J Hered (1959) 50 (4): 177-187. (July 1959)
Cytological and Genetic Changes Induced by Vegetable Oils in Triticum
M. S. Swaminathan and A. T. Natarajan *

*Cytogeneticist and Assistant Cytogeneticist respectively, Indian Agricultural Research Institute, New Delhi-12, India. The authors are grateful to Drs. B. P. Pal and S. M Sikka for their advice and interest in the study. They are also indebted to Dr. E. R. Sears of the Missouri Agricultural Experiment Station and Dr. J. MacKey of the Swedish Seed Station Association, Svalöf, for their kind help in interpreting the data relating to the awn mutation.

DURING the course of the mutation experiments carried out at this Institute in several crop plants, the earlier findings of Gustafsson8 and other workers that there are marked differences in sensitivity to radiations among different plant species were confirmed. It was found that some oilseed plants like linseed and mustard are much less sensitive to radiation and X-rays and β-particles from P32 and S35 than cereals such as wheat and paddy. It seemed likely that the presence of oils in seeds might have a buffering effect on radiation and in an experiment designed to elicit information on this problem, seeds of Triticum monococcum, T. aestivum, Oryza sativa and Vicia faba were first soaked in some vegetable oils and edible fats and later subjected to X-irradiation. In this experiment, controls with no treatment and with seeds soaked in oils for various durations but not subsequently irradiated were kept. Observations on preparations of root tip mitosis made from this material showed that immersion of seeds in oil alone caused chromosome breakage in many cells21. Following this finding, a detailed study of the cytological and genetic effects of treatment with oils on Triticum species was undertaken. In an "Allium test" (Leven11) carried out during the earlier study, oils extracted from peanut (Arachis hypogaea), castor (Ricinus communis) and mustard (Brassica campestris var. toria) have been found to induce the highest frequency of chromosome aberrations and these three oils were therefore included in the present experiment.

Materials and Methods

Dry seeds of einkorn (T. monococcum var. Japanese Early; 2n=14), emmer (T. dicoccum, var. Khapli; 2n=28) and bread wheat (T. aestivum var. C.591; 2n=42) were soaked during the crop season of 1956, in peanut, mustard and castor oils extracted at the Division of Chemistry of this Institute. Seeds of einkorn and emmer wheats were soaked for six hours and the treatment lasted for 24 hours in bread wheat. At the end of the treatment, the seeds were wiped well with a muslin cloth and sown in the field. A few seeds were germinated in Petri dishes for the study of root tip mitosis. The root tips were fixed for 24 hours in acetic-alcohol (1:3) and were stained in leucobasic fuchsin after acid hydrolysis. Microsporogenesis was studied in Feulgen squashes. Preparations were also made from control plants raised from seeds sown either dry or after presoaking in water. Seeds of all treated plants were collected separately and the individual plant progenies were raised during 1957. Morphological observations were recorded both in the year of treatment and during the second generation.

Figure 16

Extensive fragmentation induced by oils in root tip cells. A—T. monococcum after two hours of treatment in mustard oil. B—T. aestivum, after six hours of treatment in caster oil.


Germination of seeds

The percentage of germination in different treatments is given in Table 1. Control seeds showed 96 to 100 percent germination. From the data, it is seen that in T. monococcum and T. aestivum, treatment with peanut oil caused the greatest reduction in germination. The iinhibition of germination was complete in peanut oil treated T. monococcum. The results also show that with increasing ploidy there is an enhanced survival. T. aestivum could stand a 24 hour treatment while in the diploid and tetraploid species even a six hour treatment was found to be fairly drastic. The trend of the relationship between polyploidy and sensitivity to oil treatments is thus similar to that found when ionizing radiations or other chemical mutagens are used20.

