Role of Salicylic Acid in Systemic Resistance Induced by Pseudomonas spp. Against Pythium aphanidermatum in Cucumber Roots

Pseudomonas corrugata strain 13 and P. aureofaciens strain 63-28, applied to roots, induced systemic resistance against Pythium aphanidermatum in cucumber roots. Salicylic acid (SA) from bacterial culture or plant tissues was quantified by high performance liquid chromatography. Both strains produced SA in King's B broth and also induced cucumber root to accumulate endogenous SA one day after bacterial inoculation. Using a split root system, more SA accumulated in roots treated with bacteria than in distant roots on the opposite side of the root system in the first two days, but this difference disappeared after 3–4 days. SA levels were significantly higher in plants treated with bacteria compared to the split control, from one to five days after bacterization. SA did not inhibit mycelial growth of Pythium aphanidermatum at 100–200µgml^–1 in vitro, but higher levels inhibited mycelial growth. Zoospore germination increased at concentrations of 10–500µgml^–1, but decreased at 1000µgml^–1 compared to lower concentrations. Exogenously applied SA failed to induce local or systemic resistance against a challenge infection by the pathogen in planta. The results of this study show that exogenous applied SA does not induce systemic resistance to cucumber root rot caused by P. aphanidermatum, but endogenous SA accumulation in cucumber roots may be involved in induced systemic resistance.     

病原菌诱导黄瓜对其主要病害的抗病反应

以5种黄瓜主要病原菌作为诱导抗病因子,研究其对黄瓜主要病害的作用,结果发现黄瓜经病原菌诱导后,可以产生对诱导病原菌及其它病原菌引起病害的交互保护作用,并且诱导的交互保护作用与诱导浓度、诱导间隔期、不同品种存在相关性.诱导效果不随诱导接种浓度的升高而升高.在黑星病菌对霜霉病菌的诱导作用中,以浓度为1×102个/ml的黑星病菌孢子悬浮液的诱导效果最好,诱导间隔期为48h黄瓜黑星病菌对霜霉病的交互保护作用最明显,抗性品种的交互保护作用明显好于感病品种;炭疽病菌可诱导黄瓜有效抑制褐斑病的发生,但挑战接种褐斑病菌后,却促进了炭疽病的发生.诱导接种炭疽病菌后再挑战接种褐斑病菌12d,对褐斑病的防效为92.07%.     

Induced Resistance of Acibenzolar-S-methyl (CGA 245704) to Cucumber and Japanese Pear Diseases

Antifungal activity of the novel compound acibenzolar-S-methyl (CGA245704: benzo[1,2,3]thiadiazole-7-carbothioic acid S-methyl ester) was examined in vitro. No remarkable activity was observed on mycelial growth and conidial germination of almost all fungi tested. Only melon isolates of Didymella bryoniae were sensitive to this compound. On potted plants, acibenzolar-S-methyl showed control efficacy on anthracnose and scab of cucumber and rust of Japanese pear but not on Fusarium wilt of cucumber. In field trials, the occurrence of both rust and scab on Japanese pear was suppressed with this compound. Based on these experiments, it was suggested that acibenzolar-S-methyl induced resistance to some but not all diseases on cucumber and Japanese pear. Induction of disease resistance in cucumber was rapidly triggered after treatment with acibenzolar-S-methyl.     

利用诱导因子抗新疆甜瓜疫霉病的田间效果

用化学诱导因子和灭活的生物诱导因子在田间自然条件下诱导了新疆甜瓜产生对疫霉病的整体抗性。1996年的试验结果表明，用化学诱导因子诱导处理，最高诱抗效果可达79．40％，平均诱抗效果在40％以上；生物诱导因子诱导处理，最高诱抗效果为68．2％，平均诱抗效果为30％以上。1997年的试验基本上验证了1996年的结果，化学诱导因子最高诱抗效果可达60％，平均诱抗效果为35．86％，经t测验分析，诱抗效果显著。     

Study of Bacterial Determinants Involved in the Induction of Systemic Resistance in Bean by Pseudomonas putida BTP1

The ability of Pseudomonas putida BTP1 to induce resistance in bean to Botrytis cinerea was demonstrated in soil experiments on plants pre-inoculated at the root level with the bacteria before challenge with the leaf pathogen. As a first step to characterize the molecules from BTP1 responsible for induction of systemic resistance in bean, heat-killed cells and supernatant from culture in an iron-limited medium were tested for their protective effect. Most of the resistance-eliciting activity of the strain was retained in the crude cell-free culture fluid. In vivo assays with samples from successive fractionation steps of the BTP1 supernatant led, (i) to the conclusion that salicylic acid, pyochelin and pyoverdin, previously identified as Pseudomonas determinants for induced systemic resistance (ISR), were not involved in systemic resistance triggered by BTP1, and (ii) to the isolation of fractions containing one main metabolite that retained most of the resistance-inducing activity in bean. Although this molecule remains to be structurally characterized, its isolation is an addition to the range of determinants from plant growth-promoting rhizobacteria (PGPR) known to stimulate plant defences.     

