Showing papers on "Rhizoctonia solani published in 2007"

Volatiles of bacterial antagonists inhibit mycelial growth of the plant pathogen Rhizoctonia solani

Abstract: Bacterial antagonists are bacteria that negatively affect the growth of other organisms. Many antagonists inhibit the growth of fungi by various mechanisms, e.g., secretion of lytic enzymes, siderophores and antibiotics. Such inhibition of fungal growth may indirectly support plant growth. Here, we demonstrate that small organic volatile compounds (VOCs) emitted from bacterial antagonists negatively influence the mycelial growth of the soil-borne phytopathogenic fungus Rhizoctonia solani Kuhn. Strong inhibitions (99-80%) under the test conditions were observed with Stenotrophomonas maltophilia R3089, Serratia plymuthica HRO-C48, Stenotrophomonas rhizophila P69, Serratia odorifera 4Rx13, Pseudomonas trivialis 3Re2-7, S. plymuthica 3Re4-18 and Bacillus subtilis B2g. Pseudomonas fluorescens L13-6-12 and Burkholderia cepacia 1S18 achieved 30% growth reduction. The VOC profiles of these antagonists, obtained through headspace collection and analysis on GC-MS, show different compositions and complexities ranging from 1 to almost 30 compounds. Most volatiles are species-specific, but overlapping volatile patterns were found for Serratia spp. and Pseudomonas spp. Many of the bacterial VOCs could not be identified for lack of match with mass-spectra of volatiles in the databases.

Rhizobacterial Volatiles Affect the Growth of Fungi and Arabidopsis thaliana

Abstract: Volatiles of Stenotrophomonas, Serratia, and Bacillus species inhibited mycelial growth of many fungi and Arabidopsis thaliana (40 to 98%), and volatiles of Pseudomonas species and Burkholderia cepacia retarded the growth to lesser extents. Aspergillus niger and Fusarium species were resistant, and B. cepacia and Staphylococcus epidermidis promoted the growth of Rhizoctonia solani and A. thaliana. Bacterial volatiles provide a new source of compounds with antibiotic and growth-promoting features.

Antifungal Activity of Five Plant Essential Oils as Fumigant Against Postharvest and Soilborne Plant Pathogenic Fungi

Abstract: citriodora oils displayed in vitro antifungal activities against four phytopathogenic fungi except for Colletotrichum gloeospori oides. The essential oil of Thymus vulgaris suppressed the mycelial growth of C. gloeosporioides, Fusarium oxysporum and Rhizoctonia solani and that of Cymbopogon citratus was active to only F. oxysporum. The chemical compositions of the five active essential oils were determined by gas chromatography-m ass spectrometry. This study sug­ gests that both E. citriodora and C. cyminum oils have a potential as antifungal preservatives for the control of storage diseases of various crops.

Mycoparasitism studies of Trichoderma harzianum strains against Rhizoctonia solani: evaluation of coiling and hydrolytic enzyme production

Abstract: The genus Trichoderma is a potential biocontrol agent against several phytopathogenic fungi. One parameter for its successful use is an efficient coiling process followed by a substantial production of hydrolytic enzymes. The interaction between fifteen isolates of Trichoderma harzianum and the soil-borne plant pathogen, Rhizoctonia solani, was studied by light microscopy and transmission electron microscopy (TEM). Macroscopic observations of fungal growth in dual cultures revealed that growth inhibition of the pathogen occurred soon after contact with the antagonist. All T. harzianum isolates tested exhibited coiling around the hyphae of R. solani. The strains ALL23, ALL40, ALL41, ALL43 and ALL49 did not differ in coiling frequency and gave equal coiling performances. No correlation between coiling frequency and the production of cell wall-degrading chitinases, N-acetyl-beta-D-glucosaminidase and beta-1,3-glucanases, was found.

Using Pseudomonas spp. for Integrated Biological Control.

