RESUMO
Fungi and bacteria associated to phytoparasitic nematodes Globodera rostochiensis and Meloidogyne spp. in Algeria were identified and characterized. Trichoderma spp. showed the highest prevalence in the cysts of G. rostochiensis. A number of isolates were identified through PCR amplification and the sequencing of the internal transcribed spacer (ITS)1-2 and Rpb2 gene regions. The most represented species were T. harzianum and T. afroharzianum. The latter and T. hirsutum were reported for the first time in Algeria. Fusarium spp., including F. oxysporum and F. solani, comprised a second group of fungi found in cysts. Taxa associated to females of Meloidogyne spp. included T. harzianum, Fusarium spp. and other hyphomycetes. To assess the efficacy of Trichoderma spp., two assays were carried out in vitro with the culture filtrates of two T. afroharzianum and T. harzianum isolates, to check their toxicity versus the second stage juveniles of M. incognita. After 24-48 h exposure, a mortality significantly higher than the control was observed for both filtrates at 1% dilutions. The TRI genes involved in the production of trichothecenes were also amplified with the PCR from some Trichoderma spp. isolates and sequenced, supporting a putative role in nematode toxicity. Bacteria isolated from the cysts of G. rostochiensis included Brucella, Rhizobium, Stenotrophomonas and Bacillus spp., identified through 16S rRNA gene sequencing. The potential of the microbial isolates identified and their mechanisms of action are discussed, as part of a sustainable nematode management strategy.
RESUMO
A novel crown rot pathogen of wheat discovered during pathogen surveys in Algeria in 2014 and 2015 is formally described as Fusarium algeriense. Multilocus molecular phylogenetic data resolved the eight isolates of this pathogen as a genealogically exclusive species lineage in the F. burgessii species complex. The previously described species of this complex, F. burgessii and F. beomiforme, produce abundant chlamydospores in culture, and their optimal temperature for growth is 30 C. In comparison, F. algeriense did not produce chlamydospores under the conditions tested and its optimal temperature for growth is 25 C. Furthermore, F. algeriense differs from F. burgessii because it does not produce polyphialides and F. beomiforme, because it does not produce globose-to-napiform conidia in the aerial mycelium. Isolates of F. algeriense induced moderate crown rot on the susceptible spring wheat cultivar Norm in a temperature-controlled incubator. Fusarium burgessii and F. beomiforme, in contrast, only induced mild symptoms of this disease. BLASTn searches of the whole-genome sequence of F. algeriense strains NRRL 66647 and 66648, using homologs of genes that are responsible for synthesis of toxic secondary metabolites, indicated that they have the potential to produce several polyketide and non-ribosomal peptide-derived mycotoxins. However, moniliformin and 2-AOD-ol (2-amino-14,16-dimethyloctadecan-3-ol) were the only mycotoxins detected by liquid chromatography-mass spectrometry (LC-MS) analyses of strains cultivated in vitro on a solid medium. A polymerase chain reaction (PCR) assay for MAT idiomorph revealed that MAT1-1 and MAT1-2 strains of F. algeriense were present in Algeria, which suggests this pathogen might possess a heterothallic sexual reproductive mode.