Mosaic Diseases

a group of viral diseases of plants, characterized by mottling of affected organs (mainly leaves and fruits) and by various green spots differing in size, shape, and intensity of color.

Mosaic diseases, which are ubiquitous, substantially decrease plant yields and lower the quality of produce. Mosaic diseases retard plant growth and alter the shape of the leaf blades. Pathological changes occur primarily in the chlorophyll-bearing tissues. The palisade parenchyma is affected; some plastids decompose and others experience a decrease in the chlorophyll content, as a result of which the energy of photosynthesis diminishes and the carbohydrate content in the leaves decreases. A few individual cells and areas of tissue atrophy.

Mosaic plant diseases are easily transmitted through seeds, by the juice of diseased plants during the transplanting of seedlings, during sucker removal, and when diseased and healthy plants touch each other and slight mutual traumatization occurs (for example, when there is wind). Mechanical carriers of the virus are aphids, true bugs, mites, ticks, and soil nematodes. The virus penetrates the plant through injured tissues; it is preserved in soil, plant remains, and seeds. The most harmful mosaic plant diseases are tobacco mosaic (causative agent is Nicotina virus 1), green cucumber mosaic and cucumber mosaic (Cummis virus 2), potato mosaic and potato vein banding mosaic (Solanum virus 1 and Solanum virus 2, respectively), sugarbeet mosaic (Beta virus 2), cabbage mosaic (Brassica virus 3), and mosaics of soybeans, peas, beans, fruit trees, shrubs, and ornamental plants.