Showing papers on "Rhizoctonia solani published in 2005"

Suppression of soil-borne plant diseases with composts: A review

Abstract: Numerous container-based studies in greenhouses or growth rooms have consistently demonstrated a suppressive effect of composts on soil-borne diseases such as damping-off and root rots (Pythium ultimum, Rhizoctonia solani, Phytophthora spp.), and wilts (Fusarium oxysporum and Verticillium dahliae). Composts have also been shown to suppress several diseases in the field, although the effects have been generally smaller and more variable than in container experiments. Several diseases of turf grass were suppressed by top-dressing with compost. These diseases are Fusarium patch (Microdochium nivale), red thread (Laetisaria fuciformis), damping-off (Pythium graminicola), brown patch (Rhizoctonia solani), dollar spot (Sclerotinia homoeocarpa) and snow mould (Typhula ishikariensis). The disease suppressive effect of compost generally increased with rate of application. Compost inclusion rates of at least 20% (v/v) were normally required to consistently obtain a disease suppressive effect, particularly in peat-b...

Brassica napus seed meal soil amendment modifies microbial community structure, nitric oxide production and incidence of Rhizoctonia root rot

Abstract: A low glucosinolate content (21.8 mmol g K1 ) Brassica napus seed meal (RSM) applied to orchard soils altered communities of both pathogenic and saprophytic soil micro-organisms. RSM amendment reduced infection by native and introduced isolates of Rhizoctonia spp. and recovery of Pratylenchus spp. from apple roots. Root infection by Rhizoctonia solani AG-5 was also suppressed in split-root assays where a portion of the root system was cultivated in RSM-amended soils and the remainder grown in the presence of the pathogen but lacking RSM. R. solani hyphal growth was not inhibited by RSM amendment. Suppression of Pratylenchus was attained to an equivalent extent by amending soils with either RSM or soybean meal (SM) when applied to provide a similar N content. Thus, glucosinolate hydrolysis products did not appear to have a significant role in the suppression of Rhizoctonia spp. or Pratylenchus spp. obtained via RSM amendment. RSM amendment elevated populations of Pythium spp. and of ammonia-oxidizing bacteria that release nitric oxide but suppressed fluorescent pseudomonad numbers. Streptomyces spp. soil populations increased significantly in response to RSM but not SM amendment. The vast majority of Streptomyces spp. recovered from the apple rhizosphere produced nitric oxide and possessed a nitric oxide synthase homolog. We propose that transformations in the bacterial community structure are associated with the observed control of Rhizoctonia root rot, with NO production by soil bacteria potentially having a role in the induction of plant systemic resistance. q 2005 Elsevier Ltd. All rights reserved.

Improvement of the Fungal Biocontrol Agent Trichoderma atroviride To Enhance both Antagonism and Induction of Plant Systemic Disease Resistance

Abstract: Biocontrol agents generally do not perform well enough under field conditions to compete with chemical fungicides. We determined whether transgenic strain SJ3-4 of Trichoderma atroviride, which expresses the Aspergillus niger glucose oxidase-encoding gene, goxA, under a homologous chitinase (nag1) promoter had increased capabilities as a fungal biocontrol agent. The transgenic strain differed only slightly from the wild-type in sporulation or the growth rate. goxA expression occurred immediately after contact with the plant pathogen, and the glucose oxidase formed was secreted. SJ3-4 had significantly less N-acetylglucosaminidase and endochitinase activities than its nontransformed parent. Glucose oxidase-containing culture filtrates exhibited threefold-greater inhibition of germination of spores of Botrytis cinerea. The transgenic strain also more quickly overgrew and lysed the plant pathogens Rhizoctonia solani and Pythium ultimum. In planta, SJ3-4 had no detectable improved effect against low inoculum levels of these pathogens. Beans planted in heavily infested soil and treated with conidia of the transgenic Trichoderma strain germinated, but beans treated with wild-type spores did not germinate. SJ3-4 also was more effective in inducing systemic resistance in plants. Beans with SJ3-4 root protection were highly resistant to leaf lesions caused by the foliar pathogen B. cinerea. This work demonstrates that heterologous genes driven by pathogen-inducible promoters can increase the biocontrol and systemic resistance-inducing properties of fungal biocontrol agents, such as Trichoderma spp., and that these microbes can be used as vectors to provide plants with useful molecules (e.g., glucose oxidase) that can increase their resistance to pathogens.