Mitotic aberrations

In preparations made 24, 48 and 72 hours after germination, several chromosome aberrations were observed. Both seen at metaphase and in some cells there was extensive fragmentation (Figure 16 A and B). Following treatment for six hours, the mean number of breaks per cell in T. monococcum was 0.882 in the case of castor oil and 0.647 in mustard oil. Treatment for one hour in peanut oil produced 1.28 breaks per cell. A striking feature of the metaphase plates in all the treatments was the absence of any evidence of reunion among broken fragments. In some chromosomes, the chromatids at the region of a break were asymmetrical, thus indicating the possibility that they were separately and independently broken. These observations would suggest that breakage occurs near

TABLE I. Percentage of germination of seeds in different treatments

Material Duration of
Percentage of germination in
Peanut oil Castor oil Mustard oil
T. monococcum 6 hrs. 0 12 8
T. dicoccum 6. hrs. 38 6 20
T. aestivum 24 hrs. 46 69 58


Figure 17

Abnormalities in root tip cells of T. monococcum treated with mustard oil for two hours. A—Anaphase with an ‘error’ configuration (arrow); B—tripolar spindle; C and D—binucleate cells with non-synchronised division.

the time of reduplication and is spread over a period of time. At anaphase, "error" configurations similar to those observed by LaCour and Rutishauser10 in endosperm cells of Scilla sibirica exposed to X-rays were found (Figure 17 A). The "error" bridge occurred only in mustard oil reared T. monococcum, in which this configuration recurred frequently. No point effects were noticed near the centromere and both intra-chromatid and inter-chromatid associations leading respectively to loop like structures and configurations with unequal arms distal to the point of union, were seen. The mechanism controlling the formation of such configurations is not clear and it is difficult to say whether sub-chromatid breaks are involved, as assumed for similar configurations by Swanson23 and LaCour and Rutishauser10 or whether the matrix maintains the connection between the full chromatid pieces that were associated prior to breakage, thereby giving the appearance of part-chromatid breaks, as suggested by Ostergren and Wakonig16. Lagging chromosomes or fragments also occurred frequently at anaphase.

No chromosome stickiness was induced by any of the treatments. In fact, treatment of seeds with some oils, particularly that of castor for two hours or less, caused a marked clarification of the karyotype22. In T. monococcum, a few tetraploid cells with 2n=28 occurred in [180] all the treatments. Binucleate cells were also present, arrested cytokinesis being probably responsible for these aberrations. Mitosis was not synchronized in some binucleate cells; in one cell one nucleus was in telophase and another in early anaphase (Figure 17C) and in another cell, one nucleus was in interphase and another in metaphase (Figure 17D). Other combinations such as interphase and prophase and interphase and anaphase also occurred. Spindle abnormalities such as tripolar (Figure 17B) and multipolar spindles were found in a few cells.

Meiosis in treated plants

Meiosis was studied during microsporogenesis in three to four plants of each species in every treatment. Meiosis was regular in the control plants and the abnormalities induced by the treatments are described below:

T. monococcum: No abnormality was found in plants raised from castor oil treated seeds. In a plant belonging to the mustard oil treatment, however, all the cells had six bivalents and two univalents (Figure 18B). The two univalents were unequal in size and appeared as rings. Caldecott and Smith8 have described similar configurations in X-rayed barley and have termed them "pseudo iso-chromosomes" since they considered that such configurations arise as a result of translocations between opposite arms of homologous chromosomes. The univalents observed in T. monococcum could also be pseudo iso-chromosomes of this description.

T. dicoccum: In some mustard and peanut oil treated plants, there were one quadrivalent and 12 bivalents at metaphase. The quadrivalents were of the chain or ring type. The frequency of chiasmata per nucleus (mean of 100 cells) was 35.4, 39.7, 37.8 and 37.9 in control, mustard oil, castor oil and peanut oil treatments respectively. A chromosome number other than 28 occurred in some microsporocytes and the frequency of their occurrence in the different treatments is given in Table II. Such "chromosome mosaic" cells (Frankhauser7 ), probably arise as a result of spindle abnormalities or chromosome non-disjunction and lagging during pre-meiotic mitosis. Anaphase I and subsequent stages were regular except for occasional irregular disjunction of the quadrivalent.

T. aestivum: Some cells at pachytene in a mustard oil treated plant snowed deficiency-duplication configurations (Figure 18 A). At diakinesis and metaphase I, one quadrivalent and 19 bivalents were seen in many cells (Figure 18 C, D and E). The quadrivalents were either rings or simple chains. Occasionally, a trivalent and a univalent were present in the place of a quadrivalent. An unequal bivalent was found in a peanut oil treated plant. As in T. diococcum, there was no reduction in chiasma frequency in the treated plants, the mean frequency of chiasmata per cell (mean of 100 cells) in control and peanut oil, castor oil and mustard oil treatments being 49.5, 50.8, 57.0 and 56.6 respectively. Chromosome mosaic cells occurred in T. aestivum also and the data are given in Table II. At anaphase I, laggards ranging from one to eight in number were seen. In mustard and peanut oil treatments, dicentric bridges and acentric fragments also occurred (Figure 18 F), indicating heterozygosity for inversions. The percentage of cells with laggards or bridges at anaphase I were 22.06, 35.9 and 25.3 in castor, mustard and peanut oil treatments respectively. Laggards were also seen in some cells at anaphase II and second division restitution leading to dyad fomation was observed in a few cells.

