Showing papers on "Rhizoctonia solani published in 1998"

Genes from mycoparasitic fungi as a source for improving plant resistance to fungal pathogens.

Abstract: Disease resistance in transgenic plants has been improved, for the first time, by the insertion of a gene from a biocontrol fungus. The gene encoding a strongly antifungal endochitinase from the mycoparasitic fungus Trichoderma harzianum was transferred to tobacco and potato. High expression levels of the fungal gene were obtained in different plant tissues, which had no visible effect on plant growth and development. Substantial differences in endochitinase activity were detected among transformants. Selected transgenic lines were highly tolerant or completely resistant to the foliar pathogens Alternaria alternata, A. solani, Botrytis cinerea, and the soilborne pathogen Rhizoctonia solani. The high level and the broad spectrum of resistance obtained with a single chitinase gene from Trichoderma overcome the limited efficacy of transgenic expression in plants of chitinase genes from plants and bacteria. These results demonstrate a rich source of genes from biocontrol fungi that can be used to control diseases in plants.

The incompatible interaction between Phytophthora parasitica var. nicotianae race 0 and tobacco is suppressed in transgenic plants expressing antisense lipoxygenase sequences

Abstract: Nicotiana tabacum 46-8 cultivar displays an incompatible interaction with race 0 of Phytophthora parasitica var. nicotianae (Ppn), a fungal pathogen of most tobacco cultivars. At the plant level, incompatibility is characterized by the induction of lipoxygenase (LOX, EC = 1.13.11.12) activity and localized hypersensitive cell death before defense gene activation. To evaluate the involvement of LOX in the onset of plant defense, tobacco 46-8 plants were genetically engineered using full-length or partial-length antisense (AS) tobacco LOX cDNA constructs. AS expression strongly reduced elicitor- and pathogen-induced LOX activity. Eight independent AS-LOX lines were selected and assayed for their response to Ppn. After root or stem inoculation with race 0, all AS-LOX lines but one displayed a compatible phenotype whereas control transformed plants, not containing the AS-LOX cassette, showed the typical incompatible reaction. The presence of the fungus in transgenic lines was demonstrated by PCR amplification of a Ppn-specific genomic sequence. A linear relationship was found between the extent of LOX suppression and the size of the lesion caused by the fungus. The AS-LOX plants also showed enhanced susceptibility toward the compatible fungus Rhizoctonia solani. The results demonstrate the strong involvement of LOX in the establishment of incompatibility in plant–microorganism interactions, consistent with its role in the defense of host plants.

Suppression of Rhizoctonia solani in Potting Mixtures Amended with Compost Made from Organic Household Waste.

Abstract: Compost made from organic household and garden waste was used to substitute part of the peat in potting mixtures used for growing woody ornamental nursery stock The effects of amendment with compost on the colonization of potting mixture by Rhizoctonia solani (AG1) were studied in greenhouse experiments A bioassay was developed using cucumber as a sensitive herbaceous test plant as a substitute for woody ornamental cuttings Pathogen growth in the potting mixture was estimated by measuring the distance over which damping-off of seedlings occurred Compost from two commercial composting facilities suppressed growth of R solani in potting mixtures with 20% of the product when the compost was fresh (directly after delivery) or long matured (after 5 to 7 months of additional curing) In contrast, short-matured compost (1 month of additional curing) from the same batches stimulated pathogen growth In vitro mycelial growth of R solani on mixtures with mature compost was inhibited by microbial antagonism Compost-amended potting mixtures responded differentially to the addition of cellulose powder; the effect on suppressiveness depended on curing time and origin of the compost In long-matured compost, suppressiveness to R solani was associated with high population densities of cellulolytic and oligotrophic actinomycetes The ratio of the population density of actinomycetes to that of other bacteria was around 200-fold higher in mature suppressive compost than in conducive compost

Secondary Metabolite- and Endochitinase-Dependent Antagonism toward Plant-Pathogenic Microfungi of Pseudomonas fluorescens Isolates from Sugar Beet Rhizosphere