Suppression of Seedling Damping-Off Caused by Pythium ultimum, P. irregulare, and Rhizoctonia solani in Container Media Amended with a Diverse Range of Pacific Northwest Compost Sources.

Abstract: Suppression of seedling damping-off disease caused by Pythium spp. and Rhizoctonia solani is a potential benefit of formulating soilless container media with compost. Thirty-six compost samples from Pacific Northwest commercial composting facilities were analyzed for a number of physical, chemical, and biological properties, including suppression of damping-off caused by Pythium ultimum, P. irregulare, and R. solani. The samples were produced from diverse feedstocks and composting technol ogies; this was reflected in a large degree of variability in the measured properties. When mixed with sphagnum peat moss and inorganic aggregates, 67% of the compost samples significantly suppressed P. irregulare damping-off of cucumber, 64% suppressed P. ultimum damping-off of cucumber, and 17% suppressed damping-off of cabbage caused by R. solani. Suppression of Pythium damping-off was related to the potential of compost to support microbial activity and a qualitative index of ammonia volatilization. Suppress...

Post harvest spoilage of sweetpotato in tropics and control measures

Abstract: Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylen...

Phytohormones and Antibiotics Produced by Bacillus subtilis and their Effects on Seed Pathogenic Fungi and on Soybean Root Development

Abstract: Bacteria belonging to the genus Bacillus were isolated from soil samples of Parana State, Brazil, with the aim of evaluating their potential biological control of soybean seed pathogens Strain PRBS-1 was selected, showing similar effectiveness to that of the strain AP-3, used as a reference due to its known antibiotic potential The sequencing of the ribosomal 16S rRNA gene confirmed that both strains belong to the species B subtilis, although showing high genetic diversity in relation to this species Both strains inhibited five soybean seed pathogenic fungi in vitro, Rhizoctonia solani, Colletotrichum truncatum, Sclerotinia sclerotiorum, Macrophomina phaseolina and Phomopsis sp Furthermore, the metabolites of AP-3 increased production of root hairs, while the metabolites of PRBS-1 stimulated outgrowth of lateral roots in soybean The antibiotic effect of both strains seemed to be related to compounds of the iturin group, while the root growth promotion by PRBS-1 was at least partially related to the production of indoleacetic acid The results have shown the potential of using selected strains of B subtilis in the biological control of seed pathogens, as well as in promoting soybean growth

Fungal-feeding habits of six nematode isolates in the genus Filenchus

Abstract: The family Tylenchidae is a large group of soil nematodes but their feeding habits are not fully known. We studied the fungal-feeding abilities of nematodes in the genus Filenchus. We measured population growth rates (PGRs) of six nematode isolates, representing three Filenchus species, when feeding on seven fungal species on two types of culture media. On Potato Dextrose Agar (PDA) Filenchus misellus, Filenchus discrepans and an unidentified Filenchus sp. generally showed moderate to large PGRs on saprophytic fungi (Rhizoctonia solani, Chaetomium globosum, Coprinus cinereus, Flammulina velutipes) and low PGRs on plant-pathogenic fungi (Fusarium oxysporum, Pythium ultimum). In soil medium amended with chopped soybean plant material or wheat bran, the status of most of the fungi as food for the nematodes was similar to that on PDA, although PGRs tended to be lower in the soil medium. However, C. globosum, a good food on PDA, only supported low PGR in soil for each of the three nematodes. The PGRs of F. misellus on C. globosum in soil were still low even when types and amounts of organic matter amendments were varied. A nematophagous fungus, Pleurotus ostreatus (oyster mushroom), was determined to be a food for Filenchus on PDA or in soil, based on PGR measurements corrected for extraction efficiency. To determine whether fungal species and culture media affected nematode extraction efficiencies and, consequently, the apparent PGRs, we compared efficiencies between R. solani, C. globosum and C. cinereus, and between PDA and soil. The relatively low extraction efficiencies across fungal species in soil seemed responsible for the lower nematode PGRs in soil than on PDA. On PDA generally, fungal species did not affect the assessment. In soil, effects of fungal species on extraction were significant, but not consistent, across nematode species. Nevertheless, the extraction efficiency differences in soil were considered not to affect assessment of the three fungi as food for the nematodes. The confirmation that three Filenchus species reproduce by feeding on fungi in soil suggests that fungal-feeding is not an unusual habit in the field, in this genus. We believe that in community studies, nematodes in the genus Filenchus should be considered fungal feeders or root and fungal feeders, rather than only plant feeders. Our confirmation of fungal-feeding habits in the genus Filenchus supports the hypotheses that plant-feeding nematodes evolved from those feeding on fungi.

