HYBRIDISATION AND WHEAT HYBRIDS 377 



cross Bobs x Wol Koren the hybrid F l proved to be considerably more 

 susceptible than the susceptible Wol Koren parent. 



Hayes, Parker, and Kurtzweil also investigated the susceptibility to 

 P. graminis of hybrids of wheats belonging to the races T. vulgare, T. 

 durum, and T. dicoccum. 



The susceptible vulgare wheats used were Preston, Marquis, and 

 Pioneer, the durums Kubanka and three other resistant forms, in addition 

 to a form of T. dicoccum (White Spring Emmer), being used as the second 

 parents. 



In the Fj of the vulgare x durum crosses susceptibility was dominant, 

 and in some of the F 2 and F 3 generations transgressive segregation occurred, 

 a few plants being more susceptible or more resistant than either of the 

 grandparents. 



In the vulgare x dicoccum hybrids susceptibility was recessive. There 

 was also evidence of linkage of the durum and dicoccum characters and 

 resistance to rust. 



I. HYBRIDS OF THE WILD WHEATS Triticum aegilopoides AND Triticum 

 dicoccoides WITH EACH OTHER AND WITH SPECIES OF Aegilops AND RYE 



1. T. aegilopoides x T. dicoccoides. The wild wheats T. aegilopoides and 

 T. dicoccoides are very frequently found growing near each other in various 

 parts of Syria and Palestine, and transitional forms between these were 

 observed by Aaronsohn. Whether these intermediates were the products 

 of natural hybridisation or varietal forms of the wild wheats was not 

 determined. 



From a study of the glume characters Schulz considers that some of 

 the specimens sent by Aaronsohn to Germany as T. dicoccoides were hybrids 

 of T. aegilopoides, var. Thaoudar, and T. dicoccoides. 



I am inclined also to the view that some of the wild wheats which I 

 received from the eastern side of Mount Hermon were hybrids, the empty 

 glumes having the characteristic lateral tooth of T. aegilopoides, while the 

 size and general features of the ear as well as the vegetative characters of 

 the plants were those of T. dicoccoides. 



2. T. dicoccoides x Aegilops ovata. Cook refers to the discovery in 

 Syria of a supposed hybrid between the wild dicoccoides and Aegilops 

 ovata, the plant exhibiting intermediate characters of ear, rachis, and 

 awns. Aaronsohn considered it a hybrid between the two species, and the 

 figure of the spikelets given by Cook is suggestive of the cross. 



Tschermak, in his papers on " Rare Cereal Hybrids," states that he 

 crossed T. dicoccoides with Aegilops ovata and also with Aegilops cylindrica, 

 using the wild wheat as the maternal parent. The hybrids were sterile. 



3. T. dicoccoides x Secale cereale. Tschermak states that Jesenko 

 crossed the wild T. dicoccoides with rye and found the hybrid sterile. 



