The Canadian Horticulturi^ 



'ol. XXXII 



JUNE, 1909 



No. 6 



The Principles of Plant Breeding' 



Prof. W. Lochhead, Macdonald College 



THIS is a large subject nowadays. 

 The last seven years have been 

 "fat" years for the student of plant 

 and animal breeding, and it is almost im- 

 possible to keep up with the tremendous 

 strides that are being taken by hundreds 

 of scientific investigators both in America 

 and Europe. Every morning we enquire 

 what new discovery was made the day 

 before, lest we overlook some important 

 advance and fall behind in the onward 

 march of the times, 

 fc On account of the recent discovery 

 K of some of the fundamental principles of 

 fcheredity the plant breeder is now able 

 IPto work with some degree of certainty in 

 the production of new forms of plants. 

 The haphazard guess-work of former 

 days is to some extent replaced by defin- 

 m iteness, and "the breeder may proceed to 

 H build up synthetically, character by char- 

 B acter, the plant which he requires. His 

 ^ chief limitations will be those imposed by 

 Nature upon the variations of living 

 forms." — (Punnett.) 



It is my purpose to discuss the newer 

 aspects of plant breeding, not from the 

 standpoint of a practical plant breeder, 

 but rather from the standpoint of the 

 biologist who is interested primarily in the 

 principles that underlie scientific plant 

 breeding. In the time at my disposal it 

 is impossible to deal at all fully even with 

 the principles of plant breeding, inas- 

 much as each of the main methods of 

 plant improvement is now regulated by 

 certain principles of its own. The ideas 

 of "elementary species" and "muta- 

 tions" belong distinctly to the twentieth 

 century ; hence they are not yet out of 

 their infancy stage, and no one is bold 

 enough to state how far-reaching the in- 

 fluences of the new ideas may be. Al- 

 ready in many quarters Darwin's ex- 

 planation of the process of evolution is 

 being superseded by that offered by De 

 Vries in his theory of mutations. It is be- 

 coming more and more evident that the 

 principles underlying plant breeding are 

 closely connected with the question of the 

 origin of species and of evolution. 



Plant breeding may be defined as "the 

 intentional production and perpetuation 



Part of an address delivered before last conven- 

 tion of the Quebec Pomological Society. The 

 next instalment will deal with the separation of 

 mutations that have desirable qualities. The 

 third instalment will discuss the question of 

 hybridization. 



of desirable varieties of cultivated 

 plants." The three main methods now 

 in use for the improvement of plants 

 are: i. Continued selection of superior 

 individual plants ; 2. Separation from 

 mixtures of such individuals as show de- 

 sirable qualities, and at the same time 

 breed true to type ; 3. Combination of the 

 desirable qualities of tvvo strains or varie- 

 ties by hybridization. 



It is plain that all three methods 

 cannot be employed in every case of 

 plant improvement. For example, some 

 plants are propagated by buds ; the 

 crossing of two varieties or strains to 

 form desirable hybrids is a process too 

 difficult and too involved for any person 

 but the trained plant breeder; and, 

 lastly, the separation of new and desir- 

 able elementary species requires such 



Best in America 



I sincerely appreciate the able 

 editorial management of our 

 magazine — The Canadian Horti- 

 culturist — the best in America. 

 — H. J. Snelgrove, President, On- 

 tario Horticultural Association. 



■ 



careful observation of a refined order that 

 the average man untrained along this 

 particular line will seldom meet with suc- 

 cess. 



SELECTION 



The improvement of plants by the con- 

 tinued selection of superior individual 

 plants has been in vogue since Roman 

 times. Virgil, for example, in his 

 "Georgics," wrote: "The chosen seed 

 improved through years and labor was 

 seen to run back, unless man selected by 

 hand yearly the largest and fullest ears." 

 It is probable, therefore, that our chief 

 cereals have been kept up to a high 

 standard of excellence through all the 

 centuries, by a strict process of selection. 

 The origin of most of our horticultural 

 fruit-pi-oducing plants is extremely un- 

 certain, being lost in the mists of an- 

 tiquity. 



The importance and value of selection 

 lies in the fact that plants as a rule are 

 highly variable. It is a common matter 

 of observation that plants produced from 

 seed obtained from the same parent may 

 vary more or less widely in size, shape 



121 



and other characters. Some of the plants 

 will be inferior from an economic stand- 

 point, others will be superior, but the 

 majority will be about the normal. Ex- 

 perience tells us also that if the seeds 

 from a superior plant be sown, the 

 majority of the new individuals that arise 

 from the seeds will show themselves to be 

 superior. In some cases, therefore, the 

 desirable variations are transmitted to 

 the progeny, and by continued selection 

 of the best seeds from the best plants 

 the plant grower can obtain a higher 

 yielding strain of superior quality. How- 

 ever, in order to keep the strain up to 

 this high standard it is necessary to con- 

 tinue the selection year after year, for 

 unless this is done the plants gradually 

 revert to the normal or average of the 

 strain before selection began. 



It is by adoption of this plan of selec- 

 tion that the Canadian Seed Growers' As- 

 sociation hopes to increase the crop yield 

 of Canada. Although there seems to be 

 a limit to the improvement effected by 

 selection of this kind, (i. e., that improve- 

 ment cannot continue indefinitely, but 

 has a maximum limit) yet the general 

 adoption of this principle of selection of 

 the best seed from the best plants will 

 greatly increase the value of the crops of 

 the country. 



Sometimes it is possible to force varia- 

 tion in plants which are but slightly vari- 

 able by changing the conditions sur- 

 rounding the plants. For example, it has 

 been observed that high cultivation and 

 manuring will often cause plants to vary 

 considerably, so that the plant breeder 

 is in a better position to make his selec- 

 tions. Budding, grafting and vegetative 

 propagation also tend to bring about 

 variations from which the breeder may 

 begin his selection. 



There are two methods of growing 

 plants for selection, which Webber calls 

 the "Nursery Method" and the "Field 

 Method." By the nursery method "each 

 plant is grown under the most favorable 

 conditions for its best development." By 

 the field method "the selections are made 

 from plants grown under normal field 

 conditions." Both methods are in general 

 . use by plant breeders, but the nursery 

 method requires more care and attention 

 than the ordinary breeder would care to 

 give to the work. 