Trichoderma Mitogen-Activated Protein Kinase Signaling Is Involved in Induction of Plant Systemic Resistance

Abstract: The role of a mitogen-activated protein kinase (MAPK) TmkA in inducing systemic resistance in cucumber against the bacterial pathogen Pseudomonas syringae pv. lacrymans was investigated by using tmkA loss-of-function mutants of Trichoderma virens. In an assay where Trichoderma spores were germinated in proximity to cucumber roots, the mutants were able to colonize the plant roots as effectively as the wild-type strain but failed to induce full systemic resistance against the leaf pathogen. Interactions with the plant roots enhanced the level of tmkA transcript in T. virens and its homologue in Trichoderma asperellum. At the protein level, we could detect the activation of two forms reacting to the phospho-p44/42 MAPK antibody. Biocontrol experiments demonstrated that the tmkA mutants retain their biocontrol potential against Rhizoctonia solani in soil but are not effective against Sclerotium rolfsii in reducing disease incidence. Our results show that, unlike in many plant-pathogen interactions, Trichoderma TmkA MAPK is not involved in limited root colonization. Trichoderma, however, needs MAPK signaling in order to induce full systemic resistance in the plant.

Suppression of Rhizoctonia root-rot of tomato by Glomus mossae BEG12 and Pseudomonas fluorescens A6RI is associated with their effect on the pathogen growth and on the root morphogenesis.

Abstract: Rhizoctonia solani root-rot is a major soilborne disease causing growth and yield depression. The ability of Glomus mosseae BEG12 and Pseudomonas fluorescens A6RI to suppress this soilborne disease in tomato was assessed by comparing the shoot and root growth of plants infested with R. solani 1556 when protected or not by these beneficial strains. The epiphytic and parasitic growth of the pathogenic R. solani 1556 was compared in the presence and absence of the biocontrol agents by microscopical observations allowing the quantification of roots with hyphae appressed to epidermal cells (epiphytic growth) and of roots with intraradical infection (parasitic growth). The root architecture of the tomato plants under the different experimental conditions was further characterized by measuring total root length, mean root diameter, number of root tips and by calculating degree of root branching. G. mosseae BEG12 and P. fluorescens A6RI fully overcame the growth depression caused by R. solani 1556. This disease suppression was associated with a significant decrease of the epiphytic and parasitic growth of the pathogen together with an increase of root length and of the number of root tips of inoculated tomato plants. The combined effects of G. mosseae BEG12 and P. fluorescens A6RI on pathogen growth and on root morphogenesis are suggested to be involved in the efficient disease suppression.

A New Method for the Quantification of Rhizoctonia solani and R. oryzae from Soil

Abstract: Paulitz, T. C., and Schroeder, K. L. 2005. A new method for the quantification of Rhizoctonia solani and R. oryzae from soil. Plant Dis. 89:767-772. Rhizoctonia solani anastomosis group (AG) 8 and R. oryzae are important root pathogens on wheat and barley in the dryland production areas of the inland Pacific Northwest. R. solani AG-8 is difficult to isolate from root systems and quantify in soil because of slow growth and low population densities. However, both pathogens form extensive hyphal networks in the soil and can grow a considerable distance from a food base. A quantitative assay of active hyphae was developed, using wooden toothpicks as baits inserted into sample soils. After 2 days in soil, toothpicks were placed on a selective medium, and the numbers of colonies that grew after 24 h were counted under a dissecting microscope. R. solani and R. oryzae could be distinguished from other fungi based on hyphal morphology. This method was tested in natural soils amended with known inoculum densities of R. solani AG-8 and R. oryzae. Regressions were used to compare the inoculum density or toothpick colonization curves to a predicted curve based on the volume of the toothpicks. The slopes and y intercept of log-log transformed regressions did not differ from the predicted curves in most cases. This technique was used to assess the hyphal activity of R. solani AG-8 and R. oryzae from soil cores taken from various positions in and around Rhizoctonia bare patches at two locations. Activity of R. solani was highest in the center and inside edge of the patch, but there was no effect of patch position on R. oryzae. This simple and inexpensive technique can be used for detection and diagnosis in grower fields and to study the ecology and epidemiology of Rhizoctonia spp.

