Tomato necrotic yellows induced by a novel strain of alfalfa mosaic virus.

Tomato crops in Apulia (Southern Italy) with a chlorotic/necrotic disease named necrotic yellows were found to be infected by a strain of alfalfa mosaic virus (AMV), referred to as AMV-Da. AMV-Da alone was responsible for the symptoms, although other viruses were often present as well. AMV-Da was distinct from other AMV isolates recently recorded in Italy. In particular, it was recognised by only one out of the four monoclonals routinely used for AMV identification and it did not give rise to any type of virus particle aggregation in cells of tobacco plants. The sequence of AMV-Da coat protein (CP) was deduced and compared with that of the AMV strains 425 and YSMV. The deduced amino acid homology was 96% with AMV-425 and 98% with YSMV. A striking difference from YSMV was the presence of the codon Gln-29 in the AMV-Da CP; this does not occur in strains that induce necrotic responses in inoculated leaves of Samsun NN tobacco