mac key: induced mutation in crop improvement 341 



Table 4. — Types of Chlorophyll Mutations and Their Relative Prevalence in 



M 2 OF X-RAY- AND NeUTRON-TREATED 2x, 4x, AND 6x WHEAT. 



The relative prevalence in Mo of 



Species N xantha 



albina xan.alb. virido- tigrina viridis All 



alb.xan. albina other 



2x monococcum wheat .. . 295 42.4 6.4 9.8 2.7 34.6 4.1 



4x dicoccum wheat 191 27.8 4.2 6.3 18.3 40.S 2.6 



6x vulgare wheat 15 6.7 26.7 53.3 13.3 



Test of heterogeneity 



X 2 d.f. P 



2x - 4x wheat 43.4 5 <0.001 



4x - 6x wheat 3.9 1 * <0.05 



2x - 6x wheat 12.5 1 * <0.001 



*Albina, xantha-types and viridoalbina is one group: tigrina and viridis is another. "All other" 

 omitted. 



tions, which generally though not always (10, 43, 64, 74, 111) are 

 detrimental, and refer only to diploids, we will find great differences 

 in the relative commonness especially of albums between cereals, on 

 the one hand (72), and large-seeded leguminous plants, such as peas 

 (89), lupines (110), soybeans (117), and beans (Sjodin, unpublished), 

 on the other. It is also symptomatic that Steuckhardt (103) found the 

 albina mutations gradually increasing in relative frequency when 

 irradiation of millet was repeated over successive generations and the 

 buffering in this way gradually broken down. 



The varying degree of progress in the use of mutation experi- 

 ments in crop improvement may partly be due to differences like 

 those discussed here. The relatively high frequency of lethal or sub- 

 vital mutations and a very strict, morphological architecture of, e.g., 

 the barley plant, may partly account for the comparatively meagre 

 results in contrast to those with peas, beans, and peanuts. Similar 

 differences but of different magnitude can also be found on an inter- 

 varietal level within species. To take only one example, Hagberg 

 (46) found different erectoides loci more or less stable with a different 

 pattern for different varieties. In the variety Gull 4 out of 8 

 induced erectoides mutations involved locus b which never has been 

 found to mutate in the varieties Maja and Bonus, Avhere 7 and 87 