Proteomic response of the biological control fungus Trichoderma atroviride to growth on the cell walls of Rhizoctonia solani

Abstract: Trichoderma atroviride has a natural ability to parasitise phytopathogenic fungi such as Rhizoctonia solani and Botrytis cinerea, therefore providing an environmentally sound alternative to chemical fungicides in the management of these pathogens. Two-dimensional electrophoresis was used to display cellular protein patterns of T. atroviride (T. harzianum P1) grown on media containing either glucose or R. solani cell walls. Protein profiles were compared to identify T. atroviride proteins up-regulated in the presence of the R. solani cell walls. Twenty-four protein spots were identified using matrix-assisted laser desorption ionisation mass spectrometry, liquid chromatography mass spectrometry and N-terminal sequencing. Identified up-regulated proteins include known fungal cell wall-degrading enzymes such as N-acetyl-β-d-glucosaminidase and 42-kDa endochitinase. Three novel proteases of T. atroviride were identified, containing sequence similarity to vacuolar serine protease, vacuolar protease A and a trypsin-like protease from known fungal proteins. Eukaryotic initiation factor 4a, superoxide dismutase and a hypothetical protein from Neurospora crassa were also up-regulated as a response to R. solani cell walls. Several cell wall-degrading enzymes were identified from the T. atroviride culture supernatant, providing further evidence that a cellular response indicative of biological control had occurred.

Application of Talc Formulations of Pseudomonas fluorescens Migula and Trichoderma viride Pers. ex S.F. Gray Decrease the Sheath Blight Disease and Enhance the Plant Growth and Yield in Rice

Abstract: The effect of talc formulations of Pseudomonas fluorescens Migula and Trichoderma viride Pers. ex S.F. Gray applications either alone or in combination on crop growth, sheath blight disease and grain yield in rice was investigated in three different field experiments. Increased root and shoot lengths, dry weight and plant height were recorded following treatment of plants with P. fluorescens and T. viride either alone or in combination when compared with control. Application of P. fluorescens and T. viride resulted in a significant reduction of sheath blight incidence caused by Rhizoctonia solani Kuhn and was comparable to the treatment with a systemic fungicide, Carbendazim. The number of productive tillers, grains per panicle and grain test weight were also significantly increased in the treated plots with commensurate increase in grain and straw yields when compared with control. The promotion of plant growth and yield and suppression of sheath blight disease were marginally improved following combined application of P. fluorescens and T. viride. Although the combined application of both biocontrol agents did not lead to statistically significant additive effects in reducing the sheath blight and increasing grain yield when compared with their individual applications, no negative effect was recorded in this combined application treatment. Hence, the talc formulations of biocontrol agents either alone or in combination can be recommended as one of the crop protection strategies for the management of sheath blight of rice.

Effectiveness of 3 antagonistic bacterial isolates to control Rhizoctonia solani Kühn on lettuce and potato.

Abstract: Rhizoctonia solani causes yield losses in numerous economically important European crops. To develop a biocontrol strategy, 3 potato-associated ecto- and endophytically living bacterial strains Pse...