Pseudomonas aeruginosa 7NSK2-induced Systemic Resistance in Tobacco Depends on in planta Salicylic Acid Accumulation but is not Associated with PR1a Expression

Root colonization by rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to systemic acquired resistance induced by a localized pathogen infection. We used the tobacco–tobacco mosaic virus model to investigate whether the systemic resistance induced by the rhizobacterium Pseudomonas aeruginosa 7NSK2 is mediated by the systemic acquired resistance signal transduction pathway. Experiments with nahG-transformed tobacco revealed that Pseudomonas aeruginosa 7NSK2-induced resistance depended on in planta salicylic acid accumulation for its expression but not for its induction and is, in this respect, similar to systemic acquired resistance. However, Pseudomonas aeruginosa 7NSK2-induced resistance was, unlike systemic acquired resistance, not associated with PR1a expression at the time of challenge with tobacco mosaic virus. This suggests that Pseudomonas aeruginosa 7NSK2 treatment would only potentiate defense gene expression in systemic tissue, which would also explain why its level of resistance is lower than in case of systemic acquired resistance. Because we demonstrated that induced resistance by Pseudomonas aeruginosa 7NSK2 exclusively depends on the production of salicylic acid by this strain our conclusions might also account for other salicylic acid-producing and resistance-inducing rhizobacteria.     

Induction of systemic resistance against Cucumber mosaic virus by Penicillium simplicissimum GP17‐2 in Arabidopsis and tobacco

The plant growth‐promoting fungus, Penicillium simplicissimum GP17‐2, was evaluated for its ability to induce resistance against Cucumber mosaic virus (CMV) in Arabidopsis thaliana and tobacco plants. Treatment with barley grain inoculum (BGI) of GP17‐2 significantly enhanced fresh weight, dry weight and leaf number of A. thaliana and tobacco plants 6 weeks after planting. Two weeks after CMV inoculation, all plants treated with BGI of GP17‐2 or its culture filtrate (CF) showed a significant reduction in disease severity compared with non‐treated control plants, which exhibited severe mosaic symptoms by the end of the experiment. The enzyme‐linked immunosorbent assay (ELISA) demonstrated that CMV accumulation was significantly reduced in plants treated with GP17‐2 or its CF relative to control plants. Based on RT‐PCR, plants treated with GP17‐2 (BGI or CF) also exhibited increased expression of regulatory and defence genes involved in the SA and JA/ET signalling pathways. These results suggested that multiple defence pathways in A. thaliana and tobacco were involved in GP17‐2‐mediated resistance to CMV, although neither the transgenic NahG line, nor the npr1, jar1 or ein3 mutants disrupted the response in A. thaliana. This is the first report to demonstrate the induction of systemic resistance against CMV by GP17‐2 or its CF.     

Evaluation of Induction of Systemic Resistance in Pepper Plants (Capsicum Annuum) to Phytophthora capsici Using Trichoderma harzianum and its Relation with Capsidiol Accumulation

The effect of pepper seed and root treatments with Trichoderma harzianum spores on necrosis caused in stems by Phytophthora capsici inoculation and on the course of capsidiol accumulation in the inoculated sites were studied. The results indicate that seed treatments significantly reduced stem necrosis, which fell by nearly a half compared with the values observed in plants grown from non-treated seeds. Necrosis was also reduced in plants whose roots were drenched with various doses of T. harzianum spores, although the extent of necrosis was not correlated with the dose used. Attempted isolation of P. capsici and T. harzianum from the zones immediately contiguous with the necrotic zones revealed the presence of the former but not of the latter, suggesting that there was no direct contact between them in the zones of isolation, which means that there was no competition for space. The percentage of P. capsici isolated 9 days after inoculation was greater in non-treated inoculated plants than in treated inoculated plants. These results suggest that T. harzianum, introduced into the subterranean part of the plant, induces a systemic defense response against P. capsici in the upper part of the plant. Analysis of capsidiol in the stems of treated inoculated plants by the end of the sixth day after inoculation, revealed that its concentration was more than seven-fold greater than in non-treated and inoculated plants, while after 9 days, the concentration of capsidiol decreased in the treated inoculated plants and increased in the non-treated inoculated plants. The high concentration of capsidiol detected in treated and inoculated stems after 6 days might be one of the contributing factors, but not necessarily the main factor, in delaying lesion development in the stems of pepper plants.     

