THE LONG-RANGE OUTLOOK FOR PRODUCTION OF RUST RESISTANT 

 TREES BY INDUCED MUTAGENESIS 



S. Kedharnath 

 Forest Research Institute and Colleges 

 PO New Forest, Dehra Dun, India 



ABSTRACT 



In crop plants induced mutagenesis has been effectively used 

 and an array of mutants has been assembled. In the past, more 

 attention was directed to selecting macromutations . More 

 recently the importance of micromutations or polygene mutations 

 has been recognized for improvement of quantitative characters. 

 Chemical mutagens seem to hold promise for increasing the mutation 

 frequency as compared to physical mutagens. Right choice of the 

 mutagen and improvement in the methods of screening the mutants 

 can increase the value of induced mutagenesis as a tool in breeding 

 for disease resistance. 



INTRODUCTION 



In the last 18 years or so a large number of induced morphological 

 and physiological mutants has been assembled for a number of crop plants. 

 Several reviews have appeared that cover this subject of induced mutation. 

 Some of these are: Konzak (1956), MacKey (1956), Singleton ez al. (1956), 

 Smith (1958), Sttlbbe (1958), Prakken (1959) and Gaul (1958, 1964). Intra- 

 specific macromutations (mutations with major gene effects) are the most 

 common type of mutations selected. Small mutations or micromutations 

 (mutations with minor gene effects) have not received the attention they 

 deserve from plant breeders. In recent years the importance of these 

 small mutations in breeding programs has been emphasized by Xybom (1954) , 

 Gregory (1955a, b, 1956) and Gaul (1958). 



Most plant attributes of interest to breeders are quantitative 

 characters which are controlled by many genes or polygenes. It is reason- 

 able therefore to expect that mutation of the polygenes will affect a 

 quantitative character in a measurable way. In fact, there is some 

 evidence of this in the studies of Gregory (1955a, b, 1956) on peanuts 

 with regard to genetic variance for yield in the progenies of normal 

 appearing M2 plants which were selected at random. He succeeded in 

 selecting mutants with higher yielding capacity. Oka, Hayashi , and 

 Shiojiri (1958) in rice and Moes (1958, 1959) in barley have also reported 

 small mutations exerting a quantitative effect in respect to a number of 

 characters . 



In the field of induced mutation for disease resistance, the first 

 report of positive results is that of Freisleben and Lein (1942) in 

 barley for resistance to mildew. Since that time many workers have 



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