1:." F? 'f L . J3 . a {1 .. 2: .D m a :1: O m z .11 in INHERITANCE OF X-RAY INDUCED MUTANTS IN THE NAVY BEAN Thesis for the Degree of M. S. MICHIGAN STATE COLLEGE Earl Stewart Homer 1942 \' Him“ INHERITANCE 0F X-RAY INDUCED MUTANTS IN THE NAVY BEAN EARL S‘I‘ENVART HORNER A THESIS Suhnitted to the Graduate School of Michigan State College of Agriculture and Applied Science in partial fulfilment of the requiranente for the degree of MASTER OF SCIENCE Department of Farm Crops 1942 THESL‘. ACKNOWLEmmaNT The writer acknowledges the assistance, advice, and con- structive criticism of Dr. E. E. Dom and Mr. H. II. Bram in carrying on this study and in preparing this manuscript. 1.42806 CONTENTS gagg Introduction 1 Methods of Experimentation 1 Description of the Mutant Types 1 anaerimental Plan 3 Results 1. Crosses Within Types 1. Crosses Between Types 5 Crosses Between the Mutant and Normal Types 6 Backcrosses to the Mutant Parents 10 Smary ll INTRODUCTION In the spring of 1938 Genter irradiated several lots of Michelite bean (Phaseolus flgaris) seed, both dormant and germinated, with vary- ing dosages of X—rays (2). Of the rather largenumber of mutants re- sulting from this experiment, only a few produced seed in sufficient quan- tities to permit continuation of the individual lines. Abnormal plants (mutants) selected from the second generation of X-rayed material in 1939 bred true in 1940. Several lines of mutants were thus obtained. These could be grouped into four types, according to vegetative appearance. The present study was undertaken to determine whether the similar appearing progenies in each type were genetically alike; whether the dif- ferent types were alike genetically; and how many factors were responsible for the expression of the mutant character in each case. Prior to the work of Genter in 1939, no study had been made on the genetic effects of X—rays on beans. METHODS OF EXPERDIENI‘ATION Descrigtion of £133 Mutant Mes The four types of mutants studied were designated as A, B, C, and D. Their descriptions follow: Type A: The plants were about three-fourths as large as the normal (Hiehelite) , the leaves proportionately smaller; the branches were smaller in diameter and considerably more numerous than those of the normal; fewer runners were produced (Fig. 1A). Fig. 1. Typical plants from the normal and the four mutant types. Type B: The plants were irregularly shaped and about one-third as large as normal, the leaves proportionately smaller; similar to type A in that it had numerous slender, viny branches; no runners were produced (Fig. 13). Type C: The plants were about one-fourth to one-half as tall nor» mal, cylindrical in shape with thick, leathery leaves and only a few short, stubby branches produced en a rather thick, stiff central stem (Fig. 1C). Type D: These were quite similar to type B, except that the plants were more regular in shape and that more of the slender, viny branches were produced (Fig. 1D). Types A, B, and C were obtained from dormant seed Xérayed 30 minutes. Types A, B, and C were obtained from.dormant seed Israyed 30 minutes. Type D resulted from dormant seed.X-rayed 60 minutes. gaperimental Plan The.mutant parental lines consisted of two progenies each of types A, B, and C, and of three progenies of type D. These were designated as Al and A2, El and 32, and so on. All the seed in a progeny_came from a single plant grown in 1940. Seed for the normal type was taken from a lot of certified Michelite bean seed. In.order to determine whether or not the mutants were genetically alike, crosses were made between the individual lines in each type—-that is, lines Al and A2 were crossed together, and so on. For a similar pur- pose crosses were made between the different types. All possible combinp ations were attempted. To determine the number of factors responsible for the inheritance of each.mutant type, crosses were.made between all the mutant types