In vitro antagonism of Trichoderma species against six fungal plant pathogens [Biological disease control]

Virus Diseases of Peanut

Many Trichoderma species are applied as biofungicides and biofertilizers to agricultural soils to enhance crop growth. These filamentous fungi have the ability to reduce plant diseases and promote plant growth and productivity through overlapping modes of action including induced systemic resistance, antibiosis, enhanced nutrient efficiency, and myco-parasitism. Trichoderma species are prolific producers of many small metabolites with antifungal, antibacterial, and anticancer properties. Volatile metabolites of Trichoderma also have the ability to induce resistance to plant pathogens leading to improved plant health. In this study, Arabidopsis plants were exposed to mixtures of volatile organic compounds (VOCs) emitted by growing cultures of Trichoderma from 20 strains, representing 11 different Trichoderma species. We identified nine Trichoderma strains that produced plant growth promoting VOCs. Exposure to mixtures of VOCs emitted by these strains increased plant biomass (37.1–41.6 %) and chlorophyll content (82.5–89.3 %). Trichoderma volatile-mediated changes in plant growth were strain- and species-specific. VOCs emitted by T. pseudokoningii (CBS 130756) were associated with the greatest Arabidopsis growth promotion. One strain, T. atroviride (CBS 01-209), in our screen decreased growth (50.5 %) and chlorophyll production (13.1 %). Similarly, tomatoes exposed to VOCs from T. viride (BBA 70239) showed a significant increase in plant biomass (>99 %), larger plant size, and significant development of lateral roots. We also observed that the tomato plant growths were dependent on the duration of the volatile exposure. A GC–MS analysis of VOCs from Trichoderma strains identified more than 141 unique compounds including several unknown sesquiterpenes, diterpenes, and tetraterpenes. Plants grown in the presence of fungal VOCs emitted by different species and strains of Trichoderma exhibited a range of effects. This study demonstrates that the blend of volatiles produced by actively growing fungi and volatile exposure time in plant development both influence the outcome of volatile-mediated interactions. Only some of our growth promoting strains produced microbial VOCs known to enhance plant growth. Compounds such as 6-pentyl-2H-pyran-2-one were not common to all promoting strains. We found that biostimulatory strains tended to have a larger number of complex terpenes which may explain the variation in growth induced by different Trichoderma strains.

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Volatile organic compounds emitted by Trichoderma species mediate plant growth

Plant-parasitic nematodes cause significant damage to a broad range of vegetables and agricultural crops throughout the world. As the natural enemies of nematodes, nematophagous microorganisms offer a promising approach to control the nematode pests. Some of these microorganisms produce traps to capture and kill the worms from the outside. Others act as internal parasites to produce toxins and virulence factors to kill the nematodes from within. Understanding the molecular basis of microbe-nematode interactions provides crucial insights for developing effective biological control agents against plant-parasitic nematodes. Here, we review recent advances in our understanding of the interactions between nematodes and nematophagous microorganisms, with a focus on the molecular mechanisms by which nematophagous microorganisms infect nematodes and on the nematode defense against pathogenic attacks. We conclude by discussing several key areas for future research and development, including potential approaches to apply our recent understandings to develop effective biocontrol strategies.

Molecular mechanisms of nematode-nematophagous microbe interactions: basis for biological control of plant-parasitic nematodes.

