6 BULLETIN 562, U. S. DEPARTMENT OF AGRICULTURE. 



Cuban, Turkish, and Sumatra tobaccos. Practically all domestic 

 types of tobacco were represented, but none showed a high degree 

 of resistance, TO to 90 per cent of the plants succumbing to the dis- 

 ease. Work with local flue-cured varieties has been continued up 

 to the present. Each year seed from plants which had survived in 

 the previous year's test has been planted, but no progress has been 

 made in developing a resistant strain. In the tests with foreign 

 varieties, including varieties from South America, Mexico, Cuba, 

 Sumatra, Turkey in Asia, Turkey in Europe, Italy, and Russia, it 

 was found that the Sumatra, a Turkish variety from Cavala in Mace- 

 donia, and a variety from Italy designated by Comes as Nicotiana 

 tabacum fruticosa showed considerable resistance to the wilt, and 

 selections from these were grown for several years. The Sumatra 

 and Turkish were crossed also with the local flue-cured type in an 

 effort to develop a highly resistant commercial variety. The most 

 striking feature of these experiments was the fact that the resistance 

 of the above-mentioned varieties depends largely on seasonal con- 

 ditions. Under conditions tending to produce slow growth, par- 

 ticularly dry weather, these varieties have shown a relatively high 

 degree of resistance, and in some years less than 10 per cent of the 

 plants died. Under conditions favoring rapid growth, especially 

 periods of wet weather, on the other hand, nearly all plants died. 

 No highly resistant types were obtained from any of the hybrids. 



A type of imported Cuban tobacco showed a resistance of 12 per 

 cent in 1911, 96 per cent in 1912, 78 per cent in 1913, and 46 per 

 cent in 1914, variations apparently due to seasonal conditions. Tak- 

 ing the tests as a whole, the Sumatra variety has shown the highest 

 resistance of all varieties. In this connection it should be stated 

 that Honing (2), working along the same lines in Sumatra, tested 

 varieties from various parts of the world, including 30 or more 

 American varieties, and found none more resistant than the native 

 Deli (Sumatra). The Halladay, a type developed in Connecticut 

 from a cross of Sumatra on Connecticut Havana, also has shown con- 

 siderable resistance in the present tests. 



Since the investigations failed to show sufficient resistance in any 

 of the varieties of tobacco belonging to the ordinary species grown 

 in America {Xicotimia tabacum), it seemed worth while to test 

 various other species, wild and cultivated. Tests were made with 

 several varieties of Nicotiana rustica from Italy, Russia, China, and 

 elsewhere, but all of these were found to be very susceptible. Other 

 species tried were longiflora, glauca, glutinosa, latngsdorfii, silvesiris, 

 affinis, and sanderae (hybrid), none of which showed higher resist- 

 ance than the ordinarv tobaccos. 



