1All-Russian Institute for Plant Protection, St Petersburg, 189620, Russia; 2Dept. of Botany, St Petersburg State University, St Petersburg, 199034, Russia

Background and objectives
The study of the effect of virus infection on the manifestation of a number of fungal diseases and the development of phytophagous insects on grain cultures is of scientific interest in connection with plant complex resistance. In the majority of cases, early virus infection considerably increases plant susceptibility to some fungal diseases (root rots, leaf spots) caused by Rhizoctonia, Fusarium, Bipolaris and other fungi. On the other hand, some viruses can promote reduction of fungal disease caused by Puccinia, Uromyces and Erysiphe.

Results and conclusions
Results of our research have shown that various barley cultivars infected by barley stripe mosaic virus (BSMV) are differentially infected by root rots and leaf spots as well as the frit-fly Oscinella pusilla [1]. In field experiments there was a stable tendency towards increase of damage by net blotch, Drechslera teres, and frit fly on 13 barley cultivars studied after their early artificial inoculation with BSMV. Synergism of virus and fungal infections became more apparent on the cultivars Nosovsky 9 and Abava, but not was noted on the cultivars Donetsky and Omsky 13709 - resistant to BSMV. The degree of damage of frit fly on the resistant cultivars by larvae of O. pusilla increased to only a small extent and no significant differences were seen between a BSMV-infected variant and the uninfected control. The influence of virus infection on the degree of plant damage by frit fly was more pronouced on the cultivars which were susceptible to BSMV: Abava, Belogorsky, Nosovsky and Zazersky 85.

In the Belgorodsky and Rostovsky regions, the relationship of virus and fungal infections on 9 wheat cultivars and 3 barley cultivars was investigated [2]. Stereotyped reactions were found at the cultivar level to viruses from the mosaic group, powdery mildews, leaf spots and frit fly. More resistant to viruses and, hence, to other harmful organisms were the winter wheat cultivars Albatros odessky, Zeriiogi-adka 8, Novinka 4 and Don 85. These results offer the opportunity to use viruses from the mosaic group as markers of complex resistance of grain cultures to frit fly, powdery mildew, leaf spots and rust.

1. Sincinikov EA, Tzvplenkov AE, 1994. Arch. Phytopath. Pflanz. 29, 111-118.
2. Tzyplenkov AE, Vlasov DY, Sinelnikov EA, 1995. Bull. Inst. Plant Protection 121-129.