FAMILY LETHACEAE 



1223 



FAMILY VI. LETHACEAE HOLMES. 

 (Handb. Phytopath. Viruses, 1939, 135.) 

 Virus strains of the Spotted-Wilt Group, causing diseases characterized by bronzing 



of foliage, streaking of stems, blighting of tips, necrotic spotting of foliage 

 higher plants; vectors, thrips (THRIPIDAE). There is a single genus 



Hosts, 



Genus I. Lethiun Holmes. 

 (Loc. cit., 135.) 

 Characters those of the family. Generic name from Latin lethum, death. 



At 



present there is but one known species, though this is reported to be nearly world-wide 

 in distribution. In some areas it may have been confused with entities needing sep- 

 arate recognition. 



The t3'pe species is Leihum australiense Holmes. 



1. Lethum australiense Holmes {loc. 

 cit., 136). From Australia, where virus 

 was first described. 



Common names : Tomato spotted-wilt 

 virus, kromnek or Kat River disease 

 virus. Also, pineapple yellow-spot or 

 side-rot virus (according to Sakimura, 

 Phytopath., 30, 1940, 281-299). 



Hosts : Very numerous species in manj^ 

 families of higher plants. Among those 

 most often noted are : SOLAN ACE AE— 

 Lycopersicon esculentum Mill., tomato; 

 Nicotiana tabacum L., tobacco; Solanutn 

 tuberosum L., potato. COMPOSITAE 

 — Lactuca saliva L., lettuce. LEGUM- 

 INOSAE—Pisum sativum L., pea. 

 BROMELI ACE AE— Ananas comosus 

 Merr., pineapple. 



Geographical distribution: Australia, 

 British Isles, United States, South Africa 

 Hawaii, Xew Zealand, Europe, China, 

 South America. 



Induced disease : In tomato, bronze 

 ring-like secondary lesions, plant stunted, 

 some necrosis; later yellowish mosaic 

 with some leaf distortion. Fruit fre- 

 quently marked with concentric rings of 

 pale red, yellow, or white. In tobacco, 

 primary necrotic lesions followed by sys- 

 temic necrosis, with stem streak, crook- 

 neck, often stunting with subsequent 

 wilting and death, sometimes temporary 

 recovery followed by recurrence of sys- 

 temic necrosis. In lettuce, plant yel- 

 lowed, retarded in growth; brown blem- 



ishes in central leaves, affected spots 

 dying, becoming like parchment but with 

 brown margins. Axillary shoots may 

 show chlorotic mottling. In pea, pur- 

 plish necrotic streaks on stem; at first, 

 leaves mottled; later, necrotic spots 

 damage foliage; pods show circular ne- 

 crotic spots or wavy lines, or, if severely 

 affected, may collapse; seeds may show 

 necrotic lesions. In potato, zonate ne- 

 crotic spots on upper leaves, necrotic 

 streaks on stems; stems collapse at top; 

 plant is stunted, yield of tubers small. 

 In pineapple, at first an initial spot or 

 primary lesion | to * inch in diameter, 

 raised, yellowish, on upper surface of 

 young leaf; later chlorotic spotting of 

 young leaves, crook-neck because of 

 necrotic foci in stems and fruits (side 

 rot) ; plant may die. 



Transmission : By inoculation of ex- 

 pressed juice; the addition of fine car- 

 borundum powder to inoculum facilitates 

 transmission bj' rubbing methods. By 

 thrips, Frankliniella lycopersici Andre- 

 wart ha (formerly identified as F. insu- 

 laris Franklin), F. occidentalis Perg., F. 

 moultoni Hood, and F. schultzei (Try- 

 bom) {THRIPIDAE). Also by Thrips 

 tabaci Lind. {THRIPIDAE). In F. 

 lycopersici, thrips must pick up virus 

 while still a nymph; virus persists 

 through pupation and emergence as adult ; 

 preinfective period in vector, 5 to 9 days. 

 Virus is not transmitted through eggs of 



