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ROSEMARIE TEDESCHI CRISTINA VISENTIN ALBERTO ALMA DOMENICO BOSCO 《The Annals of applied biology》2003,142(3):285-290
Adults of Cacopsylla melanoneura, vector of the apple proliferation (AP) phytoplasma, were collected every 2 weeks from January until May in 2000 and 2001 by the beating tray method in eight apple orchards of the Aosta Valley (northwestern Italy). Total DNA was extracted from batches of five insects and amplified with the universal phytoplasma primers P1/P7 in direct PCR. A nested PCR assay was then performed on P1/P7 amplicons using the primers fO1/rO1, specific for the AP‐ phytoplasma group. The digestion of fO1/rO1 amplicons with Ssp I restriction endonuclease confirmed that C. melanoneura adults harboured the AP phytoplasma. The data obtained with PCR were used to estimate the proportion of AP‐positive insects in over wintered and offspring adults. Percentages of AP‐positive insects of 3.6% and 0.8% were estimated in 2000 among over wintered and offspring psyllids respectively. In 2001 only the over wintered insects were found infected, with an estimated proportion of 2.8%. The seasonal abundance of the vector was measured using yellow sticky traps. C. melanoneura was always present at a low population level, and the highest density was recorded from mid‐February until mid‐March in both years. The results show that the overwintered population is higher and spends a longer period in apple orchards, suggesting the crucial role of the overwintered adults in vectoring AP. 相似文献
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We have evaluated codon usage bias in Drosophila histone genes and have
obtained the nucleotide sequence of a 5,161-bp D. hydei histone gene repeat
unit. This repeat contains genes for all five histone proteins (H1, H2a,
H2b, H3, and H4) and differs from the previously reported one by a second
EcoRI site. These D. hydei repeats have been aligned to each other and to
the 5.0-kb (i.e., long) and 4.8-kb (i.e., short) histone repeat types from
D. melanogaster. In each species, base composition at synonymous sites is
similar to the average genomic composition and approaches that in the small
intergenic spacers of the histone gene repeats. Accumulation of synonymous
changes at synonymous sites after the species diverged is quite high. Both
of these features are consistent with the relatively low codon usage bias
observed in these genes when compared with other Drosophila genes. Thus,
the generalization that abundantly expressed genes in Drosophila have high
codon bias and low rates of silent substitution does not hold for the
histone genes.
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