OCCURRENCE OF STERILE SPIKELETS IN WHEAT 



By A. E. Grantham, Agronomist, Delaware Agricultural Experiment Station, and 

 Frazier Groff, Student, Delaware College 



INTRODUCTION 



The average spike of wheat (Triticum spp.) contains from 15 to 20 

 spikelets, each of which under favorable conditions is capable of pro- 

 ducing two or more kernels. Ordinarily, however, the lower two or 

 three spikelets on the spike do not develop. The only indications of 

 their absence are the joints or nodes of the rachis which are thus exposed 

 (PI. XXVII). Hunt states that often in the cultivated varieties and 

 always in the wild species the lower one to four are sterile. In this paper 

 the term "sterile spikelet" is used to designate those spikelets at the base 

 of the spike which for some reason fail to develop and produce seed. No 

 account was taken of the sterile florets which might occasionally occur 

 within the spikelet. The absent spikelets, as shown by the naked rachis, 

 were the only ones estimated as sterile. 



MATERIAL AND METHODS 



During the summer of 191 5 the writer had the opportunity of making 

 a detailed study of the occurrence of sterile spikelets in a large number 

 of varieties of wheat under test by the Department of Agronomy at the 

 Delaware Agricultural Experiment Station. These varieties and strains 

 of wheat, 188 in number, had been sown the previous autumn by two 

 methods: First, by a grain drill as under ordinary field conditions, at the 

 rate of 7 pecks per acre; second, by the centgener or hill method, leaving 

 the individual plants 6 inches apart each way. By the former method 

 the plants were very close in the rows, which were 8 inches apart. This 

 gave an opportunity to determine to what degree the closeness of the 

 plants or rate of seeding influenced the frequency of sterile spikelets. 



The data for each variety were secured in the following manner: The 

 total number of fertile and sterile spikelets were counted on 25 represen- 

 tative spikes of each variety. The means of the fertile spikelets and the 

 sterile spikelets were taken separately and the percentage of sterile spike- 

 lets was determined for each variety of wheat. Where the varieties were 

 planted in hills 6 inches apart each way, five plants of five culms each con- 

 stituted the 25 spikes, the spikelets of which were counted. In this man- 

 ner the actual number of sterile spikelets and the percentage of the total 

 number of spikelets were determined for the 188 varieties and strains 

 under the two methods of planting. 



Journal of Agricultural Research, Vol. VI, No. 6 



Dept. of Agriculture, Washington, D. C. May 8, 1916 



dk Del.— 2 



(235) 



