Antagonistic bacteria of composted agro-industrial residues exhibit antibiosis against soil-borne fungal plant pathogens and protection of tomato plants from Fusarium oxysporum f.sp. radicis-lycopersici

Rhizospheric and root-associated/endophytic (RAE) bacteria were isolated from tomato plants grown in three suppressive compost-based plant growth media derived from the olive mill, winery and Agaricus bisporus production agro-industries. Forty-four (35 rhizospheric and 9 RAE) out of 329 bacterial strains showed in vitro antagonistic activity against at least one of the soil-borne fungal pathogens, Fusarium oxysporum f.sp. radicis-lycopersici (FORL), F. oxysporum f.sp. raphani, Phytophthora cinnamomi, P. nicotianae and Rhizoctonia solani. The high percentage of total isolates showing antagonistic properties (13%) and their common chitinase and β-glucanase activities indicate that the cell wall constituents of yeasts and macrofungi that proliferate in these compost media may have become a substrate that favours the establishment of antagonistic bacteria to soil-borne fungal pathogens. The selected bacterial strains were further evaluated for their suppressiveness to tomato crown and root rot disease caused by FORL. A total of six rhizospheric isolates, related to known members of the genera Bacillus, Lysinibacillus, Enterobacter and Serratia and one RAE associated with Alcaligenes faecalis subsp. were selected, showing statistically significant decrease of plant disease incidence. Inhibitory effects of extracellular products of the most effective rhizospheric biocontrol agent, Enterobacter sp. AR1.22, but not of the RAE Alcaligenes sp. AE1.16 were observed on the growth pattern of FORL. Furthermore, application of cell-free culture extracts, produced by Enterobacter sp. AR1.22, to tomato roots led to plant protection against FORL, indicating a mode of biological control action through antibiosis.     

Evaluation of coumarin derivatives as anti-fungal agents against soil-borne fungal pathogens

Development of new and safer pesticides that are target-specific is backed by a strong Federal, public and commercial mandate. In order to generate a new generation of pesticides that are more ecologically friendly and safe, natural products are being evaluated for pesticidal activities. Many plant-derived chemicals have proven pesticidal properties, including compounds like sesamol (3,4-Methylenedioxyphenol), a lipid from sesame oil and coumarins (1,2-Benzopyrone) found in a variety of plants such as clover, sweet woodruff and grasses. Both of these plant-derived compounds have been shown to inhibit a range of fungi and bacteria and it is believed that these cyclic compounds behave as natural pesticidal defense molecules for plants. These compounds represent a starting point for the exploration of new derivative compounds possessing a range of antifungal activity and for use as seed protectants. Within this study, six derivatives of coumarin that resembled sesamol's structure were screened for their antifungal activity against a range of soil-bome plant pathogenic fungi. Fungi in this in vitro screen included Macrophomina phaseolina (causal agent of charcoal rot) and Pythium spp. (causal agent of seedling blight), two phylogenetically diverse and economically important plant pathogens. Preliminary studies indicate that many of these novel coumarin derivatives work very effectively in vitro to inhibit fungal growth and several coumarin derivatives have higher antifungal activity and stability as compared to either the original coumarin or sesamol compounds alone. Interestingly, several of these highly active coumarin derivatives are halogenated compounds with solubility in water, and they are relatively easy and inexpensive to synthesize. These halogenated coumarin derivatives remained active for extended periods of time displaying 100% inhibition of fungal growth for greater than 3 weeks in vitro. In addition to the in vitro fungal inhibition assays, preliminary phytotoxicity assays of these halogenated coumarin compounds show no obvious plant toxicity issues or interference in plant development. These results support additional research in this area of natural pesticide development.     

