Section 13 — Plant Genetics and Breeding 



13.61. Inheritance and Utilization of Five Dwarfs in 

 Pearl Millet (Pennisetum glaucum) Breeding. W 

 Glenn W. Burton and James C. Fortson 

 (Tifton, U.S.A.). 



Over 39,000 parent, Fi, F2, and backcross 

 spaced plants of hybrids involving five dwarf and 

 four normal inbreds (Gahi-1 lines) of pearl 

 millet were grown in replicated randomized 

 blocks in 1962. The dwarfs ranged from 32 to 

 60 in. in height, one-half to three-fourths the 

 height of normal inbreds. Most dwarf x normal 

 Fi hybrids were significantly taller (up to 38 per 

 cent) than the normal parent. Fi hybrids be- 

 tween four dwarfs were as tall as normal x 

 dwarf hybrids proving that these dwarfs car- 

 ried different recessive genes for dwarfness. 

 One dwarf x dwarf hybrid was little taller than 

 the taller dwarf parent, suggesting that both 

 carried the same dwarf genes. Inheritance of 

 dwarfness appeared to be conditioned largely 

 by one or two recessive genes. Evidence that 

 the normal inbred in some instances introduced 

 modifying factors was observed. 



Where pearl millet is grown as a cereal, 

 converting existing tall varieties to dwarfs can 

 reduce lodging and facilitate harvesting. Dwarfs 

 can be used to reduce the cost of producing 

 hybrid seed of tall forage millets. Experience 

 indicates that a field planted to a mixture of 

 equal numbers of seeds of four different dwarfs 

 will by natural crossing produce seed, 75 per 

 cent of which will be Fi hybrids. These hybrids 

 will be tall, will carry hybrid vigor (up to 50 per 

 cent), will crowd out the inbred seedlings, and 

 will give forage yields comparable to 100 per 

 cent hybrid seed. Cytoplasmic male-sterile 

 dwarfs recently developed can be used as 

 females to facilitate single-cross seed production 

 and will give tall hybrids if normal or different 

 dwarf males are used. 



Cooperative investigations at Tifton, Ga., of 

 the Crops Research Division, ARS, USDA, 

 and the University of Georgia, College of 

 Agriculture Experiment Station, Coastal 

 Plain Experiment Station. 



times made that ssp. spelta originated as a simple 

 deficiency for Q. 



A line with chromosome 5A of ssp. spelta 

 substituted into ssp. vulgare var. Chinese Spring 

 was used for testing the effect of increased dosage 

 of the spelta allele q. Squareheadedness was 

 chosen as the character that most clearly 

 distinguishes the vulgare from spelta phenotype. 

 Five doses of q resulted in squareheadedness, 

 while six doses caused even further compaction 

 of the spikes. Evidently q is not a deficiency 

 nor an amorph but is an allele which has an 

 effect similar to that of Q but of a lesser degree. 

 Relative to Q, q is a hypomorph, and five doses 

 of q corresponds to two doses of Q. The threshold 

 level for squareheadedness lies between four 

 and five doses of q. 



Being qq, spelta should be closer to vulgare in 

 phenotype than is speltoid, which is deficient for 

 the q locus. That the reverse is true is attributed 

 to the effect of modifying genes. Modifiers are 

 also assumed to account for the ambiguities of 

 dominance that are found in the Fi between ssp. 

 vulgare and ssp. spelta. 



Evidence has been obtained for the existence 

 of duplicates of q on the homoeologous chromo- 

 somes, 5B and 5D that are similar in effect, but 

 probably not identical, to q. 



13.63. The Nature of Supergenes in Polyploid 

 Wheats. D. Zohary, M. Feldman and Z. 

 Brick (Jerusalem, Israel). 



It is proposed that supergenes differentiating 

 between the principal types of hexaploid wheats 

 (i.e. spelta or Q factor, sphaerococcum or S 

 factor, compactum or C factor) are alien chromo- 

 somal segments that have been incorporated into 

 the polyploid wheats by means of distant in- 

 trogression from several genera of the Triti- 

 cinae. Such mode of origin explains why these 

 factors are genetically compound and why 

 they lack homology in the respective chromo- 

 somes of the primitive wheats (i.e. show null- 

 allelic situation). These supergenes are confined 

 to the polyploid level since polyploidy buffered 

 the incorporation of alien segments. 



13.62. The Nature of the Spelta Gene q. Mikio 

 Muramatsu (Columbia, U.S.A.). 



Deficiency of the vulgare gene Q on chromo- 

 some 5A (IX) in hexaploid common wheat, 

 Triticum aestivum ssp. vulgare, results in a 

 phenotype called speltoid because it is very 

 similar to ssp. spelta. The assumption is some- 



13.64. Induced Mutations at the "Q" Locus in 

 Relation to the Phylogeny of Hexaploid 

 Triticum Species. M. S. Swaminathan (New 

 Delhi, India). 



Induced mutations leading to the loss or du- 

 plication of the free-threshing gene Q located 



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