Searching by Differential Display for New Genes Implicated in Induced Disease Resistance of Cucumber Treated with Acibenzolar-S-methyl

Acibenzolar-S-methyl (ASM) is a chemical activator of systemic disease resistance in plants. In this study, we used differential display to identify ASM-inducible defense response genes involved in induced disease resistance. As a result, we cloned three ASM-inducible genes from cucumber, encoding a chitinase, a putative protein disulfide isomerase and a putative mitochondrial-protein-like protein. Expression of these genes was induced within 24 hr after treatment of cucumber leaves with ASM. These results suggest that differential display is a useful tool for understanding the mode of action of ASM and defense responses. Received 6 September 2000/ Accepted in revised form 11 April 2001     

多因子联合诱导系统的构建及对黄瓜白粉病防治试验

由多个不同的抗病诱导因子组成植物抗病诱导系统的1个子系统。每个因子都是这个系统中的1个要素。系统的性质不但取决于系统中的要素,还取决于要素的结构。合理的配伍可以使要素与要素之间、要素与系统之间的关系得以优化,使系统的功能得以强化。把筛选得到的多个不同的抗病诱导因子进行配伍,组合成新的"诱导组合体",其诱导效应比单一因子显著提高;用不同的"诱导组合体"进行"相继诱导"和"循环诱导",则进一步提高诱导效应,对黄瓜白粉病的田间防治效果达到78.16%,高于常规杀菌剂的防治效果。     

不同处理及pH变化对果胶酶诱导抗病性的影响

从不同处理方法、酶液pH变化等方面对果胶酶诱导黄瓜抗黑星病效能的影响进行了研究。结果表明，在果胶酶的4种不同处理试验中，以全株表面喷雾法处理的黄瓜黄化子叶黑星病的病情指数降低最多，浓度100和200U／ml的诱导防病效果分别为56．34％和64．13％；下胚轴注射、灌根和漫种等3种处理方法的诱导抗病效果均不显著。经果胶酶诱导处理的黄瓜绿苗叶片病情明显降低，而处理叶上部的未处理叶片发病情况与相应对照差别不大。该结果表明，果胶酶诱导黄瓜绿苗抗黑星病的作用属于局部诱导。果胶酶处理次数的增加可增强其诱导抗病效果，并延长诱导抗病时间。酶液pH变化对果胶酶的诱导抗病作用影响显著，pH5．5时，2个浓度的诱导效果最好，分别为51．87％和66．42％。     

Application of Rhizobacteria for Induced Resistance

This article provides a review of experiments conducted over a six-year period to develop a biological control system for insect-transmitted diseases in vegetables based on induced systemic resistance (ISR) mediated by plant growth-promoting rhizobacteria (PGPR). Initial experiments investigated the factors involved in treatment with PGPR led to ISR to bacterial wilt disease in cucumber caused by Erwinia tracheiphila. Results demonstrated that PGPR-ISR against bacterial wilt and feeding by the cucumber beetle vectors of E. trachiphiela were associated with reduced concentrations of cucurbitacin, a secondary plant metabolite and powerful beetle feeding stimulant. In other experiments, PGPR induced resistance against bacterial wilt in the absence of the beetle vectors, suggesting that PGPR-ISR protects cucumber against bacterial wilt not only by reducing beetle feeding and transmission of the pathogen, but also through the induction of other plant defense mechanisms after the pathogen has been introduced into the plant. Additional greenhouse and field experiments are described in which PGPR strains were selected for ISR against cucumber mosaic virus (CMV) and tomato mottle virus (ToMoV). Although results varied from year to year, field-grown tomatoes treated with PGPR demonstrated a reduction in the development of disease symptoms, and often a reduction in the incidence of viral infection and an increase in tomato yield. Recent efforts on commercial development of PGPR are described in which biological preparations containing industrial formulated spores of PGPR plus chitosan were formulated and evaluated for use in a transplant soil mix system for developing plants that can withstand disease attack after transplanting in the field.     

