Washington, D. C. April, 1926 
A COMPARISON OF MAIZE-BREEDING METHODS 
By G. N. Couns, Senior Botanist in Charge of Office of Biophysical Investiga- 
tions, Bureau of Plant Industry 
CONTENTS 
Page Page 
TPES er Lg tas Sos ae eee ee ee 1 Correlation of number of plants with yield per 
Description of the experiments nigh Be ast FAM 2 plants #2 eS eee 11 
Preliminary comparisons_-_--__... .----------~_- 3} Measures of inbreedimg: 9s . = es eae 11 
Abnormalities in Sacaton June corn___-_--_._- 4 Sbisewssion —-t ..-}.-4. Se AS 2. ees =. ee 14 
Parent-offspring correlations in the selfed ex- Mutations: 22 oe ee es eee 14 
7 Seri Gin ig Sas a eee ee ne eee ee ee 4 Segregation of simple Mendelian charac- 
Plants from high-yielding rows compared with Fs) ee ae SY oa ee ie 14 
high-yielding plants selected without regard Segregation of multiple-factor charac- 
to the progeny performance----_-------_---- 5 | bCIS ).2¢22-2— == 8 Seer 58. 16 
Yield comparisons of the two breeding methods GorchiSiOHS: ee eos See ee eee 18 
“TL SAS eo LE es Ses Bee eee PES ee eee 6 Suimliniany 3s $2. 2522 bee as a oe re ses 20 
Yield comparisons of the two breeding methods i lteratureened 2.22 ee ee ee 21 
UI Lakes Ue SE TE Soi 2 7 
INTRODUCTION 
Methods of breeding for the improvement of agricultural plants 
are undergoing many changes as a result of rapid progress in the 
science of genetics. In self-pollinated species methods of selection, 
although conducted with more insight, have not been modified 
greatly. The principal change has been the i increasing use of hybrid- 
ization. In maize and other cross-fertilized species, however, 
entirely new methods of selection are being tried. 
The change from the old method of mass selection or of selection 
by progeny performance followed the work of Shull, who in 1908 
pointed out the diversity in selfed lines and suggested. the improve- 
ment of maize by combining selected selfed strains. 
The experiments here reported were begun in 1918 to determine 
the possible advantage of a method of close breeding in which 
inferior lines were eliminated through selfing and the surviving strains 
recombined to restore the vigor, lost by selfing. 
It seemed clear that increases in yield resulting from the ear-to-row 
method of crossbreeding were due almost entirely to an increased 
uniformity of performance. In other words, the maximum yield of 
the individual corn plant was not increased, though the general aver- 
age might be raised through a reduction in ‘the number of unproduc- 
tive or sterile plants. Many forms of sterility were known to be 
71737—26¢—1 
ee eee 