TABLE II. Frequency of PMC’s with varying chromosome numbers in emmer and bread wheats
T. dicoccum
Treatment No. of pollen-mother-cells with 2n = Mosaic Cells
  12 14 18 20 26 27 28 34 Total %
Castor oil 1 1 0 1 0 1 167 0 4 2.3
Mustard oil 1 1 0 1 0 2 173 0 5 2.8
Peanut oil 0 1 2 0 1 1 44 1 6 12.0
T. aestivum
Treatment No. of pollen-mother-cells with 2n = Mosaic Cells
  38 40 41 42 43 44   Total %
Castor oil 3 3 0 70 1 1      
Mustard oil 0 0 1 175 1 1      
Peanut oil 3 31 2 206 2 1      


Figure 18

A—T. aestivum, after 24 hours of treatment in peanut oil showing pachytene with deficiency-duplication configurations (arrow). B—T. monococcum after six hours of treatment in mustard oil, showing six bivalents and a pair of 'pseudo iso-chromosomes'. C, D and E—Metaphase I in T. aestivum treated with mustard, castor and peanut oils respectively showing one quadrivalent and 19 bivalents. F—T. aestivum, after 24 hours of treatment in peanut oil showing anaphase I with a dicentric bridge and an acentric fragment.


Figure 19
A—Earhead variations in the second generation plants of oil treatments, (C.591). 1. Reduced awns in the lower spikelets (castor oil) 2. Long tipped (castor oil); 3. Red glume (peanut oil); 4. Red glume-speltoid (peanut oil); 5. Speltoid (mustard oil); 6. Lax (castor oil); 7. Dense spike of erectoid mutant (peanut oil); 8. Beardless mutant (peanut oil). B—Control (extreme left) and erectoid plants. C—Earheads of control, beardless mutant, two types of F1 hybrids and the respective F2 segregants, (C.591).

Pollen and seed fertility

A reduction of five to seven percent in pollen fertility (as measured by stainability in aceto-carmine) occurred in the treated plants of T. monococcum and T. dicoccum. In T. aestivum, a maximum reduction of nine percent occurred in a peanut oil treated plant. Seed setting in T. aestivum was decreased to the extent of 14.3, 22.5 and 24.6 percent in relation to the control in peanut, mustard and castor oil treatments respectively. Fifteen to 20 percent reduction in seed setting occurred in T. dicoccum also. Practically no reduction in seed setting occurred in T. monococcum. It seems likely that in this diploid species, a strong intra-somatic selection may operate in the early stages following treatment which causes the elimination of a majority of affected cells.

Morphological changes observed in the first generation: Except for a little stunted growth in the early stages, no other abnormality was noticed in einkorn and emmer wheats in the year of treatment. In bread wheat, on the other hand, several changes relating to earhead characters were observed. C.591, the variety of bread wheat used, is a very stable and homogeneous variety characterized by a fully bearded earhead, white and pubescent glumes, amber colored grains and medium maturity. No spontaneous mutation has been observed in the large control material of this variety grown each season during the past four years. Among the changes observed in the year of treatment were speltoid, sub-compactoid and lax earheads. In addition, one plant in the peanut oil treated material had completely beardless earheads. In all other characters this plant resembled C-591. The frequency of.different first generation changes induced by the three oils is given in Table III. Each plant was harvested separately for raising the second generation. Crosses were made between the awnless plant and normal C-591 with the former as pistillate parent. Mutations observed in the second generation: The individual plant families of einkorn, emmer and bread wheats were grown in separate rows and carefully screened for the occurrence of mutations.

