BREEDING SNAPDRAGONS FOR RESISTANCE TO RUST 



By Harold E. W hite. 

 Assistant Research Professor of Floriculture 



Geographical Distribution and Economic Importance of Rust Disease 



Rust disease, Puccinia antirrhini Diet. & Holw., of snapdragons, Antirrhhiimi 

 maJHS, was localized in its distribution to the West Coast area of theUnited States 

 prior to 1913 but eventually spread eastward across the country. Specimens of 

 the disease, according to Peltier (10), were recorded by Dr. J. C. Arthur of Pur- 

 due University as early as 1879; and Blasdale (1) in 1895 reported it as being 

 common on snapdragons in gardens around San Francisco, California. In 1913, 

 a severe epidemic of the disease was reported in greenhouses in Illinois by Peltier 

 (10) ; and by 1915 the occurrence of rust was noted throughout most of theMiddle 

 Western States and as far east as Massachusetts. By 1931 the disease was re- 

 ported in France (7); in 1933 in England; 1934, in Germany and Denmark; 1935, 

 in Italy, Switzerland, Hungary, Austria, and Sweden; 1936, in Poland, Latvia, 

 Rumania, Egypt, and Morocco; and finally, by 1937 it was reported from Soviet 

 Russia at Leningrad, Odessa, Veronezh, and the Caucasus. 



The rust disease of snapdragons, presumably, was introduced into Europe 

 from North America; at least, the British reports credit the disease as having 

 come from the United States. What basis the English have for their contention 

 is not known, but since the disease is not transmitted by seeds the probable mode 

 of introduction may have been on imported plant materials. 



Snapdragons were not widely cultivated under glass as a cut-flower crop in 

 the early 190O's nor were they as popular in gardens as they are at present. At 

 that time, varieties were limited, and wider distribution to the trade was restricted 

 because they were propagated vegetatively by cuttings. The passing on of varie- 

 ties of snapdragons in the form of rooted plant material by interstate shipments 

 probably was one means of rapidly disseminating the rust disease. However, it 

 is also quite possible that the disease may have been present for many years in 

 the Middle Western and Eastern States but was brought to the attention of 

 pathologists only when it became defin'tely destructive. In those days, and 

 occasionally even now, the loss of a crop was ascribed by growers to an all-inclu- 

 sive cause such as "blight," which frequently included fungus diseases and poor 

 cultural practices. 



The destructiveness of snapdragon rust in the greenhouse resulted in a change 

 from the customary method of propagation by cuttings to the present practice of 

 using seed. The latter method permitted the grower to get a start with rust-free 

 plants provided he gave careful attention to cultural conditions such as tempera- 

 ture and humidity, and applied fungicides to protect the young plants. Intro- 

 duction of seed propagation methods made for a more rapid and wider distribu- 

 tion of snapdragons as well as encouraging the production of a better choice of 

 varieties. In the greenhouse, rust disease can be very destructive, particularly if 

 careful cleanup and control practices are not followed. However, under garden 

 and field conditions of culture, snapdragon rust is also destructive, not only to 

 the decorative value of the flowers but to the seed production capacity of the 

 plants as well. All the snapdragon seed used for production of ornamental garden 

 material is grown on a large acreage basis in California. According to Emsweller 

 and Jones (4), because of rust disease the production of seed is more often a matter 

 of a few pounds per acre than the possible 75 pounds per acre, which is rarely 

 attained. 



