PRODUCTION OF RUST RESISTANT TREES BY MUTAGENESIS 559 



you find that you have eliminated some of the clones, and you bring down 

 your base to 20 or 30 desirable trees. Inducing mutations will be an 

 additional source of inducing minor alterations in this material and to 

 that extent it can be useful, and also it may be useful in upsetting the 

 fine balance that exists within the pathogen and the host. 



BORLAUG: I'd like to make one comment about this kind of work. 

 About 5 years ago Dr. George Varughese who did his work at the Indian 

 Agriculture Research Institute produced, by mutation, a white seeded 

 Sonora sixty-four, which was one of the introduced wheat varieties that 

 fit very well in India. There is a series of alleles that influence 

 grain color and Sonora sixty-four had one gene for red. White grain is 

 preferred, it really constitutes a premium of about 20% on the market, 

 and he came up with this gene. The plant itself was indistinguishable 

 from Sonora sixty-four, in adaptation, yield and other characteristics, 

 so that the trait couldn't be identified until the second generation after 

 treatment. In the development of this kind of work, it's very important 

 to grow a very large number of plants, and also you must have a very keen 

 eye to examine these for very small differences. It's these small ones 

 that you want. Not the big ones where there is a lot of injurious effects 

 that go along with it. 