and the normal type. In addition, backcrosses between the F1 and the corresponding mutant parent were made in the spring of 194.1. For a detailed description of the Wbridizing technique, see Down and Thayer (l). The parent types and F1 plants were grown in the greenhouse in the winter and spring of 1940-1941. The P2 generation and a row of each parent type were grown in the field in 191.1. When the F1 plants were grown it became evident that all the mu- tants were recessive to the normal type, as all the F1 plants in cross- es between the mutants and normal were normal in appearance. In cases where mutants were the female parents this information was used to de- cide whether the F1 plants were really twbrids or were self-pollinated. When it was not possible to discard selfs on this basis, segregation in the 1’2 was used as a criterion. The F1 plants used in the backcrosses were all results of normal pollen and mutant female parents, so the use of true mbrids was assured. All counts were made after the plants had nearly reached full size. The ratios obtained were tested by PQN formulae. RESULTS grosses Within 1:222 Only a limited number of F2 progenies were obtained from crosses made within types (Table l). Table l. Crosses Within Types —— wir— Crosgar No.4prqgenies__ ‘_§lfigppearance F2 appearance Al/A2 1. Mutant All mutant A2/Al 7 " " " 31/32 2 - n a Dl/D2 2 u n u D2/Dl 2 fl " " _Iotal lZ_ It seems safe to conclude that the similar appearing progenies in each type are genetically alike, since in 17 crosses all F1 plants were similar to the.mutants and no segregation took place in the F2. If we can eXpect about five per cent selfing (of 136 crosses made between the mutant types and between the mutants and the normal, seven were selfs), it still is not probable that all 11 of the seeds obtained from crosses between the two type A lines were selfs. Only two progenies were obtain- ed from pollinations between the two type B lines, but these too indi— cated that similar appearing lines were identical genetically. Similar conclusions could be drawn from the reaction of the four progenies ob- tained from crosses between the three lines of type D, none of which seg- regated. No data were obtained that would indicate whether or not the two type 0 lines were identical. _§rgsses Between Types In all crosses involving different types of mutants, the F1 plants were nonmal in appearance. This proves that the four types were gene- tically different from.each other. It was not possible in the field to distinguish between mutant types A, B, and D. Hence all mutants expected in a 9: 3: 3:1 ratio were grouped together. In all instances ratios were obtained that correspond very closely to a 9 normal to 7 mutant type ratio (Table 2). It was not possible in the first series of pollinations to obtain Iqbrids between type C and arm of the other mutant types. Later, however, three hybrids between 62 and D1 were gotten. These F1 plants were growl in the field in 191.1 and the F2 in the greenhouse in the fall of 191.1. The F2 ratio was 63 normal: 5 type D: 9 type C: 2 of a new type, probab- ly the double recessive (Fig. 2). This is not a good fit to a 9:333xl ratio, there being too few recessives, but with larger nunbers better re— sults might be expected. These results do show, however, that both types that went into the hybrids were recovered, and, in addition, a new type resulted which was intermediate between the two parent types. Crosses Beiween the Mutant and the Normal $29!. As a result of pollinations between the normal and the mutant types, a total of 88 F2 progenies were obtained. The F1 plants were all normal in appearance, and in the F2 the segregation of normal to mutant more or less closely approximated a 3:1 ratio (Table 3). Crosses between types A and D and the normal gave almost exactly 331 ratios. The results of crosses between types B and C and the normal were not so satisfactory, there