490 MUTATION AND PLANT BREEDING 



row confines of form, taste, and color. Under such confines, plant 

 breeders, often against their better judgment, tend to become var- 

 iability destroyers to satisfy immediate objectives. The importance 

 of preserving genetic variation in "world collections" to counteract 

 this tendency has been stressed, but must still be regarded as restric- 

 tive in that the limits imposed by evolutionary history are still 

 operative. 



Technological advances, often unrelated to plant breeding 

 objectives, sometimes dramatically remove the binding restrictions 

 of consumer acceptance. For years we have tailored cultural prac- 

 tices in maize to row widths determined by the convenience of 

 handling a team of horses. We have tailored the form of the corn 

 ear to the esthetic satisfaction of the farmer who contemplated a 

 hand-harvested ear before tossing it against the bang-board of his 

 wagon. I venture to predict that the advent of the picker-sheller for 

 corn harvesting will now permit exploitation of a greater array of 

 corn germ plasm variability than would have been dreamed pos- 

 sible just 3 years ago. The grain combine harvester removed the 

 requirement for smooth awns in barley some years ago. 



Whether or not there is an immediate need for attempts to 

 induce specific mutations can be decided only by the interests of 

 each individual breeder in relation to his present objectives. I 

 would be the last to advocate indiscriminate use of mutation induc- 

 tion in every breeding program. On the other hand, I would be 

 among the first to encourage continuation and extension of the 

 use of the powerful tools now available for increasing variability. 

 The use of appropriate mutants and their application to gaining an 

 understanding of, and exploiting heredity and variation at all levels 

 of development by geneticists and breeders, is indispensable to con- 

 tinuing progress. 



Comments 



Sparrow: Perhaps the variability in crossover frequency may already 

 exist and should be more carefully sought and selected for. In Trillium 

 erectum, collected from the wild, there is an extremely wide range of 

 chiasmata frequency. If one assumes this character to be genetically 

 controlled, selection of high chiasmata frequency plants should be 

 considered in plant breeding programs where this character would be 

 useful or desirable. 



