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Euphytica 21 (1972) : 280-284

ACTINOMYCIN-D AND VARIETALADAPTATION IN WHEAT

P. K. DAS* and H. K. JAIN

Division of Genetics, Indian Agricultural Research Institute, Delhi-12, India

Received 17 June 1971

SUMMARY

Six Indian wheat varieties differing in their adaptation were selected for the study .They were treated with 350 µg/ml aqueous solution of antimetabolite Actinomycin-D .The effect of this antimetabolite was studied in seedling growth of six varieties . VarietyC. 306, which is known to be best adapted among all the varieties, was found to be re-latively less affected as compared to several other varieties. It showed minimum per-centage of growth inhibition. No significant interseedling variability was found fol-lowing the antimetabolite treatment. On the other hand, the poorly adapted varietyN.P . 823 was found to be very much affected when treated with Actinomycin-D . It wasobserved by the fact that variety N .P . 823 showed maximum percentage of growth in-hibition and produced a significant interseedling variability . It suggested a strongbuffering capacity of variety C . 306 against the treatment of Actinomycin-D .

INTRODUCTION

Differences in varietal adaptation are well knwon . The genetic determination forvarietal adaptation like that of some other characters is far from simple in nature . Itis not possible in general, to identify individual genes which have marked effects onadaptation. The only point on which there seems to be general agreement at present isthat differences in varietal adaptation are genotypically determined (ALLARD andBRADSHAW, 1964) ; the genetic mechanism underlying these differences remain obscure.This makes the task of breeding widely adapted varieties a difficult one .

The practice most commonly used to test varieties for their wider adaptation is tosubject them, when they have reached the fixed and final stage of development, to amulti-location test over a number of years, in which genotype-environmental interac-tions are estimated . The smaller the genotype-environmental interactions, the betterthe varietal adaptation (FINLAY and WILKINSON, 1963) . Thus, the main purpose withmulti-location tests is to identify those genotypes which give superior performance overa number of environments. The main object of the present study was to find whether itis possible to identify some other characteristics of wheat plants at an early stage ofdevelopment, which would indicate wider adaptation in the case of some varieties andpoorer adaptation for others without a recourse to multi-location tests . It was felt that

* Present address : Department of Agricultural Botany, University College of Wales, Aberystwyth,Cardiganshire, Wales, U .K .

identification of such a characteristic would aid in the development of varieties withgood adaptation . Keeping this in view six Indian wheat varieties were selected whichare known to differ greatly in their adaptation . They were treated with Actinomycin-D (AD) and the effect of AD was studied on the seedling growth of the six varieties .Although a wide range of inhibitors is available AD was selected because its biochem-istry has been studied in detail . It selectively inhibits RNA synthesis by blocking effect-ively the function of DNA as a template of RNA-polymerase (REICH, 1964) . As a re-sult protein synthesis is also susceptible to inhibition by AD (CASPERSON et al ., 1965) .It is possible that a highly adapted genotype may show strong buffering action so faras these metabolic functions are concerned .

MATERIALS AND METHODS

Six Indian varieties of bread wheat (Triticum aestivum L.) formed the experimentalmaterial . On the basis of multi-location yield trials for several years it is concludedthat the wheat variety C . 306 possesses a high degree of adaptability while the varietiesN.P. 823 and N.P. 825 adapted themselves poorly . The other varieties N .P. 824, C . 303and N.P. 798 showed a medium degree of adaptation . Seeds of the six varieties weresoaked in distilled water for 24 hours at 20 °C. Subsequently, they were grown in 350ll.g/ml aqueous solution of Actinomycin-D . The height of the 7-day seedlings was meas-ured to record the effect of antimetabolite . For this, 20 seedlings were scored from eachreplication. Data recorded were statistically analysed . Interseedling variability follow-ing the antimetabolite treatment was estimated for each variety as described by GRIF-FING and LANGRIDGE (1963). These interseedling variances were further subjected toBartlett's test of heterogeneity . It was anticipated that the less interseedling variabili-ty there would be, the more stable the varieties would be with respect to the anti-metabolite treatment .

RESULTS

Growth inhibitionObservations on the effect of AD on seedling height of differenf varieties after a 7-daygrowth are summarized in Table 1 . The results show that the AD treatment has a

Table 1 . Mean effect of Actinomycin-D on seedling height (cm) .