Abstract: Forty-seven isolates representing all biovars of Pseudomonas fluorescens (biovars I to VI) were collected from the rhizosphere of field-grown sugar beet plants to select candidate strains for biological control of preemergence damping-off disease. The isolates were tested for in vitro antagonism toward the plant-pathogenic microfungi Pythium ultimum and Rhizoctonia solani in three different plate test media. Mechanisms of fungal inhibition were elucidated by tracing secondary-metabolite production and cell wall-degrading enzyme activity in the same media. Most biovars expressed a specific mechanism of antagonism, as represented by a unique antibiotic or enzyme production in the media. A lipopeptide antibiotic, viscosinamide, was produced independently of medium composition by P. fluorescens bv. I, whereas the antibiotic 2, 4-diacetylphloroglucinol was observed only in glucose-rich medium and only in P. fluorescens bv. II/IV. Both pathogens were inhibited by the two antibiotics. Finally, in low-glucose medium, a cell wall-degrading endochitinase activity in P. fluorescens bv. I, III, and VI was the apparent mechanism of antagonism toward R. solani. The viscosinamide-producing DR54 isolate (bv. I) was shown to be an effective candidate for biological control, as tested in a pot experiment with sugar beet seedlings infested with Pythium ultimum. The assignment of different patterns of fungal antagonism to the biovars of P. fluorescens is discussed in relation to an improved selection protocol for candidate strains to be used in biological control.

Systemic Induction of Peroxidases, 1,3-beta-Glucanases, Chitinases, and Resistance in Bean Plants by Binucleate Rhizoctonia Species.

Abstract: Inoculation of bean hypocotyls with a nonpathogenic binucleate Rhizoctonia (BNR) species induced systemic resistance and protection of the roots and cotyledons to later challenge with the root rot pathogen Rhizoctonia solani or the anthracnose pathogen Colletotrichum lindemuthianum. Bean seedlings that were treated with BNR 48 h prior to their challenge with R. solani or C. lindemuthianum had few necrotic lesions and reduced disease severity as compared with seedlings not treated with BNR. Treatment with BNR 48 h prior to their challenge also elicited a significant and systemic increase in all cellular fractions of peroxidases, 1,3-beta-glucanases, and chitinases compared with the diseased and control plants. Compared with control plants, total peroxidases and glucanases increased twofold and eightfold, respectively, in all protected bean tissues. BNR 232-CG could not be recovered from the challenged hypocotyls or cotyledons, indicating that there was no contact between the inducer and the pathogen. Both the 1,3-beta-glucanases and the peroxidases were positively correlated with induced resistance.

Characterization of Genes Involved in Biosynthesis of a Novel Antibiotic from Burkholderia cepacia BC11 and Their Role in Biological Control of Rhizoctonia solani

Abstract: Genetic manipulation of fluorescent pseudomonads has provided major insight into their production of antifungal molecules and their role in biological control of plant disease. Burkholderia cepacia also produces antifungal activities, but its biological control activity is much less well characterized, in part due to difficulties in applying genetic tools. Here we report genetic and biochemical characterization of a soil isolate of B. cepacia relating to its production of an unusual antibiotic that is very active against a variety of soil fungi. Purification and preliminary structural analyses suggest that this antibiotic (called AFC-BC11) is a novel lipopeptide associated largely with the cell membrane. Analysis of conditions for optimal production of AFC-BC11 indicated stringent environmental regulation of its synthesis. Furthermore, we show that production of AFC-BC11 is largely responsible for the ability of B. cepacia BC11 to effectively control the damping-off of cotton caused by the fungal pathogen Rhizoctonia solani in a gnotobiotic system. Using Tn5 mutagenesis, we identified, cloned, and characterized a region of the genome of strain BC11 that is required for production of this antifungal metabolite. DNA sequence analysis suggested that this region encodes proteins directly involved in the production of a nonribosomally synthesized lipopeptide.

Fluorescent Pseudomonas spp. as biocontrol agents against forage legume root pathogenic fungi

Abstract: Native fluorescent pseudomonads isolated from the rhizosphere of Lotus corniculatus were screened in vitro for their antagonistic activity against the phytopathogenic fungi Pythium ultimum and Rhizoctonia solani. About 12% of the bacterial isolates inhibited one or both fungi in vitro. Isolates which exhibited the greatest antagonistic activity were assayed in vivo against the pathogens. Three Pseudomonas fluorescens strains were selected from these assays: UP61, UP143 and UP148. These strains produced HCN and siderophores, but addition of iron to the medium did not affect the antagonistic activity. Lytic enzymes such as chitinase and β-1,3-glucanase were not detected. The simultaneous inoculation of Pseudomonas strains and Rhizobium loti B816 did not affect nitrogen fixation efficiency in L. corniculatus plants. Sterile peat was successful as a carrier for these P. fluorescens strains.

