Genetic Variability of Beauveria bassiana and a DNA Marker for Environmental Monitoring of a Highly Virulent Isolate Against Cosmopolites sordidus

Isolates of the Nematophagous Fungus Pochonia chlamydosporia Are Endophytic in Banana Roots and Promote Plant Growth

The biocontrol fungus Pochonia chlamydosporia colonizes banana roots endophytically. Root hairs and root surface were colonized by a stable GFP (green fluorescent protein) transformant of the fungus. Hyphal penetration in root cells was also observed. Spores of P. chlamydosporia 123, significantly increase root and leaf length and weight in banana plantlets (Musa acuminata cv. ‘Dwarf Cavendish’) in growth chamber experiments 30 days post-inoculation. In greenhouse 8-L pot experiments, P. chlamydosporia 123 spore inoculation significantly increases root, corm and leaf length, and leaf weight in banana plants (75 days post-inoculation). Spore inoculation of P. chlamydosporia strains from diverse origin (Pc21, Pc123, Pc399, and Pccat), significantly increase root, corm and leaf length and weight in banana plantlets. Pc21 from Italy was the best colonizer of banana roots. Consequently, this strain significantly increases banana root and leaf length most. Root colonization by P. chlamydosporia was also detected using cultural techniques and qPCR.

Volatile Organic Compounds from Entomopathogenic and Nematophagous Fungi, Repel Banana Black Weevil (Cosmopolites sordidus)

Fungal Volatile Organic Compounds (VOCs) repel banana black weevil (BW), Cosmopolites sordidus (Germar, 1824), the key-pest of banana [Musa sp. (Linnaeus, 1753)]. The entomopathogens Beauveria bassiana (Bb1TS11) and Metarhizium robertsii (Mr4TS04) were isolated from banana plantation soils using an insect bait. Bb1TS11 and Mr4TS04 were pathogenic to BW adults. Bb1TS11, Bb203 (from infected palm weevils), Mr4TS04 and the nematophagous fungus Pochonia clamydosporia (Pc123), were tested for VOCs production. VOCs were identified by Gas Chromatography/Mass Spectrometry-Solid-Phase Micro Extraction (GC/MS-SPME). GC/MS-SPME identified a total of 97 VOCs in all strains tested. Seven VOCs (styrene, benzothiazole, camphor, borneol, 1,3-dimethoxy-benzene, 1-octen-3-ol and 3-cyclohepten-1-one) were selected for their abundance or previous record as insect repellents. BW-starved adults in the dark showed the highest mobility to banana corm in olfactometry bioassays. 3-cyclohepten-1-one (C7), produced by all fungal strains, is the best BW repellent (p < 0.05), followed by 1,3-dimethoxy-benzene (C5). The rest of the VOCs have a milder repellency to BW. Styrene (C1) and benzothiazole (C2) (known to repel palm weevil) block the attraction of banana corm and BW pheromone to BW adults in bioassays. Therefore, VOCs from biocontrol fungi can be used in future studies for the biomanagement of BW in the field.

Brazil nuts are subject to infection with B and G aflatoxin-producing fungus, Aspergillus pseudonomius

The exploitation of the Brazil nut is one of the most important activities of the extractive communities of the Amazon rainforest. However, its commercialization can be affected by the presence of aflatoxins produced by fungi, namely Aspergillus section Flavi. In the present study, we investigated a collection of Aspergillus nomius strains isolated from Brazil nuts using different approaches, including morphological characters, RAPD and AFLP profiles, partial β-tubulin and calmodulin nucleotide sequences, aflatoxin patterns, as well as tolerance to low water activity in cultured media. Results showed that most of the isolates do belong to A. nomius species, but a few were re-identified as Aspergillus pseudonomius, a very recently described species. The results of the analyses of molecular variance, as well as the high pairwise FST values between A. nomius and A. pseudonomius suggested the isolation between these two species and the inexistence of gene flow. Fixed interspecific nucleotide polymorphisms at β-tubulin and calmodulin loci are presented. All A. pseudonomius strains analyzed produced aflatoxins AFB1, AFB2, AFG1 and AFG2. This study contains the first-ever report on the occurrence in Brazil nuts of A. pseudonomius. The G-type aflatoxins and the mycotoxin tenuazonic acid are reported here for the first time in A. pseudonomius.

Identification of Genes Differentially Expressed Between Ochratoxin-Producing and Non-Producing Strains of Aspergillus westerdijkiae

Approximately 70 % of Aspergillus westerdijkiae strains are able to produce ochratoxin A (OTA), a nephrotoxic and carcinogenic mycotoxin which have been found in cereal and food commodities. Despite of its importance there is, up to now, no information available about which genes are differentially expressed between A. westerdijkiae ochratoxin-producing and non-producing strains. Using cDNA RDA approach we successfully sequenced 231 raw ESTs expected to be enriched in the ochratoxin-producing strain. BLASTX searches against the public databases showed that of these, 205 ESTs (79 %) exhibited significant similarities with proteins of known functions, 28 ESTs (11 %) had matches to hypothetical proteins, and the remaining 27 ESTs (10 %) had no significant hits. EST alignment resulted in a total of 14 non-redundant consensus sequences. Three putative genes encoding oxidoreductases were validated as up-expressed in the OTA producer strain using RT-qPCR approach. The expression of the putative genes encoding a cytochrome P450 family protein, 3-hydroxyphenylacetate-6-hydroxylase, and endoplasmic reticulum oxidoreductin were higher (32-, 2.8- and 20-fold respectively) in the OTA producer strain compared to the non-producer strain.