86 



BREEDING CROP PLANTS 



crosses between resistant emmers and durunis with susceptible 

 Marquis. A single rust form was used in making the artificial 

 epidemic. The durum-Marquis crosses were as susceptible as 

 Marquis in FI. Using white spring emmer as the resistant parent, 

 the FI was resistant, though not so resistant as the emmer parent. 

 Segregation for resistance and botanical characters was studied 

 in later generations. Some linkage in transmission was apparent, 

 for while it was quite easy to obtain resistant emmer or durum 



FIG. 20. Resistance of parents and crosses to a strain of stem rust. From 

 left to right: Culms of resistant Durum wheat; FI of Durum X Marquis, 

 susceptible; Marquis, susceptible; F\ of Emmer, Minn. 1165 X Marquis, as 

 resistant as the Durum varieties; Emmer, Minn. 1165, a very resistant variety. 



plants it was much more difficult to obtain resistant common 

 wheats. In an examination of more than 20,000 F$ plants, a few 

 with vulgar e spike characters and resistance were obtained. 

 Resistant plants resembling emmer, durum, and common 

 wheats were also proved resistant by greenhouse inoculation 

 studies. 



Gaines (1918, 1920) has studied the inheritance of resistance 

 of wheats to bunt (Tilletia tritici). It is estimated that this 