TABLE III. Changes observed in the first generation in bread wheat

Treatment No. of
Total no.
of spikes
No. of
No. of spikes of type Percentage
of affected
Speltoid Sub-
Lax Awnless
Peanut oil 46 323 299 20 0 1 3 7.42
Castor oil 69 326 319 7 0 0 0 2.07
Mustard oil 58 383 363 18 1 0 0 4.92

TABLE IV. Mutations observed in the second generation in bread wheat

Treatment No. of plant
No. of mutants of type  
Erectoid Early Dwarf Red glume Speltoid Compactoid Awn
Per plant
progeny (%)
Peanut oil 29 9 0 1 6 24 1 2 1 44 155.5
Castor oil 54 0 4 0 0 22 0 1 4 33 61.1
Mustard oil 55 0 0 0 0 1 0 1 0 2 3.6

A large control population was also raised. No phenotypically detectable mutation occurred in the progenies of einkorn and emmer wheats. There were, however, many prominent mutations in bread wheat (Figure 19 ^4) and the frequency of their occurrence is given in Table IV. While mutations affecting earhead characters were the most predominant, some early, dwarf, grass clump and erectoides mutations also occurred. The erectoides mutation was characterized by a short and stiff straw and compressed earhead (Figure 19 B). Both control and erectoid mutants had on an average 23 spikelets per earhead; the mean length of the earhead was, however, only 8.4 cms in the erectoid plants in comparison with 10.4 cms. found in the control. The variety C.591 had on an average six internodes while none of the erectoid plants had more than five internodes. The relative internode lengths in the control and erectoid plants are given in Figure 20. The study of the cross-section area in the middle region of each internode revealed a significant increase in area in the lower three internodes of the erectoid plants. The erectoid mutation was thus characterized by (1) a decrease in the number of internodes; (2) a relatively shorter basal internode and a longer uppermost internode and (3) an increased cross-section area in the basal and middle internodes. These results are similar to the observations of von Wettstein (quoted by Ehrenberg et al.6), in erectoid mutations in barley and wheat.

Among speltoid mutants there were two types — one with glabrous glumes and red grains and another with the normal pubescent glumes and amber grains. In the peanut oil treatment, some mutants with red glumes occurred (Figure 19 A). In two plants, the red glumes were present only in some tillers, the other tillers having normal white glumes. The shade of glume color was lighter in such chimeras than in mutants in which all the tillers had red glumes. One long tipped mutant (awns to 2 cms. in length, present in the uppermost spikelets) as well as one mutant in which the awn length was reduced to half the normal length occurred in the castor oil progeny.

Figure 20

Histogram showing the relative lengths of internodes in control and erectoid mutants of C.591. Note that in the erectoid mutants there is an increase in the length of the uppermost internode (I) and a reduction in the length of the basal internole (V). The control has six internodes, while the erectoids have only five.

Genetics of beardless mutation

As mentioned earlier, a plant with completely beardless spikes occurred in the material raised from seeds soaked in peanut oil. There were four ear-bearing tillers in this plant. One spike was fixed for the study of microsporogenesis, one spike was crossed with a control C-591 plant and the remaining two spikes were selfed. Deficiency-duplication configurations at pachytene, heteromorphic bivalents at metaphase I and chromosome mosaic cells were some of the abnormalities found during meiosis in this plant. In the selfed progeny, beardless, long tipped and fully bearded plants occurred. Among eight F1 plants from the cross beardless x control, two were fully bearded, two were long tipped to half bearded (Figure 19 C) and four were grass clumps and did not flower. The fully bearded F1 plants bred true, while the F2 from the tipped F1 had fully bearded, long tipped and beardless plants in the ration 1:2:1 (Figure 19 C). The date are given in table V. Meiosis in the fully bearded, long tipped and beardless segregants also indicated several changes such as inversions, interchanges and deletions had been transmitted to the progeny. The chromosome number was 2n=42 in all the plants studied except in a grass clump occurring in the selfed progeny which had 2n=40 in the root tops. A significant change associated with the loss of awns was a heavy reduction in tillering. Thus, while the normal C.591 plants grown in the field had on an average 24.3 ear-bearing tillers (mean of 50 plants) the beardless C.591 mutants had only 13.4 tillers per plant (mean of 22 plants). The yield of grains per plant in the control and beardless mutant were 40.3 ± 2.13 grams and 16.4 ± 1.88 grams respectively.

