In 2007, sweet corn plants (Zea mays cv. Challenger) with symptoms of mosaic resembling those caused by Maize dwarf mosaic virus (MDMV) were observed in production fields in the Centre Region of France. In 10 sweet corn fields surveyed, yield production was decreased by 10 to 20%. Potyvirus-like particles were observed by electron microscopy. Twenty samples from affected plants (cv. Challenger) showing severe mosaic symptoms were tested by ELISA with rabbit polyclonal antibodies to MDMV (Montpellier SupAgro, France) and SCMV (Sugarcane mosaic virus) (Bioreba, Reinach, Switzerland). For all leaves tested, slight and strong positive reactions were observed for MDMV and SCMV, respectively, indicating that the plants were infected by SCMV. Filtered phosphate buffer extracts of infected leaves of field plants (cv. Challenger) were used to mechanically inoculate leaves of different corn plants at the three-leaf stage. Sweet corn cultivars (Atugan, Challenger, Golda, Max, and Rana) and seed corn cultivars (DK315, DK3152, DKC3420, Marcello, and PR38H20) were tested. Two weeks after inoculation, mosaic symptoms were observed on leaves. The sweet corn cultivars (with the exception of cv. Max) were considerably more sensitive to the virus. Using two lots of 1,000 seeds each (cv. Challenger), a rate of seed transmission was estimated to be 0.5 to 0.6%. Total RNA was extracted from infected leaves of cv. Challenger 3 weeks after mechanical inoculation. To confirm the potyvirus species involved, a short conserved fragment of the coat protein gene was reverse transcribed, PCR amplified and sequenced (3). The sequence was deposited in GenBank (Accession No. HM014060). Multiple sequence alignment and phylogenetic analysis clearly grouped this isolate called SCMV-MFc (Maize France centre) in the ‘Maize’ cluster of SCMV, which consists exclusively of isolates from maize. Nucleotide sequence comparison showed that SCMV-MXVrP, a Mexican isolate (2), and SCMV-P3, a Polish isolate (4), have the two closest sequences (285 identical nucleotides of 286). SCMV-MFc is more distantly related with the described SCMV German isolates (1). This is in contrast to SCMV isolates from the traditional Saccharum officinarum cultivars that can be clustered by geographical origin (1). This result could be a consequence of the possible seed transmission of the maize isolates of SCMV. In the future, it will be interesting to check the occurrence of SCMV-MFc in maize fields to assess its economical importance.
References: (1) O. Alegria et al. Arch. Virol. 148:357, 2003. (2) F. Espejel et al. Arch. Virol. 151:409, 2006. (3) V. Marie-Jeanne et al. J. Phytopathol. 148:141, 2000. (4) K. Trzmiel. Plant Dis. 93:1078, 2009.
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