Section 13 — Plant Genetics and Breeding 



in the long arm of chromosome 5A were studied 

 in sub-species vulgare, compaction and sphaero- 

 coccwn of T. aestivum {2n = 42). In vulgare, 

 the loss of Q leads to the origin of speltoid char- 

 acteristics and an overdose of Q results in sub- 

 compactoid and compactoid phenotypes. Vari- 

 ous defects in floral organs and rachilla elonga- 

 tion as in vavilovi occur only in the absence of 

 Q. Orderly flower morphogenesis is thus one 

 among the many traits brought about by Q. 

 In compactum, the loss of Q makes the plant 

 grow taller and the ear less dense, in addition to 

 making the glumes tight thereby rendering 

 threshing difficult. A phenotypic resemblance 

 to a speltoid form of vulgare is thus generated, 

 though true speltoids are obtained only when 

 both Q and C are deleted from compactum. 

 An over-dose of Q in the presence of C gives 

 rise to hyper-compactoid ears. Similar phenoty- 

 pic consequences are observed in sphaerococcum 

 when Q is absent or is present in a tetrasomic 

 condition. Thus, the absence of Q alters radically 

 the key characteristics of sub-species vulgare, 

 compactum and sphaerococcum of T. aestivum. 

 Q has not so far been found to occur either 

 spontaneously or in irradiated populations in 

 the non-free-threshing hexaploid sub-species 

 spelt a, vavilovi, macha and zhukovskyi. If Q 

 is added to these sub-species by crossing them 

 with Q containing sub-species they also lose 

 their key characteristics. Q is thus a most interest- 

 ing locus from the phylogenetic angle, besides 

 being of immense importance from the agro- 

 nomic and adaptive standpoints. 



13.65. (D). Genome Manifestation of Wheat in 

 Aegilops Cytoplasm. Hitoshi KiHARA(Misima, 

 Japan). 



In order to investigate the effect of alien 

 cytoplasm on genome manifestation, genome 

 complements of 4x and 6x wheat have been 

 introduced by successive backcrosses into the 

 cytoplasm of Aegilops caudata or Ae. ovata. 

 The backcrosses have been carried out 14 times 

 for the most advanced materials and only twice 

 in the least advanced ones. 



Influence of the alien plasm has been noticed 

 in morphological and physiological wheat 

 characters. It was most remarkable in the floral 

 organs. When their genomes were introduced 

 into caudata cytoplasm, two varieties of 6x 

 and four of 4x wheat showed complete or 

 incomplete pistillody and all became male sterile. 

 Fourteen other varieties or strains became also 

 male sterile but no pistillody occurred. Those 

 were seven varieties of 6 x wheat, three of 4 x 

 wheat, three strains of synthesized 6x wheat 



and one Triticale. A 6x wheat, Triticum com- 

 pactum var. No. 44, differed from the others in 

 being normally male fertile. In general, genome 

 manifestation of 4 x wheat in this respect was 

 more influenced by caudata cytoplasm than that 

 of 6x wheat. This was critically shown in the 

 difference between 4x wheat (pistilloid) and 

 the hexaploids (male sterile but not pistilloid) 

 synthesized from the former as one of the parents. 



Genomes of four 4 x wheats were introduced 

 into ovata cytoplasm, and all became male 

 sterile. Pistillody did not occur in any strains. 



Effect of the alien cytoplasm was also noticed 

 in the increased occurrence of haploid and 

 twin seedlings. The extent of the increase varied 

 greatly with the genotype. 



13.66. Mutable Alleles at the R Locus in the Soybean 



Leonard F. Williams (Columbia, U.S.A.). 



In the soybean (Glycine max), four alleles are 

 known at the R locus, R (black seed-coat pig- 

 ment), r m (brown base with concentric black 

 stripes), r x (black with brown hilum), and r 

 (brown). R and r have been described. r m and r x 

 are in use by soybean breeders. In the USDA 

 World Collection of soybean lines, R and r are 

 most common, r m is uncommon, and r x is rare. 

 Varieties and genetic types with these genotypes 

 breed true, and no mutation has been reported 

 at this locus in established lines. Dominance is 

 complete and in the order: R, r m , r x , r. In cer- 

 tain crosses of r m with r, r x sectors appear on 

 a few Fl and F2 plants, and a few F2 plants oc- 

 cur that are completely r x . Linkage associations 

 indicate that the mutants are derived from r m 

 rather than r. Crosses between true-breeding 

 / x lines and mutant r x lines gave no segregation 

 in F2, indicating that the mutant is identical to, 

 or very similar to r x . In crosses with R, r m 

 and r, the mutant r x and original r x give similar 

 segregations in F2. However, certain crosses of 

 mutant r x with R and r give a small proportion 

 of / x plants sectored with r m and a very small 

 proportion of r m plants. One mutant r x line has 

 been maintained for 15 generations without 

 change, but others tend to reverse mutate to 

 r m . No mutants to or from R or r have been ob- 

 served in these crosses. These results indicate 

 that the mutability of r m and r x is intrinsic, but 

 the degree is influenced by other genetic factors. 



1 3.67. Mutational Tendency of Different Genes with 

 the Same Phenotypic Expression. L. B. Mazoti 

 (Llavallol, Argentina). 



In a maize pedigree studied throughout 20 



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