Brief Summary of Minutes of Annual Meeting

Objective 1:
A survey of California avocado groves has been initiated to identify local groves which have soils which are suppressive to Phytophthora cinnamomi. Two criterions are used to identify a suppressive soil. It is a soil which degrades P. cinnamomi hyphae or chlamydospores, or one which has high populations of Phytophthora but the trees continue to thrive. Greenhouse tests with autoclaved soil indicated that autoclaving will destroy the suppressiveness of the Vanoni soil, indicating microorganisms are responsible for the suppressiveness. Other soils thought to be suppressive to P. cinnamomi did not appear to be suppressive in pot tests, indicating that drainage or some charactersitic of the field soil must be responsible for the suppressiveness. Twenty-four groves have been surveyed with four showing suppressiveness to Phytophthora. Individual trees in other groves also show suppressive characteristics. We have identified two microorganisms which are directly pathogenic to P. cinnamomi.

The goal of studies by Borneman (UCR) was to identify bacteria and fungi involved in soil suppressiveness against the plant-parasitic nematode Heterodera schachtii. Since H. schachtii cysts isolated from the suppressive soil can transfer this beneficial property to nonsuppressive soils, analysis of the cyst-associated microorganisms should lead to the identification of the causal organisms. Our experimental approach was to identify bacterial and fungal rDNA associated with H. schachtii cysts obtained from soil mixtures with varying levels of suppressiveness. We hypothesized that we could identify microorganisms involved in the suppressiveness by correlating population shifts with differing levels of suppressiveness. Bacterial rDNA associated with H. schachtii cysts were identified by Borneman using a culture-independent method termed oligonucleotide fingerprinting of ribosomal RNA genes (OFRG). Five major taxonomic groups were identified: Actinobacteria, Cytophaga-Flexibacter-Bacteroides, a-Proteobacteria, b-Proteobacteria, and c-Proteobacteria. Three bacterial rDNA groups contained more clones from the highly suppressive soil treatments than the less suppressive treatments, indicating a potential involvement in the H. schachtii suppressiveness. When these three groups were examined with specific PCR analyses performed on H. schachtii cysts that developed in soils treated with three biocidal compounds, only one bacterial rDNA group with moderate to high sequence identity to rDNA from several Rhizobium species and uncultured a-Proteobacterial clones was consistently associated with the highly suppressive treatments. Borneman also identified fungi through an rDNA analysis termed oligonucleotide fingerprinting of ribosomal RNA genes (OFRG). Cysts obtained from soil mixtures consisting of 10% and 100% suppressive soil predominantly contained fungal rDNA with high sequence identity to Dactylella oviparasitica. The dominant fungal rDNA in the cysts isolated from the soil mixtures comprised of 0.1% and 1% suppressive soil had high sequence identity to Fusarium oxysporum).

Pink rot of potato (caused by Phytophthora erythroseptica), potato late blight (caused by Phytophthora infestans), gray mold (caused by Botrytis cinerea), and damping-off (caused by Rhizoctonia solani) are all economically destructive diseases. For many years, control of these diseases relied primarily on the use of chemical fungicides. Increasing awareness of the development of fungicide-resistant strains of pathogens, chemical residues in the food chain and the adverse effects of pesticides on human health are having profound impacts on the management of plant diseases. With a diminishing number of means to control disease, growers are seeking alternatives that are both safe and environmentally benign. T. atroviride is a versatile, aggressive hyperparasite that can parasitize a wide spectrum of pathogenic fungi, including Phytophthora erythroseptica, Rhizoctonia solani, Phytophthora infestans and Botrytis cinerea. T. atroviride has a temperature range of 4 to 33 0C and prefers high humidity. Results of compatibility studies by McBeath (AK) show that T. atroviride growth is not adversely affected by common fungicides and/or herbicides, even at field applicable levels. However, performances of T. atroviride are limited by high soil temperatures and sub-optimal dosages. A coordinated biochemical response has been observed in T. atroviride during biocontrol of plant pathogenic fungi. Production of chitinases, chitosanases, and glucanases, seemed to play a significant role in hyperparasitism involved in the suppression of diseases.