TABLE V. Segregation for awn character

Material No. of plants observed
Beardless Long tipped Fully bearded
C. 591 -- -- all plants
Selfed progeny of beardless plant found in peanut oil treatment 22 14 5
F1 beardless x control 0 2 2
F2 from fully bearded F1 0 0 170
F2 from long tipped F1 20 34 23

Watkins and Ellerton24 using conventional methods and Sears18 by monosomic analysis have established that varieties of bread wheat possess a series of genes which either inhibit or promote the development of awns. The symbols commonly used to designate these genes are B1 and B2 for the dominant awn inhibitors present in chromosomes 9 and 10 respectively, Hd for a factor in chromosome 8 which reduces the awns and makes them curved and a2, a13 and a20 for the awn-producing genes, the suffix representing the chromosomes which have definitely been shown to have an awn promoting effect. The beardless C.591 plant could thus have arisen as a result of a mutation leading to the origin of a dominant awn inhibitor or due to a deletion or mutation at the "a" locus. Based on the view9 that an "A" gene is non-epistatic but incompletely dominant over an awn-producing allele "a", a gene mutation at the "a" locus resulting in the loss of awn development would also be a dominant mutation. The segregation observed for awning in the F1 as well as in the selfed progeny of the beardless plant would suggest one of the following possibilities. First, the beardless plant could itself be F1 of a stray outcrossing between C.591 and a beardless wheat variety. This possibility seems unlikely since in crosses between all the bearded and beardless wheats in our collection, the F1 shows some tipping and is not completely beardless. Also, the beardless plant had all the other characteristics of C.591 and showed segregation only for awning upon selfing. Secondly, the initial beardless plant could have had a chimerical composition with the germinal layer, giving rise to the glumes being homozygous for the mutation and the layer giving rise to the micro- and mega-sporocytes being heterozygous for it. This explanation may be satisfactory for a single earhead but is very unlikely for the whole plant since three to four ear primordial are already differentiated in the treated seed. Also, for one cell to become homozygous for the mutation it would be necessary that there be a non-disjunction of the chromosome concerned and at the same time a non-disjunction to the other pole of the homologous chromosome carrying the non-mutated allele. This cell would then have had to become the only surviving cell in the entire germinal layer concerned. The third possibility is that the particular combination of deficiencies and other chromosome structural changes found in the beardless plant may have had a modifying effect so as to make the heterozygous mutant plant fully beardless. Some such reason may also account for the excess of beardless plants in the selfed progeny of the mutant (Table V).

While it is thus difficult to offer a convincing explanation for the observed results, it is of interest that the F1 of the cross beardless X control was either fully or half bearded. This would rule out the possibility that dominant epistatic factors are involved in the mutation to the beardless condition. It seems more likely that the beardless mutation owes its origin to the deletion of the awn producing genes present in C.591. The data in Table V would indicate that the awn promoting effect of chromosomes 2, 13 and 20 is due to single genes. The differences in awn expression observed between homozygous and heterozygous genotypes in the C.591 cross would suggest that the awn producing alleles are neither wholly dominant nor wholly recessive. However, from the observation that, in the absence of inhibitory factors, awn development is permitted even in heterozygous genotypes, it would be more logical to refer to awn producing genes by dominant symbols.


The results of the present study clearly establish that some vegetable oils can induce both chromosome breakage and viable mutations in wheat. These two properties of the oils may be correlated since many viable mutations in bread wheat arise from part or whole chromosome deficiencies or duplications12. It is particularly interesting that while chemical mutagens like nitrogen mustard have not been useful for inducing visible mutations in bread wheat14, agents like peanut oil are very effective. In fact, among various mutagens like X-rays, fast neutrons, P32, S35, nitrogen mustard and different oils used by us to induce mutations in the variety C.591, peanut oil gave the highest mutation rate per plant progeny17. The maximum mutation rate per plant progeny obtained by MacKey12 in bread wheat variety Rival was 167 percent using fast neutrons at the dose of 16,800 dis units. In our experiments in C.591, peanut oil gave a mutation rate of 155.5 percent and the mutagen which gave the next rate was S35 (94 percent). In contrast to the high mutation rate observed in bread wheat following treatment with oils, no mutation was found in einkorn and emmer wheats. This further supports the conclusion of MacKey13 that the polyploid state, far from being a handicap in mutation experiments as anticipated by Stadler19, is really an advantage since it permits many chromosome structural changes.

