A contribution to the ecology of Sugarcane mosaic potyvirus (SCMV) and Maize dwarf mosaic potyvirus (MDMV) in Germany

Since 1982, yearly investigations have been carried our with regard to inci dence and geographical distribution of SCMV and MDMV in Germany. The percen tage of infested maize crops varied to a large extend from less than 10 % a t the beginning of the eighties to almost 100 % in 1989 and 1990. The perce ntage of MDMV has been declined continuously from about 40 % in 1985 to les s than 2 % in 1394. Concerning the ecology of SCMV and MDMV, we investigate d the possibilities of seed transmission and overwintering of viruses in na tive grasses as well as the effectiveness of aphid vectors. Despite remarka ble amounts of virus particles in the pericarp of kernels harvested from in fected maize plants normally the emerging seedlings were virus-free. Accord ing to our findings the grasses with winterannual life span Bromus arvensis L., B. commutatus Schrader, B. hordeaceus L., B. racemosus L., B. secalinu s L., B. sterilis L, and B. tectorum L, as well as those with perennial lif espan Hordelymus europaeus (L.) lessen ex Hart and Roegneria canina (L.) Ne vski could serve as overwintering and longterm hosts, respectively Accordin g to our observations, Rhopalosiphum padi (L.) and Metopolophium dirhodum ( Walk.) are probably the most important aphid species far virus transmitting into and spreading within maize crops. We found a low transmission effecti veness for M. dirhodum. However, this fact could be compensated regarding i ts predominance on maize. Due to our results, we suppose that the decline o f MDMV is related to the lower effectiveness of transmission by native aphi d species compared with SCMV.