A PCR-based method to distinguish fungi of the rice sheath-blight complex, Rhizoctonia solani, R. oryzae and R. oryzae-sativae

Abstract: Identification of Rhizoctonia solani, R. oryzae and R. oryzae-sativae, components of the rice sheath disease complex, is extremely difficult and often inaccurate and as a result may hinder the success of extensive breeding programmes throughout Asia. In this study, primers designed from unique regions within the rDNA internal transcribed spacers have been used to develop a rapid PCR-based diagnostic test to provide an accurate identification of the species on rice. Tests on the specificity of the primers concerned showed that they provide the means for accurate identification of the Rhizoctonia species responsible for sheath diseases in rice.

Use of strains of Bacillus isolated in China to suppress take-all and rhizoctonia root rot, and promote seedling growth of glasshouse-grown wheat in Australian soils

Abstract: Several strains of Bacillus subtilis and B . cereus , isolated and selected in China for their ability to promote plant growth and control root disease (yield-increasing bacteria), were tested for their potential to control take-all, caused by Gaeumannomyces graminis var. tritici , and rhizoctonia root rot caused by R . solani AG-8 on wheat seedlings grown in field soils in a glasshouse. Bacillus cereus isolate A47 and B . subtilis B908 consistently reduced the severity of take-all of wheat grown in a sodic acid soil. The amount of disease control was similar to that obtained with the biocontrol isolate Pseudomonas corrugata 2140. B . subtilis B931 was considerably more effective than other bacterial treatments in reducing the severity of rhizoctonia root rot in a calcareous sandy loam soil. Control of rhizoctonia root rot with isolate B931, and also with B . cereus strains A47 and M22 was both substantial and reproducible. Seedling growth promotion effects following bacterial treatment were less consistent than disease control effects. B . subtilis B908 and B . cereus A47-2 and A47-3 gave the most frequent positive growth responses (wheat seedling root weight, shoot weight and shoot length) in the absence of pathogen inoculum. This is the first reported research outside China where these Bacillus isolates have given control of soil-borne root diseases and promoted growth of healthy seedlings under glasshouse conditions.

Ecological Studies of Transformed Trichoderma harzianum Strain 1295-22 in the Rhizosphere and on the Phylloplane of Creeping Bentgrass.

Abstract: A β-glucuronidase (GUS) reporter gene and a hygromycin B (hygB) phosphotransferase gene were integrated separately into the Trichoderma harzianum strain 1295-22 genome, using biolistic transformation. The mycelial growth and biocontrol ability of the transformed strains did not differ from that of the original strain. The transformed Gus+-kanamycin-resistant (Gus+KanR) strains were used to monitor growth and interactions with Rhizoctonia solani on creeping bentgrass plants. The hygB-resistant (hygBR) strains were used to selectively recover strain 1295-22 from the rhizosphere soil and phylloplane of creeping bentgrass after spray applications. The population levels of two hygBR strains and the original strain were very similar for all treatments. All three strains persisted for the duration of the experiment (28 days) in both the rhizosphere soil and on leaves, although population levels declined somewhat over the course of the experiment in unautoclaved soils. In this study, the results demonstr...