Green manures and crop sequences influence alfalfa root rot and pathogen inhibitory activity among soil-borne streptomycetes

Abstract: A two-year trial was conducted to determine the effects of green manures and crop sequences on plant disease, streptomycete and bacterial densities, and inhibitory activity of indigenous streptomycetes against four target pathogens. Green manure treatments, buckwheat (Fagopyrum esculentum L.), canola (Brassica napus L.), sorghum-sudangrass (Sorghum bicolor) (L.) Moench × Sorghum sudanense (Piper) Stapf.), and fallow control were tested in conjunction with three crop sequences in a Phytophthora-infested soil placed in containers. Alfalfa (Medicago sativa L.), potato (Solanum tubersoum L.), or corn (Zea mays L.) was grown in the first year, and alfalfa was grown in all containers in the second year. Compared to fallow controls, alfalfa grown in sorghum-sudangrass- or buckwheat-treated soil had significantly greater stand counts and total biomass, respectively. In addition, alfalfa grown in fallow-treated soils had the greatest Phytophthora root rot as a function of stand count. Crop rotation also had a significant effect on alfalfa root rot and yield. Potato scab disease intensity was greatest on tubers grown in fallow-treated soils, while tubers grown in canola-treated soils had the highest yields (total tuber weight). Green-manure-treated soils tended to have greater streptomycete and bacterial densities than fallow-treated soils. In addition, buckwheat- or sorghum-sudangrass-treated soils had greater proportions of streptomycetes that were antagonistic against the target pathogens than fallow-treated soils. The proportion of antagonists in soil was negatively correlated with alfalfa root rot, and positively correlated with alfalfa stand counts. Inhibitory activity of the streptomycetes was also negatively correlated with potato scab and positively correlated with potato yield. These data suggest that green manures may provide a strategy for increasing pathogen inhibitory activity within the streptomycete community in soil, and, in conjunction with crop rotation, may contribute to the control of a diverse collection of soil-borne plant pathogens on multiple crop species.

Influence of Sulfur Fertilization on Infection of Potato Tubers with Rhizoctonia solani and Streptomyces scabies

Abstract: Under conditions of sulfur (S)-deficient soil, applied S fertilization had a significant repressive effect on fungal infections such as that of oilseed rape and grapes with light leaf spot (Pyrenopeziza brassicae) and powdery mildew (Uncinula necator), respectively. For potatoes (Solanum tuberosum L.) it has been shown in earlier literature that elemental sulfur fertilization increased yield of potato tubers and improved tuber quality and resistance against Streptomyces scabies; the bactericidal effect was attributed to a reduced soil pH. So far, however, no information is available about the influence of S supply on bacterial and fungal diseases in potatoes. It was the aim of the present investigation to quantify the influence of S form and dose on infections of potato tubers with Rhizoctonia solani and Streptomyces scabies as a contribution to plant nutrition strategies for healthier plants. Field experiments with potatoes were conducted in 2001 and 2002 in Poland in a split-plot design with di...

Fungicidal activity of marine actinomycetes against phytopathogenic fungi

Abstract: A total of 160 isolates of marine actinomycetes were isolated from the sediment samples drawn from mangroves, estuary, sand dune, and industrially polluted coast Of these, mangrove sediments were rich sources of marine actinomycetes Each isolate was tested against four phytopathogenic fungi, viz Rhizoctonia solani, Pyricularia oryzae, Helminthosporium oryzae (causing sheath blight, blast and leaf spot diseases of rice) and Colletotrichum falcatum (causing red rot disease of sugar cane) About 51% of isolates were found effective against H oryzae and P oryzae, 31% against R solani, and 125% against C falcatum Of 160 isolates, 10 showed a potent activity against all the fungi tested These isolates appeared to produce high antifungal compounds at 120 hrs of incubation period of production medium culture Glucose and soybean meal were the best carbon and nitrogen sources, respectively and 175 ppt was the best salinity level for maximum antibiotic production Cylinder plate method was found better for antifungal assay than the disc diffusion method Based on the morphological and culture characteristics, the potent strains were identified as the species belonged to the genus Streptomyces These strains may prove to be the potent source for isolation of agrobased fungicides

Characterization of Variability in Rhizoctonia solani by Using Morphological and Molecular Markers

