MONOPLOIDS IN MAIZE 397 



a cross. As shown in Table 25.4, monoploid derivatives are particularly 

 favorable parthenogenetic stocks. In this series of crosses the stock V used as 

 the pollen parent is a purple marker which is better than average as a stimu- 

 lator of parthenogenesis. The seed parent in each case was a monoploid de- 

 rivative; either a homozygous diploid (HI 59), or a single cross hybrid 

 between two monoploids (H152 H14v3), or an advanced generation of such a 

 hybrid. 



The average frequency ])er 1000 for the stock from which H15y was de- 

 rived (the Stifif Stalk Synthetic) is about 1.21. In each case the frequency of 

 parthenogenesis is higher than that of the stock or stocks from which the 

 monoploid derivatives were obtained. The hybrid H152/H143 and the fre- 

 quency of monoploids in its progeny are particularly interesting in that HI 52 

 was a monoploid extracted from Inbred P39 and H143 a monoploid from 

 Inbred P51. Thus the cross of the two is the single cross hybrid Golden Cross 

 Bantam, based on monoploid parents. Normal Golden Cross Bantam crossed 

 by marker stock V has a monoploid frequency of about 4.00 per thousand. A 

 high rate of parthenogenesis is characteristic not only of the four stocks listed 

 in Table 25.4 but of all monoploid derivatives adequately tested. 



H159 not only has a high rate of parthenogenesis among its progeny but 

 also a high degree of fertility among the monoploids produced. Of the 15 

 monoploids obtained from the cross with stock F, 12 were grown to maturity. 

 All of these had one or more diploid sectors in the tassel and all set good seed. 



On the average about one monoploid in ten is self fertile — in the sense that 

 it yields a successful homozygous diploid progeny. One would like to obtain 

 diploid self progeny from all monoploids. Since any increase in the rate of 

 somatic diploidization should result in increased fertility, a number of treat- 

 ments with polyploidizing agents have been tried. Colchicine, as used, 

 brought about an increase in fertility but injury to the plants killed so many 

 that no over-all gain was effected. In these treatments, solutions of approxi- 

 mately .5 per cent aqueous colchicine were injected into the scutellar nodes of 

 the monoploid seedlings. It is possible that use of more dilute solutions in- 

 jected repeatedly would be more effective. 



Podophyllin, as a saturated aqueous solution, produced drastic stunting 

 and inhibition of the development of the ears and tassels. Heat treatment, 

 tried on a very minor scale, seemed to be about as effective as colchicine and 

 had the same disadvantage. In this problem, as in that of increasing the rate 

 of parthenogenesis, genetic methods seem to offer the best available solution. 

 That is, stocks derived from self fertile monoploids are better sources of self 

 fertile monoploids than the stocks from which the original monoploids were 

 obtained. 



Synthetic varieties that combine high monoploid frequency, high mono- 

 ploid fertility, and high general agronomic desirability can probably be de- 

 veloped from homozygous diploids, both sweet and dent, already on hand. 



