A British isolate of potato aucuba mosaic potexvirus (PAMV) was transmitted by aphids (Myzus persicae) which had fed previously on a source of potato Y potyvirus (PVY). Nucleotide sequence analysis of the PAMV coat protein gene indicated that amino acid residues 14 to 16 from the N terminus of the coat protein have the sequence DAG, which is also found in the coat proteins of potyviruses and is required for their aphid transmissibility. A recombinant virus isolate (TXPA7) was produced in which a segment of the coat protein gene of PAMV encoding the 40 N-terminal amino acids was inserted in the genome of potato X potexvirus (PVX) in place of the segment encoding the 28 Nterminal amino acids of PVX coat protein. This isolate, and a second similar recombinant (TXPAS) in which the DAG motif was changed to YTS, were mechanically transmissible to intact plants, in which they caused slightly milder symptoms than PVX. Particles of TXPA7 reacted in immunosorbent electron microscopy with PVX-and PAMV-specific antibodies and so were antigenically distinguishable from PAMV and PVX particles, which reacted only with their homologous antibody, and from TXPA5 particles, which reacted only with the PVX antibody. Recombinant TXPA7 was transmitted by aphids that had already fed on a source of PVY whereas TXPA5 and PVX were not. TXPA7 was not transmitted by aphids that had not fed on a PVY source. It is concluded that (i) the potyvirus-dependent aphid transmissibility of PAMV results from possession of a domain which includes the DAG motif and is located near the N terminus of the virus coat protein, and (ii) potyvirus-dependent aphid transmissibility can be conferred on PVX, a non-aphid-borne potexvirus, by substituting this domain for the N-terminal part of its coat protein.
The accurate quantification of non-Basmati rice in Basmati rice is central to the successful prosecution of adulteration, where non-Basmati rice has been substituted for Basmati rice. The current method and three alternatives of constructing calibration curves for the measurement of non-Basmati rice in Basmati rice using microsatellite analysis were investigated. The methods compared involved power regression, linear regression (with and without log(10) transformation) and hyperbolic regression of the ratio of Basmati to non-Basmati peak areas. Assessments were made using error uncertainty, standard error at the agreed limit of adulteration, and 95% confidence intervals for five example data sets. The linear regression of the ratio of peak areas to the ratio of content proportions was found to give the most precise calibration and thus enhanced quantification of the level of adulteration of Basmati rice with non-Basmati rice.
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