In Pacific Northwest cereal cropping systems, little is known about the populations and virulence of Pythium and Rhizoctonia spp. Pythium spp. that cause root rot and significant yield reductions in wheat and barley. ARS scientists at Pullman, Washington sequenced the rDNA of the ITS 1 region of Pythium isolates from an extensive collection in eastern Washington. In addition to identifying 11 known species, a totally new species was discovered, named Pythium abappressorium sp. nov. Paulitz et Mazzola, which is widespread and pathogenic. Knowledge of the diversity of Pythium spp. is critical for plant breeders, who will utilize these isolates to screen for resistant wheat and barley germplasm.

Rhizoctonia oryzae along, with R. solani AG-8, causes the disease of wheat and barley know as Rhizoctonia root rot, but Rhizoctonia oryzae was not considered to be a problem in previous surveys. ARS scientists at Pullman, Washington conducted an extensive survey of wheat and barley fields. They showed that Rhizoctonia oryzae is widespread on cereals in eastern Washington, it causes damping-off and stunting of barley and wheat, it attacks peas and other broadleaf rotation crops, some isolates are more virulent than R. solani AG-8, variation in virulence exists among isolates, and there is a significant cultivar X isolate interaction.

Rhizoctonia oryzae causes chronic root rot and stunting of wheat and barley. ARS scientists at Pullman, Washington in conjunction with a scientist at Washington State University adapted spatial generalized linear mixed models to detect spatial correlation and develop disease maps. Using GPS-located sites on a 90-acre farm over two years, an aggregated, overdispersed distribution of the pathogen and the disease was detected. These tools will have applications for disease mapping in precision agriculture.

For the past few years, Ole Becker and cooperators have investigated a beet cyst nematode-suppressive soil at a field station near UCR. After the initial nematode infestation of this field 9E in the 1970s and a high population build-up caused by frequent cropping to susceptible hosts, the population declined and has remained fairly constant at a low level. Although previous research had investigated the progression of the suppressiveness during a cropping season, several data gaps required a more in-depth analysis of the beet cyst nematode population dynamics. Consequently, the population development of Heterodera schachtii on Swiss chard (Beta vulgaris L. subsp. cicla (L) cv. Large White Ribbed) in suppressive and conducive soil was monitored for two generations in greenhouse trials. Staining of the second-stage juveniles in the roots 75 degree days (DD) after soil infestation with the pest revealed no significant differences between the number of nematodes grown in suppressive soil and conducive soil. After the first nematode generation, the beet cyst nematode populations in the suppressive and the conducive soil were not significantly different as indicated by the number of males and cysts as well as by the number of eggs and second-stage juveniles within those cysts. However, after two beet cyst nematode generations, the number of all monitored life stages were significantly lower in the suppressive soil than in the conducive soil.

Objective 2:
Potato is an economically important crop to Alaska as well as in the US. Identification of molecular markers associated with disease resistance and adaptability to extreme Northern climates may help molecular breeders in the development of cultivars more suitable to these conditions. Osmotins represent a multigene family that has been implicated in disease resistance and cold tolerance. Isolation and characterization of osmotin genes may help in understanding host-pathogen interactions as well as in the development of enhanced biological control agents for the control of plant diseases.
Research by Leland Pierson (AZ) involving further characterization of the molecular mechanisms responsible for phenazine gene regulation in Pseudomonas aureofaciens 30-84 is providing additional evidence for how a bacterium senses its environment and response to it by altering patterns of gene expression. In addition to the molecular analyses, ecological approaches are being used to quantify the role of cross-communication among rhizobacteria on phenazine gene expression in situ. Wheat genes that govern disease suppression can be identified and mapped using classical genetics. To examine genetic variation in root colonization, ARS scientists at Pullman, Washington compared wheat root colonization by the aggressive P. fluorescens strain Q8r1-96 with that of the weaker colonizer Q2-87 for 28 Pacific Northwest (PNW) cultivars. Five cultivars supported higher root populations of Q8r1-96, and although PNW cultivars differed in root morphology and growth, no single factor was correlated with preference for Q8r1-96. Genetic variation in root traits of PNW wheat cultivars can be exploited for genetic, biochemical and molecular approaches to host-mediated disease suppression.