Induced Resistance in Hypocotyl of Cucumber by Infection with Colletotrichum lagenarium in Leaves

Localized infection of cucumber leaves with Colletotrichum lagenarium induced resistance against infection after challenge inoculation with pathogenic fungi, including C. lagenarium and Pythium ultimum var. ultimum. Systemic acquired resistance in the hypocotyl was observed when challenge inoculation was made 4 to 7 days after the first inoculation of cotyledons. Seven days after the first inoculation of a primary leaf, induced resistance against the challenge inoculation in the hypocotyl was also observed. However, the hypocotyl did not develop induced resistance when plants were challenged by a wound inoculation with P. ultimum. Received 9 June 1999/ Accepted in revised form 13 December 1999     

Induced Systemic Resistance (ISR) by Pseudomonas spp. Impairs Pre- and Post-Infection Development of Pythium aphanidermatum on Cucumber Roots

The effect of induced systemic resistance (ISR) by Pseudomonas rhizobacteria on the pre- and post-infection development of Pythium aphanidermatum on cucumber roots was investigated. Cucumber plants (cv. Corona) were grown in vermiculite, roots were split with one side bacterized with Pseudomonas corrugata strain 13 or P. aureofaciens strain 63-28 (bacterized roots) and the other distant side was treated with water (distant, induced roots). For the non-induced control, roots on the bacterized side were treated with buffer instead of the bacterial treatment. Intact, non-split roots were also treated with the bacteria or buffer as a control. Cucumber root tissue from these treatments were harvested and incubated with a zoospore suspension of P. aphanidermatum for three hours. Most of the zoospores in the suspension were stimulated to encyst or germinate. The numbers of germinated zoospores were significantly decreased on distant induced cucumber roots in comparison to non-induced controls. Germination was also reduced on intact bacterized roots, compared to controls. There was less attachment, germ tube production and penetration on roots bacterized or induced by the rhizobacteria compared to non-induced roots. Effects were significantly greater on bacterized roots (roots colonized by bacteria) compared to distant induced roots (roots with the opposite side bacterized). Systemic resistance induced by the two Pseudomonas spp. also reduced pathogen spread on split cucumber roots in planta. Crown infection from induced or bacterized roots was delayed for four to six days in comparison to the non-induced control. Results indicated that Pseudomonas spp. can exert both an indirect influence on P. aphanidermatum zoospore behaviour and infection via induced systemic resistance (ISR) and a local influence via antibiosis or local induced resistance.     

Induction of Systemic Acquired Resistance in Pepper Plants by Acibenzolar-S-methyl against Bacterial Spot Disease

The ability of acibenzolar-S-methyl to induce resistance in pepper plants against Xanthomonas campestris pv. vesicatoria was investigated in both growth chamber and open field conditions. Growth chamber experiments showed that acibenzolar-S-methyl (300M) treatment protects pepper plants systemically and locally against X. campestris pv. vesicatoria. Evidence for this was a reduction in the number and diameter of bacterial spots and bacterial growth in planta. Systemic protection was also exerted by the acibenzolar-S-methyl acid derivative, CGA 210007, which may be produced by hydrolysis in the plant. The efficacy of acibenzolar-S-methyl was also found in open field conditions, where both leaves and fruit were protected from the disease. The highest efficacy (about 67%) was obtained by spraying the plants 6–7 times every 8–12 days with a mixture of acibenzolar-S-methyl and copper hydroxide (2.5 + 40ghl^–1 active ingredient). Persistence and translocation data obtained from the growth chamber experiments revealed a persistence of acibenzolar-S-methyl lasting five days after treatment with rapid translocation and negligible levels of acid derivative formation. Since the protection exerted by acibenzolar-S-methyl against bacterial spot disease was observed when the inducer was completely degraded, it would appear to be due to SAR activation.     

Biological Control of Plant Diseases: The European Situation

The most common approach to biological control consists of selecting antagonistic microorganisms, studying their modes of action and developing a biological control product. Despite progress made in the knowledge of the modes of action of these biological control agents (BCAs), practical application often fails to control disease in the fields. One of the reasons explaining this failure is that the bio-control product is used the same way as a chemical product. Being biological these products have to be applied in accordance with their ecological requirements. Another approach consists of induction of plant defence reactions. This can be done by application of natural substances produced by or extracted from microorganisms, plants, or algae. Since they do not aim at killing the pathogens, these methods of disease control are totally different from chemical control. Although promising, these methods have not been sufficiently implemented under field conditions. A third approach consists of choosing cultural practices that might decrease the incidence or severity of diseases. These methods include the choice of an appropriate crop rotation with management of the crop residues, application of organic amendments and the use of new technology such as the biological disinfestation of soils. Biological control practices need an integrative approach, and more knowledge than chemical control.     

Control of Leveillula taurica in Tomato by Acremonium alternatum is by Induction of Resistance, not Hyperparasitism

Spores of the hyperparasite Acremonium alternatum reduced powdery mildew infection by Leveillula taurica on greenhouse tomato. The effect was slightly increased when spores were applied killed, and therefore not due to direct parasitism. The effect was systemic, protecting untreated leaves above the treated ones. Spores killed by heat had more effect than when killed by UV, so the effect was presumably due to induction of host resistance by substances released when cells were heat killed. The size of the effect depended upon leaf age and level of infection. Effects on primary infection and expansion of successful infections appear to be under independent control.