The Autoploids 333 



The SX beets aie more vigorous; ihey grow better and always yield 

 more than other beets. Large-scale tests in 1919 and 1950 proved the 

 superiority of the 3X beets. 



/9.2-3.- TripJoid fruits. Some ol the best varieties ol ajjplies, Stay- 

 man, ^\'inesap, and Baldwin, are widely known. Since giant sports 

 can l)c- produced by colchicine, in similar fashion to the natmally 

 o((iuring types, the drug has ready application in apple breeding. 

 Trijjloids can be made from hybrids between tetraploid and regular 

 diploid varieties. These have possibilities for winter hardiness ac- 

 cording to tests by special laboratory equipment."^ Among 31 tetra- 

 ploids, two \'arieties were exceptionally hardy. Mains barrafa, a dip- 

 loid species, has been polyploidized and might \\ell l)e the start for 

 breeding stock. 



Triploid guavas have been reported occurring in natme. Such 

 tvpes are seedless. Tetraploids induced by colchicine were promising 

 soiuces for making crosses between diploid and tetraploid.'"' Assum- 

 ing that other qualities cotdd be controlled, polyploidy for this eco- 

 nomic crop and particularly seedless fruit jModuction should repre- 

 sent an important improvement.'^'' 



13.3: Monoploids and Autodiploids 



The fust monoploid plant discovered in 1922 proved that plants 

 existed with one set ol cliromosomes. More than 30 genera have been 

 added to the list \vith monoploids reported for one or more species."'' 

 The impro\ement of methods for detecting monoploids is an impor- 

 tant part of the program. At once geneticists recognized that doubled 

 monoploids became homozygotis diploids, lire theoretical and prac- 

 tical use for breeding jnnposes should not be underestimated. Since 

 the first monoploids were reported, the practical value for homozygous 

 breeding stock to produce hybrid maize has been developed ex- 

 tensively."^ 



1 he frequencies of the appearance of monoploids are low. Their 

 propagation after isolation from diploid cultures depends u|>on the 

 doubling of chromosomes in tissues that develoj) the pollen and egg 

 (clls. Colchicine serves adequately for increasing the sectors that 

 double to give rise to fertile tissues. The problem that remains is 

 to find -ways to increase the frequency of producing monoploids, 

 apjjlicable to a large number of plants. 



A prediction was made that the discovery of methods to increase 

 the frequency of monoploids woidd mark another period in the his- 

 tory of polyploidy breeding (cf. Chapter 11, Ref. No. 43) . According 

 to this scheme the Drosera research by Rosenberg marked the be- 

 ginning: a distinction between allopoly|}loid\ and autopolyploidy was 

 the second phase: and colchicine in 1937 was the beginning of the 



