4 CIRCULAR 72 7, U. S. DEPARTMENT OF AGRICULTURE 



For the purpose of obtaining wilt resistance, an extensive collection 

 of tobacco varieties was made from Mexico, Central America, and 

 South America. Preliminary tests conducted in the greenhouse with 

 1,034 lots eliminated all but 129. These were tested on field soil so 

 badly infected by wilt that standard varieties were usually killed 100 

 percent by midsummer. One South American lot was found with a 

 high degree of resistance, and, fortunately, its growth characteristics 

 were similar in many respects to those of flue-cured tobacco. This 

 collection, T. I. 448A, 3 obtained from Colombia, was first tested in 

 the field in 1938. It showed consistently a high degree of wilt resist- 

 ance in succeeding years, including 1939 and 1943, seasons of excep- 

 tional wilt severity. The cured leaf of T. I. 448 A was of fair color 

 and had no undesirable aroma, but otherwise its quality was poor. 

 Further information on this strain and other breeding stocks was 

 given in an earlier publication. 4 



BREEDING WORK 



To develop wilt-resistant strains of good quality, T. I. 448A was 

 crossed with 7 flue-cured varieties. Most of the F : hybrids were 

 grown in winter in the greenhouse, and seedlings of the F 2 were planted 

 in spring for field tests. More than 5,200 plants of the F 2 were grown in 

 1940 and 1941 on wilt-infected field soil, and resistant selections were 

 self -pollinated. The progeny of 166 F 2 selections were tested in the F 3 . 

 One line, from T. I. 448 A X 400, 5 was of outstanding promise in both 

 wilt resistance and curing trials. Selections of this line made in the 

 F 3 and F 4 gave several F 5 lines that were highly resistant to wilt and 

 produced tobacco of good quality. The most promising selection 

 was distributed for increase to certified seed growers under the name 

 Oxford 26. 



Breeding trials are being continued with hybrids from the original 

 cross of T. I. 448 A X 400 and considerable material from the first 

 backcross to the flue-cured type (T. I. 448A X 400 X 401). Improved 

 wilt-resistant strains similar to standard varieties in all growth 

 characteristics are clearly in prospect. The need for a flue-cured 

 strain with resistance to wilt was so acute, however, that it was 

 necessary to make Oxford 26 available for immediate use. 



DESCRIPTION OF OXFORD 26 



The variety Oxford 26 is highly resistant to bacterial wilt (fig. 3). 

 As many as 20 percent of the plants may show wilt early in the season, 

 but nearly all recover and make normal growth except for one or two 

 stunted leaves. Under disease conditions, where less than 1 percent 

 of standard varieties remained alive, survival of Oxford 26 was 95 to 

 100 percent. 



The plant has a small stalk, flowers 3 to 7 days later than standard 

 varieties, appears to withstand drought better, and has a vigorous 



3 Refers to accession number, Division of Tobacco Investigations, Bureau of Plant Industry, Soils, and 

 Agricultural Engineering. 



i See footnote 2, p. 2. 



5 Moss, E. G., and Bullock, J. F. two new varieties of flue-cured tobacco, 400 and 401. N. C. 

 Agr. Expt. Sta. Bui. 337, 8 pp., illus. 1942. 



