552 



BREEDING 



BREEDING 



643. Plant of aquilegia with 

 flowers covered with bags in 

 hybridization work. 



in the careful breeding and improvement of corn. The 

 corn plant has been shown, as a result of experiments 

 made by various investigators, as, for example, the 

 Illinois Experiment Station and the United States 

 Department of Agriculture, to lose vitality very 

 rapidly when self-fertilized. Within three or four 

 generations, by the most careful inbreeding, it is pos- 

 sible to reduce corn almost to total sterility. The 

 general practice of corn- 

 breeders who have been 

 giving attention to the pro- 

 duction of pedigree strains 

 is to plant the rows of corn 

 from different select ears 

 side by side, giving a row 

 to each select ear, and each 

 year selecting, from the 

 progeny of those rows that 

 give the largest yield, plants 

 to continue further the 

 selection. Planting these 

 select ears together every 

 year, therefore, means that 

 they are more or less inbred, 

 as the closest relatives are 

 planted together in the 

 same row. While in follow- 

 ing this practice at first no 

 effect was visible, corn- 

 breeders are now finding in 

 some cases an apparent de- 

 crease in yield, which seems 

 to be traceable to the effect of inbreeding. It seems 

 necessary, therefore, in corn and in other plants that 

 are affected by inbreeding, to use methods that will 

 avoid close inbreeding. The detrimental effect of in- 

 breeding is largely limited to those plants that are 

 normally cross-fertilized, this fact being strikingly 

 brought out in Darwin's "Effects of Cross and Self 

 Fertilization in the Vegetable Kingdom." Tobacco, 

 wheat, and some other plants that are normally self- 

 fertilized do not show this decrease in vigor as a result 

 of inbreeding. 



Considerable effort has been made within recent years, 

 in the selection of certain crops, particularly corn, 

 to follow both parents, choosing good males and good 

 females of known parentage and crossing these by 

 artificial means. There can be no doubt but that 

 by the use of such methods more rapid progress could 

 be made, but in the greater number of cases the meth- 

 ods thus far devised require so much work as to be 

 almost prohibitive. 



A method of breeding has recently been devised by 

 J. B. Norton in the improvement of asparagus, which is 

 worthy of careful consideration and may be applicable, 

 at least in modified form, to use in the improvement of 

 various crops. Asparagus is dioecious, the male and 

 female flowers being borne on different plants. The 

 first part of the process consists in selecting a number 

 of superior plants of both sexes, attention being given 

 to all important characters such as yield, quality, rust- 

 resistance, and the like. This having been done, the 

 next process consists in crossing each female with each 

 selected male plant and testing the progeny produced by 

 the cross. If, for example, ten superior females and ten 

 superior males were chosen, a sufficient number of 

 flowers on female No. 1 would be crossed with pollen 

 of each of the ten males to obtain sufficient seed to test 

 the comparative value of the progeny of female No. 1 

 with each of the ten males. The ten lots of seed from the 

 crosses on female No. 1 would be grown separately and 

 the comparative value of the different progenies deter- 

 mined by careful observations on vigor, rust-resistance, 

 quality of product, yield, and the like. In this way, it 

 would ultimately be determined which of the ten male 

 plants was the superior one to use in crossing with 



female No. 1. In like manner, female No. 2 would be 

 crossed with each male and the progenies tested to 

 determine the superior male in this combination. 

 Finally the combination of each female with each male 

 can be compared and if the work has been conducted 

 with sufficient care and for a long enough period, it can 

 be determined which combination has uniformly given 

 the best results. 



Asparagus is perennial and is easily propagated 

 vegetatively by separation of the roots, so that when 

 once the superior male and female combination has been 

 determined, these may be propagated vegetatively as 

 clons, in alternate rows in an isolated place so that all 

 seeds developed will be of the desired combination. 

 Asparagus produces numerous seeds and by such a 

 method an indefinite quantity of seed of the desired 

 combination can be produced. It would doubtless be 

 possible in a few years, if desired, to have all of the 

 seed used commercially grown from a single superior 

 combination. 



If experiments of this nature could be made on an 

 extensive scale so that the males and females of the 

 highest or maximum grade could be discovered, they 

 would be of almost fabulous value. The importance 

 of this method of breeding may be better appreciated 

 by imagining the value of the best bull and the best 

 cow in the world if they would live indefinitely and if 

 it were possible for them to reproduce rapidly enough 

 to supply all of the individuals desired. 



The direct application of this method is possible only 

 with perennial dioecious plants that can be propagated 

 as clons and that develop numerous seeds. The hop is 

 another plant to which this method of improvement 

 could be applied. 



Hybridization. 



Aside from selection, hybridization has pla3'ed the 

 most important role in the formation of the varieties 

 and races of our cultivated plants; but the results 

 obtained are in many cases closely connected with selec- 

 tion. Ever since the time of Knight, hybridization has 

 been used extensively in plant-breeding, and it seems 

 that this is the only sure means that the breeder can 

 use in producing new and desirable combinations of 

 characters. In hybridization, as generally used, the 

 breeder does not expect to cause or produce new unit- 

 characters, although such changes may occasionally 

 occur under the stimulus of hybridization. What he 

 can do with certainty is to secure hybrids combining 

 the different characters of two distinct sorts. The 

 extent to which such recombination of characters can 

 be carried is almost unlimited. In many cases, two or 

 three or even four distinct species and the characters 

 represented in their various varieties have been 

 recombined in hybrids. 



In older literature, the term hybrid was restricted to 

 crosses resulting from the combination of distinct 

 species, while combinations of different races of the same 

 species were known as crosses or mongrels. The term 

 hybrid is here used as designating any product of a 

 cross when the parents were noticeably distinct from 

 each other, whether the parents belonged to different 

 clons, races or species. This broader use of the term 

 hybrid has become almost universal in recent years. 

 If, in discussion, it is necessary to refer to the degrees or 

 grades of difference in the parents, the hybrids may be 

 characterized as species hybrids, racial hybrids, clonal 

 hybrids and the like. 



Choosing varieties to hybridize. 



In starting any work in hybridization, the first 

 important step is the choice of the varieties to be 

 hybridized. It is interesting to make crosses of any two 

 plants with distinct characters and observe the recom- 

 binations of characters which result, but this haphazard 

 work takes too much time and is not to be recom- 



