12 CIRCULAR 692, U. S. DEPARTMENT OF AGRICULTURE 
susceptible to wilt were not associated with the variations in extent of wilt on 
tobacco grown the next year. 
GENETIC ReEsIsTANCE COMBINED WitTH ROTATION 
Strains of tobacco now in stock have slight, moderate, and high levels of resist- 
ance to wilt (J). Strain 448A is especially valuable for breeding, because of its 
resistance to bacterial wilt and mosaic. Hybrids of this strain crossed on flue- 
cured varieties have shown a high degree of wilt resistance and considerable 
resemblance to the flue-cured type. In considering the use of resistant strains 
in commercial tobacco production, the question arose as to whether a rotation 
could be combined with genetic resistance to obtain a still higher degree of wilt 
control. To study this phase of the problem, 24 plots 200 feet long were set up on 
uniformly infested soil. In 1939 tobacco was grown on half of each plot and corn 
on the other half. In 1940 six strains of tobacco were tested for resistance in eight 
randomized blocks, four on soil planted in tobacco in 1939 and four planted in 
corn in 1939. The relative resistance of the strains used is shown in counts made 
August 1 (table 5). 
TABLE 5.—FEffect of retation on degree of wilt in resistant strains of tobacco 
Wilt on tobacco 
grown after— 
Strain __ Difference 
Tobacco Corn 
Percent Percent , Percent 
(ashi) Se ee ar = a a eee a etc el ple. meer el eo 193. 25 | 1 63. 50 229.75 
ST) DVIS (DGG Lee Sa ea pg RES 75. 50 48.25 2 27.25 
A Tyee (ea! Wik Weert eae ire hice thee ren erates Cee ah enka oa) 37. 00 | SATS 13. 25 
DLW AH 0 eerste era ee neh pepe ar Slee NS oer aye ee age ele GL 28.00 | 22.00 6. 00 
A es Ip. VB ee aero Cereal e  N es See ee eS 23.25 | 12.75 210. 0 
YS rene an oe Mi ae cer a a Ra ge Sn eae Ag Se 16. 75 | 8.75 8. 00 
1 Mean of 4 replicates; approximately 50 plants per plot. 
? Significant at the 5-percent level for 3 degrees of freedom. 
Cash, one of the standard flue-cured varieties, was the susceptible control. 
Davis Special was slightly resistant, T. I. 79A and Xanthi were moderately 
resistant, and T. I. 448A and 79X highly resistant. The differences between 
rotations within each strain are also shown in table 5. Cash had 29 percent less 
wilt when grown after corn than when grown after tobacco. The slightly resistant 
strain Davis Special showed a similar reduction in degree of wilt when grown in 
the corn rotation. In the other strains, however, the difference between rotations 
was considerably smaller, showing that little increased control was obtained from 
the use of moderately or highly resistant strains in combination with the corn 
rotation. 
UreA TREATMENT COMBINED WitrH ROTATION 
In the continuation of studies on soil treatment by the North Carolina station 
(4), Poole and the writer found heavy rates of nitrogenous materials to be of 
promise. In further tests, 420 pounds of nitrogen an acre applied as urea, 
ammonium carbonate, or ammonium sulfate gave wilt control when broadcast 
on the soil surface and mixed into the cultivated layer with spade, moldboard 
plow, or disk. Urea appeared of more promise for commercial use, and soil 
treatment with this compound controlled wilt on seven other host plants, includ- 
ing tomato, Irish potato, and eggplant. 
Application was more effective in spring than in fall, especially with rates of 
urea supplying 210 and 105 pounds of nitrogen an acre. Transplants set 6 weeks 
after treatment in spring were stunted during the early part of the growing season, 
but following treatment in fall, plant injury of consequence was not experienced. 
Tobacco grown in the summer after treatment was worthless commercially 
because of the excessive nitrogen applied. The leaf did not ripen even though 
treatment was made the previous fall to promote leaching and the erop fertilized 
with an 0-10-10 mixture at the rate of 1,000 pounds an acre in an attempt to 
rebalance the nutrient supply. 