Induction of resistance against Fusarium wilt of tomato by combination of chitosan with an endophytic bacterial strain: ultrastructure and cytochemistry of the host response

The potential of Bacillus pumilus (PGPR strain SE 34), either alone or in combination with chitosan, for inducing defense reactions in tomato (Lycopersicon esculentum Mill.) plants inoculated with the vascular fungus, Fusarium oxysporum f. sp. radicis-lycopersici, was studied by light and transmission electron microscopy and further investigated by gold cytochemistry. The key importance of fungal challenge in the elaboration of defense mechanisms is discussed in relation to the possibility that an alarm signal provided by the pathogen itself is required for the expression of resistance in plants previously sensitized by biotic agents. Ultrastructural investigations of the infected root tissues from water-treated (control) plants showed a rapid colonization of all tissues including the vascular stele. In root tissues from bacterized tomato plants grown in the absence of chitosan, the limited fungal development coincided with marked changes in the host physiology. The main facets of the altered host metabolism concerned the induction of a structural response at sites of fungal entry and the abnormal accumulation of electron-dense substances in the colonized areas. A substantial increase in the extent and magnitude of the cellular changes induced by B. pumilus was observed when chitosan was supplied to bacterized tomato plants. These changes were characterized by a considerable enlargement of the callose-enriched wall appositions deposited onto the inner cell wall surface in the epidermis and the outer cortex. The use of the wheat germ agglutinin-ovomucoid-gold complex provided evidence that the wall-bound chitin component in Fusarium cells colonizing bacterized tomato roots was not substantially altered. One of the most-typical fungal cell reactions, observed only when bacterized tomato plants were grown in the presence of chitosan, was the formation of abnormal chitin-enriched deposits between the retracted plasma membrane and the cell wall. Results of the present study provide the first evidence that combination of biocontrol approaches is a promising step towards elaborating integrated pest management programmes. Received: 6 June 1997 / Accepted: 8 July 1997     

一株拮抗赤霉病的小麦内生细菌的筛选和抑菌活性

对安徽省淮北市小麦植株根、茎、叶中内生细菌的数量进行了调查和筛选,并测定了其抑菌活性.小麦根、茎和叶中的内生细菌的数量分别为7.01×105、4.26×105和0.94×105CFU·g-1鲜重.从健康小麦植株体内分离到131株内生细菌,通过对峙实验,筛选到6株对禾谷镰刀菌有拮抗作用的菌株,占所分离内生细菌总数的4.58%.来自根系组织中的菌株HB022的抑菌效果最佳,抑菌半径为17.0mm.根据形态特征、生理生化特性和16SrDNA序列分析,将菌株HB022初步鉴定为多粘类芽孢杆菌(Paenibacillus polymyxa).抑菌试验结果表明,100倍稀释的菌株HB022无菌发酵滤液对禾谷镰刀菌菌丝生长具有明显抑制作用,5倍稀释的无菌发酵滤液可完全抑制禾谷镰刀菌分生孢子萌发.可见,内生细菌HB022具有潜在生防应用前景.     

Induction of defense response against Rhizoctonia solani in cucumber plants by endophytic bacterium Bacillus thuringiensis GS1

An endophytic bacterium, Bacillus thuringiensis GS1, was isolated from bracken (Pteridium aquilinum) and found to have maximal production of chitinase (4.3 units/ml) at 5 days after culture. This study investigated the ability of B. thuringiensis GS1 to induce resistance to Rhizoctonia solani KACC 40111 (RS) in cucumber plants. Chitinase activity was greatest in RS-treated plants at 4 days. beta-1,3- Glucanase activity was highest in GS1-treated plants at 5 days. Guaiacol peroxidase (GPOD) activity increased continuously in all treated plants for 5 days. Ascorbate peroxidase (APX) activity in RS-treated plants was increased 1.5-fold compared with the control at 4 days. Polyphenol oxidase (PPO) activity in RS-treated plants was increased 1.5-fold compared with the control at 3 days. At 5 days after treatment, activity staining revealed three bands with chitinase activity (Ch1, Ch2, and Ch3) on SDSPAGE of cucumber plants treated with GS1+RS, whereas only one band was observed for RS-treated plants (Ch2). One GPOD isozyme (Gp1) was also observed in response to treatment with RS and GS1+RS at 4 days. One APX band (Ap2) was present on the native-PAGE gel of the control, and GS1- and GS1+RS-treated plants at 1 day. PPO bands (Po1 and Po2) from RS- and GS1+RS-treated plants were stronger than in the control and GS1-treated plants upon native-PAGE at 5 days. Taken together, these results indicate that the induction of PR proteins and defense-related enzymes by B. thuringiensis GS1 might have suppressed the damping-off caused by R. solani KACC 40111 in cucumber plants.     