Strains of Pseudomonas fluorescens producing the antifungal metabolite 2,4-diacetylphloroglucinol (DAPG) are important biocontrol agents against dampingoff, root rot and wilt diseases, and are responsible for the natural suppressiveness of some soils against root diseases. ARS scientists at Pullman, Washington used DNA fingerprinting methods to identify genetic groups or subspecies within populations of DAPG producers. Seventeen distinct genetic groups were identified, and certain groups were shown to have superior abilities to colonize the roots of wheat or pea or both crops, and control root diseases.

Objective 3:

Research by Mike Stanghellini (UCR) is directed at developing a disease management strategy for the control of vine-decline of melons caused by the root-infecting fungus Monosporascus cannonballus. Ascospores of M. cannonballus, the primary inoculum for root infection and survival of the fungus in soil, play a major role in vine decline. Our previous studies indicate that the development of an effective disease management strategy in known pathogen-infested fields is dependent upon (i) reducing the amount of primary inoculum in soil with a preplant soil fumigant and then (ii) maintaining low population densities by inhibiting pathogen reproduction on melon roots left in the field after harvest.

Strategies identified in 2000 for inhibiting pathogen reproduction included (i) the application of metam sodium or (ii) soil cultivation to expose and dry the roots immediately after the final harvest or collapse of the vines. These postharvest strategies, if successful, would reduce the necessity for yearly applications of the more costly preplant soil fumigants. Based on this, we initiated a three-year study to evaluate the efficacy of the above strategy for management of vine-decline of melons. The Spring 2002 crop constituted the second of three consecutive spring crops (subject only to postharvest treatments) following a single application of a preplant soil fumigant in the Spring of 2001.

ALASKA

Gay, P. A., and McBeath, J. H. 2002. Cold tolerant Trichoderma atroviride, biotype CHS 861, ATCC 74015, 42 kD endochitinase gene, partial sequence. Genbank accession number AY162405, submitted.

Gay, P. A., and McBeath, J. H. 2002. Cold tolerant Trichoderma atroviride, biotype 453, ATCC74016, 42 kD endochitinase gene, partial sequence. Genbank accession numberAY162406, submitted.

Gay, P. A., and McBeath, J. H. 2002. Cold tolerant Trichoderma atroviride, biotype 901C, ATCC 74017, 42 kD endochitinase gene, partial sequence. Genbank accession number AY162407, submitted.

Gay, P. A., and McBeath, J. H. 2002. Cold tolerant Trichoderma atroviride, biotype 603, ATCC
74018, 42 kD endochitinase gene, partial sequence. Genbank accession number AY162408, submitted.

McBeath, J.H. 2002. Snow Mold-Plant-Antagonist Interactions: Survival of the Fittest under the Snow. APSnet Feature Article, March Issue.

McBeath, J.H. 2002. Snow Mold-Plant-Antagonist Interactions: Survival of the Fittest under the Snow. Plant Health Instructor. DOI:10.1094/PHI-1-2002-1010-01.

McBeath, J.H. Snow Mold: Nemesis of Turfgrasses. Golf Course Management. (in press)


ARIZONA

Chancey, S.T., Wood, D.W., Pierson, E.A. and L.S. Pierson III. 2002. Survival of GacS/GacA mutants of the biological control bacterium Pseudomonas aureofaciens 30-84 in the wheat rhizosphere. Appl. Environ. Microbiol. 68: 3308-3314.

Loh, J., Pierson, E.A., Pierson, L.S. III, Stacy, G., and Chatterjee, A. 2002. Quorum sensing in plant-associated bacteria. Curr. Opin. Plant Biol. 5:1-5.

Zhang, Z. and Pierson, L.S. III. 2001. A second quorum sensing system regulates cell surface properties but not phenazine antibiotic production in Pseudomonas aureofaciens. Appl. Environ. Microbiol. 67: 4305-4315.


CALIFORNIA

Dirac, M. and J.A. Menge. 2002. High temperatures are not reponsible for lack of infection of citrus roots by Phytophthora citrophthora during the summer, but supressive microorganisms may inhibit infection by P. citrophthora. Plant and Soil 241:243-249.

