Fusarium oxysporum Fo47 confers protection to pepper plants against Verticillium dahliae and Phytophthora capsici,and induces the expression of defence genes

The application of the nonpathogenic isolate Fusarium oxysporum 47 (Fo47) reduced the symptoms of verticillium wilt, phytophthora root rot and phytophthora blight in pepper plants. Botrytis cinerea was also tested on the leaves of plants treated with Fo47, but no protection was observed. Verticillium dahliae colonies cultured in the presence of Fo47 grew slower than control cultures, but Phytophthora capsici growth was unaffected by Fo47. At least part of the protection effect observed against V. dahliae could therefore be due to antagonism or competition. In order to search for induced resistance mechanisms, three defence genes previously related to pepper resistance were monitored over time. These genes encode a basic PR‐1 protein (CABPR1), a class II chitinase (CACHI2) and a sesquiterpene cyclase (CASC1) involved in the synthesis of capsidiol, a phytoalexin. These three genes were transiently up‐regulated in the roots by Fo47 in the absence of inoculation with the pathogen, but in the stem only CABPR1 was up‐regulated. In plants that were inoculated with V. dahliae after the Fo47 treatment, the three genes had a higher relative expression level than the control in both the roots and the stem.     

Real-Time Polymerase Chain Reaction Quantification of Phytophthora capsici in Different Pepper Genotypes

ABSTRACT Reliable and sensitive quantification of Phytophthora capsici in pepper plants is of crucial importance in managing the multiple syndromes caused by this pathogen. A real-time polymerase chain reaction (PCR) assay was developed for the determination of P. capsici in pepper tissues. DNA levels of a highly virulent and a less virulent isolate were measured in different pepper genotypes with varying degrees of resistance. Using SYBR Green and specific primers for P. capsici, the minimal amount of pathogen DNA quantified was 10 pg. Pathogen DNA was recorded as early as 8 h postinoculation. Thereafter, the increase was rapid in susceptible cultivars and slower in resistant ones. The amount of pathogen DNA quantified in each pepper genotype correlated with susceptibility to Phytophthora root rot. Likewise, there was a relationship between the virulence of the pathogen and the degree of colonization. Differences also were found in oomycete amount among pepper tissues, with maximal pathogen biomass occurring in stems. The real-time PCR technique developed in this study was sensitive and robust enough to assess both pathogen development and resistance to Phytophthora root rot in different pepper genotypes.     

黄柄曲霉ASD对辣椒疫病根际真菌菌群结构及土壤功能的影响

为阐明辣椒疫病生防菌黄柄曲霉ASD的土壤微生态调控机理,本研究利用化学方法与Illumina HiSeq平台分析了ASD菌液对罹病辣椒根际土壤特性及真菌多样性的影响.结果表明,ASD菌液的施入可以明显提高罹病土壤硝态氮与有效钾含量,降低铵态氮含量与N-乙酰基-β-D-氨基葡糖苷酶活性.ASD菌液增加了罹病辣椒根际土壤真...     

接种体密度、土壤水分基质势和土壤温度对辣椒疫病死苗率的影响

 在生长箱内控制条件下分析测定了接种体密度、土壤水分基质势和土壤温度对辣椒疫病死苗率的影响。结果表明,在每克干土中接种1个辣椒疫霉菌孢子囊就能造成侵染,引致辣椒死苗,随着接种体密度升高死苗率增大,直至接种体孢子囊密度达到50~80个/g干土时死苗率达到最高。土壤温度和土壤水分状况是决定辣椒疫病死苗率的重要因子,病菌侵染的最适土温是22~28℃,土壤水分接近饱和,即土壤水分基质势(Ψ_m值)为0时最容易侵染发病,土壤过于干燥和过饱和都不利于侵染发病。辣椒疫病死苗率与土壤温度、土壤水分基质势及其互作之间可用数学模式描述。     

两株对辣椒疫霉菌有拮抗作用的拮抗菌分泌蛋白的研究

用平板对峙生长法筛选到两株对辣椒疫霉菌具有较强拮抗作用的细菌,经鉴定为芽孢杆菌属。测定了无菌滤液的抑菌活性及两菌产生拮抗物的热稳定性。用硫酸铵沉淀法提取到对辣椒疫霉菌有拮抗作用的抗菌蛋白。发酵条件的研究表明,用Ｇ培养基、ｐＨ７、培养３２小时,ＸＡ１、ＸＦ１能产生具有较强拮抗作用的拮抗物。     

Effects of Irrigation and Verticillium dahliae on Cauliflower Root and Shoot Growth Dynamics

