nybom: vegetatively propagated species 285 



(6), the variation among available varieties with regard to size of the 

 trusses (ease of picking) or length of the dormancy period (resistance 

 against late frosts) is not as wide as Ave might wish. What do we do 

 then, start crossing or irradiating? 



In blackberries we have some relatively acceptable varieties, 

 which are, however, all terribly spiny. There are extremely few thorn- 

 less types available for breeding, like the diploid weak-growing and 

 winter-sensitive Rubus ulmifolius inermis. It might take us 15 years 

 to bring its recessive inermis gene over into acceptable polyploid 

 varieties, if we do succeed. Which will be cheapest, crossing or 

 irradiation? If given resources, we should of course try both ways, 

 well knowing that not all breeding projects started so far have resulted 

 in improved varieties. 



Even after critical consideration there are applications like these 

 and others where the mutation method indeed seems worth trying 

 and where it no doubt in many cases will turn out to be economically 

 feasible. With regard to the chimaeric nature of somatic mutations 

 there are also occasions when the mutation method offers quite 

 unique possibilities, or even turns out to be the only practicable way. 



We should not forget those plants that lack regular sexual repro- 

 duction, e.g., the apomictic types, or where this can not be utilized 

 because of self-sterility or incompatibility or the absence of flower 

 formation. In the imperfect microorganisms, e.g., the antibiotic pro- 

 ducing ones, deliberate mutation breeding has turned out to be highly 

 successful (5). Also, the possibility of using pollen irradiation in order 

 to realize difficult species crosses certainly deserves more attention 

 among vegetatively propagated plants (27, 78, 90). 



Especially if we extend the concept to include all applications 

 of mutagenic agents, it seems beyond doubt that the mutation method 

 will become not only a valuable but even an indispensable tool for 

 the plant breeder. But we shall have to learn much more before we 

 can say when and how to apply it. 



References 



1. Anonymous. 1956. The Starkrimson (Bisbee Strain) Delicious apple. 



Fruit Var. and Hort. Dig., 11: 31. 



2. Asseyeva, T. 1927. Bud mutations in the potato and their chim- 



erical nature. Jour. Genet., 19: 1-26. 



