.8, and as good as a German landrace of cabbage noted for its resistance, Bohmerwaldkohl 10.5. In comparison, the mean of five kale controls, cvs Bittern, Canson, Condor, Kestrel and Merlin, was 61.1 and the value for the most susceptible control, cabbage cv. Septa, was 89.3. In the final assessment, there were no clubroot population x B. oleracea genotype interactions and in the initial assessment of cultivars there were only small interactions which could be removed by an angular transformation of the data. It was concluded that a high level of non-differential resistance had been achieved and that it may prove durable. It was also concluded from a small field trial that this level of resistance would prevent serious yield losses in practice.     

松花菜种质资源评价及根肿病、黑斑病兼抗材料筛选

松花菜是目前我国花椰菜消费的主要类型。根肿病和黑斑病是直接影响松花菜产量及品质的重要病害。选育商品性好、高抗多抗品种是松花菜的主要育种目标之一。本研究首次建立了松花菜种质资源花球性状评价体系,从花球紧实度、球形、球面光滑度、球面颜色、球面蕾粒大小、二级侧枝长度、花梗颜色、球面长毛情况8个方面对66份松花菜自交系进行评价,并对不同性状赋值以便统计、比较。利用上述体系共筛选出11份花球性状优良的材料。采用苗期人工接种技术分别对松花菜根肿病和黑斑病抗性进行鉴定评价,结果显示无免疫根肿病材料,有2份高抗材料,9份抗病,16份中抗;无免疫和高抗黑斑病材料,有4份抗病材料,10份中抗。另外,兼抗两种病害的材料较少,其中GY-40对两种病害均表现抗病,GY-21对根肿病表现抗病,对黑斑病表现中抗,GY-39对两种病害均表现中抗。值得一提的是,GY-40性状优良且同时对根肿病和黑斑病具有较高抗性,是选育商品性好、抗病性强松花菜品种的理想亲本。本研究结果为评价松花菜种质资源花球相关性状提供了参考,对于规范资源的收集、整理和保存具有重要意义,同时为开展抗根肿病和黑斑病松花菜品种选育提供了优异材料。