Occurrence and etiology of death of young olive trees in southern Spain

Abstract: New plantations of olive tree in southern Spain are being severely affected by wilt or dieback and death, which has been locally called ‘Drying Syndrome’. To determine the etiology of this problem, a study was carried out in samples of affected young trees collected during a seven year period (1989‐1995), and in two field surveys in 1994‐95 and 1996. Besides some insect damage and agronomic problems, the ‘Drying Syndrome’ was associated with Verticillium wilt, winter frost and root rot fungi. Although ‘Drying Syndrome’ can be distinguished from Verticillium wilt, the latter was included in this study, since, frequently, Verticillium wilt symptoms were unspecific and Verticillium dahliaecould not be always isolated in the diagnostic work that preceded this study. Early winter frost caused a vascular necrosis and wilt of the young olive trees. This unusual and severe damage was related with the lack of frost hardiness due to warm temperatures during the previous autumn. Root rot fungi were very frequent in the samples of diseased olive trees of field or nursery origin, and they were the main cause of ‘Drying Syndrome’ in the second field survey, when a heavy rainfall level occurred during winter. Pathogenicity tests showed that five fungal species ( Cylindrocarpon destructans, Phytophthora megasperma, P. palmivora, Pythium irregulare and Sclerotium rolfsii) were pathogenic to olive trees and reproduced symptoms of ‘Drying syndrome’ in rooted cuttings of cultivar Picual. Other fungal species associated with root rot of olive trees in the field or in the nurseries, including Fusarium acuminatum, F. eumartii, F. oxysporum, F. solani, Macrophomina phaseolina and Rhizoctonia solani, were weakly or not pathogenic. Pathogenicity of P. megasperma, P. palmivoraand P. irregulare depended on soil water content, since isolates tested caused extensive root rot and sudden plant death only when the soil was continuously waterlogged. The high frequency of P. megasperma in waterlogged field soils and its pathogenicity dependence on soil water content suggest that this pathogen may play an important role in the well known sensitivity of young olive trees to ‘root asphyxiation’. Abbreviations: DS ‐ drying syndrome of young olive trees; PHSC ‐ plant health service in C´ ordoba (Spain).

In vitro and in vivo antagonism of Streptomyces violaceusniger YCED9 against fungal pathogens of turfgrass

Abstract: The biocontrol agent Streptomyces violaceusniger YCED9 inhibited in vitro growth of seven fungal pathogens of turfgrass Three different antibiotics were produced by the actinomycete, including nigericin, geldanamycin and a complex of macrocyclic lactone antibiotics Each had a different spectrum of antifungal activity Only nigericin was detected in soil or in grass rhizospheres inoculated with YCED9 However, all three antibiotics were produced when YCED9 was grown in a mixture of moistened grass and thatch In greenhouse experiments, a grass seedling disease caused by the Rhizoctonia solani and a crown-foliar disease caused by Sclerotinia homeocarpa were partially controlled with commercial spore formulations of YCED9

Characterization of a new cultural type (LP) of Rhizoctonia solani AG2-2 isolated from warm-season turfgrasses, and its genetic differentiation from other cultural types

Abstract: Isolates of Rhizoctonia solani AG2-2 obtained from turf with symptoms of large-patch disease of warm-season turfgrasses were compared with known AG2-2 isolates belonging to cultural types IIIB and IV Some isolates that were previously identified as type IV have been separated here and named LP isolates Comparisons among isolates were based on cultural morphology, hyphal growth rate, pathogenicity and restriction fragment length polymorphism (RFLP) analysis in the nuclear encoded ribosomal DNA (rDNA) genes The cultural characteristics of LP isolates varied from those of types IIIB and IV LP isolates did not show distinct sclerotial formation and zonation, and the colour of their mycelia and pigment deposition was dark brown LP isolates had slower hyphal growth rates than types IIIB and IV, with an optimum temperature of 25°C compared with 28°C for types IIIB and IV LP isolates were less virulent on radish but highly virulent on zoysia grass when compared with isolates of types IIIB and IV Genomic DNA was digested separately with Eco RI, Ban III, Xba I and Sal I, and probed with cloned rDNA from Alternaria alternata in Southern hybridizations LP isolates had one RFLP pattern, while both IIIB and IV possessed four different patterns each Cluster analysis of RFLPs showed that R solani AG2-2 is divided into three genetic subgroups, consisting of the IIIB, IV and LP isolates, respectively The polymerase chain reaction (PCR) amplified rDNA internally transcribed spacer (ITS) regions of the IIIB, IV and LP isolates had the same length but produced different restriction patterns when digested with Msp I and Taq I These results indicate that there are three cultural types in R solani AG2-2, namely IIIB, IV and LP

A Formulation of Trichoderma and Gliocladium to Reduce Damping-off Caused by Rhizoctonia solani and Saprophytic Growth of the Pathogen in Soilless Mix

