Patterns of Occurrence and Activity of Entomopathogenic Fungi in the Algarve (Portugal) Using Different Isolation Methods

Entomopathogenic fungi (EPF) are distributed in natural and agricultural soils worldwide. To investigate EPF occurrence in different botanical habitats and soil-ecoregions, we surveyed 50 georeferenced localities in the spring of 2016 across the Algarve region (South Portugal). Additionally, we compared three EPF isolation methods: insect baiting in untreated or pre-dried-soil and soil dilution plating on a selective medium. We hypothesized that forest habitats (oak and pine semi-natural areas) and the acidic soil ecoregion may favor EPF occurrence. Overall, EPF species were present in 68% of sites, widely distributed throughout the Algarve. The use of selective media resulted in higher recovery of EPF than did either soil-baiting method. Contrary to our hypothesis, neither vegetation type nor ecoregion appeared to influence EPF occurrence. Traditional and molecular methods confirmed the presence of five EPF species. Beauveria bassiana (34% of sites), was the most frequently detected EPF, using pre-dried soil baiting and soil dilution methods. However, baiting untreated soil recovered Fusarium solani more frequently (26% of sites), demonstrating the utility of using multiple isolation methods. We also found Fusarium oxysporum, Purpureocillium lilacinum and Metarhizium anisopliae in 14%, 8% and 2% of the sites, respectively. Three abiotic variables (pH, soil organic matter and Mg) explained 96% of the variability of the entomopathogen community (EPF and entomopathogenic nematodes) in a canonical correspondence analysis, confirming the congruence of the soil properties that drive the assemblage of both entomopathogens. This study expands the knowledge of EPF distribution in natural and cultivated Mediterranean habitats.

Morphological and molecular characterisation of Distolabrellus veechi (Rhabditida: Mesorhabditidae) from India

Summary A redescription of Distolabrellus veechi (Rhabditida: Mesorhabditidae) from agricultural soils in Uttarakhand and Uttar Pradesh, India, is provided. Specimens were extracted from soil using the Galleria soil baiting technique, with two strains of nematodes named JP1 and JP2 being obtained. Morphological and morphometric studies on the species agree well with previous records. Molecular analyses are provided using 18S, 28S and ITS rRNA sequences, the ITS sequences being obtained for the first time in this species. These analyses show that the material examined agrees well with previously studied populations. Phylogenetic analyses showed Distolabrellus to be the sister group of Crustorhabditis and Teratorhabditis, all having the male spicules fused for more than 50% of their length. Illustrations and phylogenetic trees based on 18S, 28S and ITS rRNA sequences are provided.

Pathogenicity, Fungicide Resistance, and Genetic Variability of Phytophthora rubi Isolates from Raspberry (Rubus idaeus) in the Western United States

Root rot of raspberry (Rubus idaeus), thought to be primarily caused by Phytophthora rubi, is an economically important disease in the western United States. The objectives of this study were to determine which Phytophthora species are involved in root rot, examine the efficacy of different isolation methods (cane, root, and root/soil baiting with young raspberry plants), and determine if pathogenicity, fungicide resistance, and/or genetic variation exists among P. rubi isolates collected from raspberry fields in Washington, Oregon, and California. Of 275 samples, direct isolation from cane material resulted in a greater number of P. rubi isolates (39%), whereas root/soil baiting yielded the least (11%). Sequencing of the internal transcribed spacer region of 210 of the total 597 collected Phytophthora isolates showed that all but one isolate (identified as P. bisheria) were P. rubi. Results of the pathogenicity and fungicide resistance to mefenoxam comparing 14 total isolates from Washington, Oregon, and California showed that isolates were similarly virulent against red raspberry and the EC50 frequency distributions showed no significant difference. These results, combined with amplified fragment length polymorphism results show that P. rubi isolates from Washington, Oregon, and California represent one large mixed population. This work provides novel insights into the isolation and biology of P. rubi in western U.S. raspberry production systems.

Detection, Distribution, Sporulation, and Survival of Phytophthora ramorum in a California Redwood-Tanoak Forest Soil

Recovery of Phytophthora ramorum from soils throughout sudden oak death-affected regions of California illustrates that soil may serve as an inoculum reservoir, but the role of soil inoculum in the disease cycle is unknown. This study addresses the efficacy of soil baiting, seasonal pathogen distribution under several epidemiologically important host species, summer survival and chlamydospore production in soil, and the impact of soil drying on pathogen survival. The efficacy of rhododendron leaves and pears as baits for detection of soilborne propagules were compared. Natural inoculum associated with bay laurel (Umbellularia californica), tanoak (Lithocarpus densiflorus), and redwood (Sequoia sempervirens) were determined by monthly baiting. Summer survival and chlamydospore production were assessed in infected rhododendron leaf disks incubated under bay laurel, tanoak, and redwood at either the surface, the litter/soil interface, or in soil. Rhododendron leaf baits were superior to pear baits for sporangia detection, but neither bait detected chlamydospores. Most inoculum was associated with bay laurel and recovery was higher in soil than litter. Soil-incubated inoculum exhibited over 60% survival at the end of summer and also supported elevated chlamydospore production. P. ramorum survives and produces chlamydospores in forest soils over summer, providing a possible inoculum reservoir at the onset of the fall disease cycle.

SURVEYS FOR FUNGAL PATHOGENS OF LOCUSTS AND GRASSHOPPERS IN AFRICA AND THE NEAR EAST

A total of 181 isolates of Metarhizium anisopliae (Metschnikoff) Sorokin, M. flavoviride Gams and Rozsypal, Beauveria bassiana (Balsamo) Vuillemin, and Sorosporella sp. was found in a survey of Orthoptera in West Africa, Madagascar, Oman, and Pakistan between 1990 and 1993. Prior to this survey, there were only 28 isolates of hyphomycete fungi from Orthoptera held in international culture collections. Seventeen of the recently acquired Metarhizium isolates have been determined to be highly virulent during screening tests as part of a research programme for the development of a microbial insecticide against locusts and grasshoppers in Africa. Ninety-five isolates came from Benin which was the country where survey activities were most concentrated, and 63 of these isolates were found in Malanville, northern Benin, between 1991 and 1992 during an epizootic of M. flavoviride. Recordings from Oman and Pakistan represent the first specimens from these countries to be deposited in international culture collections. No deductions can be made on the best method for survey; both incubation of live grasshoppers and field searches for cadavers yielded results. Soil baiting with Orthoptera was used with some success. Limited soil screening using selective agar media was not found to be particularly useful.