JOIMALOFAGBiaiTllRALffiSEARCH 



Vol. XXII Washington, D. C, October 8, 192 1 No. 2 



COMPARATIVE VIGOR OF F^ WHEAT CROSSES AND 

 THEIR PARENTS ' 



By Fred Griffee ^ 



Instructor in Plant Breeding, Division of Agronomy and Farm Management, Depart- 

 ment of Agriculture, University of Minnesota 



The comparative vigor of Fj crosses and their parents is a subject of 

 much interest to the plant breeder. In crops where the technic of cross- 

 ing is comparatively easy, the increase in vigor obtained in the F^ cross 

 often more than pays for the additional trouble of producing the hybrid 

 seed. In self-fertilized crops like the small grains where considerable 

 labor is involved in making artificial crosses, it is apparent that F^ crosses 

 can not be used commercially as a means of increasing crop yields. The 

 suggestion, however, has been made by Anderson (ly that the added 

 vigor of the heterozygous condition might be utilized in small grains by 

 making a large number of crosses between strains which, when crossed, 

 show a considerable increase in yield. Produce from Fj and F3 progeny 

 could be used for seeding the general field, and the crosses could be 

 repeated each year in order to keep up the supply of seed. 



Several theories have been advanced to explain the phenomenon of 

 heterosis. The discovery of genetic linkage has led to the development 

 of an adequate Mendelian explanation of the vigor so often obtained in 

 Fi crosses. An excellent review of the development of this theory is 

 given by East and Jones (<?). The theory explains the increase in vigor 

 shown in the first hybrid generation as being due to the meeting in the 

 zygote of dominant or partially dominant growth factors some of which 

 are contributed by each parent. Linkage is given as the reason why all 

 dominant factors can not be combined in a homozygous individual. Ac- 

 cording to this hypothesis the maximum number of favorable growth 

 factors can be obtained only in the heterozygous condition. 



In producing new varieties by crossing, forms may be obtained in the F3 

 generation which appear homozygous for botanical and agronomic char- 



• Published with the approval of the Director as Paper No. 259 of the Journal Series of the Minnesota 

 Agricultural Experiment Station. 



' The writer wishes to express his appreciation to H. K. Hayes, Head of the Section of Plant Breeding, 

 Division of Agronomy and Farm Management, for suggestions and criticisms during the progress of this 

 study. 



• Reference is made by number (italic) to "Literature cited," p. 62-63. 



Journal of Agricultural Research, Vol. XXIL No. 2 



Washington, D. C. Oct. 8, 1921 



ir Key No. Minn.-« 



(53) 



