2 4 



Breeding of Wheat. 



the rust attack has been at its worst they have shown only the 

 merest traces of infection. Such immune varieties were at once 

 crossed both with moderately and with extremely susceptible 

 varieties to determine whether the power of resisting- disease 

 would prove a unit character. In each case the hybrid plant 

 proved susceptible to yellow rust, whilst its offspring consisted of 

 immune and susceptible forms in the proportion of one of the 

 former to three of the latter. In the many cases examined the 

 segregation has proved to be exceedingly sharp. The property 

 of resisting the attacks of yellow rust is thus shown to be a 

 Mendelian recessive, and consequently all extracted immunes 

 should breed true to this feature in succeeding generations. This 

 point has now been tested many times, with concordant results 

 in all cases. Further, the experiments have shown that immunity 

 is independent of any recognisable morphological characters. 

 Thus in the case of yellow rust there appears to be no valid reason 

 why the plant breeder should not mitigate the evils of its attacks 

 by using this knowledge as a basis for the production of resistant 

 varieties. The attempts already made seem to show conclusively 

 that this is practical. One example must suffice. From a cross 

 between Square Head's Master and a resistant variety found in 

 Russian Ghirka wheat two very promising wheats, one immune 

 and one susceptible, were isolated and grown on for comparison. 

 In 1909, a moderately bad rust year, three-acre plots of these 

 varieties were grown alongside one another. The susceptible 

 variety gave one of the most striking plots of wheat on the 

 experimental farm ; the immune variety also grew into a good 

 crop, though farmers visiting the station almost invariably pre 

 ferred the former, in spite of its rustiness. At thrashing time, 

 however, the effects of the attack became obvious, as the sus- 

 ceptible variety only yielded some forty-two bushels of grain per 

 acre, as compared with fifty-four bushels per acre from the immune 

 variety. The grain of the former was also so shrivelled that it 

 was only fit for chicken food, whilst from the latter less than a 

 half per cent, could be screened when dressing it for seed. 



If the attacks of yellow rust can be controlled in this manner 

 it is reasonable to suppose that the still more serious black rust 

 (Puccinia graminis) can also be brought under control. At the 

 present time the most that can be said is that some evidence 

 pointing in this direction has been obtained. The problem will, 

 however, have to be solved elsewhere, for even with plantations 

 of the alternative host, the Barberry, in the vicinity of the trial 

 plots, we cannot count on a yearly epidemic of this rust to test 

 the varieties thoroughly. 



