332 



Colchicine 



crose than either diploid or tetraploid, in this case, the 2X or 4X sugar 

 beets. Intervarietal 3X hybrids between high-yielding tetraploids and 

 disease-resistant diploids will prove better than any of the present 

 tri|)loids. 



Large-scale production of SX seed remains a serious problem. 

 However, the self-incompatibility of the species can be used to ad- 



0_ 



'- X:!pjo, 



lO 



15 



20 23 



Individual beet weight ^100GM. units 



Fig. 13.3 — Weight of root and percentage of sucrose production does not decrease at 

 same rate as in diploid when large roots are produced. The addition of another set of 

 chromosomes does not pass the optimum for sugar production per acre. (After Peto 



and Boyes) 



vantage. This alternate planting of 4X and 2X varieties can be used. 

 Seventy j^er cent of the seeds from the 4X plants are triploid on an 

 open pollination basis. About 30 per cent from diploid are triploid 

 seed. Other factors arc involved, such as maturity dates, jiollen tid^e 

 growth, and environment that inlluences seed production. The 

 optimum number of chromosomes has not been exceeded in the trip- 

 loid.i^ii-^ 



Through the cooperative activities of the National Institute of 

 Genetics Laboratory of Plant Breeding, Hokkaido University, the 

 Hokkaido Agricultural Experiment Station, and the jajKUi Beet Sugar 

 Manufa(tiuing Company, improvement of sugar beet by means of 

 induced polyploidy has progressed very satisfactorily.--" 



