Section 13 — Plant Genetic and Breeding 



the coefficient of variation is 7.3 per cent for the 

 latter and varies between 10.7 and 15.0 per cent 

 for the former. 



Though the quantity of viable pollen in tetra- 

 ploid flowers is still sufficient, the number of 

 grains deposited on the stigmata is generally 

 lower than in diploid plants and a variable 

 percentage of spikelets are not at all pollinated. 



The pollen germinates on the stigma as soon 

 and as well in tetraploid as in diploid plants. 

 Nevertheless, many pollinated flowers fail to 

 set seed; thus if the low pollination is one cause 

 of the partial sterility of tetraploid rice, it is 

 not the only one. 



These data on pollination and the study of 

 other causes of sterility will be published later, 

 probably in La Cellule. 



13.20. The Location of a Gene for Male-sterility in 

 Linkage Group I of Barley. J. Milohnic 

 (Zagreb, Yugoslavia). 



Crosses have been made between male-sterile 

 (ms ms; Suneson) lines of H. vulgare and normal 

 (Ms Ms) H. distichum. The former species is 

 six-rowed (v v) and has a low number of rachis 

 internodes (rin rin). The latter species is V V 

 Rin Rin. F2 analysis shows that ms is linked to 

 the two chromosome I loci. The order is as fol- 

 lows (rec. per cent by product-ratio): v - 30.7 - 

 rin - 33.8 - ms. Rec. per cent between v and ms 

 is 48.7. It was also found that ms ms reduces 

 the number of rachis internodes in the Rin-rin 

 genotypes. 



13.19. Pollen Morphology in Relation to Pollen 

 Germination and Seed Set in Tetraploid Red 

 Clover. Marie Bragdo, (Vollebekk, Norway). 



Pollen morphology, judged by the aceto- 

 carmine-glycerine-method, and seed set were 

 studied in 1961 in 176 plants. The following 

 characters were observed: 



Xi Per cent good pollen grains (well stained 



and not shrivelled). 

 X2 Diameter of good pollen grains. 

 X3 Variation in diameter of good pollen grains. 



y Number of seeds per head after open polli- 

 nation in the field. 



AsXi was closely correlated with X2, the latter 

 was discarded. No correlation was detected 

 between Xi and X 3 . Y was positively correlated 

 with Xi, and negatively correlated with X3. 



Some plants, selected for pollen quality ac- 

 cording to morphology, were propagated by 

 cuttings. In 1962, 15 plants of each clone were 

 planted in a field and pollen morphology stu- 

 died. There was a good agreement between the 

 percentages of good pollen grains in 1961 and 

 1962. A test of pollen germination on sugar-agar 

 showed this to be significantly correlated with 

 percentage of morphologically good pollen. 

 Thus, pollen morphology, judged by the aceto- 

 carmine-glycerine-method gave a fairly good 

 indication of the relative germinability. The 

 average of germinated pollen grains was lower 

 than the average of morphologically good pollen. 



On account of the selfsterility in red clover, 

 the seed set cannot be much influenced by the 

 pollen quality of the same plant. The association 

 must be due to some other factor, with which 

 both are correlated, probably the quality of the 

 female gametes. 



13.21. Tetraploid Inheritance of Monogerm Charac- 

 ter and Male-sterility in Beta vulgaris L. (Sugar- 

 beet). V. F. Savitsky (Salinas, U.S.A.). 



1. Monogerm character (gene in) is inherited 

 in tetraploids on the basis of chromatid assort- 

 ment at an intermediate frequency of double 

 reduction (parameter a). Value of a is stipulated 

 by an intermediate frequency of crossovers 

 between the locus and kinetochore (parameter 

 e), and by an intermediate number of quadri- 

 valents formed (parameter a). Gene expression: 

 nulliplex nu produces monogerm fruits; sim- 

 plex Miiri3 and the rest of genotypes produce 

 multigerm fruits. 



2. Gene a, responsible for mendelian male- 

 sterility, and gene m are located in different chro- 

 mosomes. Gene a is inherited on the basis of 

 chromatid assortment, but the value of its 

 parameter a is greater than the value of a for 

 the gene m. Gene a is located further from its 

 kinetochore than the gene m. Gene expression: 

 nulliplex a4 causes complete male-sterility; 

 simplex Aia3 and all other genotypes are male- 

 fertile. 



3. Inheritance of cytoplasmic-genetic type of 

 male sterility in tetraploids indicated the pre- 

 sence of only 1 basic gene which controls pollen 

 fertility in cytoplasmic male-sterile races, not of 

 2 genes as often assumed in studies of diploid 

 heredity. This gene is inherited on the basis of 

 chromatid assortment. 



13.22. (D.) Sterility in Broad Bean (Vicia faba L.). 

 D. G. Rowlands (Bedford, Great Britain). 



The demonstration shows that sterility in 

 Broad Bean is not a simple system but operates at 



215 



