Potential of Serratia marcescens strain B2 for biological control of rice sheath blight

Serratia marcescens strain B2 inhibited mycelial growth of the rice sheath blight pathogen Rhizoctonia solani AG-1 IA. Rice plants were treated with bacterial suspension and then challenge inoculated with the pathogen. Application of S. marcescens effectively reduced the incidence of sheath blight. S. marcescens survived in soil under glasshouse conditions at ca. 10⁸ colony forming units g^-1 of soil for 4 weeks after application. These results suggest that S. marcescens has potential as an effective and persistent biological control agent for rice sheath blight.     

Efficacy ofTrichoderma chitinases againstRhizoctonia solani, the rice sheath blight pathogen

Thirty-five strains ofTrichoderma viride andT. harzianum were screened for their antagonistic ability against the rice sheath blight pathogen,Rhizoctonia solani. The strains that inhibited/overgrew the phytopathogenic fungus were considered effective. Light microscopic studies showed the antagonism of the hyphae of effectiveTrichoderma strains towards their host hyphae. Chitinase activity ofTrichoderma culture filtrates was enhanced, when colloidal chitin was used as the sole carbon source, instead of glucose. Chitinase pattern differed among the four select strains. The chitinase isoforms are induced differentially by carbon sources. The chitin affinity column fraction ofTrichoderma culture filtrate inhibited,in vitro, the growth ofR. solani.     

Genomic-assisted characterisation of Pseudomonas sp. strain Pf4, a potential biocontrol agent in hydroponics

In an attempt to select potential biocontrol agents against Pythium spp. and Rhizoctonia spp. root pathogens for use in soilless systems, 12 promising bacteria were selected for further investigations. Sequence analysis of the 16S rRNA gene revealed that three strains belonged to the genus Enterobacter, whereas nine strains belonged to the genus Pseudomonas. In in vitro assays, one strain of Pseudomonas sp., Pf4, closely related to Pseudomonas protegens (formerly Pseudomonas fluorescens), showed noteworthy antagonistic activity against two strains of Pythium aphanidermatum and two strains of Rhizoctonia solani AG 1-IB, with average inhibition of mycelial growth >80%. Strain Pf4 was used for in vivo treatments on lamb’s lettuce against R. solani root rot in small-scale hydroponics. Pf4-treated and untreated plants were daily monitored for symptom development and after two weeks of infection, a significant protective effect of Pf4 against root rot was recorded. The survival and population density of Pf4 on roots were also checked, demonstrating a density above the threshold value of 10⁵?CFU?g^?1 of root required for disease suppression. Known loci for the synthesis of antifungal metabolites, detected using PCR, and draft-genome sequencing of Pf4 demonstrated that Pseudomonas sp. Pf4 has the potential to produce an arsenal of secondary metabolites (plt, phl, ofa and fit-rzx gene clusters) very similar to that of the well-known biocontrol P. protegens strain Pf-5.     

Interpretation of variety × sowing date × sowing depth interaction for bean–Fusarium–Rhizoctonia pathosystem

Through this study, the sowing date?×?sowing depth?×?variety interaction for Rhizoctonia root rot (RRR) development was investigated in field trials over two growing seasons. Four-way Wald tests indicated that there was a lower RRR incidence in var. Red compared to var. White in the majority of experimental plots. At a 5?cm seeding depth, RRR incidence for plantings on 22 May and 5 June was often lower than that for 5 May date. A hierarchical cluster analysis grouped experimental plots using averages of RRR incidence, Fusarium root rot (FRR) index and the number of seeds per plant. Sowing depth influenced FRR, RRR and productivity more than variety and date factors. Comparison of clusters recognised lower disease and greater production levels for sowing on 22 May and 5 June at 5?cm depth. Thus, shallow seeding of bean varieties in late spring should be incorporated into FRR–RRR-control programmes.     

棉立枯丝核菌(Rhizoctonia solani)中的一个dsDNA病毒

自从1962年Hollings在栽培蘑菇(Agaricus bisporus)中发现第一例真菌病毒以来,迄今已在100多种真菌中发现了病毒,多数含双链RNA基因组。1972年Bozarth报道在R.solani中发现病毒,但未报道该病毒的理化性质。1975年Finlker在R.solani的一个强致病力菌株中分离到双链RNA病毒,它含3个组分dsRNA。     

Use of Rhizobacteria in the Control of Root Rot–Root Knot Disease Complex of Mungbean

Thirty-two isolates of Pseudomonas aeruginosa and a Bacillus subtilis strain were isolated from rhizosphere and rhizoplane of four wild and 15 cultivated plants. Biocontrol and growth-promoting potentials of the bacterial isolates were tested under laboratory, greenhouse and field conditions. The bacterial isolates not only exhibited nematicidal activity by killing the second stage larvae of Meloidogyne javanica to a varying degree but also produced inhibition zones by inhibiting the radial growth of Macrophomina phaseolina, Fusarium solani and Rhizoctonia solani . Strain IE-2 and IE-6 of P. aeruginosa also lysed the fungal mycelium. P. aeruginosa and B. subtilis used as seed dressing or as soil drench significantly suppressed root rot–root knot infection and nematode population densities under greenhouse and field conditions and thereby enhanced plant growth and yield in mungbean.     

立枯丝核菌营养菌丝多型性观察

采用了2种不同的方法对立枯丝核菌营养菌丝的形态进行了观察和比较,观察到2种不同的营养菌丝的形态,即菌核类和假分生孢子类。为以后进一步研究立枯丝核菌营养菌丝的多型性奠定了一定的基础。     

Variations in culture morphology and pathogenicity among protoplast-regenerated strains of Rhizoctonia solani

Abstract Protoplast-regenerated cultures derived from mycelia of cereal-infecting field isolates of Rhizoctonia solani exhibited major variations in cultural morphology and in pathogenicity. Each field isplate yielded three of four distinct morphological types of protoplast cultures. The presence of the new morphological phenotypes was attributed to the selection of homokaryons arising from protoplasts with single nuclei. Highly pathogenic field isolates produced protoplast cultures with higher virulence than those from weakly virulent pathogenic isolates, and homokaryotic strains were generally less pathogenic than the parental field isolate.     

Identification and sequencing of a novel insertion sequence, IS1471, in Burkholderia cepacia strain 2a

Abstract Eighty-one isolates of Rhizoctonia solani AG4 were obtained from soil samples with diverse geographic origins in Korea. Forty-five out of 81 isolates (56%) contained at least one dsRNA molecule with their sizes ranging from 2.3 to > 23.1 kb. Nine different sizes of dsRNA molecules were found and extensive variation in banding patterns was observed among isolates. By comparing the sizes and combinations of dsRNAs, 21 distinct banding patterns were observed. Cytoplasmic fractions from 3 isolates showed the same dsRNA band patterns as those from the total cell extracts. The dsRNAs were stable through 10 successive hyphal tip cultures and serial transfers onto the potato dextrose agar supplemented with cycloheximide or emetine. The presence or absence of dsRNAs was not apparently correlated with disease severity, phenol oxidase activity, and geographic origin.     

A simple and rapid nuclear staining method for Rhizoctonia solani Kuhn

Abstract

We developed a modified staining technique using acridine orange to stain the nuclei of Rhizoctonia solani. Acridine orange solution was prepared in acetic acid buffer, pH 7.2. Staining for 15 min was critical for observing the nuclei. All of the isolates were found to be multinucleated. The nuclei appeared bright green with light orange background. This method is simple, rapid and reproducible.