ABSTRACT Cauliflower root and plant growth and Verticillium wilt development were evaluated under different moisture regimes in the presence or absence of V. dahliae. Treatments included two main plots (V. dahliae-infested and fumigated), two subplots (furrow and subsurface drip irrigation), and three sub-subplots (deficit, moderate, and excessive regimes) that were arranged in a split-split-plot design in the field. Soil cores with roots were periodically sampled at 5 and 25 cm distance from plants. Total roots in each soil core were extracted with a hydropneumatic root elutriator, and root length from each sample was determined with a digital image analysis system. Incidence and severity of Verticillium wilt, plant height, number of leaves, and dry weights of leaves and roots were determined on 10 plants sampled at 7- to 10-day intervals 1 month after cauliflower transplanting and continued until harvest. To evaluate the effects of Verticillium wilt-induced stress on cauliflower plants, stomatal resistance was measured in upper healthy and lower (or diseased) leaves. Root length density at 5 and 25 cm from plant was significantly (P < 0.05) higher in subsurface drip than in furrow irrigation. Root length density was significantly higher in excessive irrigation regime than in the other regimes. Concomitantly, there was higher wilt incidence and severity in excessive and moderate regimes than deficit regime regardless of the irrigation method. Plant height was affected by irrigation methods and deficit regime. Neither the method of irrigation nor the quantity of water affected the other variables. Stomatal resistance in lower diseased leaves was significantly higher in infested than in fumigated plots but it was not in the upper healthy leaves. In this study, cauliflower yield was not affected by V. dahliae and irrigation method, but the deficit irrigation regime resulted in reduced yield even though it suppressed wilt in cauliflower. Thus, higher moisture levels resulted in higher root length density in V. dahliae-infested plots that in turn lead to greater incidence of Verticillium wilt and severity. The pathogen also affected physiological processes such as hydraulic conductance of cauliflower leaves, but not shoot growth or yield under these experimental conditions.     

Verticillium dahliae Modifies the Concentrations of Proline, Soluble Sugars, Starch, Soluble Protein and Abscisic Acid in Pepper Plants

The objective of this research was to study the levels of some organic solutes, such as total protein, total soluble sugars, starch and proline in leaves, as well as abscisic acid concentration in xylem of pepper plants inoculated with Verticillium dahliae Kleb. Healthy and inoculated plants were always kept well watered. Measurements were made at time intervals after inoculation. Leaf water potential rapidly decreased as a consequence of fungal infection. However, relative water content in leaves only changed significantly from day 20 after inoculation, and such decreases coincided with a sharp build up of proline and total soluble sugars in leaves. Starch and protein levels, as well as abscisic acid concentration in xylem, declined in healthy and inoculated peppers as they became older. However, such decreases were more pronounced in infected plants, especially soon after inoculation. Results suggest that proline and total soluble sugars accumulation could be sensors of the damage caused by the fungal infection.     

环烷基磺酰胺类化合物对辣椒疫霉的抑制作用

采用菌丝生长速率法,以甲霜灵、氟吗啉原药和10%氰霜唑悬浮剂作对照药剂,从20种环烷基磺酰胺类化合物中筛选出N-(2,4,5-三氯苯)-2-羟基环烷基磺酰胺(化合物149)和N-(2-三氟甲基-4-氯苯)-2-羟基环烷基磺酰胺(化合物104)2种对辣椒疫霉菌丝生长有抑制作用的化合物,其EC50分别为9.58μg/mL和15.96μg/mL。对辣椒疫霉生育阶段抑制试验结果表明,化合物149和104对孢子囊形成均有较强的抑制作用,EC50分别为0.03μg/mL和4.62μg/mL,其中化合物149的抑制率高于对照药剂90%氟吗啉原药;化合物149和104抑制辣椒疫霉游动孢子释放和萌发,其中化合物104的EC50为0.18μg/mL,高于对照药剂90%甲霜灵原药;化合物149和104对辣椒疫霉菌丝生长量均表现出较好的抑制效果。     

25%嘧菌酯悬浮剂防治辣椒疫病药效试验

试验结果表明．对辣椒茎基部喷淋施用25％嘧菌酯悬浮剂，随着施药浓度的增大，防病效果逐渐升高，对辣椒疫病发病初期防病效果好、持效期较长，施用本品24-72g／667m^2，加水60kg稀释．对开花座果初期的辣椒具有较高的安全性，并有刺激辣椒生长的作用，具有较高的推广应用价值。推荐本品使用药量以48g／667m^2为宜。     

Survival of strawberry-pathogenic fungi Fusarium oxysporum f. sp. fragariae, Phytophthora cactorum and Verticillium dahliae under anaerobic conditions

The growth and survival of three strawberry pathogens, Fusarium oxysporum f. sp. fragariae (FOF), Phytophthora cactorum, and Verticillium dahliae, were examined in anaerobic (anoxic) conditions at several temperatures (10–40 °C). The growth and survival of these fungi were suppressed by anaerobic conditions in comparison with those in cultured aerobically. Under anaerobic conditions at 22.5 °C, tested isolates of FOF and P. cactorum grew slightly, but V. dahliae did not grow. The three fungi survive for markedly shorter time in the anaerobic conditions compared with the aerobic conditions at all tested temperatures except 40 °C for FOF and P. cactorum. Moreover, survival periods shortened as the cultivation temperature increased. These results demonstrate that anaerobic conditions contribute to eradicating these pathogens during flooding or reductive soil disinfestation.     

