Monica L. Elliott

A two-locus DNA sequence database for typing plant and human pathogens within the Fusarium oxysporum species complex

We constructed a two-locus database, comprising partial translation elongation factor (EF-1alpha) gene sequences and nearly full-length sequences of the nuclear ribosomal intergenic spacer region (IGS rDNA) for 850 isolates spanning the phylogenetic breadth of the Fusarium oxysporum species complex (FOSC). Of the 850 isolates typed, 101 EF-1alpha, 203 IGS rDNA, and 256 two-locus sequence types (STs) were differentiated. Analysis of the combined dataset suggests that two-thirds of the STs might be associated with a single host plant. This analysis also revealed that the 26 STs associated with human mycoses were genetically diverse, including several which appear to be nosocomial in origin. A congruence analysis, comparing partial EF-1alpha and IGS rDNA bootstrap consensus, identified a significant number of conflicting relationships dispersed throughout the bipartitions, suggesting that some of the IGS rDNA sequences may be non-orthologous. We also evaluated enniatin, fumonisin and moniliformin mycotoxin production in vitro within a phylogenetic framework.

Interaction between the subterranean termite Reticulitermes flavipes (Isoptera: Rhinotermitidae) and the entomopathogenic fungus Metarhizium anisopliae in foraging arenas.

Abstract The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin was tested in the laboratory against field-collected groups of eastern subterranean termite, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae), in foraging arenas to determine the potential effect of a “trap and treat” protocol (trapping a part of the population, treating it with a biological control agent and releasing it back into the original population). Individual termites were treated with a suspension of M. anisopliae conidia and released back into the arenas containing untreated termites. After 5 d, 90% of the treated termites died in the arena, but untreated termites did not exhibit a significant increase in mortality within 90 d after release, indicating no transfer of viable M. anisopliae and no epizootic. Although M. anisopliae was isolated from the arenas after 90 d, the average number of fungal colony-forming units recovered was <0.1% of the conidia introduced.

Extended disease resistance emerging from the faecal nest of a subterranean termite

Social insects nesting in soil environments are in constant contact with entomopathogens but have evolved a range of defence mechanisms, resulting in both individual and social immunity that reduce the chance for epizootics in the colony, as in the case of subterranean termites. Coptotermes formosanus uses its faeces as building material for its nest structure that result into a ‘carton material’, and here, we report that the faecal nest supports the growth of Actinobacteria which provide another level of protection to the social group against entomopathogens. A Streptomyces species with in vivo antimicrobial activity against fungal entomopathogens was isolated from the nest material of multiple termite colonies. Termite groups were exposed to Metarhizium anisopliae, a fungal entomopathogen, during their foraging activity and the presence of Streptomyces within the nest structure provided a significant survival benefit to the termites. Therefore, this report describes a non-nutritional exosymbiosis in a termite, in the form of a defensive mutualism which has emerged from the use of faecal material in the nesting structure of Coptotermes. The association with an Actinobacteria community in the termite faecal material provides an extended disease resistance to the termite group as another level of defence, in addition to their individual and social immunity.

EFFECT OF MELANIN BIOSYNTHESIS INHIBITING COMPOUNDS ON GAEUMANNOMYCES SPECIES

AbstractInhibition of melanin production was observed in Gaeumannomyces isolates treated with DHN-melanin inhibiting compounds (tricyclazole, pyroquilon, fthalide and chlobenthiazone) but not with ...

Survival, growth and pathogenicity of Gaeumannomyces graminis var. graminis with different methods of long-term storage

The fungal plant pathogen Gaeumannomyces graminis var. graminis was preserved with 12 different storage methods. Five strains, each with unique morphological and pathological characteristics, were used for comparison of the methods. The storage treatments included potato-dextrose agar slants, with or without mineral oil, stored at either 4 C, 28 C or ambient temperature; colonized agar plugs placed in glycerol solution at either −75 C or −20 C; colonized agar plugs placed in sterile deionized water at either 4 C or ambient temperature; and mycelial growth on intact or precut pieces of filter paper, desiccated and stored at ambient temperature. Survival was evaluated at 6, 12, 24, 36, 48 and 120 mo. The three best treatments for survival were PDA slants, with or without mineral oil, and colonized agar plugs stored in water, all at ambient temperature. All five fungal strains were recovered from all four replicates at each sampling date for agar plugs stored in water at ambient temperature. The worst treatments were agar slants and agar plugs in water stored at 4 C and agar plugs stored in glycerol at −20 C. Morphological characteristics were not affected by storage treatments. In general, there were minimal or no effects on growth and pathogenicity for all strains for all storage treatments with survival. Colonized agar plugs stored in water at ambient temperature provides an economical storage method (materials and labor) that does not need an electrical power for long-term maintenance.

