玉米苗中DIMBOA与几种酚酸类物质抑菌活性比较

本文从室内培养的7日龄玉米幼苗中提取、分离、鉴定了抗性次生化合物丁布(2,4-d ihydroxy-7-m ethoxy-2H-1,4-benzoxazin-3(4H)-one,D IMBOA),并就该物质对玉米纹枯病病原菌立枯丝核菌(Rhizoctonia solani)的活性与三种酚酸类物质(阿魏酸、对羟基肉桂酸和咖啡酸)进行了离体比较研究。结果表明,丁布(D IMBOA),对立枯丝核菌有很强的生物活性,在浓度为50μg/mL时即可抑制立枯丝核菌菌丝的生长,抑制率为18.52%。阿魏酸、对羟基肉桂酸和咖啡酸,这三种酚酸在浓度250μg/mL时对立枯丝核菌菌丝的生长有抑制作用,抑制率分别为26.30%、8.50%和6.30%。不仅如此,丁布与对羟基肉桂酸之间、以及三种酚酸两两组合之间还存在一定的协同作用。在浓度相等的情况下,丁布与对羟基肉桂酸的等量混合液的抑菌率显著高于这两种物质单独存在时的抑菌率之和;同样,对羟基肉桂酸与阿魏酸的等量混合液的抑菌率比单一的对羟基肉桂酸溶液的抑菌率高18.89%,比单一的阿魏酸溶液的抑菌率高13.33%;对羟基肉桂酸与咖啡酸的等量混合液,抑菌率比两者单独试验时分别高9.63%和14.83%;阿魏酸与咖啡酸的混合液,抑菌率比两酸单独试验时分别高11.48%和22.23%。这一结果提示植物体内产生适当比例不同次生化合物的组合对植物抗病性的提高是至关重要的。     

Mitigation of growth retardation effect of plant defense activator,acibenzolar-<Emphasis Type="Italic">S</Emphasis>-methyl,in amaranthus plants by plant growth-promoting rhizobacteria

Four rhizobacterial strains and acibenzolar-S-methyl (ASM), a chemical activator, which suppressed foliar blight of amaranthus (Amaranthus tricolor L.) caused by Rhizoctonia solani Kühn were evaluated for their effect on plant growth. The experiments were performed both under sterile and non-sterile soil conditions, in the presence or absence of the pathogen. In all cases, plants treated with ASM showed significant reduction in growth, as determined by shoot length, and shoot and root dry weight when compared to other treatments. The growth retardation effect of ASM was more profound with respect to shoot length. Reduction in shoot length was least when plants were treated with a combination of the chemical activator and Pseudomonas putida 89B61 under non-sterile soil conditions in the absence of the pathogen. Both under sterile and non-sterile soil conditions, in the presence of the pathogen, reduction in shoot length due to application of ASM was diminished significantly when plants were treated with rhizobacterial strain Pseudomonas fluorescens PN026R. Combined use of plant growth-promoting rhizobacteria (PGPR) and ASM was found to be beneficial as the growth retardation effect of the plant defense activator was reduced by the growth-promoting ability of the rhizobacteria.     

核酸技术在立枯丝核菌分类与生态学研究中的应用

立枯丝核菌是一种传播广、危害大的土传病原菌,对其展开的研究已涉及各个方面并逐渐深入,近几年借助于核酸技术对其所展开的研究更成为热点。对核酸技术在立枯丝核菌的分类学研究(主要包括G Cmol%含量测定、核酸杂交、各种DNA指纹技术、特异PCR扩增、测序DNA的序列分析)、监测群体动态变化的生态学研究(实时荧光PCR技术)中的应用作一简要的介绍。     

Evaluation of Argemone mexicana for Control of Root-Infecting Fungi in Tomato

Argemone mexicana L. (Papaveraceae), a tropical annual weed, is known to be phytotoxic to many crop species. This study was designed to examine the possible impact of A. mexicana on root‐infecting fungi, changes in fungal community structure and the growth of tomato. A. mexicana decaying shoots in soil provided a marked decrease in the infectivity of Fusarium solani and Rhizoctonia solani but Macrophomina phaseolina remained unaffected. Plant height and shoot growth of tomato plants increased markedly though high concentration of A. mexicana (5% w/w) was deleterious to tomato plants. General species diversity of soil fungal communities increased in the amended soils over the controls and greater increase in diversity occurred at higher concentrations of decaying A. mexicana. Likewise, equitability and richness components of diversity increased in treatments compared to controls but declined with increasing sampling period. Aspergillus nidulans, Cephaliophora irregularis, Drechslera halodes, Paecilomyces lilacinus and Trichoderma viride were isolated exclusively from the amended soils. Aqueous extract of A. mexicana when applied in soil greatly suppressed all three of the above root‐infecting fungi, and at lower concentration actually enhanced plant growth. The influence of different levels of N‐fertilization with NH₄NO₃ on the modification of the effect of decaying A. mexicana on root‐infecting fungi was also investigated. N‐fertilization to some extent alleviated the phytotoxicity to tomato plants while suppressing the root‐infecting fungi. A. mexicana in conjunction with Pseudomonas aeruginosa, a plant growth‐promoting rhizobacterium, significantly suppressed root‐infecting fungi with concomitant increase in plant growth. Whereas P. aeruginosa was reisolated from the rhizosphere and inner root tissues of tomato, its population slightly declined in the amended soil but not to an extent that could reduce the biocontrol and growth promoting potential of the bacterium.     

