A MORE ACCURATE METHOD OF COMPARING FIRST- 

 GENERATION MAIZE HYBRIDS WITH THEIR PARENTS 



By G. N. Collins, 



Botanist, Office of Acclimatization and Adaptation of Crop Plants, 

 Bureau of Plant Industry 



INTRODUCTION 



That the crossing of two distinct varieties of maize usually results 

 in an increase of vigor and larger yields in the first, or F,, generation 

 has come to be generally recognized. The amount of the increase, how- 

 ever, varies greatly in different hybrids, and in many cases the increase 

 is not large enough to be determined by ordinary experimental methods, 

 if it exists at all. 



So far as known, no case has been reported where a decrease below 

 the mean vield of the parents has been adequately demonstrated. It 

 is highly desirable to know the conditions under which significant in- 

 creases occur, but thus far little light has been thrown on this important 

 point. If really incompatible varieties exist, a study of their behavior 

 in hybrid combinations should afford a favorable opportunity to learn 

 something regarding the conditions necessary for large increases. One 

 serious obstacle to learning the factors involved in the increased yields 

 of first-generation hybrids is the difficulty of accurately comparing the 

 vigor and yield of a hybrid with that of the parent varieties. 



Hybrids in maize are made either by hand pollination between indi- 

 vidual plants or by planting in alternate rows the varieties to be hybrid- 

 ized and removing the tassels from all the plants of one of the varieties. 



The customary method of comparing the behavior of a hybrid with 

 its parents is to plant the hybrid seed in rows or blocks alternating with 

 similar areas planted with the seed of the parents. If the series is re- 

 peated a sufficient number of times, reliable averages may be obtained, 

 but in actual practice the number of repetitions is usually limited by 

 lack of seed or space. ^ 



In making a comparison between a hybrid and its parents where the 

 hybrid is made by planting the varieties in alternate rows, the question 

 arises as to what seed will best represent the parents. If the original 

 seed of the parent varieties is used, it will be one year older than the 

 hybrid seed, and the uncertain element of deterioration with age is in- 

 troduced.- By saving the seed from the plants used as a source of pollen 

 in making the hybrid, fresh seed of the male parent can be secured, but 

 if fresh seed of the female parent is obtained, it must be grown at some 

 distance from the place where the hybrid is made. To use seed grown 

 under different conditions introduces an element of uncertainty that 



^ In experiments with maize extendinK over a number of years in many different localities, we have 

 found that with rows loo feet long and the series repeated lo times, it has seldom been possible to detect 

 with assurance differences in yield of less than lo per cent. 



2 For a discussion of this point, see Hartley. C. P., Brown. E. B.. Kyle, C, H.. and Zook, L. L. Cross- 

 breeding com. U. S. Dept. Agr., Bur. Plant Indus. Bui. 21X, p. 13-10, 1912. One and two-year-old seed 

 of selection No. iiga.the variety used as male parent in the Maryland experiments, occurred side by side 

 42 times. The average superiority of the new seed was 7 ± i.j per cent. 



Journal of Agricultural Research, Vol. Ill, No. i 



Dept. of Agriculture, Washington, D. C. Oct. 15, 1914 



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