Abstract: Twenty-four isolates of Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) collected from soil, root and collar rot or foliage blight-infected plants from several locations of north India were used for the analysis of variability by using morphological and molecular markers. Among the morphological characters, variation was observed in hyphal cell size. Seventeen isolates produced few to abundant) white to dark brown or black, small to large sclerotia generally in the middle of the colony. Genetic variation was also analysed by using 11 random amplified polymorphic DNA primers (RAPD), four universal rice primers (URPs) and two inter simple sequence repeat (ISSR) markers and fingerprint patterns generated for each isolate. The size of amplified DNA bands ranged from 0.3 to 3.5 kb in all the isolates with RAPD, URP and ISSR markers. The isolates obtained from same hosts and same geographical regions showed similarity in DNA fingerprint profiles barring few exceptions. All the isolates were classified into four groups using DNA markers. A comparison of the data obtained from different markers showed that URPs are superior to RAPD, ISSR and morphological markers in detecting genetic variability among the isolates of R. solani. Hence, use of URP's, which have long primer and higher annealing temperature, would be more sensitive and reliable markers in characterizing genetic diversity in R. solani.

Inheritance and Genetic Mapping of Resistance to Rhizoctonia Root and Hypocotyl Rot in Soybean

Abstract: Rhizoctonia root and hypocotyl rot, caused by Rhizoctonia solani Kuhn [teleomorph Thanatephorus cucumeris (Frank) Donk], is an important disease of soybean [Glycine max (L.) Merr.]. Planting resistant cultivars would be an effective and environmentally sound strategy to minimize economic losses from this disease. To facilitate developing resistant cultivars, a study was conducted to: (i) investigate inheritance of resistance to Rhizoctonia root and hypocotyl rot in the moderately resistant soybean PI 442031, and four moderately susceptible commercial cultivars and (ii) identify simple sequence repeat (SSR) markers associated with resistance to Rhizoctonia root and hypocotyl rot. Genetic analysis of several segregating populations indicated that resistance to Rhizoctonia root and hypocotyl rot in soybean was quantitatively inherited and controlled by both major and minor genes with additive gene effects. The estimates of broad sense heritability of resistance were low to moderately high. Transgressive segregants with enhanced levels of resistance were developed by crossing adapted but moderately susceptible commercial soybean cultivars. Three SSR markers (Satt281, Satt177, and Satt245) were significantly associated with host resistance in both F 2 and F 4:5 populations of PI 442031 x Sterling, wherein both parents contributed resistant alleles. This is the first report on mapping of Rhizoctonia root and hypocotyl rot resistance genes in soybean. Our results indicate that marker assisted selection, coupled with phenotypic selection in later generations, should help to facilitate the development of soybean cultivars resistant to Rhizoctonia root and hypocotyl rot.

Suppression of Meloidogyne javanica by antagonistic and plant growth-promoting rhizobacteria.

Abstract: Four rhizobacteria selected out of over 500 isolates from rhizosphere of the vegetables in China were further studied for suppression of the root-knot nematode and soil-borne fungal pathogens in laboratory and greenhouse in Belgium. They were identified as Brevibacillus brevis or Bacillus subtilis by Biolog test and partial 16s rDNA sequence comparison. They not only inhibited the radial growth of the root-infecting fungi Rhizoctonia solani SX-6, Pythium aphanidermatum ZJP-1 and Fusarium oxysporum f.sp. cucumerinum ZJF-2 in vitro, but also exhibited strong nematicidal activity by killing the second stage larvae of Meloidogyne javanica to varying degrees in the greenhouse. The toxic principles of bacterium B7 that showed the highest juvenile mortality were partially characterized. The active factors were heat stability and resistance to extreme pH values. B7 used either as seed dressing or soil drench significantly reduced the nematode populations in the rhizosphere and enhanced the growth of mungbean plants over the controls in the presence or absence of R. solani.

Real-Time Quantitative RT-PCR of Defense-Associated Gene Transcripts of Rhizoctonia solani-Infected Bean Seedlings in Response to Inoculation with a Nonpathogenic Binucleate Rhizoctonia Isolate.

