12 Robert S. Kirby 



planted cereals, apparently because of their shorter growing season, 

 usually escape the disease, and therefore it is unlikely that they will ever 

 suffer an appreciable loss from it. 



VARIETAL SUSCEPTIBILITY IN WHEATS 



No variety of wheat has been found which is immune to take-all, although 

 there seem to be marked varietal differences in susceptibility. Pridham 

 (1919) found on testing eighty-one varieties that the percentage of badly 

 infected plants varied from 1 to 33.7 per cent. Previous workers agree 

 that red wheats are more resistant than white wheats. In the Union of 

 South Africa (Anonymous, 1922 a), take-all is said to attack the hard 

 durum types mofe than the soft vulgar -e wheats. Pridham (1919) reports 

 early-maturing wheats to be the most nearly free from the disease in 

 Australia, while in England (Anonymous, 1913) and in New Zealand 

 (Waters, 1920 a) early or short-season varieties are held to be the most 

 susceptible. Spring wheats are reported as escaping the disease (Foex, 

 1919 b). 



In a previous paper (Kirby, 1922) the writer reported tests with sixty- 

 two varieties of wheat for relative susceptibility under greenhouse con- 

 ditions. These tests showed that common, or vulgar e, wheats exhibit 

 about the same degree of susceptibility whether they are of spring or 

 winter habit, soft or hard, and red or white. Of the various kinds of 

 wheat the durum and poulard wheats were all heavily infected, and these 

 are probably the most susceptible varieties. The club, emmer, and 

 common wheats varied in their degree of infection from heavy to moderate, 

 and were more resistant than the durum and poulard wheats. The 

 Polish and spelt wheats were only moderately infected, and these are 

 apparently more resistant than the common type. Einkorn seems to 

 be the most resistant, since it was only slightly infected. 



In order to determine the relative susceptibility of a few winter wheats 

 grown in New York, ten varieties were planted in triplicate plots in the 

 fall of 1921. In the bottom of each drill row in one of the three plots, 

 an equal amount of pure culture of the take-all organism growing on steril- 

 ized wheat kernels was placed at the time of planting. At the same 

 time an equal amount of take-all-infested soil and infested parts of 

 wheat plants, respectively, were added to each row in the other two plots. 



In July, 1922, when the wheat had matured, the plants of each variety 

 were dug and data were taken on the percentage of infected and of healthy 

 plants, and the degree of stunting. Then, for the healthy plants and for 

 each of the three degrees of stunting, data were taken on the average 

 number of heads per plant and the average weight and number of seeds 

 produced per head. The average yield per plant was obtained by multi- 

 plying the average number of culms by the average weight of seeds pro- 

 duced per head. By this method it was hoped that reduction in yield 



