Tomato Spotted Wilt Virus 



I h omato spotted wilt is the 



■"l^ I name of a virus which 

 I I we first discovered 

 I I causing a wilt and 



l-^^^J spotting of tomatos. Al- 

 though named for the plant in which 

 it was first found, tomato spotted wilt 

 virus (TSWV) can infect an ex- 

 tremely wide range of plants (New 

 Guinea Impatiens, gloxinia, cycla- 

 men, exacum) and a large number of 

 weeds. 



Formerly the disease was a 

 problem only in tropical and sub- 

 tropical regions of the world. In more 

 temperate regions, it occurred 

 sporadically in greenhouses where the 

 environmental conditions were 

 favorable for growth and the insects 

 that transmit (or vector) the virus. 

 Thrips are the only known vectors of 

 TSWV. 



Symptoms 



Due to the wide host range and 

 the several strains of virus that exist, 

 symptoms are variable and may 

 resemble those caused by fungi. 

 Symptoms may include irregular 

 necrotic (dead) spots on leaves, 

 discolored veins, black or purple stem 

 streaks, falling of leaves or buds, 

 stunting, irregular leaf shapes, black 

 leaf spots, necrotic young leaves, and 

 colored spots or stripes on petals. 

 Black, brown, reddish, or yellowish 

 concentric rings, although not always 

 present, are virtually certain symp- 

 toms of virus infections. In general, 

 symptoms vary a great deal from crop 

 to crop and infected plants may show 

 no symptoms at all. Specific ex- 

 amples will be given for four crops. 



Tomato 



Two or more of the following 

 occur on the foliage: downward 

 curling of leaves; leaf distortion; 

 whole plant stunting and yellowing; 

 bronze or purplish marking on leaves, 

 including "thumbprints" or dots sur- 

 rounded by rings (ringspots), or 

 flecking; dark purplish stem streaks, 

 tip or seedling dieback; or wilting. 



On green fruit, blotches or spots of 

 pale green or white, or small bumps 

 near the surface. On maturing fruit, 

 yellow, orange, or green spots or 

 blotches, vertical cracks, corky 

 patches or lines, black spots, ring- 

 spots, or lumps may be present. 

 Severely affected plants may form no 

 fruit at all, or the fruit may be very 

 small and unmarketable. Diseased 

 plants do not yield well. 



Impatiens 



Small dark purple ringspots 

 often occur on leaves; flowers may 

 also display ringspots, but here the 

 rings are usually white. Dark streaks 

 on stems or leaves, especially 

 involving the mid-rib; leaf yellow- 

 ing, leaf malformation; leaf drop; and 

 stunting may occur. Plants infected 

 while still young, or older plants 

 severely affected may lose many 

 leaves, look "leggy" and generally 

 appear unthrifty. 



Cyclamen 



The most distinctive symptom of 

 TSWV is the thumbprint-like yellow 

 ringspots on leaves. Brown streaks, 

 in addition to rings, may be present 

 on petioles. Flowers are often mal- 

 formed. Corms may be constricted 

 into an elongated shape and, when 

 cut, the vascular tissues of the corm 

 appear as brown streaks. Plants stop 

 growing, brown spots appear on 

 leaves and leaf edges, and eventually 

 plants wilt and die. The roots usually 

 look fine until the plant is near death. 

 It may take three months or longer 

 from the time the plants were first in- 

 fected for symptoms to appear, 

 during which time the plants look 

 perfectly healthy. 



Gloxinia 



Young plants will show symp- 

 toms similar to certain fungal 

 diseases. Symptoms may appear as 

 stunting of new leaves or browning 

 of the central or basal portion of the 

 plant, followed by collapse and plant 

 death. Plants that are older when 



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