Use of non-pathogenic or hypovirulent fungal strains to protect plants against closely related fungal pathogens

Nonpathogenic (avirulent), or low virulent (hypovirulent) strains are capable of colonizing infection site niches on the plants' surfaces and protecting susceptible plants against their respective pathogens. Such phenomena have been demonstrated for a considerable number of plant pathogens. The modes of protection differ among the nonpathogenic strains, and one strain can protect by more than one mechanism. Competition for infection sites, or for nutrients (such as carbon, iron) as well as induction of the host plant resistance, have been demonstrated for several pathogens such as Rhizoctonia spp., Fusarium spp. and Pythium spp. Mycoparasitism was shown for Pythium spp. Transmission of double stranded RNA mycoviruses from hypovirulent strains to virulent strains renders the virulent strains hypovirulent. Chestnut trees infected with the chestnut blight pathogen, Cryphonectria (Endothia) parasitica, recovered after inoculation with transmissible hypovirulent strains. Nonpathogenic strains of various fungi are potential candidates for development of biocontrol preparations. Some strains are already used in Agriculture.     

Heterosis in root microbiota inhibits growth of soil-borne fungal pathogens in hybrid rice

In nature, plants are colonized by various microbes that play essential roles in their growth and health. Heterosis is a natural genetic phenomenon whereby first-generation hybrids exhibit superior phenotypic performance relative to their parents.It remains unclear whether this concept can be extended to the “hybridization” of microbiota from two parents in their descendants and what benefits the hybrid microbiota might convey. Here, we investigated the structure and function of the root microbi...     

根际真菌对黄瓜土传病害的抑制作用

为了了解根际真菌对黄瓜土传病害的影响,通过平板对峙试验和温室人工接种盆栽试验,对分离自根际土的16株真菌开展了对土传病原真菌的拮抗作用和黄瓜土传病害的抑制作用研究.结果表明: 有4株真菌对一种或多种供试病原真菌表现有拮抗作用,其中经鉴定为土曲霉的菌株JCL143对黄瓜枯萎病菌、立枯病菌和菌核病菌3种供试病原真菌均有较强的拮抗作用.在温室盆栽试验中,接种菌株JCL143对黄瓜3种病害的相对防效均在74%以上;而在不灭菌育苗基质的盆栽试验中,接种菌株JCL143对立枯病和菌核病的防效均在85%以上.在用自然土进行的温室盆栽试验中,接种菌株JCL143对伸蔓期黄瓜枯萎病的相对防效平均达84.1%.菌株JCL143的发酵液对3种供试病原真菌菌落生长都有不同程度的抑制作用,对菌核病菌的菌落生长抑菌率达63.3%.发酵液的抑菌活性随处理温度的升高而下降,对碱性pH值比酸性pH值敏感,而对蛋白酶处理不敏感.说明土曲霉是土壤中抑制植物土传病害的重要因素,菌株JCL143的抑病效果稳定,具有潜在的生防应用价值.     

Biocontrol of Rhizoctonia solani damping-off and promotion of tomato plant growth by endophytic actinomycetes isolated from native plants of Algerian Sahara

Thirty-four endophytic actinomycetes were isolated from the roots of native plants of the Algerian Sahara. Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomyces genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently tested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils, and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seeds with antagonistic isolates significantly reduced (P < 0.05) the severity of damping-off of tomato seedlings. Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction as thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P < 0.05) were observed. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling length and the root length of the seed-treated seedlings compared to the control. The taxonomic position based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2 were related to Streptomyces mutabilis NBRC 12800^T (100% of similarity) and Streptomyces cyaneofuscatus JCM 4364^T (100% of similarity), respectively.     

Mechanisms of plant protection against two oxalate-producing fungal pathogens by oxalotrophic strains of Stenotrophomonas spp.

Plant Molecular Biology - Oxalotrophic Stenotrophomonas isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including...     

