Monosomic and Conventional Analyses in Common wheat. III. Lethalityl) National Institute of Genetics, Misima

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1 Monosomic and Conventional Analyses in Common wheat. III. Lethalityl) Koichiro TSUNEWAKI National Institute of Genetics, Misima Received February 6, 1960 The inheritance of lethality in common wheat hybrids has been the subject of several investigations (2, 3, 4, 5 and 7). Those deal mainly with the number of factors involved and as yet little is known how the factors for lethality are located on the chromosomes. In a study comparing the monosomic with the conventional method of gene analysis in common wheat, Tsunewaki and Jenkins (8), noted that certain crosses produced only semilethal F1, plants which in F2 segregated into normals, semi-lethals and lethals. The determination of the number and the location of the factors responsible for this phenomenon formed the basis of this investigation. Materials and Methods For the comparative study (8) eight varieties, Prelude, Kharkov, Jones Fife, Chinese Spring, Red Bobs, S-615, Elgin and Red Egyptian, were crossed in diallell combination. In the F1 generation the crosses PreludeXKharkov and Prelude x Jones Fife produced only semi-lethal plants. All other crosses produced only normal F1 and F2 progeny. To determine if Kharkov and Jones Fife carried the same gene, an additional cross (Jones Fife x Kharkov) F1 X Prelude was made. To determine the chromosomal location of the lethality genes, Prelude was crossed with the Kharkov monosomic series and Kharkov with the Prelude monosmic series. The F1 generations were observed for the occurrence of semi-lethal plants. Results Conventional Analysis of the Lethal Factors. The F1 hybrids from crosses between Prelude and Kharkov or Jones Fife were all semi-lethal bearing about 10 seeds per plant. In the F2 generation the cross Prelude X Kharkov produced the ratio 41 lethals to 30 normals and the cross Prelude x Jones Fife 57 lethals to 43 normals. Both closely fit a 9 : 7 ratio indicating that lethality is caused by two dominant complementary genes. Kharkov and Jones Fife apparently carry the same gene because the cross (Kharkov x Jones Fife) FX X Prelude produced 252 lethal plants and a single normal plant. All other varieties included in the 1) Contributions from the Department of Plant Science, Univ. of Manitoba, Winnipeg, Canada and the National Institute of Genetics, Misima, Japan, No. 307.

2 72 TEE JAPANESE JOu RNAL 0P GENETICS Vol. 35 No. 3 earlier study must be doubly recessive for these genes. Monosomic Analysis of the Lethal Factors. In order to determine the location of the complementary lethal genes the monosomic series of Prelude was crossed with Kh arkov and the Kharkov monosomic series with Prelude. Data on the phenotypic segregation of the semi-lethal expression in the Fl generation are summarized in Table 1 for the Prelude monosomics and in Table 2 for the Kharkov monosomics. Table 1. Sere gation of Prelude semi-let al plants in t e Fl eneration of monosomics x Kharkov. Monosomoic series of Prelude and Kharkov were both derived from the Chines Spring series by backrossing. Both series, particularly that of Prelude, are in an early stage of development as the second column of Tables 1 and 2 shows. Because the monosomic plants used for crosses were obtained by self-pollination, it is expected that genes on a disomic chromosome can be heterozygous or homozygous

3 K. TSUNEWAK I: MONOSOMIC AND CONVENTIONAL GENE ANALYSES 73 Table 2. Segregation Kharkov of semi-lethal monosomics x plants in the F1 Prelude. generation of for either dominant or recessive factors. However, genes on the monosomic chromosome must be derived from Prelude in the Prelude monosomics and from Kharkov in the Kharkov monosomics. Assuming that a Prelude chromosome carries a gene, A, and a chromosome of Kharkov carries another gene, B, which together cause lethality, the following segregation is expected in the F1 generation of Prelude monosomics x Kharkov : i) Non-critical monosomic lines of Prelude (-.) X Kharkov (~ ) (a) If.. is homozygous for (b) If.j~- is hetero- (c) If.. is homo- zygous for Prelude gene zygous Chinese gene P generation : AAbb X aabb Aabb x aabb aabb x aabb AaBb /\ AaBb aabb aabb F1 generation : all semi- normal all semi-lethal lethal normal 1:1 ii) Critical monosomic line of Prelude (-~) X Kharkov (~) P generation : A-bb x aabb A /\ abb a-bb F1 generation : semi- normal lethal 1:3