Dirac, M. and J.A. Menge. 2002. Comparison of seasonal infection of citrus roots by Phytophthora citrophthora and Phytophthora nicotianae. Plant Disease 86: (In Press).

Marais, L.J., J.A. Menge, G.S. Bender and B. Faber. 2002. Phytophthora root rot. AvoResearch, California Avocado Commission. 4p.

Marais, L. J, J.A. Menge, G.S. Bender and B. Faber. . 2002. Avocado stem canker or collar rot. AvoResearch, California Avocado Commission. 4p.

Menge, J.A. A.J. Downer, K. Steddom and J. Borneman. 2002. Biocontrol of Phytophthora cinnamomi. Proceedings Calif. Conf. Biological Control. Aug15-16. Davis, CA.

Menge, J.A. and R. Ploetz. 2002. Diseases of avocado. In Diseases of Tropical and Subtropical Fruit Crops. R. Ploetz (ed.) CABI Publishing, Oxford. 50 pp. (In Press)

Menge, J.A. and L.J. Marais. 2002. Strategies to control Phytophthora cinnamomi root rot of avocado. Subtropical Fruit News 10: (In Press).

Steddom, K, O. Becker and J.A. Menge. 2002. Repetitive applications of the biocontrol agent Pseudomonas putida 06909-rif/nal and effects on populations of Phytophthora parasitica in citrus orchards. Phytopathology 92:850-856.

Steddom, K., J.A. Menge, D. Crowley and J. Borneman. 2002. Effect of repetitive application of the biocontrol bacterium Pseudomonas putida 06909-rif/nal on citrus soil microbial communities. Phytopathology 92:857-862.

Yang, C.-H., D. E. Crowley and J. A. Menge. 2001. 16S rDNA fingerprinting of rhizosphere bacterial communities associated with healthy and Phytophthora infected avocado roots. FEMS Microbial Ecology 35: 129-136.

Yin, B, Valinsky, L., Gao, X., Becker, J.O., and J. Borneman. Bacterial rDNA associated with soil suppressiveness against the plant-parasitic nematode Heterodera schachtii. Appl. Environ. Microbiol. (accepted with revisions).

Valinsky, L., Della Vedova, G., Jiang, T., and Borneman, J. 2002. Oligonucleotide fingerprinting of ribosomal RNA genes for analysis of fungal community composition. Appl. Environ. Microbiol. 68:5999-6004.

Waugh, M.M., D.H. Kim, D.M. Ferrin, and M.E. Stanghellini. 2003. Reproductive potential of Monosporascus cannonballus. Plant Dis. 87: 45-50.

Valinsky, L., Della Vedova, G., Scupham, A. J., Alvey, S., Figueroa, A., Yin, B., Hartin, J., Chrobak, M., Crowley, D. E., Jiang, T., and Borneman, J. 2002. Analysis of bacterial community composition by oligonucleotide fingerprinting of rRNA genes. Appl. Environ. Microbiol. 68:3243-3250.


WASHINGTON

Cook, R.J., Weller, D.M., El-Banna, A.Y., Vakoch, D., Zhang, H. 2002. Yield responses of direct-seeded wheat of rhizobacteria and fungicide seed treatments. Plant Disease. 86: 780-784.

Landa, B.B., de Werd, H.A.E., McSpadden Gardener, B.B., Weller, D.M. 2002. Comparison of three methods for monitoring populations of different genotypes of 2,4-diacetylphorlglucinol-producing Pseudomonas fluorescens in the rhizosphere. Phytopathology. 92: 129-137.

Landa, B.B., Mavrodi, O.V., Raaijmakers, J.M., McSpadden Gardener, B.B., Thomashow, L.S., Weller, D.M. 2002. Differential ability of genotypes of 2,4-diacetylphloroglucinol-producing Pseudomonas fluorescens strains to colonize the roots of pea plants. Applied and Environmental Microbiology. 2002. 68: 3226-3237.