Abstract: Commercially manufactured cellulose granules (Biodac) were mixed with a sticker and fermentor-produced biomass of isolates of Trichoderma spp. and Gliocladium virens to produce a formulation in which chlamydospores in the biomass were "activated" with dilute acid. Activation resulted in the formation of young, actively growing hyphae of the biocontrol fungi within a 2- to 3-day period under no special aseptic conditions. Activated Biodac with biomass of isolates Gl-3, Gl-21, and Gl-32 of G. virens and isolate TRI-4 of T. hamatum applied to soilless mix at a rate of 1.5% (wt/wt) reduced damping-off of eggplant caused by Rhizoctonia solani (R-23) and resulted in stands comparable to that (88%) in noninfested soilless mix. Saprophytic growth of the pathogen was also reduced. The application of either of two activated Biodac formulations to provide the same amount (1.5% with 9.4 mg of biomass per g of Biodac or 0.2% with 75.0 mg of biomass per g of Biodac) reduced preemergence damping-off as well as saprophytic growth of R-23. Also, there was about a 103-fold population increase of Gl-3 and TRI-4 in the soilless mix at the time of plant harvest compared with that provided to the soilless mix at the time of formulation addition. Activated Biodac of Gl-3 also reduced the spread of R-23 in soilless mix when the pathogen was applied at specific foci rather than evenly distributed. The inhibition of pathogen spread significantly reduced the postemergence damping-off of cucumber, eggplant, and pepper seedlings.

Induction of thaumatin-like proteins (TLPs) in Rhizoctonia solani-infected rice and characterization of two new cDNA clones

Abstract: Thaumatin-like proteins (TLPs) were shown to be induced in lice plants (cv IR58) that were infected with the sheath blight fungus, Rhizoctonia solani Western blot analysis revealed the presence of two TLPs with sizes of 25 and 24 kDa which are different from a previously reported TLP with a size of 156 kDa from rice plants infiltrated with the non-pathogenic bacterium, Pseudomonas syringae pv syringae By probing a cDNA expression library prepared from RNA isolated from R solani-infected rice plants with a TLP antibody, several putative TLP CDNA clones were isolated and sequenced The cDNA clones appeared to be derived from two different genes which shared only 77Yi sequence identity with each other and a lower percentage of sequence identity with the previously reported TLP cDNA clone Southern blot analysis with the two TLP cDNAs revealed different rice genomic DNA fragments Northern blot analysis also confirmed that a ll-kb RNA detectable by the TLP cDNA inserts was induced by fungal infection Thus rice TLPs are encoded by a family of at least three genes which are differentially expressed in responses to bacterial or fungal pathogens

Evaluation of methyl iodide as a soil fumigant in container and small field plot studies

Abstract: Methyl iodide was evaluated as a soil fumigant as a potential replacement for the widely used soil fumigant methyl bromide. In container trials, methyl iodide was significantly more effective than methyl bromide against the plant parasitic nematodes Meloidogyne incognita, Heterodera schachtii and Tylenchulus semipenetrans and the plant pathogenic fungus Rhizoctonia solani. In small field plots, soil populations of root-knot nematodes were no longer detected after methyl iodide fumigation at an application rate of 112 kg ha-1. However, after growing a susceptible lima bean host for two months, substantial root-knot galling occurred, while Rhizobium nodulation was absent. At 168 kg ha-1 of methyl iodide, root-knot galling was reduced to less than 1%, and no Pythium propagules were recovered on selective detection media. These efficacy data support the conclusion that methyl iodide is a likely candidate for replacing methyl bromide as a soil fumigant. © 1998 SCI.

Protection of Brassica seedlings against downy mildew and damping‐off by seed treatment with CGA 245704, an activator of systemic acquired resistance

Abstract: Control of seedling diseases is a major priority in many crop systems. Seed treatments that induce systemic resistance after seedling emergence may be an ideal way to provide protection against disease during the establishment of the crop. CGA 245704, a chemical activator of systemic acquired resistance, was tested as a seed treatment against two Brassica diseases with contrasting infection biologies, the airborne downy mildew pathogen, Peronospora parasitica, and the soilborne fungus, Rhizoctonia solani. Seeds of two Brassica spp. were either imbibed with various concentrations of the compound or imbibed and then dried. Both the imbibition treatment alone and the imbibition treatment followed by seed drying had a significant effect on the sporulation intensity of P. parasitica for all concentrations of the compound used, whereas the imbibition treatment provided some control of damping-off caused by R. solani, with the degree of control being highly dependent on the concentration applied to the seed. Seed treatment with the plant activator CGA 245704 might therefore simultaneously control several seedling diseases, thereby providing a novel option for management of these diseases. © 1998 SCI.

