THE NEW CRAFT OF MAKING PLANTS TO ORDER 



II. INCREASED CROPS THROUGH USE OF HYBRID SEED 



J. L. COLLINS 



Dept. of Genetics, California Agricultural Experiment Station 



Editor's Note: — Breeding plants with a definite ideal is a positive development of recent years. The steps by which this condi- 

 tion has been reached have both the romance and charm of a fairy tale. Many gardeners, however, are still somewhat in the dark as to 

 the possibilities of hybridization, although the matter has so impressed the great seed-growing industry as to be likely to lead to quite new 

 methods of work in producing seed crops commercially. A subject of this nature is perforce full of technical terms — many of which had 

 to be made for the purpose — and cannot be presented in the words of the kindergarten; but we feel that Prof. Collins has acquitted 

 himself ably in the task of laying before our readers, in as plain terms as practicable, an outline of the present status of knowledge of 

 this newest and alluring development of the gardener's craft. The third and concluding article in this series will deal with the improve- 

 ment of our Fruits. 



MAKING BIGGER CUCUMBERS 



The effect of hybridization in Cucumbers is to increase the number 

 of fruits to the plant rather than marked increase in size. Nos. 1 

 and 3 are parents; No. 2, the first generation hybrid. Smallest 

 and largest cucumbers of parent varieties and hybrid are shown 



|T HAS been well established (as the result of numerous 

 investigations during the last half century) that the 

 first generation hybrid of two varieties, or even of two 

 species, of somewhat different constitution, is often 

 more vigorous in many ways than either of the parent varieties 

 grown under identical conditions. 



Many plant breeders have therefore been led to test the 

 possibilities of utilizing this increase in a commercial way with 

 the result that there is now at hand a considerable amount of 

 reliable information concerning kinds and varieties of plants to 

 select for parents and the best methods for securing the hybrid 

 seed. 



THE increased vigor displayed by the hybrid is known 

 technically as "heterosis," that is to say "hybrid vigor," 

 and is thought to be due to hereditary growth units carried in 

 the germ cells of the plants in just the same way as are the 

 units causing the production of flower-color or the shape of the 

 fruit. The greatest degree of this "hybrid vigor" results when 

 the cross brings together, in the hybrid, the greatest number of 

 different growth units. This condition results when the plants 

 are of different varieties not closely related. 



To secure this "hybrid vigor" in its greatest degree, the cross 

 must of course be made with plants that are not of the same 

 variety, for if they are the same they will contain the same hered- 

 itary growth units, and such a cross therefore would not increase 

 the number of different growth units. 



As a matter of business when dealing with annual plants 

 grown from seed, the subjects chosen for the work should be those 

 which produce a large number of seeds in a single fruit, because 

 only in such will the benefits derived more than compensate for 

 the expense of producing this hybrid seed. Exception can be 

 made in the case of some dioecious plants (i.e. those having 

 pistillate and staminate flowers on different plants), because one 

 variety can be "rouged" of all staminate plants and the pollen 

 applied by shaking a branch of the desired staminate plant 



over the selected pistillate plants; or the two varieties to be 

 crossed may be planted in alternate rows and all the pistillate 

 from one variety and all the staminate plants from the other 

 variety removed, thus permitting the wind and insects to do the 

 crossing. In either case all seed produced will be hybrid. 



Seedlings grown from this seed make a very much more rapid 

 growth than do plants from uncrossed seed. Which fact is a 

 distinct cultural advantage in the cucurbit family (Melons, 

 Cucumbers, etc.) as the rapidity of growth greatly reduces the 

 danger of damage by the striped cucumber bug which often at- 

 tacks the young plants as soon as they start pushing up through 

 the ground. Similarly, Corn grown from hybrid seed will pass 

 through the early seedling stage, when the cut-worm gets in its 

 work, much more rapidly than seedlings from the same varieties 

 uncrossed. 



The first generation hybrid between commercial varieties of 

 Tomatoes gives such a marked increase in yield that the produc- 

 tion of hybrid seed for commercial use has been recommended. 

 Increases ranging from 11 to 17 per cent, have been secured in 

 this way. If hybrid seed giving a i 5 per cent, increase over 

 the uncrossed varieties had been used for the Tomato crop of 

 1918 the total production in the U. S. would have been increased 

 by 2,872,367 tons. Think of it! The hybrid Tomato plants 

 produce both more and larger fruits than do the non-crossed 

 varieties. 



Indiscriminate selection of plants has given desirable results, 

 but better results would undoubtedly have been obtained if 

 high yielding mothers had been selected for one or more genera- 

 tions previous to the first crossing. Such selection can be easily 

 accomplished, as Tomatoes are readily self fertilized. The 

 high yielding pure strains having been isolated should be pre- 

 served for future crossing, and then the crosses can be duplicated 

 at any future date. This is a very important consideration for 

 the grower who is desirous of putting the same grade of product 



GETTING A QUICKER START IN LIFE 



Hybrid seed Corn will germinate much more quickly than non-hybrid 

 seed. Rows marked X are from hybrid seed, the other rows are from non- 

 hybrid seed. Both kinds of seed produced by the same parent plant 



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