Infected plants are stunted, with leaves coarsely mottled and distorted. Black spots develop on leaves which prematurely drop. Early infection of cabbage by this virus in the seedbed or soon after transplanting, can reduce yield by 75%, whereas late-season infection has little or no effect on yield. It also reduces seed yield.
Turnip mosaic virus (TuMV) has a very wide host range infecting at least 318 species in 156 genera of 43 families. TuMV infects most cruciferous plants, but is most damaging in Chinese cabbage, turnip, mustard, and radish. It also attacks beets, spinach and tobacco.
On cabbage: Mosaic, black speckling or stippling of cabbage heads at harvest or during storage can be caused by the TuMV or the cauliflower mosaic virus occurring singly or together. The latter causes lumpy or warty growths on the veins on the under surface of leaves and vein clearing. In stored cabbage, black sunken spots develop on leaves throughout the head. The spots are considerably larger than those caused by cauliflower mosaic virus. Its mode of transmission is similar to TuMV (i.e. aphids and mechanically). However, cauliflower mosaic virus has a restricted host range. It is infectious only to members of the cabbage family (brassicas).
Affected plant stages
Flowering stage, fruiting stage, seedling stage and vegetative growing stage.
Affected plant parts
Leaves, seeds, stems and whole plant.
Leaves: lesions; abnormal colours; abnormal patterns; abnormal forms; yellowed or dead.
Seeds: empty grains; lesions.
Stems: external discolouration; abnormal growth; dieback.
Whole plant: plant dead; dieback; dwarfing; early senescence.