Scientific Agriculture. 



142 



[February, 1912. 



INCREASED YIELDS PROM FIRST 

 GENERATION HYBRIDS. 



(From the Gardener's Chronicle, No. 1, 

 301, Vol. L., December 2, 1911.) 



The increased vigour exhibited by 

 hybrids is a tact which is all but univer- 

 sally known, and hence it is not surpri- 

 sing, now that so much attention is 

 beiug paid to genetics, that a systematic 

 attempt should be made to take advan- 

 tage of the fact for commercial pur- 

 poses. Indeed, with the evidence of 

 experiments with hybrids before us, it 

 is somewhat remarkable that such 

 attempts have not been made on a large 

 scale heretofore. Thus, so long ago as 

 1878, Dr. W. T. Beal found that, by 

 crossing two varieties of Maize (Corn), 

 the vigour of the hybrid expressed itself 

 in an increased yield of "seed" amount- 

 ing to 81 per cent. Dr. Beat's results 

 were confirmed from time to time by 

 other experimenters working indepen- 

 dently. The most recent experiments 

 of this kind are by Mr. G. N. Collins, of 

 the Bureau of Plant Industry, United 

 Slates (see Year Book of Department of 

 Agriculture, 1910). As the result of 

 extensive trials, Mr. Collins concludes 

 that breeding first-generation hybrids 

 of Maize for seed purposes is commer- 

 cially practicable. He estimates the 

 increased cost of producing seed from 

 cross-fertilised plants at about 2 per 

 cent, of the normal cost. 



Inasmuch as the reproductive vigour 

 of Maize hybrids is confined to, or, at all 

 events, is most marked in the first gene- 

 ration it is necessary to build up the seed 

 each year : hence the extra cost. 



In the Maize plant the procedure to be 

 adopted is rendered extremely simple 

 by the fact that male and female flowers 

 are borne on different parts of the 

 plants. Hence, all that is necessary is 

 to cover with stout paper bags the male 

 inflorescence of the plants chosen as 

 male parents. The pollen which collects 

 in the bags is then dusted on the tassels 

 (stigmas) of the plants chosen as seed- 

 bearers. Self-fertilisation, which in 

 Maize ; is always attended with reduced 

 fertility — even among hybrids— is pre- 

 vented by removing the male inflores- 

 cences before they shed their pollen— 

 from the plants destined for seed- 

 bearing. 



How far the exploitation of the en- 

 hanced fertility of first-generation hy- 

 brids is likely to obtain among other 

 plants ie an open question. 



In the first place, it may be remarked 

 that, though increased vigour is a very 



general, if not universal, phenomenon 

 among first-generation hybrids, it has 

 yet to be proved that enhanced fertility 

 is an equally general phenomenon, even 

 among varietal crosses. In the second 

 place, it remains to be proved that 

 enhanced fertility of the first generation 

 is — as appears to be the case in Maize- 

 lost in the next generation. In the 

 third place, it must be borne in mind 

 that many plant* are not so easily mani- 

 pulated as is the Maize and therefore the 

 question of the extra cost of cross-bred 

 seed as compared with ordinary seed has 

 to be considered. Nevertheless, we are 

 inclined to think that the practice may 

 be extended. We possess at the present 

 moment unpublished researches, which 

 show that first-generation hybrids bet- 

 ween varieties of culinary Peas (Pisum 

 sativum) are not only more vigorous 

 growers, but also heavier yielders than 

 are either of the parental varieties. In 

 the case of the Pea, the labour involved 

 in raising stocks of hybrid seed year 

 after year is euormously greater than in 

 the Maize. Each seed-bearing flower 

 must be emasculated and artificially 

 pollinated, and hence the number of 

 flowers which would have to be treated 

 to secure a large supply of seed is indeed 

 great. On the other hand, the oper- 

 ation of emasculation is of the simplest, 

 and could be taught to any person with 

 delicate fingers, in a few minutes, so 

 that, with practice, one worker — and 

 for such work women are better 

 adapted than men — could emasculate, 

 and pollinate, many hundreds of 

 flowers in the course of a day. 

 Another plant with respect to which the 

 first generation hybrid method is emi- 

 nently successful is the Potato. Here 

 again we have strong experimental evi- 

 dence, which professional breeders could, 

 no doubt, corroborate, of the high yield 

 of first generation varietal hybrids. Un- 

 fortunately, however, the raising of 

 potatoes from seed instead of from sets 

 is not a "commercial proposition." 

 Hence it is much to be desired that 

 exact investigation should be made as 

 to the rate of falling off in yield in sub- 

 sequent generations. The much dis- 

 cussed "running out" of varieties of 

 potato is often appealed to as evidence 

 that the vigour gained as the result of 

 the original cross is, as a matter of fact, 

 gradually lost. Whether this is so or 

 not, it is important, both from a 

 scientific and a commercial point of 

 view, to know if the loss of vigour and 

 fertility in self-fertilised or vegetatively 

 propagated plants follows any general 

 law of decreasing returns, or whether the 

 rate of loss of vigour— if such occurs— 