Abstract: Stockwell, V. O., and Stack, J. P. 2007. Using Pseudomonas spp. for integrated biological control. Phytopathology 97:244-249. Pseudomonas spp. have been studied for decades as model organisms for biological control of plant disease. Currently, there are three commercial formulations of pseudomonads registered with the U.S. Environmental Protection Agency for plant disease suppression, Bio-Save 10 LP, Bio-Save 11 LP, and BlightBan A506. Bio-Save 10 LP and Bio-Save 11 LP, products of Jet Harvest Solutions, Longwood, FL, contain Pseudomonas syringae strains ESC-10 and ESC-11, respectively. These products are applied in packinghouses to prevent postharvest fungal diseases during storage of citrus, pome, stone fruits, and potatoes. BlightBan A506, produced by NuFarm Americas, Burr Ridge, IL, contains P. fluorescens strain A506. BlightBan A506 is applied primarily to pear and apple trees during bloom to suppress the bacterial disease fire blight. Combining BlightBan A506 with the antibiotic streptomycin improves control of fire blight, even in areas with streptomycin-resistant populations of the pathogen. BlightBan A506 also may reduce fruit russet and mild frost injury. These biocontrol products consisting of Pseudomonas spp. provide moderate to excellent efficacy against multiple production constraints, are relatively easy to apply, and they can be integrated with conventional products for disease control. These characteristics will contribute to the adoption of these products by growers and packinghouses. In the 1990s, several pseudomonads were approved as registered biopesticides with the U.S. Environmental Protection Agency (USEPA). These strains are listed on the USEPA biopesticide website and described in a review by Fravel (4). Pseudomonas chlororaphis strain 63-28 was commercialized as the product AtEze, by EcoSoil Systems in California. AtEze was applied as a soil drench in greenhouse containers for the suppression of soilborne pathogens such as Pythium spp., Rhizoctonia solani, and Fusarium oxysporum. P. aureofaciens strain Tx1 also was commercialized by EcoSoil Systems as Spot-less Biofungicide. This product was intended for application through golf course irrigation systems to control dollar spot, anthracnose, pink snow mold, and diseases caused by Pythium spp. Although no longer commercially available, these two products remain registered biopesticides with the USEPA. In 1992, Plant Health Technologies, Latham, CA, registered three pseudomonads in their product called FrostBan: P. fluorescens strain 1629RS, P. syringae 742RS, and P. fluorescens strain A506. Only P. fluorescens strain A506 is commercially available and is now sold as BlightBan A506 by NuFarm Americas, Burr Ridge, IL. Two other pseudomonads, P. syringae strain ESC-10 and P. syringae strain ESC-11, were registered in 1995 and EcoScience Corporation developed these strains in the Bio-Save product line for the suppression of postharvest diseases. These products are now distributed by Jet Harvest Solutions in Florida. Bio-Save Products. Bio-Save 10 LP and Bio-Save 11 LP are used for the suppression of postharvest diseases. ESC-10 is a strain of P. syringae that was isolated from apple by scientists at EcoScience Corporation and is the active ingredient in the

Mechanism of action and efficacy of seed meal-induced pathogen suppression differ in a brassicaceae species and time-dependent manner.

Abstract: The effect of seed meals derived from Brassica juncea, B. napus, or Sinapis alba on suppression of soilborne pathogens inciting replant disease of apple was evaluated in greenhouse trials. Regardless of plant source, seed meal amendment significantly improved apple growth in all orchard soils; however, relative differences in pathogen suppression were observed. All seed meals suppressed root infection by native Rhizoctonia spp. and an introduced isolate of Rhizoctonia solani AG-5, though B. juncea seed meal often generated a lower level of disease control relative to other seed meal types. When introduction of the pathogen was delayed until 4 to 8 weeks post seed meal amendment, disease suppression was associated with proliferation of resident Streptomyces spp. and not qualitative or quantitative attributes of seed meal glucosinolate content. Using the same experimental system, when soils were pasteurized prior to pathogen infestation, control of R. solani was eliminated regardless of seed meal type. In the case of B. juncea seed meal amendment, the mechanism of R. solani suppression varied in a temporal manner, which initially was associated with the generation of allylisothiocyanate and was not affected by soil pasteurization. Among those tested, only B. juncea seed meal did not stimulate orchard soil populations of Pythium spp. and infection of apple roots by these oomycetes. Although application of B. napus seed meal alone consistently induced an increase in Pythium spp. populations, no significant increase in Pythium spp. populations was observed in response to a composite B. juncea and B. napus seed meal amendment. Suppression of soil populations and root infestation by Pratylenchus spp. was dependent upon seed meal type, with only B. juncea providing sustained nematode control. Collectively, these studies suggest that use of a composite B. juncea and B. napus seed meal mixture can provide superior control of the pathogen complex inciting apple replant disease relative to either seed meal used alone.