From the present data it is difficult to say whether any differences exist in the spectrum of mutations yielded by the different oils. The red glume color mutation as well as the erectoid mutation occurred only in peanut oil treatment. Using chlorophyll mutations indices, Ehrenberg et al.6 have demonstrated striking differences in the relative frequencies of different types of mutations induced by different chemical mutagens. The experiments with the different oil treatments would have to be repeated before it can be known whether certain types of mutations are always likely to be induced by a particular treatment.

The unsaturated fatty acid components probably form the mutgenic fraction of the vegetable oils. Auerbach and Robson1 found that the essential oil of mustard (allyl-iso-thyocyanate) had mutagenic properties but they were doubtful whether it produced chromosome aberrations. It was subsequently reported by D’Amato and Avanzi4 that allyl-iso-thiocyanate does not cause chromosome breakage. Studies in Drosophia have shown that sesame oil3 and peanut oil2 have no mutagenic properties. However, in the experiments of these authors, the oils were used to dissolve certain chemical mutagens and detailed studies on the effects of the oils themselves do not seem to have been undertaken. We are currently studying the mutagenic properties of the fractionated components of peanut, castor and mustard oils and the results may help to identify the mutagenic fraction.

A striking feature of the metaphase stage in the root tip cells, 24 to 72 hours after treatment with oils, was the absence of any evidence of reunion among broken fragments. There was extensive fragmentation in many cells which had "error" bridges at anaphase. The fact that in the same treatments, interchanges and inversions could be detected at meiosis suggests that a delayed reunion of broken chromosomes could have occurred. It is possible that treatment with oils causes chromosome breaks which remain open by some process analogous to that suggested by Wolff and Luippold25 to explain the action on chromosomes of enzyme poisons like dinitrophenol.

An important indication provided by the study of awn expression in the cross beardless mutant x normal C.591 is that in genotypes free of inhibitors, awn producing alleles show partial dominance in the heterozygous state. All beardless wheat varieties subjected to monosomic analysis have been found to possess one or more inhibitory factors. This and the occurrence of beardless or slightly tipped F1 in nearly all reported crosses between beardless and bearded varieties would suggest that strains beardless solely due to the lack of awn producing genes are rare or probably even non-existent in bread wheat. This interesting evolutionary feature tends to become obscured when the awn producing genes are referred to by recessive symbols. Sears (personal communication) has expressed the view that deficiencies of awn promoters must have occurred in the history of wheat very much more frequently than have awn inhibitors. The reason why none of them has been retained must be that such deficiencies result in too great a reduction in yield. This inference is supported by our observation that the beardless C.591 mutation is characterized by an appreciable reduction in the number of tillers and grain yield per plant. However, these plants have several chromosomal aberrations and it is difficult to be sure that the deletion of the awn producing allele alone is responsible for the reduced yield. Further studies on induced beardless mutations of fully bearded wheats would help to elucidate this interesting evolutionary problem.

Finally, the cytological and genetical effects of the vegetable oils studied by us assume importance in view of the relationship between mutagenicity and carcinogenicity. A comparative survey of the results not only radiations of different types but with mutagens suggests the view that the effects of these agents on genes and chromosomes form the basis of their effects in producing malignancies15. The role of nutrition with reference to the incidence of cancer is now widely realized and there are indications that a search for carcinogenic compounds in human dietary regimens might be worthwhile. Peanut and mustard oils are widely used as cooking media in tropical countries and it may be worthwhile pursuing the present line of work from this point of view.


Chromosome and chromatid breaks, "error" configurations, binucleate cells with or without synchronized mitosis and spindle abnormalities were observed in root tip cells of einkorn, emmer and bread wheats treated with peanut, mustard and castor oils. Though reunion following chromosome breakage appeared to be rare in mitotic plates, multivalent associations and inversion bridges were seen during microsporogenesis, thus indicating that delayed reunion may occur. Several morphological changes were observed during the year of treatment in bread wheat including a plant with completely beardless spikes. While no mutation was detected in einkorn and emmer wheats during the second generation, several viable mutations were isolated in bread wheat. Peanut oil yielded the maximum number of mutations among which the erectoides mutations may be of economic value. The genetics of the beardless mutation was followed and the results indicated that in the absence of epistatic genes, awn producing alleles are partially dominant. It seems likely that the rarity in nature of bread wheat varieties beardless due to the lack of awn producing genes, arises from heavy reduction in yield which the deletion of such genes causes.

