FAMILY ANNULACEAE 



1215 



inant allele of a gene nx, which charac- 

 terizes plants showing a mosaic of some 

 degree of intensity on infection with this 

 virus ; the variety known as S41956 is im- 

 mune to all tested strains of the virus and 

 possesses two dominant genes both re- 

 quired for resistance. In tomato, sys- 

 temic mild chlorotic mottling ; if a strain 

 of tobacco-mosaic virus is also present, 

 a severe systemic necrosis, known as 

 double-virus streak, is induced. 



Transmission : By inoculation of ex- 

 pressed juice. Experimentally, by leaf 

 contacts mainly under the influence of 

 wind. No insect vector is known. Not 

 transmitted through true seeds of the 

 potato. 



Serological relationships : Cross precip- 

 itin reactions between constituent strains 

 of this virus. No cross reaction with 

 potato aucuba-mosaic, potato mild-mo- 

 saic, potato -veinbanding, tobacco-mo- 

 saic, tobacco-etch, tobacco-ringspot or 

 pea-mosaic virus. Antisera prepared by 

 injecting rabbits intravenously with virus 

 inactivated by nitrous acid, like those 

 prepared with active virus, fix comple- 

 ment and flocculate with virus suspen- 

 sions (though not with juice of healthy 

 host plants); they are also effective in 

 neutralizing the virus. 



Immunological relationships : Tobacco 

 and Datura plants infected by the type 

 strain of this virus become immune to the 

 more severe potato-ringspot strain. No 

 protection against the severe strain is af- 

 forded by previous infection with to- 

 bacco-mosaic, tobacco-ringspot, tomato 

 spotted-wilt, or cucumber-mosaic virus. 



Thermal inactivation : At 70° C. in 10 

 minutes. 



Filterability : Passes Pasteur-Cham- 

 berland Li, L3, and L5 filters. 



Other properties : Digested by 0.02 per 

 cent solution of pepsin in 3 hours at pH 

 4, at 38° C. Digested also by trypsin. 

 Inactivated by papaine and cyanide, but 

 by neither separately. Isoelectric point 

 near pH 4. Dilute solutions show anisot- 

 ropy of flow. Concentrated solutions 

 are spontaneously birefringent. Proper- 

 ties of the type strain have been less 



studied than those of the potato-ring- 

 spot strain of this virus. 



Literature: Bawden, Proc. Roy. Soc. 

 London, Ser. B, 116, 1934, 375-395; Baw- 

 den and Pirie, Brit. .Jour. Exp. Path., 17, 



1936, 64-74 ; Bawden et al., ibid., 17, 1936, 

 204-207; Blodgett, Phytopath., 17, 1927, 

 775-782; Bohme, Phytopath. Ztschr., 6, 

 1933, 517-524; Cadman, Jour. Genetics, 

 U, 1942, 33-52; Chester, Phytopath., 27, 



1937, 903-912; Clinch, Sci. Proc. Roy. 

 Dublin Soc, 23, 1942, 18-.34; Johnson, 

 Wisconsin Agr. Exp. Sta., Res. Bull. 63, 

 1925; Koch, Phytopath., 23, 19.33, 319- 

 342; Kohler, Phytopath. Ztschr., 5, 1933, 

 567-591; 7, 1934, 1-30; Loughnane and 

 Murphy, Nature, I4I, 1938, 120; van der 

 Meer, Cent. f. Bakt., II Abt., 87, 1932, 

 240-262; Salaman, Nature, 131, 1933, 468; 

 Schultz et al., Phytopath., 27, 1937, 190- 

 197; 30, 1940, 944-351 ; Spooner and Baw- 

 den, Brit. .Jour. Exp. Path., 16, 1935, 

 218-230; Stevenson et al., Phytopath., 

 29, 1939, 362-365. 



Strains : Several variants of potato- 

 mottle virus, differing from the type, var. 

 vulgaris H. {loc. cit., 42), have been recog- 

 nized as distinctive varieties under the 

 following names : 



5a. Annulus dubius var. annulus H. 

 {loc. cit., 44). From Latin annulus, ring. 



Common name : Ringspot strain of 

 potato-mottle virus. Necrotic primary 

 and secondary ring-like lesions in experi- 

 mentally infected tobacco plants. Indis- 

 tinguishable from type strain by ordinary 

 precipitin test, but distinguishable when 

 appropriately absorbed sera are used. 

 This strain has been more frequently 

 studied than the type. Juice of infected 

 tobacco plants contains about 0.02 to 

 0.10 mg of virus per ml. Sedimentation 

 constants, 820° = 113 X lO-i^ and 131 X 

 10~i^ cm. sec.~i dyne"^ -Dissymmetry 

 constant 2.78. Molecular weight 26 X 

 10". Particle size estimated to be 433 

 by 9.8 millimicrons, 43.9 times as long as 

 wide. Isoelectric point near pH 4. 

 Stable between pH 4 and pH 9.5. Con- 

 centrated solutions are spontaneously 

 birefringent. Dilute solutions show 