Screening of bacterial isolates from various European soils for in vitro antagonistic activity towards Rhizoctonia solani and Fusarium oxysporum : Site-dependent composition and diversity revealed

Abstract: A cultivation-based approach was used to determine the in vitro antagonistic potential of soil bacteria towards Rhizoctonia solani AG3 and Fusarium oxysporum f. sp. lini (Foln3). Four composite soil samples were collected from four agricultural sites with previous documentation of disease suppression, located in France (FR), the Netherlands (NL), Sweden (SE) and the United Kingdom (UK). Similarly, two sites from Germany (Berlin, G-BR; and Braunschweig, G-BS) without documentation of disease suppression were sampled. Total bacterial counts were determined by plating serial dilutions from the composite soil samples onto R2A, AGS and King's B media. A total of 1,788 isolates (approximately 100 isolates per medium and site) was screened for antifungal activity, and in vitro antagonists (327 isolates) were found amongst the dominant culturable bacteria isolated from all six soils. The overall proportion of antagonists and the number of isolates with inhibitory activity against F. oxysporum were highest in three of the suppressive soils (FR, NL and SE). Characterization of antagonistic bacteria revealed a high phenotypic and genotypic diversity. Siderophore and protease activity were the most prominent phenotypic traits amongst the antagonists. The composition and diversity of antagonists in each soil was site-specific. Nevertheless, none of the antimicrobial traits of bacteria potentially contributing to soil suppressiveness analyzed in this study could be regarded as specific to a given site.

Manipulation of rhizosphere bacterial communities to induce suppressive soils.

Abstract: Naturally occurring disease-suppressive soils have been documented in a variety of cropping systems, and in many instances the biological attributes contributing to suppressiveness have been identified. While these studies have often yielded an understanding of operative mechanisms leading to the suppressive state, significant difficulty has been realized in the transfer of this knowledge into achieving effective field-level disease control. Early efforts focused on the inundative application of individual or mixtures of microbial strains recovered from these systems and known to function in specific soil suppressiveness. However, the introduction of biological agents into non-native soil ecosystems typically yielded inconsistent levels of disease control. Of late, greater emphasis has been placed on manipulation of the cropping system to manage resident beneficial rhizosphere microorganisms as a means to suppress soilborne plant pathogens. One such strategy is the cropping of specific plant species or genotypes or the application of soil amendments with the goal of selectively enhancing disease-suppressive rhizobacteria communities. This approach has been utilized in a system attempting to employ biological elements resident to orchard ecosystems as a means to control the biologically complex phenomenon termed apple replant disease. Cropping of wheat in apple orchard soils prior to re-planting the site to apple provided control of the fungal pathogen Rhizoctonia solani AG-5. Disease control was elicited in a wheat cultivar-specific manner and functioned through transformation of the fluorescent pseudomonad population colonizing the rhizosphere of apple. Wheat cultivars that induced disease suppression enhanced populations of specific fluorescent pseudomonad genotypes with antagonistic activity toward R. solani AG-5, but cultivars that did not elicit a disease-suppressive soil did not modify the antagonistic capacity of this bacterial community. Alternatively, brassicaceae seed meal amendments were utilized to develop soil suppressiveness toward R. solani. Suppression of Rhizoctonia root rot in response to seed meal amendment required the activity of the resident soil microbiota and was associated with elevated populations of Streptomyces spp. recovered from the apple rhizosphere. Application of individual Streptomyces spp. to soil systems provided control of R. solani to a level and in a manner equivalent to that obtained with the seed meal amendment. These and other examples suggest that management of resident plant-beneficial rhizobacteria may be a viable method for control of specific soilborne plant pathogens.

Rapid Determination of Rice Cultivar Responses to the Sheath Blight Pathogen Rhizoctonia solani Using a Micro-Chamber Screening Method