Use of Multispectral Radiometry for Assessment of Rhizoctonia Blight in Creeping Bentgrass

Abstract: The ability to identify diseases early and quantify severity accurately is crucial in plant disease assessment and management. This study was conducted to assess changes in the spectral reflectance of sunlight from plots of creeping bentgrass during infection by Rhizoctonia solani, the cause of Rhizoctonia blight, and to evaluate multispectral radiometry as a tool to quantify Rhizoctonia blight severity. After inoculation of 6-year-old creeping bentgrass turf with R. solani anastomosis group 2-2, reflectance of sunlight from the foliar canopy was measured at light wavelengths of 460 nm (blue) to 810 nm (near infrared [NIR]), at 50-nm intervals. Visual estimates of disease severity and percentage of canopy reflectance were made daily throughout each of three epidemics of Rhizoctonia blight from the onset of visible symptoms until maximum disease severity was reached. In each experiment, linear regression analysis revealed a significant reduction in the percentage of NIR (760 and 810 nm) reflectanc...

Rhizoctonia species and anastomosis groups isolated from barley and wheat in Erzurum, Turkey

Abstract: Ninety-eight isolates of Rhizoctonia spp. were obtained from barley and wheat grown in Erzurum, Turkey. Of these, 78% were Rhizoctoniasolani (AG-2 type 1, AG-3, AG-4, AG-5 and AG-11), 10% were binucleate Rhizoctonia (AG-I and AG-K) and the remainder were Waitea circinata var circinata (Rhizoctonia sp.). Among the binucleate Rhizoctonia, AG-I was not recovered from barley. In pathogenicity tests on barley and wheat, the highest disease severity was caused by isolates of AG-4 and AG-11, whereas isolates of AG-2 type 1, AG-3, AG-5 and W. c. var circinata were moderately virulent. Isolates of binucleate Rhizoctonia were all nonpathogenic. This is the first report of R. solani AG-11 and W. c. var circinata from Turkey.

Association of Binucleate Rhizoctonia with Soybean and Mechanism of Biocontrol of Rhizoctonia solani.

Abstract: The association of binucleate Rhizoctonia (BNR) AG-K with soybean and the interaction of BNR, R. solani AG-4, and soybean seedlings were investigated to elucidate the mechanism of biocontrol of R. solani by BNR. Sixty-hour-old seedlings were inoculated and incubated in a growth chamber at 24 degrees C; plants were examined with light microscopy and with scanning and transmission electron microscopy at various times following inoculation. BNR grew over hypocotyls, roots, and root hairs, but only colonized epidermal cells. Hyphae of BNR appeared to attach to the epidermis and, 5.5 h following inoculation, began penetrating cells by means of penetration pegs without forming distinct appressoria or infection cushions. There was evidence of cuticle degradation at the point of penetration. Infection hyphae moved to adjacent epidermal cells by direct penetration of epidermal radial walls. There were epidermal and cortical cell necrosis, beginning with the fragmentation of the tonoplast and followed by the disintegration of cytoplasm, organelles, and plasma membranes. Cell necrosis was also observed in adjacent cells where there was no evidence of BNR hyphae. Cell walls were not destroyed. After 144 h, there was noevidence of BNR hyphae in cortical cells. Attempted penetrations were observed, but papillae formed on the inside of cortical cell walls. Pre-inoculation of soybean seedlings with BNR 24 or 48 h before inoculation with R. solani (1 cm between inocula) affected the growth of R. solani on soybean tissue. There were fewer hyphae of R. solani, the hyphae branched sparingly, and infection cushions were rare when compared with hyphal growth on soybean inoculated only with R. solani. These effects were observed before the BNR hyphae began to intermingle with the hyphae of R. solani on the surface of the inoculated host. Preinoculation of soybean seedlings 24 h before inoculation with R. solani significantly (P = 0.05) reduced disease incidence and severity caused by R. solani AG-4. The lesions caused by R. solani always appeared distally, not proximally, to the BNR inoculum. The interactions of intermingling hyphae of BNR and R. solani were examined in vitro and on the surface of the host. There was no evidence of lysis, mycoparasitism, inhibition of growth, or any other form of antagonism between hyphae. The results of these studies strongly suggest that induced resistance is the mechanism of biocontrol of R. solani on soybean by BNR. The inhibition of hyphal growth of R. solani on the surface of soybean tissue preinoculated with BNR appears to be a novel characteristic of induced resistance.

