Maize viral diseases: A real economic threat or a mere scare?

Abstract

Maize viral diseases can be found anywhere in the world where maize is grown. The most widely spread and harmful ones in the northern hemisphere in general and Yugoslavia in particular are two viruses of the genus Potyvirus, the Maize Dwarf Mosaic Potyvirus and Sugarcane Mosaic Potyvirus. In recent years, viruses that cause maize dwarf mosaic have been increasingly spreading in our country, where they have become a real economic threat. In some years that are favorable for the development of the virus vector and an abundance of the disease sources (Johnsongrass), outbreaks of maize dwarf mosaic reach epidemic proportions and cause huge amounts of damage by reducing the yields of commercial maize by about 20% and those of seed maize by about 70%. The disease symptoms manifest themselves in the form of striped white-yellowish mosaic that appears on the leaves. The growth of systemically infected plants is stunted. Diseased plants form short ears that sterile to a greater or lesser extent. The Maize Dwarf Mosaic Potyvirus and Sugarcane Mosaic Potyvirus are both elongated viruses with a single-strand infective ribonucleic acid (RNA). They belong to the genus Potyvirus of the Potyviridae family. These viruses parasitize around 200 other species from the Poaceae family in addition to maize and Johnsongrass. They are spread by 23 leaf aphid species, the most important among which are Rhopasosiphon maydis, Myzus persicae and some others. The biggest source of infection in the wild is Johnsongrass (Sorghum halepense). There are a number of measures, all of them preventive, that can help reduce the incidence of maize viral diseases and their harmfulness. They include the eradication of weeds that host the viruses, an earlier sowing, and the growing of less susceptible or tolerant hybrids. The most effective way to protect maize crops, minimize the damage, and prevent the incidence of these viruses is to develop genotypes that are resistant to the prevalent viruses in a given area. The results of studies on maize resistance to the Maize Dwarf Mosaic Potyvirus and Sugarcane Mosaic Potyvirus confirm the existence of sources of resistant genotypes (both domestic and foreign) that can be used as sources of desirable genes in maize breeding. Resistance to the Sugarcane Mosaic Potyvirus is controlled by two dominant genes Scm1 and Scm2, and so is resistance to the Maize Dwarf Mosaic Potyvirus (genes Mdm1 and Mdm2).

Viroze kukuruza predstavljaju realnu ekonomsku opasnost kako u svetu tako i u našoj zemlji. Najznačajnija i ekonomski najopasnija viroza kukuruza je mozaična kržljavost. Ovo obolenje u našoj zemlji prouzrokuje virus mozaične kržljavosti kukuruza (maize dwarf mosaic potyvirus) i virus mozaika šećerne trske (sugarcane mosaic potyvirus). Ovi virusi poslednjih godina pokazuju sve veću ekspanziju širenja kod nas i predstavljaju veliku ekonomsku opasnost u proizvodnji kukuruza, smanjujući prinose merkantilnog kukuruza za oko 20% i semenskog za oko 70% u godinma povoljnim za širenje virusa. Najefikasniji način zaštite kukuruza i smanjenja štetnosti virusa je stvaranje otpornih genotipova prema prevalentnim virusima za dato područje. Utvrđeno je da postoje izvori otpornih genotipova, kako domaćeg tako i stranog porekla, koji se mogu koristiti kao izvori poželjnih gena u selekciji kukuruza. Otpornost prema virusima,prouzrokovačima mozaične kržljavosti je kontrolisana sa dva dominantna gena Mdm 1 i Mdm 2 a otpornost prema VMŠT takođe sa dva dominantna gena Scm 1 i Scm 2.