Abstract: An accurate greenhouse screening method has not been developed previously to identify host response to sheath blight disease caused by Rhizoctonia solani Kuhn that causes significant economic losses in rice yield worldwide. The unavailability of a robust screening system in the greenhouse has made it difficult to quantify disease reactions to R. solani, and has hampered studies on the genetics of resistance and plant breeding efforts to improve resistance. In an effort to develop a standardized laboratory micro-chamber screening method to quantify resistance to R. solani in rice, five rice cultivars, representing a wide range of observed disease reactions under field conditions, were examined in a blind inoculation test at three locations (Arkansas, Texas, and Colombia). Rice seedlings were inoculated at the three- to four-leaf stage with potato dextrose agar plugs containing mycelium and then covered with a 2- or 3-liter transparent plastic bottle for maintaining high humidity after inoculation. Two cultivars, Jasmine 85 and Lemont, that consistently have shown the highest and lowest levels of resistance, respectively, in previous field and greenhouse studies, were used as standards. Concurrent field experiments in Arkansas and Texas also were performed to compare the greenhouse disease ratings with those observed under field conditions. Overall, the relative disease ratings of the seven test cultivars were consistent between test locations and with field evaluations. Thus, the micro-chamber screening method can be used as an effective approach to accurately quantify resistance to the sheath blight pathogen under controlled greenhouse conditions and should help expedite the selection process to improve resistance to this important pathogen.

Characterization of Rhizoctonia solani from potato in Great Britain

Abstract: One hundred and thirty five isolates of Rhizoctonia solani were obtained from British potato crops between 2001 and 2003. Isolates were assigned to anastomosis group (AG) using conventional PCR assays for AG2-1 or AG3 or through the observation of hyphal interactions, where appropriate. A previously published primer set was modified in this study to enhance specificity for AG3PT. Most of the isolates (92·6%) belonged to AG3PT whilst some (6·7%) belonged to AG2-1. Only one isolate recovered (0·7%) belonged to AG5. Isolates of AG2-1 were diverse, with variation in both the length of the rDNA intergenic spacer 1 (IGS1) region and the categories of hyphal interaction observed between pairings of AG2-1 isolates. No variation in the length of the rDNA IGS1 region was observed amongst the AG3 isolates collected. Tests carried out on potato stems with a sub-set of the isolates revealed a wide range of aggressiveness amongst AG2-1 isolates. Sequencing of the rDNA internal transcribed spacer (ITS) region of the AG2-1 isolates and construction of a neighbour joining tree with other AG2-1 sequences available indicated that AG2-1 isolates with the short IGS1 region were closely related. This is the first investigation which provides evidence of the relative AG composition of R. solani populations causing disease in potato crops in Great Britain.

Study of the antifungal activity of Acinetobacter baumannii LCH001 in vitro and identification of its antifungal components.

Abstract: An Acinetobacter strain, given the code name LCH001 and having the potential to be an endophytic antagonist, has been isolated from healthy stems of the plant Cinnamomum camphora (L.) Presl, guided by an in vitro screening technique. The bacterium inhibited the growth of several phytopathogenic fungi such as Cryphonectria parasitica, Glomerella glycines, Phytophthora capsici, Fusarium graminearum, Botrytis cinerea, and Rhizoctonia solani. Biochemical, physiological, and 16S rDNA sequence analysis proved that it is Acinetobacter baumannii. When the filtrate from the fermentation broth of strain LCH001 was tested in vitro and in vivo, it showed strong growth inhibition against several phytopathogens including P. capsici, F. graminearum, and R. solani, indicating that suppression of the growth of the fungi was due to the presence of antifungal compounds in the culture broth. Moreover, the antifungal activity of the culture filtrate was significantly correlated with the cell growth of strain LCH001. The active metabolites in the filtrate were relatively thermally stable, but were sensitive to acidic conditions. Three antifungal compounds were isolated from the culture broth by absorption onto macropore resin, ethanol extraction, chromatography on silica gel or LH-20 columns, and crystallization. The structures of the bioactive compounds were identified by spectroscopic methods as isomers of iturin A, namely, iturin A2, iturin A3, and iturin A6. The characterization of an unusual endophytic bacterial strain LCH001 and its bioactive components may provide an alternative resource for the biocontrol of plant diseases.

Thaumatin gene confers resistance to fungal pathogens as well as tolerance to abiotic stresses in transgenic tobacco plants

Abstract: We report here the development of transgenic tobacco plants with thaumatin gene of Thaumatococcus daniellii under the control of a strong constitutive promoter-CaMV 35S. Both polymerase chain reaction and genomic Southern analysis confirmed the integration of transgene. Transgenic plants exhibited enhanced resistance with delayed disease symptoms against fungal diseases caused by Pythium aphanidermatum and Rhizoctonia solani. The leaf extract from transgenic plants effectively inhibited the mycelial growth of these pathogenic fungi in vitro. The transgenic seeds exhibited higher germination percentage and seedling survival under salinity and PEG-mediated drought stress as compared to the untransformed controls. These observations suggest that thaumatin gene can confer tolerance to both fungal pathogens and abiotic stresses.

