The sweetpotato whitefly Bemisia tabaci is a highly destructive agricultural and ornamental crop pest. It damages host plants through both phloem feeding and vectoring plant pathogens. Introductions of B. tabaci are difficult to quarantine and eradicate because of its high reproductive rates, broad host plant range, and insecticide resistance. A total of 791 Gb of raw DNA sequence from whole genome shotgun sequencing, and 13 BAC pooling libraries were generated by Illumina sequencing using different combinations of mate-pair and pair-end libraries. Assembly gave a final genome with a scaffold N50 of 437 kb, and a total length of 658 Mb. Annotation of repetitive elements and coding regions resulted in 265.0 Mb TEs (40.3%) and 20 786 protein-coding genes with putative gene family expansions, respectively. Phylogenetic analysis based on orthologs across 14 arthropod taxa suggested that MED/Q is clustered into a hemipteran clade containing A. pisum and is a sister lineage to a clade containing both R. prolixus and N. lugens. Genome completeness, as estimated using the CEGMA and Benchmarking Universal Single-Copy Orthologs pipelines, reached 96% and 79%. These MED/Q genomic resources lay a foundation for future ‘pan-genomic’ comparisons of invasive vs. noninvasive, invasive vs. invasive, and native vs. exotic Bemisia, which, in return, will open up new avenues of investigation into whitefly biology, evolution, and management.
The tobacco whitefly, Bemisia tabaci (Gennadius), causes severe crop losses in many agricultural systems. The worst of these losses are often associated with the invasion and establishment of specific whitefly biotypes. In a comprehensive survey of biotypes present in central China between 2005 and 2007, we obtained 191 samples of B. tabaci from 19 districts in Hubei province and its surrounds. Biotypes were identified by RAPD-PCR and by sequencing the mitochondrial cytochrome oxidase I gene (mtCO1). We determined that these central Chinese haplotypes included the world's two most invasive B. tabaci biotypes (B and Q) and two indigenous biotypes (ZHJ1 and ZHJ3). The B biotype shared >99.7% identity with other Chinese B biotypes and the Q biotype shared >99.5% of its identity with Q samples from the Mediterranean, USA, Africa and East Asia. By 2007, the Q biotype was dominant over much of Hubei province and appeared to be supplanting all other biotypes, although both the invasive and indigenous biotypes existed in sympatry in some regions. The invasion and rapid establishment of the Q biotype in China mirrors events elsewhere in the world, and we suggest that this is a consequence of its reproductive isolation, its polyphagous nature and its broad-spectrum resistance to insecticides. Its dominance has severe implications for the sustainability of some insecticide groups and for the production of a number of crops.
Lettuce (Lactuca sativa L.) is one of the most important leafy vegetable that is consumed during its vegetative growth. The transition from vegetative to reproductive growth is induced by high temperature, which has significant economic effect on lettuce production. However, the progression of floral transition and the molecular regulation of bolting are largely unknown. Here we morphologically characterized the inflorescence development and functionally analyzed the FLOWERING LOCUS T (LsFT) gene during bolting regulation in lettuce. We described the eight developmental stages during floral transition process. The expression of LsFT was negatively correlated with bolting in different lettuce varieties, and was promoted by heat treatment. Overexpression of LsFT could recover the late-flowering phenotype of ft-2 mutant. Knockdown of LsFT by RNA interference dramatically delayed bolting in lettuce, and failed to respond to high temperature. Therefore, this study dissects the process of inflorescence development and characterizes the role of LsFT in bolting regulation in lettuce.
Four strains of the Q biotype and one of the B biotype of the whitefly Bemisia tabaci collected from China were characterised for resistance to four neonicotinoid insecticides and pymetrozine. Q biotype strains showed moderate to strong resistance to imidacloprid, thiamethoxam and acetamiprid, but little or no cross-resistance to dinotefuron. Resistance to neonicotinoids was consistently associated with resistance to pymetrozine, despite the latter having a distinct (though unresolved) mode of action. The single B biotype strain proved largely susceptible to all the insecticides investigated. Resistance in the Q biotype strains was associated with over-expression of a cytochrome P450 monooxygenase gene, CYP6CM1, whose substrate specificity presumably accounts for the observed cross-resistance profiles
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