First Report of AG-A of Binucleate Rhizoctonia in China, Pathogenic to Soya Bean, Pea, Snap Bean and Pak Choy

Twenty binucleate Rhizoctonia (BNR) isolates were collected from roots of soya bean, pea, snap bean and pak choy with root rot symptoms in Yunnan Province, China. Chinese isolates anastomosed with the tester isolate of anastomosis group‐A (AG‐A; C‐517) with a high C2 fusion rate (>70%). Chinese isolates were pathogenic to soya bean, pea, snap bean and pak choy and had 97% similarity sequence of 5.8S rDNA‐internal transcribed spacer with AG‐A tester isolates SN‐2 and C‐662. When compared with other groups, AG‐Ba and AG‐Bb, Chinese isolates showed 77% sequence similarity. These results show that Chinese isolates belong to AG‐A of BNR. Growth rate, hyphal diameter, cultural characteristics and pathogenicity of the Chinese isolates differed significantly from the tester isolate of AG‐A. This is the first report on AG‐A in China.     

Prolific production of sclerotia in soil by Rhizoctonia solani anastomosis group (AG) 11 pathogenic on lupin

Rhizoctonia solani anastomosis group (AG) 11 causes serious damping‐off and hypocotyl rot of narrow‐leafed lupins (Lupinus angustifolius) in the northern grain‐belt of Western Australia. R. solani AG‐11 produced abundant sclerotia in sand overlaid on potato dextrose agar. Sclerotia were produced in larger numbers in natural Lancelin sand than in Geraldton loamy sand collected from the northern grain‐belt of Western Australia. The majority of the sclerotia produced were in >250 to <500 μam size range. The germination levels of sclerotia in the first two cycles of drying and germination were not significantly different. Sclerotia still retained 50% germination after four such cycles, indicating that they may have the ability to withstand the climatic cycles of the Mediterranean environment of southwestern Western Australia. The radial growth of the mycelium from sclerotia, however, declined with each drying and germination cycle. Inoculum potential of the pathogen increased with the size of sclerotia resulting in more severe lupin hypocotyl rot with larger sclerotia. The number of sclerotia produced in soil increased with increasing density of lupin seedlings. The results also indicate that R. solani AG‐11 can produce sclerotia on infected plant tissues as well as in soil. This is the first report of the prolific production of sclerotia by AG‐11 and their significant role in infection of lupins in soil in Western Australia.     

Comparison among four triazole fungicides on growth and development of sheath blight of rice pathogen Rhizoctonia solani Kühn AG1-1A

The sheath blight of rice pathogen Rhizoctonia solani Kühn AG1-1A has long been known as a major crisis in global rice production. The present study aimed to compare the efficacy of four triazole fungicides at different doses on the growth and development of R. solani Kühn AG1-1A. Obtained results demonstrated inhibitory effects of all four fungicides on mycelial growth, sclerotia formation and biomass production of R. solani Kühn AG1-1A with significant variation among the treatment doses as well as fungicide molecules (p ≤ 0.05). At the respective EC₅₀ doses all four fungicides inhibited cell wall degrading enzymes viz. invertase, cellulase, polygalacturonase and pectin lyase, of the sheath blight pathogen. The extent of inhibition of the enzymes significantly varied among the fungicides. It is important to note that in spite of having common mode of action, all four triazole fungicides demonstrated significant variation in their fungicidal efficacy on R. solani Kühn AG1-1A.     

Expression of Dm-AMP1 in rice confers resistance to Magnaporthe oryzae and Rhizoctonia solani

Magnaporthe oryzae and Rhizoctonia solani, are among the most important pathogens of rice, severely limiting its productivity. Dm-AMP1, an antifungal plant defensin from Dahlia merckii, was expressed in rice (Oryza sativa L. sp. indica cv. Pusa basmati 1) using Agrobacterium tumefaciens-mediated transformation. Expression levels of Dm-AMP1 ranged from 0.43% to 0.57% of total soluble protein in transgenic plants. It was observed that constitutive expression of Dm-AMP1 suppresses the growth of M. oryzae and R. solani by 84% and 72%, respectively. Transgenic expression of Dm-AMP1 was not accompanied by an induction of pathogenesis-related (PR) gene expression, indicating that the expression of DmAMP1 directly inhibits the pathogen. The results of in vitro, in planta and microscopic analyses suggest that Dm-AMP1 expression has the potential to provide broad-spectrum disease resistance in rice.     

Effect of bacterial antagonists on lettuce: active biocontrol of Rhizoctonia solani and negligible, short-term effects on nontarget microorganisms

The aim of this study was to assess the biocontrol efficacy against Rhizoctonia solani of three bacterial antagonists introduced into naturally Rhizoctonia-infested lettuce fields and to analyse their impact on the indigenous plant-associated bacteria and fungi. Lettuce seedlings were inoculated with bacterial suspensions of two endophytic strains, Serratia plymuthica 3Re4-18 and Pseudomonas trivialis 3Re2-7, and with the rhizobacterium Pseudomonas fluorescens L13-6-12 7 days before and 5 days after planting in the field. Similar statistically significant biocontrol effects were observed for all applied bacterial antagonists compared with the uninoculated control. Single-strand conformation polymorphism analysis of 16S rRNA gene or ITS1 fragments revealed a highly diverse rhizosphere and a less diverse endophytic microbial community for lettuce. Representatives of several bacterial (Alpha-, Beta- and Gammaproteobacteria, Firmicutes, Bacteriodetes), fungal (Ascomycetes, Basidiomycetes) and protist (Oomycetes) groups were present inside or on lettuce plants. Surprisingly, given that lettuce is a vegetable that is eaten raw, species of genera such as Flavobacterium, Burkholderia, Staphylococcus, Cladosporium and Aspergillus, which contain potentially human pathogenic strains, were identified. Analysis of the indigenous bacterial and endophytic fungal populations revealed only negligible, short-term effects resulting from the bacterial treatments, and that they were more influenced by field site, plant growth stage and microenvironment.