Pyramiding transgenic resistance in elite indica rice cultivars against the sheath blight and bacterial blight

Abstract: Elite indica rice cultivars were cotransformed with genes expressing a rice chitinase (chi11) and a thaumatin-like protein (tlp) conferring resistance to fungal pathogens and a serine-threonine kinase (Xa21) conferring bacterial blight resistance, through particle bombardment, with a view to pyramiding sheath blight and bacterial blight resistance. Molecular analyses of putative transgenic lines by polymerase chain reaction, Southern Blot hybridization, and Western Blotting revealed stable integration and expression of the transgenes in a few independent transgenic lines. Progeny analyses showed the stable inheritance of transgenes to their progeny. Coexpression of chitinase and thaumatin-like protein in the progenies of a transgenic Pusa Basmati1 line revealed an enhanced resistance to the sheath blight pathogen, Rhizoctonia solani, as compared to that in the lines expressing the individual genes. A transgenic Pusa Basmati1 line pyramided with chi11, tlp, and Xa21 showed an enhanced resistance to both sheath blight and bacterial blight.

Enhanced iturin A production by Bacillus subtilis and its effect on suppression of the plant pathogen Rhizoctonia solani

Abstract: Enhanced production of the antibiotic iturin A by Bacillus subtilis RB14-CS reached 4.4 g L(-1) in SM medium containing soybean meal and maltose, which was 16-fold and 2.2-fold higher than that in original and modified number 3S media, respectively. When various volumes of RB14-CS cultures grown in SM medium were applied to pot tests of tomato damping-off caused by Rhizoctonia solani, damping-off was dose-dependently suppressed by the cultures. Suppression by SM-grown cultures was significantly more effective than that by cultures grown in original or modified number 3S media. The iturin A concentrations in soil decreased to undetectable levels after 17 days of cultivation in pot tests, indicating that iturin A has a low persistence in soil.

Isolation and Identification of Rhizosphere Soil Chitinolytic Bacteria and their Potential in Antifungal Biocontrol

Abstract: Four hundred bacterial isolates were isolated from rhizosphere of some plants collected from Egypt and screened for production of chitinase enzyme Only four isolates designated MS1, MS2, MS3 and MS4 were the most potent chitinolytic bacterial species SDS-PAGE analysis of vegetative and sporulated cells of the four isolates revealed that the protein profile of the four isolates were different from each other in their banding pattern and were identified as Bacillus licheniformis, Stenotrophomonas maltophilia, Bacillus licheniformis and B thuringiensis In vitro MS1 and MS3 were the most active species, so they suppressed the growth of all tested pathogenic fungi (Rhizoctonia solani, Macrophomina phasiolina, Fusarium culmorum, Pythium sp, Alternaria alternata and Sclerotium rolfsii) Also, MS3 produced the highest level of chitinase enzyme (127 µ/ml) after 4 days incubation as compared with the other isolates In green-house experiment, B licheniformis (MS3) significantly reduced the damping off disease caused by Rhizoctonia solani, in Helianthus annus using the seed coat or soil draing treatments

Biological diversity of Rhizoctonia solani (AG‐3) in a northern potato‐cultivation environment in Finland

Abstract: A total of 119 isolates of Rhizoctonia were collected from stem canker lesions, stolon and root lesions, hymenia on stems, or from black scurf on tubers of potato plants (Solanum tuberosum) in Finland (latitudes 60–67°N). All isolates except three belonged to anastomosis group 3 (AG-3) of R. solani, as determined by phylogenetic analysis of the internal transcribed spacer sequences (ITS1 and ITS2) of ribosomal RNA (rRNA) genes. Sensitivity of the 119 isolates to the fungicide flutolanil was tested in vitro (EC50 values 0·14–0·75 µg active ingredient mL−1). The isolates also varied considerably in growth rate (5·1–14·8 mm day−1). The severity of disease caused by 99 isolates was determined based on the proportion of potato sprouts affected by lesions, discoloration or death, which was c. 1–60%. Only two isolates that were able to cause severe symptoms showed particularly low sensitivity to the fungicide and rapid growth rate. One isolate each of anastomosis groups AG-2-1 and AG-5 and an unknown, binucleate Rhizoctonia sp. were detected. The AG-5 isolate and the binucleate isolate caused mild symptoms on potato sprouts, whereas the AG-2-1 isolate was not pathogenic. Taken together, AG-3 of R. solani was the predominant causal agent of the stem canker and black scurf diseases of potato in Finland and showed considerable variability in disease severity, fungicide sensitivity and growth rate in vitro.

