Section J — Mutagenesis 



the untreated material, the heritability has in- 

 creased in treated material and was higher in the 

 R.3 than in R4. 



The genetic advance in the height of plants is 

 calculated for all lines which were expected to be 

 10 per cent shorter than the control. 



5.115. Segregation Ratios of Induced Mutations in 

 Durum Wheat. G. T. Scarascia Mugnozza, 

 A. Bozzini and F. D'Amato (Pisa, Italy). 



Since 1956 experiments were carried out on the 

 induction of mutations in durum wheat by X- 

 rays, fast and thermal neutrons, ethylmethane- 

 sulfonate, diethylsulfate and ethilenimine. So far 

 more than four hundred independently obtained 

 cases of viable mutations have been isolated; 

 moreover several hundreds of lethals are being 

 maintained as heterozygotes. This material is 

 the object of genetic and cytogenetic analyses. 

 Data are presented on segregation ratios in the 

 progeny of M2 and M3 individuals heterozygous 

 for induced mutations and of M2 progenies of 

 the cross of viable mutants to the mother line 

 (total mutations analyzed: 51). In a total of 

 28 M2 individuals heterozygous for pigment 

 mutations (2 albina, 2 xanthalba, 3 chloroalbina, 

 7 xantha, 2 virido-albina, 7 tigrina, 1 virescens, 



2 chlorina, 2 anthocyanic) 19 gave a M3 progeny 

 with a 3: 1 segregation ratio (mutant condition 

 recessive). In the remaining 9, the proportion of 

 mutant individuals was much less; but in M4 al- 

 ready four out of them attained the 3 : 1 ratio. 

 This result seems to indicate that the segregation 

 deficit shown by induced pigment mutations in 

 the first generations following treatment may be 

 reduced or eliminated, possibly through pro- 

 gressive elimination of deleterious genetic chan- 

 ges accompanying the mutation. F2 analysis of 

 the crosses between pigment mutants and the 

 mother line showed that 6 of them behaved as 

 monogenic recessive (2 tigrina, 1 virescens, 1 viri- 

 dis, 2 chlorina), whilst 2 tigrina mutations were 

 inherited as semidominant. As to morphological 

 mutations, only the progenies of 6 M2 hetero- 

 zygotes and the F 2 of 9 crosses "mutant x mother 

 line" have been analyzed so far. Out of these 15 

 mutations, 10 behaved as monogenic recessive 

 (2 with supernumerary spikelets, 2 semisterile, 



3 waxless, 1 with defective endosperm, 1 with an- 

 thocyanic glumes, 1 with solid stem); in the re- 

 maining 5 (1 dwarf, 2 waxless, 1 anthocyanic 

 glumes, 1 brachytic) a strong deficit of indivi- 

 duals with mutant phenotype was noticed, in 

 connection with a high degree of sterility. 



5.116. Chemical Mutagenesis in Triticum. H. K. 



Shama Rao (Bombay, India). 



Ethyl-methane sulfonate (EMS), unlike radia- 

 tions, has been shown to induce chlorophyll 

 deficient sectors with or without notch or punch 

 formation and necrotic patches in leaves as well 

 as speltoid, sub-compactoid, compactoid and 

 compactum-spikes, during the treated generation, 

 in the monosomies 2B and 6B of the hexaploid 

 Chinese-Spring wheat W. 



In both mono-2B and 6B, phenotypic changes 

 during M2 appeared in almost equal numbers 

 out of a total of 37 affected families amongst 

 124 progenies raised from all the Mi sectorial and 

 non-sectorial plants. However, the mutation 

 spectrum differred. The chlorophyll defectives, 

 viz. lutescent, chlorina and freckled, were noticed 

 only in mono-2B. In addition, 2 other families 

 were with grass-clump types and another with a 

 rudimentary-spike character. 



In mono-6B, lethal dwarfs having short, thick 

 and dark-green leaves were observed in 2 families. 

 Another family was with a distinctive type of 

 spike mutation, viz. "Missing-Spikelets", a 

 character not observed in any of the nulli-, or 

 tetrasomics; nor ever reported as appearing 

 following irradiation. 



The types of mutation common to both mono- 

 2B and 6B were those with increased or decreased 

 awn development and without hooded character 

 which could all be accounted for by simple 

 deficiency of known genes. Two other spike 

 mutations observed were of semi-speltoid and 

 base-compact types. 



The chlorina, a number of lethals and the 

 mutants with missing-spikelets and rudimentary- 

 spikes segregated in approximately 1 : 3 ratio 

 showing that some of these, at least, involved 

 single genes. The modes of their inheritance are 

 under investigation. 



1. Shama Rao and Sears, Records of the Genetics 

 Society of America, 1962. 



5.117. Different Mutation Spectra among Related 

 Strains of Antirrhinum majus, obtained after 

 Irradiation. Gertrud Linnert (Berlin, Ger- 

 many). 



Two subsequent radiation experiments were 

 undertaken on normal and mutant strains of the 

 pure line designated "Sippe 50" by Erwin Baur. 

 At first pollen was treated with 3000 r; the pro- 

 genies of 14 plants resulting from this experiment 

 (= X of the following experiment) were once 



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