Beet curly top virus

Beet curly top virus (BCTV) is a plant pathogenic virus of the family Geminiviridae.

Symptoms
On the whole, symptoms produced by BCTV are generally similar throughout its host range.

Beets
In sugarbeet, the most reliable, early diagnostic feature is an inward rolling of the leaf margins and a clearing of the minute veins on the youngest, innermost leaves. Initially, these symptoms are confined to a portion of the youngest leaf but, in a few days, the entire leaf is affected. Subsequently, development of wart-like protuberances on the veins of the lower leaf surfaces is characteristic. Leaves are dark, dull-green in colour, thick, crisp and brittle. Occasionally, clear, viscid droplets exude from the petioles, midribs or veins on the lower leaf surfaces of infected plants. This liquid subsequently becomes black and sticky and then dries forming a brown crust. A hairy or woolly condition of the roots develops in badly diseased sugarbeets as the number of rootlets increases. In cross section, affected sugarbeet shows black concentric rings which alternate with light areas, while in longitudinal section the dark discoloration is seen extending lengthwise.

Outdoor
In tomatoes in the field, there is an inward rolling of leaflets along the midrib; the petiole and midrib frequently curve downwards, giving the leaf a drooping but not wilting appearance. Leaves become thickened and crisp and may later assume a yellow colour with purple veins. The pith dries out leaving stems hollow. As foliage symptoms appear, the plant ceases growth and takes on an erect, rigid habit. Fruits, if formed, ripen prematurely and seeds are abortive. Starting at the tips of smaller roots, there is a decay of the roots, which may occur before aerial symptoms become apparent. The plant finally dies, the stems and leaves turning brown.

Indoor
In tomatoes in the greenhouse, initially, the most diagnostic symptom is the appearance of transparent veins. Purple venation is usually absent. Inward curling of leaflets occurs, especially in older plants. White excrescences sometimes appear on the veins and a yellowing develops between them. There is a marked stunting of plants infected at an early stage. Eventually, the whole plant turns yellow and dies.

Potato
In potatoes, the plants are stunted with yellowish, inward-rolled leaflets and sometimes a bending of the petioles. In advanced stages of infection, dwarfed shoots frequently develop in the axis of leaves near the tip of the plant. Ultimately, infected plants turn yellow and die.

Prevention
Successful control of the virus is possible through a combination of measures. Chemical control against the vector should be applied inside the production area as well as outside in order to eliminate the breeding areas of the leafhoppers. Resistant cultivars should also be used.