Abstract: Certain isolates of nonpathogenic binucleate Rhizoctonia spp. (np-BNR) are effective biocontrol agents against seedling root rot and damping-off. Inoculation of bean seed with np-BNR strain 232-CG at sowing reduced disease symptoms in bean (Phaseolus vulgaris) seedlings caused by R. solani. Molecular analyses of the spatial expression of three defense-associated genes were carried out using real-time quantitative reverse transcription-polymerase chain reaction (QRT-PCR) assays. This method allowed accurate quantitative evaluation of transcript levels of pG101 encoding for 1,3-beta-D-glucanase, gPAL1 encoding for phenylalanine ammonia lyase, and CHS17 encoding for chalcone synthase in 1- and 2-week-old bean seedlings that were inoculated simultaneously with np-BNR and infected with R. solani, and in seedlings that were singly inoculated with either fungi or not inoculated. In the seedlings that were infected with R. solani only, results revealed that, following infection, activation of all defense-associated gene transcripts was achieved with significant increases ranging from 7- to 40-fold greater than the control, depending on the defense gene and tissue analyzed. Seedlings that were treated with np-BNR and infected with R. solani had expression similar to those that were treated with np-BNR only, but the levels were significantly down-regulated compared with those that were infected with R. solani only. These findings indicate that disease suppression by np-BNR isolate is not correlated to pG101, gPAL1, and CHS17 gene activation.

Suppression of Wheat Growth and Yield by Pratylenchus neglectus in the Pacific Northwest.

Abstract: Smiley, R. W., Whittaker, R. G., Gourlie, J. A., and Easley, S. A. 2005. Suppression of wheat growth and yield by Pratylenchus neglectus in the Pacific Northwest. Plant Dis. 89:958-968. Many wheat (Triticum aestivum) fields planted annually in the Pacific Northwest are infested by high populations of the lesion nematode, Pratylenchus neglectus. Spring wheat cultivars varying in tolerance and resistance to P. neglectus were treated or not treated with aldicarb to examine relationships between the nematode and growth and yield of annual direct-seeded (no-till) wheat. Increasing initial density of P. neglectus in soil was more strongly associated with declining growth and yield of intolerant (Machete and Spear) than moderately tolerant (Frame and Krichauff) cultivars. Yield suppression by P. neglectus was generally 8 to 36% for intolerant cultivars, but reached 71% in soil also harboring Heterodera avenae, Rhizoctonia solani AG-8, and Gaeumannomyces graminis var. tritici. Intolerant cultivars had lower yields than Krichauff in rainfed but not in irrigated experiments. Density of P. neglectus in mature roots was generally lower for moderately resistant Krichauff than for susceptible Machete and Spear. Aldicarb improved yields in irrigated but not in rainfed experiments, and increased plant height and reduced variability in tiller height, canopy temperature, and density of P. neglectus in roots. This is the first report of damage to wheat by P. neglectus in the Pacific Northwest. Breeding wheat for tolerance and resistance to P. neglectus is suggested. Additional keywords: Fusarium crown rot, Fusarium pseudograminearum, Pratylenchus thornei, Pythium root rot, Pythium spp., Rhizoctonia root rot, take-all

The Influence of the Inoculum Source of Rhizoctonia solani on Development of Black Scurf on Potato

Abstract: Rhizoctonia solani, the causal agent of stem canker and black scurf on potato, survives as sclerotia on tubers, in soil and in plant residues. The objective of the present study was to evaluate the importance of inoculum source on disease development. Disease-free minitubers and seed tubers contaminated with low levels of R. solani were planted in fumigated or artificially inoculated growth mixture in greenhouse experiments. Black scurf incidence and severity were significantly higher when the inoculum was present in both seed tubers and soil, compared with either of them separately. The severity of disease symptoms on the subterranean parts of the plant also were significantly higher in plots where both seed tubers and soil were contaminated, compared with plots where the inoculum source was either the seed tubers or the soil. Thus, both major sources of inoculum, seed tubers and soil, are important in disease development. However, when both sources are present, black scurf incidence and severity are increased, leading to economical damage to tuber yield and quality. Additional results from field trials support these findings. Disease incidence and severity on daughter tubers were correlated with levels of contamination in seed tubers and soil. When seed tubers and soil were heavily infested, the levels of black scurf incidence and severity on daughter tubers were very high; when seed tuber and soil infestation were very low, black scurf incidence and severity on progeny were also lower. Disease levels were reduced by in-furrow fungicide treatment, but were less effective when the initial levels of the fungus on the seed tubers and in the soil were high.