Biocontrol of fungal root rot diseases of crop plants by the use of rhizobia and bradyrhizobia

Abstract: Twenty-oneRhizobium andBradyrhizobium strains were testedin vitro against the mycelial growth of three pathogenic fungi on solid and liquid media All tested rhizobia and bradyrhizobia significantly suppressed the growth of the three soil-borne root-infecting fungi (Fusarium solani, Macrophominia phasolina andRhizoctonia solani) either in the absence or presence of iron This indicates that the siderophore played a minor role in the biocontrol potential ofRhizobium andBradyrhizobium against pathogenic fungi Pot experiments revealed that the numbers of propagules causing disease after 4 weeks of planting varied with species and host plant The three most activeRhizobium andBradyrhizobium strains (R leguminosarum bvphaseoli TAL 182,B japonicum TAL 377 andBradyrhizobium sp (lupin) WPBS 3211 D) tested under greenhouse conditions for their ability to protect one leguminous (soybean) and two non-leguminous (sunflower and okra) seedlings from root rot caused byFusarium solani, Macrophominia phaseolina andRhizoctonia solani provided significant suppression of disease severity compared with nonbacterized control in both leguminous and non-leguminous seedlingsBradyrhizobium sp (lupin) WPBS 3211 D provided the lowest degree of resistance against all the tested pathogens with all host plants *** DIRECT SUPPORT *** A00EN058 00013

Effect of physical conditions on the spatial and temporal dynamics of the soil-borne fungal pathogen Rhizoctonia solani

Abstract: The transmission of infection by many soil-borne fungal parasites of plants depends on the ability of the fungus to grow on or through soil. Progress in analysing the effects of soil physical factors on the temporal and spatial dynamics of fungal growth has been hindered by technical difficulties of quantifying fungal biomass in soil and heterogeneity in soil properties. In this paper we use a combination of a monoclonal antibody-based immunosorbent assay and microscopy to analyse the effects of soil physical properties on the spatial and temporal dynamics of colonies of the economically important fungus Rhizoctonia solani Kuhn growing in two dimensions and three dimensions in a sand. Combinations of different particle-size distributions and matric potential are used to manipulate the air-filled pore volume and pore-size distribution independently of each other. Temporal dynamics are measured by the change in fungal biomass over time whereas spatial dynamics relate to fungal spread and are measured by the colony size, the rate of colony expansion and the biomass distribution within colonies. We show that the fungus spreads more than three times further over surfaces than through sand, even though the same amount of biomass is produced in each case. Pore-size distribution and air-filled pore space both affected the extent and rate of fungal spread in three dimensions within sand, with more rapid and extensive spread in a coarse sand compared with a fine sand at identical air-filled pore volume. The spread of fungal hyphae along surfaces was affected neither by differences in surface texture nor by air-filled volume, and was substantially more homogeneous than for three-dimensional spread. We argue that the relative impermeability of sand surfaces to penetration by hyphae might be influenced by the ability of the fungus to branch within a confined space rather than simply to penetrate the pores. The broader epidemiological and ecological consequences of preferential spread by parasitic and saprophytic fungi along surfaces rather than through the dense soil volume are discussed.

Characterization and survival of Rhizoctonia solani AG2-2 LP associated with large patch disease of zoysia grass.