Sensitivity to a Phytotoxin from Rhizoctonia solani Correlates with Sheath Blight Susceptibility in Rice.

Abstract: Sheath blight is one of the most important and intractable diseases of rice (Oryza sativa) where limited control has been achieved using traditional approaches. Quantitative inheritance, extraneous traits, and environmental factors confound genetic analysis of host resistance. A method was developed to isolate and utilize a phytotoxin from Rhizoctonia solani to investigate the genetics of sheath blight susceptibility. Infiltration of the toxin preparation into plant leaves induced necrosis in rice, maize, and tomato. Using 17 rice cultivars known to vary in sheath blight resistance, genotypes were identified that were sensitive (tox-S) and insensitive (tox-I) to the toxin, and a correlation (r = 0.66) between toxin sensitivity and disease susceptibility was observed. Given the broad host range of R. solani, genotypes of host species may be both tox-S and tox-I. A total of 154 F2 progeny from a cross between Cypress (tox-S) and Jasmine 85 (tox-I) segregated in a 9:7 ratio for tox-S/tox-I, indicati...

Analysis of the Antimicrobial Activity of Flavonoids and Saponins Isolated from the Shoots of Oats (Avena sativa L.)

Abstract: Crude extracts from the shoots of oat cv. Quoll were tested against four species of bacteria and eight species of fungi. Bacterial growth was not inhibited. The mycelia growth of all Pyrenophora species tested, except Pyrenophora avenae DAR 33699, was inhibited by the crude extract, whereas the mycelia growth of Fusarium graminearum, Mycosphaerella pinodes and Rhizoctonia solani was not affected. Partially purified fractions with high concentrations of flavone-C-glycosides had no inhibitory effect against P. teres f. sp. teres and P. teres f. sp. maculata. The saponin 26-desglucoavenacoside B accounted for most of the activity against P. teres f. sp. teres with a minor contribution from the other saponins, 26-desglucoavenacoside A and avenacosides A and B.

Bioactive endophytic streptomycetes from the Malay Peninsula

Abstract: Three novel endophytic streptomycetes have been isolated and characterized from plants with ethnobotanical uses on the Malay Peninsula including: Thottea grandiflora (family -Aristolochiaceae), Polyalthia spp. (family -Annonaceae), and Mapania sp. (family -Cyperaceae). Each isolate, as studied by scanning electron microscopy, has small hyphae, and produces typical barrel-shaped spores arising by hyphal fragmentation. Interestingly, although none has any detectable antibacterial killing properties, each has demonstrable killing activity against one or more pathogenic fungi including organisms such as Phytophthora erythroseptica, Pythium ultimum, Sclerotinia sclerotiorum, Mycosphaerella fijiensis and Rhizoctonia solani. Molecular biological studies on the rRNA gene sequence of each isolate revealed that it is distinct from all other genetic accessions of streptomyectes in GenBank, and each bears some genetic similarity to other streptomycetes. The bioactivity of each microbe was extractable in various organic solvents.

Enhanced biocontrol activity of Trichoderma virens transformants constitutively coexpressing β‐1,3‐ and β‐1,6‐glucanase genes

Abstract: SUMMARY Evidence for the role of chitinases, proteases and beta-1,3- and beta-1,6-glucanases in mycoparasitism by Trichoderma species has been well documented. Moreover, constitutive over-expression of genes encoding individual cell-wall-degrading enzymes (CWDEs) has been shown to improve the potential of biological agents. In this study, we generated transformants of T. virens in which beta-1,3- and beta-1,6-glucanase genes, TvBgn2 and TvBgn3, respectively, were constitutively coexpressed in the same genetic T. virens Gv29.8 wild-type background. The double over-expression transformants (dOEs) grow and sporulate slower than the wild-type (WT). However, the reduction in growth did not seem to affect their mycoparasitic and biocontrol capabilities, as dOEs displayed much higher levels of total beta-1,3- and beta-1,6-glucanase activity than the WT. This higher enzymatic activity of dOEs positively correlated with observed in vitro inhibition of Pythium ultimum and Rhizoctonia solani mycelia, and with enhanced bioprotection of cotton seedlings against P. ultimum, R. solani and Rhizopus oryzae. Besides effective biocontrol of all pathogens at an original inoculum level, the performance of dOEs was highly enhanced (up to 312% of WT performance) when pathogen pressure was greater (i.e. concentration of inoculum was higher or pathogens applied in combination). These results demonstrate that the strategy of introducing multiple lytic enzyme-encoding genes through transformation of a given biocontrol strain can be successfully used to achieve better biocontrol.

