224 MUTATION AND PLANT BREEDING 



Exciting progress has been made with chemical mutagens. At 

 present, two of the most powerful substances for higher plants are 

 ethylene imine (20) and especially ethyl methane sulfonate or 

 EMS (54, 55, 56). The high mutagenic efficiency of EMS is demon- 

 strated in Table 5 for chlorophyll mutations in barley. After X-irra- 

 diation of barley seeds the highest mutation rates obtained are of 



Table 5. — Some Results of the Mutagenic Efficiency of EMS (CH3SO2OC2H5) in 



Barley Seeds Obtained by Heslot. * 



•Personal communication. LD-50 is approximately for 24 hours, 24° C:V3oo, and for 3 davs, 

 3° CrVioo. 



the order of 3 to 4 per cent mutants per 100 M 2 plants (12, 33), 

 while in Table 5 with EMS 14 per cent are recorded. According 

 to Heslot (Table 5), around 12 per cent were obtained with an 

 EMS treatment that led to approximately 50 per cent Mi surviv- 

 als. The values mentioned for X-ray treatment were only reached 

 with doses exerting a greater Mi lethality, except in one experiment 

 (33, treatment 30,000 rp). Consequently, the mutagenic efficiency 

 of EMS appears to be somewhere between 3 to 8 times higher than 

 that of X-rays, if these results are reproducible. Similar high muta- 

 tion rates with EMS have now also been obtained by Ehrenberg 

 (19). Apparently EMS has a relatively low toxic effect and a high 

 genetic effect as compared with X-rays. Moreover, Heslot (56) found 

 many more morphological and physiological mutations per chloro- 

 phyll mutation after treatment with EMS than after X-raying. 

 EMS treatment results in much lower chromosome breakage (Hes- 

 lot, personal communication, also 67), however, it causes high Mi 

 sterility. This discrepancy needs to be further investigated. The 

 mutagenic activity of EMS has already been proved in other spe- 

 cies (56, 87). Apparently, EMS is the most efficient mutagen for plant 

 breeding known at present and it deserves greatest interest in further 

 theoretical and practical applications. 



Most of the applied mutation work has been done with radia- 