Mavrodi, D.V., Bonsall, R.F., Delaney, S.M., Soule, M.J., Phillips, G., Thomashow, L.S. Functional analysis of genes for biosynthesis of pyocyanin and phenazine-1-carboxamide from Pseudomonas aeruginosa PAO1. 2001. Journal of Bacteriology. 183: 6454-6465.

Mavrodi, O.V., Mavrodi, D.V., Weller, D.M., Thomashow, L.S. 2002. Genetic basis for the unique root-colonizing activity of Pseudomonas fluorescens. Phytopathology. 92(Suppl.). p. S53. (abstract).

McSpadden Gardener, B.B., Weller, D.M. 2001. Changes in populations of rhizosphere bacteria associated with take-all disease of wheat. Applied and Environmental Microbiology.67: 4414-4425.

McSpadden Gardener, B.B., Weller, D.M. 2002. Specificity, population dynamics, and biocontrol of take-all by DAPG-producing Pseudomonas spp. in a long-term wheat field. Phytopathology. 92(Suppl.). Abstract p. S54.

Okubara, P.A., Landa, B.B., Madsen, B., Kornoely, J.P. 2002.Wheat cultivar-dependent root architecture and root colonization by P. fluorescens Q8r1. Phytopathology 92(Suppl.). p. S61.

Okubara, P.A., Madsen, B., Landa, B.B. 2002. Is root colonization by P. fluorescens Q8r1 cultivar-dependent in wheat? Plant Biology 2002, American Society of Plant Biologists. 2002. p. 136. Abstract number 589.

Paulitz, T. C. 2002. Biological control of plant pathogens (fungi). D. Pimentel, editor. Marcel Dekker, NY. Encyclopedia of Pest Management. p. 64-67.

Paulitz, T. C. 2002. Biological webs of plant disease. New Phytologist.154: 272-773. Book Review.

Paulitz, T. C. 2002. Impacts and management of soil acidity under direct seed systems: Effects on soilborne crop pathogens. Proceedings of the Northwest Direct Seed Cropping Systems Conference, Spokane WA. p. 41-46.

Paulitz, T. C. First report of Rhizoctonia oryzae on pea. 2002. Plant Disease. 2002. 86: 442.

Paulitz, T. C. Pseudomonas aureofaciens strain 63-28: A new weapon in the biocontrol arsenal. Proceedings of the International Symposium on Biological Control of Plant Diseases for the New Century- Mode of Action and Application Technology, Taichung, Taiwan. 2002. p. 97-106.

Paulitz, T. C. 2002. New insights into the make-up and management of soilborne crop pathogens under direct seeding: Rhizoctonia. Proceedings of the Northwest Direct Seed Cropping Systems Conference, Spokane WA. p. 131-139.

Paulitz, T. C., Adams, K. and Mazzola, M. 2002. Pythium abappressorium- a new species from eastern Washington. Mycologia: in press.

Paulitz, T. C., Smiley, R. and Cook, R. J. 2002. Insights into the prevalence and management of soilborne cereal pathogens under direct seeding in the Pacific Northwest, U.S.A. Can. J. Plant Pathol. in press.

Paulitz, T. C., Smith, J. and Kidwell, K. 2002. Virulence of Rhizoctonia oryzae on wheat and barley cultivars from the Pacific Northwest. Plant Disease: 87: 51-55.

Paulitz, T.C., Adams, K., Mazzola, M., Livesque, C.A. 2002. A new species of Pythium from apple and wheat in eastern Washington. Phytopathology 92(Suppl.). Abstract p. S64.

Schroeder, K.L., Paulitz, T.C. 2002. Development of Rhizoctonia root rot of barley in soils from conventional and no-till fields. Phytopathology 92(Suppl.). Abstract p. S74.

Smiley, R., Cook, R. J. and Paulitz, T. 2002. Seed treatments for small grain cereals. Oregon State University Extension Publication EM 8797.

Smiley, R., Cook, R. J. and Paulitz, T. 2002. Controlling root and crown diseases of small grain cereals. Oregon State University Extension Publication EM 8799.

Weller, D.M., Raaijmakers, J.M., McSpadden Gardener, B.B., Thomashow, L.S. 2002. Microbial populations responsible for specific suppressiveness to plant pathogens. Annual Review of Phytopathology. 40: 309-348.