68 James G. Horsfall 



CLOVER MOSAIC 



Mosaic of clovers is a common virus disease to which little attention 

 as yet has been given by plant pathologists. It undoubtedly deserves 

 careful investigation. 



Suscepts 



The disease occurs commonly in New York on red, alsike, white, and 

 sweet clovers. It has been reported elsewhere on other suscepts: by Orton 

 on Trifolium incarnatum (Fromme, 1921:171); by Mains (1928:363) on 

 T. arvense, T. reswpinatum; by Elliott (1921:148) on Medicago falcata and 

 Vicia faba; and by Dickson (1922 a: 42) on Medicago lupulina. Boning 

 (1927) was able to transmit the disease to beans. It is interesting in this 

 connection that Elliott (1921) was unable to get infection on white clover 

 or alfalfa in Arkansas, whereas the virus from sweet clover and red clover 

 easily cross-infected. Dickson (1922 a: 42) had no success in transmitting 

 red-clover mosaic to sweet clover in Canada, but white clover readily 

 became diseased with the same inoculum. Dickson (1922 b:88) says, " In 

 one instance there appeared to be a successful inoculation of Medicago 

 sativa by means of aphids." In one trial also he succeeded in inoculating 

 Trifolium hybridum with juice from Pisum sativum. 



Mains says (Kirby and Archer 1927 : 199) that no varieties of clover are 

 immune to mosaic in Indiana. 



The disease 

 History and range 



The earliest reference to a clover mosaic which the writer has found 

 is that by Clinton (1915:360) who said, " Not infrequently the common 

 species of clover show yellowish-green irregular areas." McLarty (1920: 

 501) asserts that H. T. Giissow saw sweet-clover mosaic as early as 

 1912 at St. Catherines, Ontario. Several papers appeared in 1920 and 

 1921 reporting independent observations on the disease (McLarty, 1920; 

 Orton: Fromme, 1921:171; and Elliott, 1921). Dickson published some 

 observations on plants affected and on the symptomatology of the disease 

 in 1922. 



Clover mosaic has been reported from Ontario (McLarty, 1920:501) 

 from Quebec (Dickson, 1922 b); from Germany (Boning, 1927); and in 

 the United States from New York west to Montana and south to Louisiana. 



Eco n om ic importance 



Clover mosaic apparently is not a serious disease in this State, although 

 it occurs in most fields in small quantities. In isolated fields it may be 

 really serious in years when plant lice are numerous. The loss comes from 

 the stunting of plants and the reduction in the amount of seed produced 