Abstract: Prevalence and sites of survival of Rhizoctonia solani AG2-2 LP were studied in zoysia grass for 6 years. AG2-2 LP isolates commonly were recovered over all seasons at sites with a history of large patch disease. In patch margins, AG2-2 LP isolates were recovered from crowns of zoysia grass regardless of whether the disease occurred, but were most frequently isolated from the sheath tissues during disease occurrence. In healthy sites approximately 30 cm from the patch, isolates were obtained before but not during disease occurrence. Once disease occurred, patch symptoms rapidly expanded to the edge of tissue colonized by the pathogen during autumn to early spring. To verify that the pathogen spread to healthy areas, the clonal relationship among isolates was examined using their anastomosis reaction. Isolates recovered from the patch and healthy area outside the patch were of the same clone, but isolates from different patches differed. Cultural characteristics and pathogenicity of the AG2-2 LP isolates were compared with R. solani AG2-2 IIIB and R. solani AG2-2 IV. The AG2-2 LP isolates showed an irregular cluster of mycelia (not sclerotia), an irregular zonation, dark brown main hyphae, and sparse aerial hyphae on potato dextrose agar after 4 weeks of incubation. Optimum temperature for growth was 23°C. Cultural characteristics of AG2-2 subgroups IIIB and IV differed from LP isolates. All isolates of AG2-2 LP caused moderate to high levels of disease on zoysia grass, but were nonpathogenic or caused little disease on bent grass and sugar beet. These results indicate that cultural characteristics and host range of AG2-2 LP are different than those of AG2-2 IIIB and AG2-2 IV.

Prevention of fungal diseases in transgenic, bialaphos- and glufosinate-resistant creeping bentgrass (Agrostis palustris)

Abstract: Mariam Sticklen Corresponding author. Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824; sticklel@pilot.msu.edu The antifungal activity of the herbicides bialaphos and glufosinate, the active moiety of bialaphos, was assessed. Bialaphos showed a higher level of in vitro antifungal activity against Rhizoctonia solani, Sclerotinia homoeocarpa, and Pythium aphanidermatum than glufosinate. Glufosinate suppressed the mycelial growth of R. solani and S. homoeocarpa, but it had no inhibitory effect on P aphanidermatum up to the highest concentration in our testing regimes. Various concentrations of bialaphos solutions were applied to transgenic, bialaphosand glufosinate-resistant creeping bentgrass inoculated with fungal pathogens. Bialaphos applications were able to significantly reduce symptomatic infection by R. solani and S. homoeocarpa on transgenic plants. Bialaphos significantly inhibited P aphanidermatum, but not to the same degree that R. solani and S. homoeocarpa were inhibited. These results indicate that bialaphos may provide a means for the simultaneous control of weeds and fungal pathogens in turf areas with transgenic, bialaphos-resistant creeping bentgrass.

Efficacy of pseudomonas aeruginosa and paecilomyces lilacinus in the control of root rot-root knot disease complex on some vegetables

Abstract: Pseudomonas aeruginosa and Paecilomyces lilacinus used alone or together significantly (P 0.05) reduced infection of Meloidogyne javanica root knot nematode and root infecting fungi viz., Macrophomina phaseolina, Rhizoctonia solani, Fusarium solani and F. oxysporum on pumpkin (Cucurbita pepo), guar (Cyamopsis tetragonoloba), chilli (Capsicum annuum) and watermelon (Citrullus lanatus). P. aeruginosa was more effective than P. lilacinus in reducing the M. javanica root knot nematode infection. Combined use of P. lilacinus and P. aeruginosa was more effective in reducing the infection of root knot nematode in guar, M. phaseolina and F. oxysporum on pumpkin and F. solani on guar and watermelon than either used alone.

Screening of potential bacterial antagonists for control of sheath blight in rice and development of suitable bacterial formulations for effective application

Abstract: Soil samples were taken from paddy rice fields in 14 provinces in the southern part of Thailand Bacteria were isolated from these soils using the soil dilution plate method on King’s B medium and Thornton’s standardised medium Isolation yielded 323 bacterial isolates which were subsequently tested for their effectiveness in inhibiting mycelial growth of Rhizoctonia solani, the causal agent of sheath blight of rice Eight isolates were selected for their ability to create a clear zone in a dual culture test Further tests evaluated the effect of selected bacteria on sclerotial germination and subsequent mycelial growth, and also on the development of sheath blight lesions on excised rice stems Three bacterial isolates (16,26 and 29) provided the greatest inhibition of sclerotial germination and mycelial growth and maximum suppression of sheath blight lesions Isolate 26 and subsequently isolate 29 were chosen for formulation studies Granulated formulations of these bacterial isolates were developed using the wet granulation technique The main components of these bacterial formulations were bacterial cells, hydrogenated vegetable oil, monohydrate lactose, polyvinyl pyrrolidone, and crosslinked sodium carboxymethyl cellulose The efficacy of the formulation of isolate 29 in suppressing sheath blight symptoms was similar to that of fresh cells of isolate 29