DEVELOPMENT OF WILT-RESISTANT TOMATOES. 9 



its parent variety in degree of resistance transmitted. In another 

 similar case, 30 apparently resistant plants of Earliana and 118 of 

 Bonny Best, the only wilt-free plants found in two fields of 6 acres 

 each, failed to transmit more than average resistance for their re- 

 spective varieties. 



Selections from varieties that transmit resistance to their individual 

 plants somewhat diversely, such as the Stone, Greater Baltimore, and 

 Merveille des Marches, not infrequently excel their parents in the 

 transmission of wilt resistance. 



BEHAVIOR OF RESISTANT VARIETIES. 



Although none of the varieties of wilt-resistant tomatoes devel- 

 oped by the writer are immune to wilt, they are highly resistant to 

 it. In repeated tests on heavily wilt-infested soils they have main- 

 tained a high degree of resistance. A more important possession, 

 however, is their high yield and the superior quality of their fruit 

 when grown on wilt-infested soil. As they have been selected from 

 the best commercial varieties, primarily for yield and quality of 

 fruit and secondarily for wilt resistance, they possess the high yield- 

 ing power of the parent varieties in addition to resistance and are 

 therefore equal to them on wilt-free soil and far superior to them 

 on wilt-infested soil. The behavior of two of these varieties is 

 illustrated in Plates VI and VII. Plate VI, figure 1, shows the 

 Brimmer, a very popular variety in the South, while figure 2 is the 

 Norton. They were grown in opposite ends of the same rows near 

 Richmond, Va. The Brimmer was absolutely destroyed by wilt, 

 while the Norton produced an excellent crop of fruit.. In Plate VII, 

 row 1 is the Greater Baltimore and row 2 the Arlington, a selec- 

 tion from" the Greater Baltimore. Although planted at the same 

 time and given identical cultural conditions, the Greater Baltimore 

 was completely destroyed, while the Arlington was apparently free 

 from wilt and produced a good crop of fruit. 



EFFECT OF CONTINUOUS SELECTION. 



A tomato plant usually transmits to its immediate offspring as 

 much wilt resistance as can be developed from it by subsequent 

 selection. In a very small percentage of plants tested for wilt re- 

 sistance by the progeny-row method, increased resistance has been 

 obtained in the second selection, but no higher resistance has resulted 

 from a continuation of this process. As crossing occasionally occurs 

 in the tomato, the hybrid condition resulting from it may account 

 for the exceptions noted. 



The effect of continuous selection from two wilt-resistant varieties 

 developed at Washington, D. G, and from one developed in Louisiana 

 are shown in Table 2. The tests were made in rows of 16 plants 

 68713°— 22 2. 



