N. I. Vavilov 59 



Fungal Reactions of Species of Wheat and their Genetic 

 Relationships. 



Now turning again to the general characteristics of the species of 

 wheat and oats in relation to narrowly specialized fungi, we shall see 

 that they have not only significance for plant-breeders, but deserve 

 serious attention on the part of students of genetics. As is known, 

 the genetic relations of cereals are far from being solved. Every new 

 criterion for the understanding of this problem is useful and valuable. 

 It is especially so because the usual criterion of degree of affinity — 

 sterility or vice versa — fertility of hybrids cannot always be used in 

 the group of cereals. For instance, the seven species of wheat are 

 so nearly allied that they give fertile hybrids. To understand the 

 genealogy of this group, botanically restricted but nevertheless repre- 

 sented by an immense number of independent forms, we must employ 

 finer methods. 



On looking into the characteristics of eight species of wheat in relation 

 to rusts and mildew, we cannot help being struck by their complete 

 agreement with several genetic conceptions which are more or less 

 established concerning their relationship. 



eight species of wheat, according to our observations in Russia, may be slightly attacked 

 by ergot, especially when wheats are cultivated side by side with rye. 



In his second paper on " Studies in the Inheritance of Disease-resistance," Journ. of 

 Agr. Sc, Vol. iv, Part 4, 1912, Prof. Biffen communicates a curious fact of the occurrence 

 in the F„ hybrids of Eivet (Tr. tur<i'uium L.) with several varieties of Tr. rulyare of some 

 plants which were attacked by ergot, although the parent forms had never been seen 

 to be attacked by this fungus. Prof. Bift'en explains this fact, as a result of combination 

 of two Mendelian factors of susceptibility to ergot, which are separated in their parents, 

 and in separate form cannot produce the susceptibility of wheat to ergot. 



The apparent contradiction of this case of distinct difference in susceptibility to ergot 

 of wheat plants to the above-mentioned general statement, however, is easily removed by 

 a simpler and more probable interpretation of this fact, than that given by Prof. Biffen. 



Already in 1891 Prof. Rimpau, in his Kreusungsprodukte landwirtschaftlicJier Kultiir- 

 pflanzen, pp. 11 — 12, had noticed the fact that in the same crossing of Rivet and Tr. 

 vulgare there appear in F„ hybrids some slerile ■plants. The sterile plants of cereals as 

 is known flower usually with open glumes, remain many days in this state, and commonly 

 are badly attacked by ergot. (See E. Tschermak, "Die Bliih- und Fruchtbarkeitsverhalt- 

 nisse bei Roggen und Gerste und das Auftreten von Mutterkorn," Fiihlings landwlrtsclmft. 

 Zeitung, Lx. 1906.) The sterile plants of F^ of the hybrid of wheat and rye, for example, 

 are severely ergotized. 



Evidently the same fact of appearance of sterile plants was observed in the experi- 

 ments of Prof. Biffen at Cambridge, and, as might be suppo.sed, these sterile plants were 

 attacked by ergot. 



