532 



Journal of Agricultural Research 



Vol. XIX. No. II 



The fact that natural crossing often occurs in species crosses shows 

 the necessity for caution in analyzing data; and unless unusual methods 

 are employed to protect parent plants, the ancestry of the progeny can 

 not be known with certainty. 



EXPERIMENTS IN INHERITANCE OF RUST RESISTANCE 



The 1 918 data are considered most reliable in drawing conclusions 

 on the inheritance of rust resistance. This is due first to the fact that 

 all barberry bushes were removed from the immediate vicinity of the 

 rust plot early in the spring of 191 8, and second to the fact that the 

 epidemic was induced by hand spraying with inoculations of rust spores 

 from a known greenhouse culture of Piiccinia graniinis tritici} 



RUST INFECTION OF THE Fj GENERATION COMPARED WITH THAT OF 



PARENTS 



The epidemic in the rust plots was satisfactory, although there was 

 but little rust in other wheat fields on University Farm. 



A considerable number of F^ crosses between resistant durum and 

 emmer wheats and Marquis, Preston, and Pioneer were grown in the 

 rust plot. The percentages of stemrust infection on the Fj and parent 

 sorts are given in Table V. 



Table V. — Rust notes on parental -varieties and Fi crosses between resistant and sus- 

 ceptible wheats, igi8 



Variety or cross. 



Marquis 



Preston 



Pioneer 



Acme 



D-4 



Kubanka (C I 2094) 



Iumillo(CI 1736) 



Emmer (Minn. 1165) 



MarquisXIumillo (C I 1736). . 

 Marquis X Kubanka (C I 2094). 



Percentage 

 of stemrust. 



40 to 70 



70 

 40 

 10 

 10 

 20 



IS 



o 



40 



40 to 70 



Cross. 



MarquisXAcme (C I 5284) 

 PrestonXAcme (C I 5284) 



AcmeXMarquis 



D-4X Pioneer 



Acme X Preston 



Marquis X emmer 



Emmer X Marquis 



Emmer X Preston 



PrestonXemmer , . 



Percentage 

 of stemrust. 



70 

 70 

 70 

 40 

 70 

 10 

 10 

 15 

 15 



Four durum varieties were tested. The highest percentage of rust 

 infection was 20 on Kubanka (C I 2094), while there was only 10 per 

 cent on D-4 and Acme. On all of these durum varieties the uredinia 

 were smaller than on the common wheats, such as Marquis and Preston, 

 which were very susceptible. Pioneer was also susceptible, but since it 

 matures earlier than either Marquis or Preston, the percentage of infec- 

 tion was lower. 



1 The details of production of the epidemic were directed by J. G. I,each, a graduate student assistant 

 of the Pathology Division. Mr. Leach had previous experience in this work at the Tennessee Agricultural 

 Experiment Station. 