4 74 THE JAPANESE JOURNAL OF GENETICS Vol. 35 No. 3 In the non-critical monosomic lines, one can expect an F1 ratio of either 1: 0, 1:1 or 0 : 1 for the semi-lethal vs. normal plants depending upon the genotype of the -- parent. On the other hand, only a 1: 3 ratio is expected for the critical monosomic line, because all disomic F1's must be semi-lethal and the monosomics normal. The same ratios are also expected for the F1's of Kharkov monosomics X Prelude. Based on these considerations, the actual F1 ratio obtained for each monosomic line was compared with the nearest ratio among the three expected for the noncriticalline and the 1 : 3 ratio expected for the critical line. The X2-values obtained are shown in Tables 1 and 2. All F1 lines from crosses between Prelude monosomics and Kharkov, excgt those derived from mono-v, fitted one of the three ratios possible for a non-critical line. Two progenies, one from mono-viii and the other from mono-xiv fitted either a critical or non-critical ratio; other progenies within these lines fitted only the non-critical ratio. This and the small size of the populations lead to the conclusion that those chromosomes do not carry factors for lethality. The ratios obtained from lines of mono-v fitted the critical 1: 3 ratio only, indicating that chromosome V of Prelude carries one of the complementary genes. In the crosses between the Kharkov monosomics and Prelude, all F1 lines except those derived from mono-xiii satisfied one of the three ratios expected for a noncritical line but disagreed with the ratio for the critical line. On the other hand, the F1 ratio obtained in the progenies of mono-xiii failed to fit any ratio for a non-critical line but satisfied the ratio expected for the critical line. These results indicate that chromosome XIII of Kharkov carries the other gene for lethality. Discussion The gene symbol, Le, was first proposed by Caldwell and Compton (2) and followed by Heyne et al. (4). The National Committee of Genetics and Breeding of the Japan Science Council (6) also recommended the use of this symbol. Ausemus et al. (1) proposed to use the symbol Ls. However, "s" indicating the seedling stage does not have much meaning because plants become lethal at various stages of development depending upon gene dosage. Recently, Hermsen (3) reviewed the literature on gene analysis of the lethal factors and proposed to sue N indicating "necrosis". The basis of his rejection of Le is the fact that these genes do not cause lethality but semi-lethality in the F1 generation. This reason is not valid, however, because plants are completely lethal when homozygous for these genes. In order to avoid any further complication, it is proposed that Le be used exclusively. The Prelude gene on chromosome V will be designated as Let and the Kharkov and Jones Fife gene on chromosome XIII as Lee. The Let gene is apparently identical with Caldwell and Compton's (2) Le gene. It is yet uncertain whether their Lee gene is the same as the gene of Kharkov and Jones Fife. So far as the phenotypic stability of lethality is concerned, three normal plants were found among the progenies expected to give all semi-lethal plants. They were

5 K. TSUNEWAKI: MONOSOMIC AND CONVENTIONAL GENE ANALYSES 75 obtained in the crosses, Kharkov monosomics X Prelude and (Kharkov X Jones Fife) F1X Prelude. These normal plants were not produced by self-pollination, because all of them showed leaf hairiness which is a Prelude character. Therefore, it is reasonable to assume that the expression of lethality is incomplete. The rate of penetration of the recessive allele in heterozygous plants is estimated to be about 0.05%, Summary Conventional and monosomic analyses of the lethality occurring in diallel crosses of eight common wheat varieties led to the following conclusions : (1) Lethality is controlled by two dominant complementary genes. (2) The gene in Prelude is located on chromsome V and designated as Lel. (3) The gene in Kharkov and Jones Fife is the same; it is located on chromsome XIII and designated as Lee. (4) Chinese Spring, S-615, Red Bobs, Elgin and Red Egyptian carry the recessive normal alleles of both genes. (5) The genetic penetration of the recessive normal gene is about 0.05%. The experimental results indicate that monosomic analysis, using an incomplete monosomic series, can be successfully applied when a few major genes are involved in the inheritance of a specific character. Acknowledgement The author wishes to express his sincere graditude to Dr. B.C. Jenkins for supplying his Kharkov monosomic series and to Dr. R.C. McGinnis for furnishing his Prelude monosomic series. The author also owes thanks to Dr. L. E. Evans for his critical reading of the manuscript. References (1) Ausemus, ER., Harrington, J.B., Reitz, L.P. and Worzella, W.W A summary of genetic studies in hexaploid and tetraploid wheats. Majority report of Committee on Nomenclature of Genetic Factors in Wheat. Jour. Amer. Soc. Agr. 38 : (2) Caldwell, R.M. and Compton, L.E Complementary lethal genes in wheat causing a progressive lethal necrosis of seedlings. Jour. Heredity 34 : (3) Hermsen, J.G. Th Classification of wheat varieties on the basis of their genotype of necrosis. Euphytica 8 : (4) Heyne, E.G., Wiebe, G.A. and Painter, R.H Complementary genes in wheat causing death of Fl plants. Jour. Heredity 34 : (5) Kostyuchenko, I.A The premature perishing of the hybrids in wheat crosses. Bull. Appl. Bot. Ser. A. 19 : (Ref. Plant Breed. Abstr. 8 : 27). (6) National Committee of Genetics and Breeding of the Japan Science Council Rules for nomenclature and symbolization of genes, and gene symbols in wheats. Wheat Information Service (7) Schmalz, H Subvitale Fl-Kombinationen beim Weizen. I. Genetische Untersuchungen. Zuchter 29 : (8) Tsunewaki, K. and Jenkins. B. C Monosomic and conventional analyses of genes in common wheat. Proc. IX Int. Bot. Congr. 12 : 404.