Temporal Dynamics of Phytophthora Blight on Bell Pepper in Relation to the Mechanisms of Dispersal of Primary Inoculum of Phytophthora capsici in Soil

ABSTRACT The effect of components of primary inoculum dispersal in soil on the temporal dynamics of Phytophthora blight epidemics in bell pepper was evaluated in field and growth-chamber experiments. Phytophthora capsici may potentially be dispersed by one of several mechanisms in the soil, including inoculum movement to roots, root growth to inoculum, and root-to-root spread. Individual components of primary inoculum dispersal were manipulated in field plots by introducing (i) sporangia and mycelia directly in soil so that all three mechanisms of dispersal were possible, (ii) a plant with sporulating lesions on the soil surface in a plastic polyvinyl chloride (PVC) tube so inoculum movement to roots was possible, (iii) a wax-encased peat pot containing sporangia and mycelia in soil so root growth to inoculum was possible, (iv) a wax-encased peat pot containing infected roots in soil so root-to-root spread was possible, (v) noninfested V8 vermiculite media into soil directly as a control, or (vi) wax-encased noninfested soil as a control. In 1995 and 1996, final incidence of disease was highest in plots where sporangia and mycelia were buried directly in soil and all mechanisms of dispersal were operative (60 and 32%) and where infected plants were placed in PVC tubes on the soil surface and inoculum movement to roots occurred with rainfall (89 and 23%). Disease onset was delayed in 1995 and 1996, and final incidence was lower in plants in plots where wax-encased sporangia (6 and 22%) or wax-encased infected roots (22%) were buried in soil and root growth to inoculum or root-to-root spread occurred. Incidence of root infections was higher over time in plots where inoculum moved to roots or all mechanisms of dispersal were possible. In growth-chamber studies, ultimately all plants became diseased regardless of the dispersal mechanism of primary inoculum, but disease onset was delayed when plant roots had to grow through a wax layer to inoculum or infected roots in tension funnels that contained small volumes of soil. Our data from both field and growth-chamber studies demonstrate that the mechanism of dispersal of the primary inoculum in soil can have large effects on the temporal dynamics of disease.     

Pathogenicity and Virulence of the Two Dutch VCGs of Verticillium dahliae to Woody Ornamentals

Two experiments were performed in two consecutive years to test whether isolates of different vegetative compatibility groups (VCGs) differ in their ability to cause disease in woody ornamentals, to study the host specificity of the isolates and to get an insight into disease development in woody hosts. A range of woody ornamental plant species, including Acer campestre, Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Cotinus coggygria, Robinia pseudoacacia, Rosa canina, Syringa vulgaris and Tilia cordata, were root-dip inoculated with six isolates of Verticillium dahliae, belonging to the two VCGs that occur in the Netherlands (VCG NL-1 and VCG NL-2). Isolates belonging to each VCG caused severe symptoms of verticillium wilt in most plant species tested. Disease progress differed between plant species, but was generally the same for the two VCGs. No overall differences in virulence were observed between the two VCGs for external wilt symptoms, number of dead plants, or shoot length. No significant VCG × plant species interactions were present for these characteristics. However, isolates of VCG NL-1 caused more vascular discolouration than did isolates of VCG NL-2. Isolates within VCGs often differed considerably in their virulence to certain hosts, as shown by highly significant isolate × plant species interactions. Isolates were more virulent on their original host. These findings imply that VCG identification does not contribute to disease prediction for a range of woody hosts.     

棉花黄萎病菌致病力测定及评价方法研究

 棉花黄萎病菌致病力测定及评价是抗病育种及病害综合防治的基础。本文以我国三大棉区的167个黄萎菌菌株为对象,研究致病力测定及评价中不同批次之间病情指数的校准及致病力类型划分标准等关键技术环节。结果表明,以中等致病力类型菌株Vd076为校正菌株,以感病性稳定的冀棉11为校正鉴别寄主,以校正菌株在校正鉴别寄主上病情指数达到50.0±5.0时的调查结果进行各菌株的致病力评价,可获得较好的校正效果,使不同批次试验数据具有可比性;依据聚类分析结果,制定了致病力类型划分标准,强、中、弱3种致病力类型的平均校正病指分别为﹥40.0、20.1~40.0和20.0;通过对不同鉴别寄主组合的分析,推荐陆地棉中棉所41号、豫棉21、鲁棉研28、中棉所35号、中棉所8号、冀棉11作为鉴别寄主。该研究为棉花黄萎病菌致病力变异等相关研究工作提供了技术支撑。     