Literature Cited

  1. AUERBACH, C. and J. M. ROBSON. Production of mutations by allyl-iso-thiocyanate. Nature 154:81. 1944.
  2. BIRD, M. J. Chemical mutagenesis. Drosophila Information Service 25:100. 1951.
  3. CALDECOTT, R. S. and L. SMITH. A study of X-ray induced chromosomal aberrations in barley. Cytologia 17:224-242. 1952.
  4. D’AMATO, F. and M. G. AVANZI. Studio comparitivo dell’ atti vita citologica di alcume essenzi. Caryologia 1:175-193. 1949.
  5. DEMEREC, M. Induction of mutations in Drosophila by dibenzantracene. Genetics 33:334-348. 1948.
  6. EHRENBERG, L., Å. GUSTAFSSON and D. VON WETTSTEIN. Studies on the mutation process in plants—regularities and intentional control. Conference on Chromosomes, Wageningen. 1-29. 1956.
  7. FRANKHAUSER, G. The effects of changes in chromosome numbers on amphibian development. Quart Rev. Biol. 2:20-78. 1945.
  8. GUSTAFSSON, Å. The X-ray resistance of dormant seeds in some agricultural plants. Hereditas, 30:167. 1944.
  9. HEYNE, E. G. and R. W. Livers. Monosomic analysis of leaf rust reaction, awnedness, winter injury and seed color in Pawnee wheat. Agron. Jour. 45:54-58. 1953. LACOUR, L. F. and A.
  10. RUTISHAUSER. X-ray breakage experiments with endosperm. Chromosoma 6:697-709. 1954.
  11. LEVAN, A. The influence on chromosomes and mitosis of chemicals as studied by "Allium Test." Proc. 8th Int. Congr. Genet. Hereditas Suppl. 325-337. 1949.
  12. MACKEY, J. Neutron and X-ray experiments in wheat and a revision of the speltoid problem. Hereditas 40:65-180. 1954.
  13. -----------------. Mutation breeding in polyploid cereals. Acta Agri. Scand. 4:549-57. 1954.
  14. -----------------. The biological action of mustards on dormant seeds of barley and wheat. Acta Agri. Scand. 4:419-29. 1954.
  15. MULLER, H. J. The nature of the genetic effects produced by radiation. Radiation Biology 1:351-473. 1954.
  16. OSTERGREN, G., T. WAKONIG. True or apparent subchromatid breakage and the induction of labile states in cytological chromosome loci. Bot. Notiser: 357-375. 1954.
  17. PAL, B. P., S. M. SIKKA, M. S. SWAMINATHAN and A. T. NATARAJAN. Frequency and types of mutations induced in bread wheat by some physical and chemical mutagens. Wheat Information Service 7: 1958.
  18. SEARS, E. R. Cytogenetic studies in the polyploidy species of wheat. II. Additional chromosome aberrations in Triticum vulgare. Genetics 29:232-246. 1944
  19. STADLER, L. J. Chromosome number and mutation rate in Avena and Triticum. Proc. Natl. Acad. Sci. U. S. 15:876-881. 1929.
  20. SWAMINATHAN, M. S. Polyploid and sensitivity to mutagens. Ind. Jour. Genet. & Pl. Breed 17:296-304. 1957.
  21. -----------------. and A.. T. NATABAJAN. Chromosome breakage induced by vegetable oils and edible fats. Curr. Sci. 25: 382-384. 1956.
  22. -----------------. and -----------------. Chromosome spreading induced by vegetable oils. Stain Tech. 32: 43-45. 1957.
  23. SWANSON, C P. The effect of infrared treatment on the production of X-ray induced changes in the chromosomes of Tradescantia. Proc. Natl. Acad. Sci. U. S. 35: 237-244. 1947.
  24. WATKINS, A. E. and S. ELLERTON. Variation and genetics of awn in Triticum. Jour. Genet. 40: 243-270. 1940..
  25. WOLFF, S. and H. E. LUIPPOLD. The production of two chemically different types of chromosomal breaks by ionizing radiations. Proc. Natl. Acad. Sci. U. S. 42: 510-514. 1956