TWINNING IN ALFALFA 



W. SOUTHWORTH 



Associate Professor; in Charge of Plant Breeding Investigations, Manitoba 

 Agricultural College, Winnipeg, Canada 



DURING our Alfalfa investiga- 

 tions in the season of 1918, the 

 twin hybrid seedlings as illus- 

 trated in Fig. 12 appeared. As 

 this is the first time that twinning in 

 alfalfa seed has been noticed in our 

 work, it is thought that a short account 

 of the parentage of the plants giving 

 rise to the twins may be of interest to 

 other investigators who may possibly 

 have had a similar experience. 



In raising alfalfa hybrids, the method 

 practiced in this department is first 

 to germinate the seeds in small quanti- 

 ties in open pans, then to transfer the 

 sprouted seeds to prepare soil in flower 

 pots of shallow fiats. Finally, after the 

 plants are sufificiently well developed, 

 they are planted out in plots in the 

 open field. It will be seen that this 

 system enables the worker to note any 

 peculiarities which may arise during 

 actual germination, which might other- 

 wise pass unnoticed. The parent of the 

 twins shown in Fig. 13 is the recent prog- 

 eny of a series of crosses commenced in 

 the summer of 1911. 



THE ORIGINAL CROSS 



The first cross of the series was made 

 between alfalfa as the female parent 

 and Black Medick as the male parent, 

 from which, in 1912, twenty-four Fi 

 plants were raised.^ 



THE SECOND CROSS 



In 1913 a plant of the F3 generation 

 of the original cross was crossed with 

 pollen from White Sweet Clover. From 

 this second cross, five Fi plants were 

 raised, four of which produced a few 

 seeds; the fifth plant was totally sterile. 

 Many attempts were made to induce 

 this plant to produce seed, both by 

 selfing and by back-crossing with both 

 original parents, but all efforts proved 



futile, the plant remained sterile 

 throughout. In order to perpetuate 

 this plant, cuttings were taken from it 

 in 1914 and about twenty plants propa- 

 gated. Much to our surprise, most of 

 these plants in the following year pro- 

 duced a small quantity of seed. In the 

 spring of 1916 a portion of the seed thus 

 obtained was germinated and eleven 

 plants reared. 



THE THIRD CROSS 



In 1917 two out of the eleven plants 

 were back-crossed, White Sweet Clover 

 being again used as the male parent. 

 From this cross seven Fi plants were 

 raised, one of which produced forty-two 

 seeds, one of these seeds producing the 

 twins as herewith illustrated. (Fig. 

 13.) In addition to this pair of twins, 

 two other pairs were found. These 

 two pairs likewise descended from the 

 same original cross as the first pair, but 

 the subsequent crossings were both 

 different. In one case the parent which 

 produced the twin seed was obtained 

 by inter-crossing two F3 plants from the 

 original cross. In the other case the 

 parent of the twins was obtained as a 

 result of back-crossing an F2 plant from 

 the original cross, using Black Medick 

 as the male parent. 



SUBSEQUENT BEHAVIOR OF TWIN SEED- 

 LINGS 



Of the first pair of twins, one pro- 

 duced a strong healthy plant and the 

 other died from exposure. The remain- 

 ing two pairs developed into strong vig- 

 orous plants, and, though the members 

 of each pair varied somewhat in size, 

 yet each pair seemed to be quite iden- 

 tical in botanical characteristics. Of 

 the five surviving plants, four produced 

 a few seeds which will be used for fur- 

 ther investigation. 



1 See "Alfalfa Hybridization," Journal of Heredity, vol. v, No. 10, pp. 448-457. 

 182 