Sunflower (Helianthus annuus L.) is one of the few crops native to the United States. The current USDA–ARS National Plant Germplasm System (NPGS) crop wild relatives sunflower collection is the largest extant collection in the world, containing 2519 accessions comprising 53 species—39 perennial and 14 annual. To fully utilize gene bank collections, however, researchers need more detailed information about the amount and distribution of genetic diversity present within the collection. The wild species are adapted to a wide range of habitats and possess considerable variability for most biotic and abiotic traits. This represents a substantial amount of genetic diversity available for many agronomic traits for cultivated sunflower, which has a very narrow genetic base. Sunflower ranked fifth highest among 13 crops of major importance to global food security surveyed from the mid-1980s to 2005 in the use of traits from crop wild relatives. The estimated annual economic contribution of the wild species for cultivated sunflower is between US$267 to 384 million. Most of the value is derived from the PET1 cytoplasm from wild H. petiolaris, disease resistance genes, abiotic salt tolerance, and resistance to imidazolinone and sulfonylurea herbicides. Crop wild relatives provide a wide range of valuable attributes for traditional and molecular breeding, as well as for ecological experimentation, and have enabled rapid advances in ecological and evolutionary genetics. The wild species of Helianthus continue to contribute specific traits to combat emerging pests and environmental challenges and, at the same time, are preserved for future generations. G.J. Seiler, L.L. Qi, USDA–ARS, Northern Crop Science Laboratory, 1605 Albrecht Blvd. N., Fargo, ND 58102-2765; L.F. Marek, North Central Regional Plant Introduction Station, Iowa State Univ. and USDA–ARS, 1305 State Ave., Ames, IA 50014. Received 4 Oct. 2016. Accepted 7 Dec. 2016. *Corresponding author (gerald.seiler@ars.usda. gov). Assigned to Associate Editor Heathcliffe Riday. Abbreviations: AFLP, amplified fragment length polymorphism; BSR, basal stalk rot; CMS, cytoplasmic male sterile; CWR, crop wild relatives; DM, downy mildew; EST, expressed sequence tags; HR, head rot; NPGS, National Plant Germplasm System; GRIN, Germplasm Resources Information System; MSR, mid-stalk rot; QTL, quantitative trait loci; SNP, single-nucleotide polymorphism; SSR, simple sequence repeat; SuMV, sunflower mosaic virus. Published in Crop Sci. 57:1083–1101 (2017). doi: 10.2135/cropsci2016.10.0856 © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA This is an open access article distributed under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Published June 16, 2017

Utilization of Sunflower Crop Wild Relatives for Cultivated Sunflower Improvement

Control plant-parasitic nematodes with Trichoderma species and nematode-trapping fungi: The role of chi18-5 and chi18-12 genes in nematode egg-parasitism

Abstract The obligate biotrophic Oomycete, Plasmopara halstedii, causal agent of sunflower downy mildew, is capable of producing new pathogenic races over time. Although changes in the P. halstedii race composition were reviewed for the first time in 2007, since then the pathogen has continued to change its virulence character dramatically. There was a need, therefore, to update information on pathogenic diversity of P. halstedii by making accounts of the temporal and spacial changes in the pathogen populations in North and South America and Europe. This paper, based on current publications and personal communications, attempts to present an accurate overview of races in Europe and Americas for the last 7 years.

Recent Changes in the Pathogenic Variability of Plasmopara Halstedii (Sunflower Downy Mildew) Populations from Different Continents

This review summarises the progress in research on sunflower downy mildew as reported in publications of the past 10 to 15 years, the period since the last comprehensive review on Plasmopara halstedii. Particular attention is paid to subjects that showed much progress and may be of particular interest to sunflower pathologists, mycologists or molecular biologists. Accordingly, single sections are devoted to the problems of taxonomic and phylogenetic aspects, host specificity, the host—pathogen interaction including resistance phenomena, as well as epidemiology and disease management. Reflecting the progress achieved in some fields and illuminating the deficits in others should stimulate the reader's interest in this very significant pathosystem.

Advances in sunflower downy mildew research

Comparative gene expression profiles of Trichoderma harzianum proteases during in vitro nematode egg-parasitism

Leaves of Xanthium strumarium infected with downy mildew were collected in the vicinity of a sunflower field in southern Hungary in 2003. Based on phenotypic characteristics of sporangiophores, sporangia and oospores as well as host preference the pathogen was classified as Plasmopara angustiterminalis. Additional phenotypic characters were investigated such as the size of sporangia, the number of zoospores per sporangium and the time-course of their release. Infection studies revealed infectivity of the P. angustiterminalis isolate to both X. strumarium and Helianthus annuus. Inoculation of the sunflower inbred line, HA-335 with resistance to all known P. halstedii pathotypes, resulted in profuse sporulation on cotyledons and formation of oospores in the bases of hypocotyls. Infections of sunflower differential lines often led to damping-off. Molecular genetic analysis using simple sequence repeat primers and nuclear rDNA sequences revealed clear differences to Plasmopara halstedii, the downy mildew pathogen of sunflower.

Ferenc Virányi

Papers

Control plant-parasitic nematodes with Trichoderma species and nematode-trapping fungi: The role of chi18-5 and chi18-12 genes in nematode egg-parasitism

Recent Changes in the Pathogenic Variability of Plasmopara Halstedii (Sunflower Downy Mildew) Populations from Different Continents

Advances in sunflower downy mildew research

Comparative gene expression profiles of Trichoderma harzianum proteases during in vitro nematode egg-parasitism

Characteristics of a Plasmopara angustiterminalis isolate from Xanthium strumarium