Sept. I, 1920 



Genetics of Rust Resistance 



535 



near-common, and common are 3.30, 3.77, 4.08, 3.94, and 4.40, respec- 

 tively. A correlation coefficient of -f-0.244 ±0.028 for density and head 

 characters was obtained. 



Table VI. — F^ Marquis X lumillo {CI 1^216) and Marquis X Kuhanka {CI 2094)^ 

 [R=resistant to stemrust. S=susceptible to stemrust] 



' The coefficient of correlation between density of head and classes for durum, near-durum, intermediate, 

 near-common, and common is -l-o.244io.028. 



F2 generations in which the resistant durum parent was the female 

 are given in Table VII, a total of 632 plants being classified on the basis 

 of the Fg breeding test. Of these Fj plants 100 bred true to durum 

 habit, 47 resembled common, while 3 were emmerlike. Sixteen out of 

 100 durumlike plants were resistant, while only 2 out of 47 classified 

 as common were resistant. Of the three emmerlike plants, one was 

 susceptible and the other two were resistant. Here, again, as with the 

 reciprocal cross, there is an indication of linkage between common 

 wheat head characters and susceptibility to stemrust. One intermediate 

 susceptible F2 plant was grown in the F3 generation, and several plants 

 were obtained with common head characters. One of these was very 

 resistant and vigorous (Pi. 99). 



The average densities of the durum, near-durum, intermediate, near- 

 common, and common segregates were 3.76, 3.53, 4.06, 4.38, and 4.60, 

 respectively, although both durum and common wheats were found in 

 the extreme dense and lax groups. The coefficient of correlation be- 

 tween density and head type was H-o.33o ± 0.024. 



In order to confirm field observations, a study was made in the green- 

 house of the more resistant and susceptible durum, common, and emmer 

 segregates obtained from the durum-common crosses. For head char- 

 acters of types studied see Plate loi. Seedlings of F3 plants were 