being a somewhat large deficiency of mutant types in each case. Ob- servations of types B and C in the greenhouse indicated that neither was as viable nor as vigorous in growth as the normal or types A and D. The main difficulty with B was its low viability, and with C its lack of vigor (slow growth). This behavior may be used as an eJcplanation for the short- Table 2. Crosses Between Types No. of F1 F2 Segregation £32m _Dgy, ‘Qgggg Progenies_;gype Nggmg; Mutant Iota; 9;2 8,3, digg Al/ Bl 2 Normal 53 LO 93 12/31 2 w 22 29 51 12/32 2 - 27 15 42 31/11 1 w 11 12 23 31/12 9 " 86 71 157 32/12 6 n 70 66 136 11.2.1211 ' ' ’22 """" 229’ ' ”233‘ " E05 ' ’ ‘1'; ”1133111" 11/112 1 n 6 6 12 12/111 3 ' 12 26 12/113 3 " 25 20 45 111/11 3 s 62 u. 106 D3/A1 2 a 48 33 81 Sub-total " ' ’15 """" 195‘ ' His" ' £76 ’ " ’3’ "big; ‘01}? 31/111 1 w 9 9 18 32/111 2 n 1.0 38 78 111/31 2 '1 29 16 45 31/32 1 n 28 23 51 112/31 1 I 24 20 u. 's'uLEOEd ' ' '9 """" 1 So‘ " 366' " £32 ’ ’ 3 " ‘05; -o:4:1- we; all 551. $4341 1008 13 0.33_1._1;_1,_ *The odds given are against the occurrence of this deviation being due to chance alone. Odds of 1921 are at the 5% level. Fig. 2. The double recessive from a cross between types C and D. Table 3. Crosses Between Mutants and Normal Types Dev. Cross P§3g°e3iea mus Magisefiggtiogotu F313!“ "3%? Odds 111/11 9 Normal 140 52 192 12/11 3 n 64 11. 78 E/AZ.----5---2-___’+é-_.1.9---é3 ........... Substotal 16 248 85 333 2 0.22 0.231 £121""'2”'3""6;"1;"33 """""" 31/31 5 s 77 21. 101 nah! 5 v 1.17 31 11.3 N/B2 3 I 1.2 10 52 gag-£03; : :15 : : : : : 3333;383:193 : 27: :1293 :44: c1/11 21 - 415 110 525 N/Cl 1 u 9 2 11 02/11 5 a 53 12. 67 , 393322222122 : 1272:3113: .3: 3:13:23; : 111/11 6 n 120 31. 15/. 112/11 5 '1 112 u. 156 N/D2 10 n 21,2 34 326 113/! 5 u 83 21 101. N/D3 z. n 52 20 72 13.1%.; " ‘36 ' " ’ ’ ’ ’ ' 203 " '26; ’ 'eiz" ‘ ’o' ‘oio’ " 6.; ' 10 age omeutants in these two crosses, because during the week following the planting of these progenies heavy rains fell, causing rather severe crusting of the surface soil. Although various methods were used to break up this crust over the sprouting beans, some of the less vigor- ous seedlings may have perished. Backcrosses _t_<_1_ the My; Parents The results from.backcrossing are summarized in.Tab1e 4. Excluding the backcrosses involving the mutant type D, these counts tend to confinm the results Obtained from crosses between the mutants and the normal; that is, the mutant types were caused by single recessive factors. The per- ponderance of nonpnormal types in the backcrosses to the recessive par- ent D is rather difficult to explain. It may be that the pollen of this type matured earlier than was expected, with the result that a high per- centage of selfing of the recessive female parent occurred. Table A. Backcrosses. Backcross progeny Dev. from ‘23:; Cross Nonmal Mutant Total 1. 1:1 S.E. Odds 11 x 11/11 13 13 26 12 x n/12 1 5 6 BZ x N/BZ 8 11 19 Ql_X;N[C} _ - _ _5_ _ _ _2_ _ _ Z ____________________ §“E-E°Eal .. - .. 37.. .. - 21.. - -5§ ..... 3 ..... ° :52 - .. -0169. - 112 x u/112 15 27 1.2 23.391132 .. .. - -3... .. - 2°. .. -3§ .................... $32-$02“! .. .. - 23.. - - 27.. .. -39 ..... 1 Z ..... 313.. - - .621?! - SUMMARI The object of the present experiment was to test genetically four mutant types appearing in irradiated Michelite beans (Phaseolus vulgaris). It was concluded that the similar appearing progenies of the same type were genetically alike, and that the different types were geneti- cally unlike. All types were governed by single recessive factors. Linkage between the four recessives seems improbable. BIBLIOGRAPHY 1. Down, E. E., and Thayer, J. W., Jr. The Michelite bean. Mich. Me Me Stae Me 295s 1938e 2. Genter, Clarence F. , and Brown, Hubert M. X-ray studies on the field bean. Jour. Hered. 32:39-44. 1941. I ’1- "a. . y ’4 3'3. 5 "'TlTli‘flflifilLijfllLufilLiWilhflififilfllflllfllfilfiWTES 3082 7764