Morphological and Pathological Variability in Rice Isolates of Rhizoctonia solani and Molecular Analysis of their Genetic Variability

Abstract: Nineteen isolates of Rhizoctonia solani collected from different rice varieties grown in various regions of Pun-jab were studied for their morphological and pathological characterization. Majority of the isolates were fast growing with raised and fluffy colonies and hyphal width of 9.6 μm while four exhibited moderate growth rate. Colony colour in all except two isolates was light yellowish brown. While sclerotial number per 5.0 mm culture disc of the test isolates ranged between 2.1 and 11.2 mm, their size varied between 1.31 and 2.08 mm. Sclerotial colour in all except two isolates was dark brown and most of these were found scattered in the colony. There was no relationship between morphologically similar isolates and their pathogenic behaviour. Majority of the isolates produced lesion length between 45.6 and 58.2 mm on detached rice leaves (cv. PR116). Molecular characterization of genetic diversity in the test isolates was studied by using 10 inter simple sequence repeats (ISSR) and eight random amplified polymorphic DNA (RAPD) markers. The size of amplified DNA bands ranged from 0.25-3.0 to 0.5-4.0 kb with ISSR and RAPD markers, respectively. Combined data set of 155 DNA markers were analysed with UPGMA resulting five clusters with 49-89% genetic similarity. Most of the isolates showed grouping specific to the host variety. Out of these two types of DNA markers, RAPD markers were able to detect more genetic variability when compared to ISSR markers.

Production and fungitoxic activity of Sch 642305, a secondary metabolite of Penicillium canescens.

Abstract: Production of fungitoxic extrolites was evaluated in culture filtrates of several isolates belonging to Penicillium canescens and P. janczewskii that showed some extent of inhibitory activity against the plant pathogenic fungus Rhizoctonia solani. In addition to griseofulvin and dechlorogriseofulvin that are already known in these species, curvulinic acid, previously unreported in Penicillium, was produced by all isolates assayed. Another extrolite recently characterized from a P. verrucosum strain by the name of Sch 642305 was detected in 5 isolates of P. canescens only. The purified compound completely inhibited mycelial growth of isolates of Rhizoctonia solani and other plant pathogenic fungi in␣vitro. The role of this extrolite as a possible biochemical determinant of antagonism toward plant pathogenic fungi, and implications concerning chemotaxonomy are discussed.

RL-SAGE and microarray analysis of the rice transcriptome after Rhizoctonia solani infection

Abstract: Sheath blight caused by the fungal pathogen Rhizoctonia solani is an emerging problem in rice production worldwide. To elucidate the molecular basis of rice defense to the pathogen, RNA isolated from R. solani-infected leaves of Jasmine 85 was used for both RL-SAGE library construction and microarray hybridization. RL-SAGE sequence analysis identified 20,233 and 24,049 distinct tags from the control and inoculated libraries, respectively. Nearly half of the significant tags (≥2 copies) from both libraries matched TIGR annotated genes and KOME full-length cDNAs. Among them, 42% represented sense and 7% antisense transcripts, respectively. Interestingly, 60% of the library-specific (≥10 copies) and differentially expressed (>4.0-fold change) tags were novel transcripts matching genomic sequence but not annotated genes. About 70% of the genes identified in the SAGE libraries showed similar expression patterns (up or down-regulated) in the microarray data obtained from three biological replications. Some candidate RL-SAGE tags and microarray genes were located in known sheath blight QTL regions. The expression of ten differentially expressed RL-SAGE tags was confirmed with RT-PCR. The defense genes associated with resistance to R. solani identified in this study are useful genomic materials for further elucidation of the molecular basis of the defense response to R. solani and fine mapping of target sheath blight QTLs.