Antifungal activity of plants extracts against Alternaria solani,the causal agent of early blight of tomato

Aqueous extracts of 39 plants selected from local flora were evaluated for antifungal potential against Alternaria solani, causing early blight of tomato, at 4% concentration in Potato Dextrose Agar by poison food technique. Out of these, 13 plant extracts significantly reduced the mycelial growth of the pathogen, according to ANOVA, Tukey’s post-test. Inhibition rate of above 20% was shown by seven plant extracts namely Crotalaria trichotoma (36.6%), Citrus aurantifolia (27.3%), Azadirachta indica (23.7%), Polyalthia longifolia (23.3%), Datura metel (21.3%), Muntingia calabura (20.09%) and Oxalis latifolia (20.09%). At 2% concentration, six extracts showed significant growth inhibition namely, C. trichotoma (16.6%), A. indica (10%), Capsicum annum (7.1%), D. metel (6.6%), P. longifolia (6.3%) and C. aurantifolia (5.5%). The plant extracts shortlisted for pathogen inhibition have potential to be developed as potent fungicides in organic farming.     

Resistance Induction by Salicylic Acid Formulation in Cassava Plant against Fusarium solani

Fusarium root rot caused by the soil-borne fungus Fusarium solani is one of the most important fungal diseases of cassava in Thailand, resulting in high yield losses of more than 80%. This study aimed to investigate if the exogenous application of salicylic acid formulations (Zacha) can induce resistance in cassava against Fusarium root rot and observe the biochemical changes in induced cassava leaf tissues through synchrotron radiation based on Fourier-transform infrared (SR-FTIR) microspectroscopy. We demonstrated that the application of Zacha11 prototype formulations could induce resistance against Fusarium root rot in cassava. The in vitro experimental results showed that Zacha11 prototype formulations inhibited the growth of F. solani at approximately 34.83%. Furthermore, a significant reduction in the disease severity of Fusarium root rot disease at 60 days after challenge inoculation was observed in cassava plants treated with Zacha11 at a concentration of 500 ppm (9.0%). Population densities of F. solani were determined at 7 days after inoculation. Treatment of the Zacha11 at a concentration of 500 ppm resulted in reduced populations compared with the distilled water control and differences among treatment means at each assay date. Moreover, the SR-FTIR spectral changes of Zacha11-treated epidermal tissues of leaves had higher integral areas of lipids, lignins, and pectins (1,770–1,700/cm), amide I (1,700–1,600/cm), amide II (1,600–1,500/cm), hemicellulose, lignin (1,300–1,200/cm), and cellulose (1,155/cm). Therefore, alteration in defensive carbohydrates, lipids, and proteins contributed to generate barriers against Fusarium invasion in cassava roots, leading to lower the root rot disease severity.     

腐皮镰孢菌壳聚糖酶的酶学性质研究及其在酿酒酵母工业菌株中的表达

摘要：【目的】本研究旨在了解腐皮镰孢菌（Fusarium solani）壳聚糖酶的基本酶学性质及其在壳寡糖生产中的应用,构建能高效分泌表达壳聚糖酶的酿酒酵母工业菌株。【方法】采用RT-PCR扩增腐皮镰孢菌壳聚糖酶的cDNA序列;通过组氨酸标签,纯化得到E. coli表达的重组壳聚糖酶,并进行基本酶学性质研究;以薄层层析、高效液相色谱等技术对该酶的酶解产物进行分析;通过马克斯克鲁维酵母（Kluyveromyces marxianus）菊粉酶信号肽（INU1A）实现壳聚糖酶在酿酒酵母工业菌株N-27中的分泌表     

The phytohormone methyl jasmonate as an activator of induced resistance against the necrotroph Alternaria porri f. sp. solani in tomato plants

Abstract

Exogenous application of 0.1 mM methyl jasmonate (MeJA) throughout seed soaking or fumigation of seedlings could induce resistance against the necrotrophic fungus Alternaria porri f. sp. solani in tomato. MeJA applied at 0.01, 0.1, and 1 mM was found to reduce spore germination and mycelial growth in vitro. This compound at 0.01 and 0.1 mM did not cause toxic responses in the tomato plants; however, ethylene production by seedlings was observed to increase after using of all concentrations. A significant increase in the levels of defense markers such as total phenolics, anthocyanins, and phenylalanine ammonia-lyase activity, in response to exogenous MeJA, was observed. Pretreatment of tomato by soaking the seeds in MeJA or treating them with gaseous MeJA efficiently reduced the development of disease caused by Alternaria only when MeJA was applied at 0.1 mM concentration. Seed priming is an easier method of resistance induction than exposure to gaseous MeJA.