Abstract
BackgroundFrankliniella occidentalis (Thysanoptera: Thripidae) is a highly rasping-sucking pest of numerous crops. The entomogenous fungi of Lecanicillium spp. are important pathogens of insect pests, and some species have been developed as commercial biopesticides. To explore Lecanicillium spp. resources in the development of more effective F. occidentalis controls, efficient barcode combinations for strain identification were screened from internal transcribed spacers (ITS), SSU, LSU, TEF, RPB1, and RPB2 genes.ResultsSix genes were used to reconstruct Lecanicillium genus phylogeny. The results showed that ITS, TEF, RPB1, and RPB2 could be used to identify the strains. All phylogenetic trees reconstructed by free combination of these four genes exhibited almost the same topology. Bioassay studies of a purified conidial suspension further confirmed the infection of second-instar nymphs and adult female F. occidentalis by seven Lecanicillium strains. L. attenuatum strain GZUIFR-lun1405 was the most virulent, killing approximately 91.67% F. occidentalis adults and 76.67% nymphs after a 7-day exposure. L. attenuatum strain GZUIFR-lun1405 and L. cauligalbarum strain GZUIFR-ZHJ01 were selected to compare the fungal effects on the number of eggs laid by F. occidentalis. The number of F. occidentalis nymphs significantly decreased when F. occidentalis adults were treated with L. cauligalbarum strain GZUIFR-ZHJ01.ConclusionsThe combination of ITS and RPB1 could be used for fast recognition of Lecanicillium spp. This is the first report of the pathogenicity of L. attenuatum, L. cauligalbarum, L araneogenum, and L. aphanocladii against F. occidentalis. Additionally, L. cauligalbarum strain GZUIFR-ZHJ01 caused high F. occidentalis mortality and inhibited the fecundity of the pest.
Highlights
With the development of molecular methods, it has become easier for biodiversity researchers to identify species by DNA barcoding than by morphological methods (Verkley et al, 2013; Vu et al, 2019)
The phylogenetic relationship analysis revealed that the large subunits of the rDNA (LSU) and the small subunits of the rDNA (SSU) could not be used for identifying the strains alone because of the small interspecific differences
The sequence dataset consisted of 2,735 bases, including inserted gaps (ITS: 523 bp; the transcription elongation factor-1α (TEF): 772 bp; DNA-directed RNA polymerase II subunit rpb1 (RPB1): 555 bp; and DNA-directed RNA polymerase II subunit rpb2 (RPB2): 885 bp)
Summary
With the development of molecular methods, it has become easier for biodiversity researchers to identify species by DNA barcoding than by morphological methods (Verkley et al, 2013; Vu et al, 2019). Multilocus (TEF, RPB1, RPB2, LSU, and SSU) sequence data has been used to identify the phylogenetic relationship of some fungi, including as the Ophiocordycipitaceae (Sung et al, 2007; Kepler et al, 2017). It would be laborious if analysis of six genes was required to identify each newly collected strain. To explore Lecanicillium spp. resources in the development of more effective F. occidentalis controls, efficient barcode combinations for strain identification were screened from internal transcribed spacers (ITS), SSU, LSU, TEF, RPB1, and RPB2 genes
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