Planar Arenas for use in Laboratory Bioassay Studies of Subterranean Termites (Rhinotermitidae)

ABSTRACT Reliance on use of the Petri dish for bioassay studies has resulted in the majority of subterranean termite research being conducted in a manner that has not taken into account one of the most important feature of subterranean termites ecology: the soil in which they live. This artificial environment for bioassays, favored for its ease of use, may have resulted in accumulation of data about termite physiology, toxicology, pathology and behavior with limited biological relevancy. Caution should be taken when drawing conclusion from such experiments, because recent studies that made use of planar arenas (or ‘two-dimensional arenas’), which provided soil-foraging conditions for termites and visibility for observation, have produced findings that are either contradictory to or more complete than corresponding Petri dish studies. The result of this study showed that groups of termites kept in planar arenas had better vigor and survivorship after 60 d than groups kept in Petri dishes. We also describe a list of technical advantages that the use of planar arenas can provide over the use of Petri dishes, and suggest that entomologists planning future laboratory studies on subterranean termites should consider using a similar protocol that involves planar arenas.

Comparison of media and diluents for enumeration of aerobic bacteria from Bermuda grass golf course putting greens

To increase our knowledge of soil and rhizosphere bacteria associated with bermuda grass grown on golf courses, a standardized procedure has been developed. Seven aerobic bacterial groups were selected for enumeration. For each group selected, appropriate media were compared to determine which one was best for enumeration of that group. Six diluents were evaluated across all media for the seven bacterial groups. The best diluent was sodium pyrophosphate with glycerol. The following media were best for enumeration: solidified 10% tryptic soy broth for total culturable aerobic bacteria and heat tolerant bacteria; reduced arginine soluble salts medium for actinomycetes; S1 medium for fluorescent pseudomonads; XMSM for Stenotrophomonas maltophilia; Bacto azide blood agar base for gram-positive bacteria; crystal violet agar for gram-negative bacteria.

Resource competition between two fungal parasites in subterranean termites

Subterranean termites live in large groups in underground nests where the pathogenic pressure of the soil environment has led to the evolution of a complex interaction among individual and social immune mechanisms in the colonies. However, groups of termites under stress can show increased susceptibility to opportunistic parasites. In this study, an isolate of Aspergillus nomius Kurtzman, Horn & Hessltine was obtained from a collapsed termite laboratory colony. We determined that it was primarily a saprophyte and, secondarily, a facultative parasite if the termite immunity is undergoing a form of stress. This was determined by stressing individuals of the Formosan subterranean termite Coptotermes formosanus Shiraki via a co-exposure to the virulent fungal parasite Metarhizium anisopliae (Metch.) Sorokin. We also examined the dynamics of a mixed infection of A. nomius and M. anisopliae in a single termite host. The virulent parasite M. anisopliae debilitated the termite immune system, but the facultative, fast growing parasite A. nomius dominated the mixed infection process. The resource utilization strategy of A. nomius during the infection resulted in successful conidia production, while the chance for M. anisopliae to complete its life cycle was reduced. Our results also suggest that the occurrence of opportunistic parasites such as A. nomius in collapsing termite laboratory colonies is the consequence of a previous stress, not the cause of the stress.

Fumigation effects on bacterial populations in new golf course bermudagrass putting greens

Abstract Golf course putting greens in the United States are normally built with a root-zone mix composed of >80% sand and a peat source. Populations of seven aerobic bacterial groups, commonly associated with soil or plant roots, were monitored during the building, planting and establishment of miniature bermudagrass putting greens, with a different set of greens built in each of 2 years. At each phase of construction, including pre- and post-fumigation, the following bacterial groups were enumerated: fluorescent pseudomonads, Gram-positives, Gram-negatives, Stenotrophomonas maltophilia , actinomycetes, heat-tolerant and total aerobic. The fumigants methyl bromide, dazomet and metam sodium were used at either normal or 10× field rates. In both years, by 50–70 days after fumigation, which included 4 weeks after planting, the size of the populations for all of the bacterial groups were either greater than or similar to the size of the populations prior to fumigation. The sand source, peat source, and fumigant source and amount did not have any long-term detrimental effects on size of the populations of any of the bacterial groups evaluated.

Effect of organic nitrogen fertilizers on microbial populations associated with bermudagrass putting greens

Abstract Four natural organic fertilizers, alone or in combination with the synthetic organic fertilizer isobutylidene diurea (IBDU), were compared with IBDU alone for their effect on soil/root microbial populations associated with bermudagrass grown on a golf course putting green in southern Florida, USA. Populations of total fungi, total bacteria, fluorescent pseudomonads, Stenotrophomonas maltophilia, actinomycetes and heat-tolerant bacteria were monitored every 3 months during the 2-year study. On only one sampling date and for only one bacterial population (S. maltophilia) was a significant difference in microbial populations obtained among the fertilizer treatments. However, the S. maltophilia populations associated with the natural organic fertilizer treatments were not significantly different from the synthetic organic IBDU fertilizer treatment.