468 MUTATION AND PLANT BREEDING 



of mutation breeding, experiments designed to make comparisons 

 between conventional breeding procedure and mutation breeding 

 are required. Gregory (20) suggested that radiation-induced variance 

 should be cumulative with that induced by hybridization. Pre- 

 liminary results have been reported (21) on expressions of F 2 dom- 

 inance in hybrids of mutant selections from the same pure line. In 

 the absence of such work from other laboratories it is my purpose 

 to devote the remainder of this paper to the description of such an 

 experiment conducted with peanuts. (See, however, Krull, C. F., 

 Agronomy Abstracts, 1960, page 50.) 



In 1953 all possible hybrid combinations were made among six 

 lines of peanuts. All of these lines had been reproduced from initial 

 single plant selections followed by sufficient automatic self-fertiliza- 

 tion to assure their relative homozygosity. Three of them were 

 selections in X 5 generation of high-yielding mutants from the same 

 pure line. The other three were selections in F n generation from 

 the hybridization and progeny testing program which, at that time, 

 was conducted separately from the radiation experiments. A suffi- 

 cient number of cross-pollinations was made to produce at least 

 100 F x seeds of each of the 15 possible Fi hybrids. In each cross 

 the 100 F x seeds were divided into two lots of 50 each. One 50-seed 

 lot of each hybrid and a 125-seed sample of each parent were 

 given a treatment of 15 Kr of X-rays. 



The packages of peanuts were arranged all at a time upon a 

 curved target surface in random order. At half time the packages 

 were all removed, turned over, re-randomized, and placed upon 

 the target surface for the remainder of the treatment. The radia- 

 tion was delivered at the rate of 62 to 63r per minute at a distance 

 of 1 meter from a 1,000-Kv tube equipped with beryllium window. 

 It is thought that all received equal and uniform doses of X-rays. 

 The seed had been stored dry for 6 months prior to irradiation and 

 moisture content was uniform. (The author is indebted to Dr. 

 William T. Ham, jr. (25) for dosimetry measurements and the 

 use of the X-ray tube, Biophysics, Medical College of Virginia, 

 Richmond.) The treated seeds and their controls were planted in 

 individual plots the day following X-ray treatment. In the fall of 

 1954 the plants were harvested individually. The treated hybrids 

 were designated as FiX^ The F 2 and FoX 2 generations were grown 



