MASS. EXPERIMENT STATION BULLETIN 432 



ako tested under severe black root rot promoting conditions on the Experiment 

 Station farm. The first two of these tests were conducted for two and three 

 years respectively; the other test was continued over a longer period as suitable 

 plants were found. 



If specimens that possessed satisfactory resistance to black root rot could 

 have been found in the strains of regular Havana Seed tested, it would probably 

 have provided a convenient solution to the problem, because regular Havana 

 Seed is already acceptable to cigar manufacturers for type and quality. Un- 

 fortunately, although the strains tested differed somewhat in degree of resistance, 

 none of them possessed sufficient resistance to make them suitable for growing 

 under moderate to severe black root rot promoting conditions. It seemed doubt- 

 ful whether more extensive testing of regular Havana Seed would serve any useful 

 purpose. Therefore, controlled breeding procedures were used in an effort to 

 produce new strains of Havana Seed which would possess high resistance to the 

 disease in combination with acceptable type and quality, when grown under 

 Connecticut Valle\- conditions. 



The production of new strains by means of controlled breeding methods in- 

 volved several necessary phrases of work: 



1 . The first phase was the choice of parental stocks that between them possessed 

 tke desired properties, and the crossing of selected parental plants. 



Obvioush-, since the new strains had to be of true Havana Seed type, it was 

 necessary that at least one parent be of that type. Actually, for a large part of 

 the work, both parents were chosen from Havana Seed stock — one from a 

 strain highly resistant to black root rot, the other from a strain highly acceptable 

 in type and quality. 



The hybridizing work consisted of making crosses and reciprocal crosses of the 

 parental stock plants and back-crossing first generation plants from these crosses 

 to their regular Havana Seed parent. The reason for making both crosses and 

 reciprocal crosses was to increase the chances of recombining in single individuals 

 the desired characters possessed by the two parents. The back-crossing was 

 done to improve type and quality in the progeny. The technique of crossing 

 used was similar in all essential points to that used generally to breed new strains 

 of tobacco under controlled conditions. Garner, Allard and Clayton (5) de- 

 scribe in considerable detail the usual technique for hybridizing tobacco. Those 

 interested in these details are referred to their article. 



2. The second phase was small-plot testing of the progeny of the various 

 crosses, and the selection of plants that seemed to be suitable for further use in 

 the project. They were first tested thoroughly under severe black root rot pro- 

 moting conditions, to make possible the selection of plants highly resistant to 

 the disease and also capable of producing satisfactory \-ields of acceptable to- 

 bacco under these adverse conditions. 



The controls were Havana 142 and acceptable strains of regular Havana Seed. 

 Havana 142, known to be satisfactorily resistant to black root rot under Con- 

 necticut Valley conditions, was used as a standard of resistance to the disease. 

 Highly susceptible strains of regular Havana Seed were used as indicators of the 

 severity of black root rot attack that was capable of developing under the en- 

 vironmental conditions that prevailed each year of the test. By comparing the 

 severity of infection of black root rot, and also the type, quality, and yielding 