Effects of Verticillium dahliae on tomato root morphology considering plant growth response and defence

The soilborne pathogen Verticillium dahliae invades its host via the root, and spreads systemically throughout the plant. Although a functional root system of appropriate size is essential for water and nutrient uptake, to date, effects of pathogens on root morphology have not been frequently investigated. Therefore, this study aims to improve knowledge of how V. dahliae infection impairs root morphological characteristics of tomato, considering plant growth and physiological responses, particularly those involved in defence in roots and leaves over a growing period of up to 28 days post‐inoculation. Verticillium dahliae infection suppressed the growth of both shoot and root. Diseased plants developed a smaller leaf area, and exhibited a reduction in the rate of photosynthesis and stomatal conductance. An early response to pathogen invasion in the host root was the up‐regulation of several defence‐related genes, such as proteinase inhibitor II (Pin2), β‐1,3‐glucanase A (GluA) and two pathogenesis‐related genes (PR‐1a, PR‐1b). However, this response did not prevent colonization of the roots by the pathogen. Although a high variability in pathogen density was found within the root system, a significant increase of both the specific root length and surface area was observed in response to pathogen invasion; these traits correlated with water use efficiency. Morphological changes of the root may represent an adaptive response evolved to sustain the supply of both water and nutrients in the presence of the pathogen.     

茄子黄萎病菌毒素对茄子愈伤组织几种酶活性的影响

 病原物侵染可引起一些酚类代谢相关酶的活性增强,其中,最常见的是苯丙氨酸解氨酶(PAL)、多酚氧化酶(PPO),这些酶活性的变化与植物的抗病机制有密切关系。     

Effects of Crop Rotation and Irrigation on Verticillium dahliae Microsclerotia in Soil and Wilt in Cauliflower

ABSTRACT Experiments were conducted in field plots to evaluate the effects of broccoli residue on population dynamics of Verticillium dahliae in soil and on Verticillium wilt development on cauliflower under furrow and subsurface-drip irrigation and three irrigation regimes in 1994 and 1995. Treatments were a factorial combination of three main plots (broccoli crop grown, harvested, and residue incorporated in V.dahliae-infested plots; no broccoli crop or residue in infested plots; and fumigated control plots), two subplots (furrow and subsurface-drip irrigation), and three sub-subplots (deficit, moderate, and excessive irrigation regimes) arranged in a split-split-plot design with three replications. Soil samples collected at various times were assayed for V. dahliae propagules using the modified Anderson sampler technique. Incidence and severity of Verticillium wilt on cauliflower were assessed at 7- to 10-day intervals beginning a month after cauliflower transplanting and continuing until harvest. Number of propagules in all broccoli plots declined significantly (P < 0.05) after residue incorporation and continued to decline throughout the cauliflower season. The overall reduction in the number of propagules after two broccoli crops was approximately 94%, in contrast to the fivefold increase in the number of propagules in infested main plots without broccoli after two cauliflower crops. Disease incidence and severity were both reduced approximately 50% (P < 0.05) in broccoli treatments compared with no broccoli treatments. Differences between furrow and subsurface-drip irrigation were not significant, but incidence and severity were significantly (P < 0.05) lower in the deficit irrigation regime compared with the other two regimes. Abundance of microsclerotia of V. dahliae on cauliflower roots about 8 weeks after cauliflower harvest was significantly (P < 0.05) lower in treatments with broccoli compared with treatments without broccoli. Rotating broccoli with cauliflower and incorporating broccoli residues into the soils is a novel means of managing Verticillium wilt on cauliflower and perhaps on other susceptible crops. This practice would be successful regardless of the irrigation methods or regimes followed on the susceptible crops.     

Genetic variability of tolerance to Verticillium albo-atrum and Verticillium dahliae in Medicago truncatula

Verticillium wilt caused by Verticillium albo-atrum and Verticillium dahliae is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. In the present work, 25 Medicago truncatula genotypes from a core collection and six V. albo-atrum and V. dahliae strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant and the plant’s susceptibility to the pathogens. The experiment was designed as factorial with randomised complete blocks and with three repetitions. The wilt symptoms caused by V. albo-atrum and V. dahliae were scored on a disease index scale from 0 to 4, during 30 days after inoculation of 10-day-old plantlets. Disease severity was quantified by maximum symptom scores (MSS) and areas under the disease progress curves (AUDPC), which integrate the time course of symptom development. Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86. The most severe symptoms were caused by the alfalfa strain V. albo-atrum V31-2 and the least severe by V. dahliae JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was the most susceptible genotype by mean values obtained with the six fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results can be used to choose parents for studying the genetics of resistance in Medicago truncatula to Verticillium strains with different levels of aggressiveness.