VARIETAL ADAPTATION IN WHEAT

C. D . values are 0.396 for variety means, 0 .230 for treatment means, and 0 .560 for interaction.

Euphytica 21 (1972)

28 1

Variety To -= control T = 350µg/ml Mean % of reductionin seedling height

C . 303 6 .232 2 .835 4.533 54 .5C. 306 7.773 3 .458 5 .615 55 .5N .P . 824 9.002 3 .757 6 .379 58 .2N .P . 823 9.145 3 .815 6 .480 69 .2N.P . 825 8.160 3 .093 5 .626 62 .1N.P . 798 8 .555 3 .340 5 .947 60 .9

Mean 8.144 3 .383

7b OF REDUCTION IN SEEDLING HEIGHT70 .0

68 .0

66.0

64.0

62.0

60.0

58 .0

56 .0

54 .0

52.0N .P.823 N .P.825N.P.798N.P.82 4 C.306 C .303

significant effect in reducing seedling growth (Fig . 1) . It is further found that the varie-ties differ significantly in their reaction to this compound . The percentage of reductionin seedling height is found to be highest in the case of variety N .P. 823 (69 .2 %) . Incontrast, the varieties C . 303 and C. 306 show a minimum percentage of reduction inseedling height (54 .5 % and 55 .5 %, respectively) . Varieties N .P. 824, N .P. 825 and N .P .798 show an intermediate type of behaviour . The above observations indicate that thereduction in heights which a variety shows following AD treatment, is not correlatedwith its seedling height . This is borne out by the observations that varieties N .P. 823and N.P. 824 manifest a similar height under normal conditions, but are affected quitedifferently following treatment with antimetabolite .

Table 2 . Inter-plant variability for seedling height following Actinomycin-D treatment.

P. K. DAS AND H . K. JAIN

+ Ve difference = Variability is higher at treated condition .- Ve difference = Variability is less at treated condition .* Significant at 5 % level .

Fig. 1 . Effect of AD on seedling height of dif-ferent varieties . Varity N .P. 823 shows the highestpercentage of reduction (69 .2%) in seedlingheight.

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Variety To = control T, = 350µg/mlof Actinomycin-D

T,-To X 2

C. 303 1 .606 0 .493 -1.113C. 306 1 .023 1 .139 +0.116 0.094N.P. 824 1 .256 1 .387 +0.131 0.072N.P. 823 1 .180 2 .505 +1.325 5.195*N.P. 825 0.713 0 .692 -0.021N.P. 798 2.879 0.950 -1 .929

Variation in the height of treated seedlingsThe effect of AD on different varieties has been studied in another way . The inter-seedling variation in height following the treatment has been analysed for each of thesix varieties . The variation has been measured by estimating the variance in each case,as shown in Table 2 . These estimates of variance presented in Table 2 show that in thecase of some of the varieties, the interseedling variation in height is greater in the caseof treated material as compated to the control material . In other words, some of thevarieties show a smaller degree of stability compared to the others following the treat-ment. The variety N .P. 823 shows the largest variance for interseedling height follow-ing the treatment . A test of heterogeneity shows that the increase in the interseedlingvariance after the treatment in the case of this variety is real (P > 0 .05) . The varietiesC. 306 and N.P. 824 also show an increased interseedling variance for seedling heightafter being treated with AD . A test of heterogeneity, however, shows that the control-led and treated seedlings do not differ significantly in their variances in the case of thesevarieties. In other words, the interseedling variability for seedling height is of the sameorder in the treated and controlled material in the case of the two varieties .

DISCUSSION AND CONCLUSION

Stability in performance of a variety is estimated by measuring the genotype-environ-mental interactions after growing the variety over a number of years at a large numberof locations . The less the genotype-environmental interaction the better the varietaladaptation . In the present study a particular kind of environmental disturbance ofmetabolism is created artificially, by the use of antimetabolite AD nd the reaction ofthe plants of different varieties to this environment has been investigated . In this sense,the present approach does not differ greatly from the standard procedure, but here nomulti-location testis involved, and varietal reaction to the antimetabolite is tested atthe early stage of seedling growth .

AD reduces seedling height . However, different varieties react differently to thisantimetabolite. This can be observed by the fact that the best adapted variety C . 306is relatively less affected compared to several of the other varieties . It shows a minimumpercentage of seedling growth inhibition and at the same time does not produce anysignificant interseedling variability following treatment with AD . On the other handthe variety N.P. 823, which is less adapted, shows maximum percentage of seedlinggrowth inhibition and its phenotypic stability with respect to seedling height is verypoor. It shows a significant interseedling variability after antimetabolite treatment .

It is well understood that any interference in nucleic acid synthesis and proteinsynthesis will cause inhibition of growth (BROWN, 1963). It is not surprising thereforein the present case, that a reduction in seedling height in all the varieties is observedafter the treatment with AD . AD interferes with RNA synthesis and thereby inhibitsprotein synthesis . What is most interesting here is the relatively poor sensitivity of thebest adapted variety C . 306 to the antimetabolite, which is observed by its minimumgrowth inhibition . It is worth noting at this point that the variety C . 306 not onlyshows minimum growth inhibition in seedling height, but its inhibited growth is verymuch uniform in the sense that seedlings show no significant interseedling variabilityin relation to height (Table 2) . This phenotypic stability is very much unique to the

VARIETAL ADAPTATION IN WHEAT

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P . K. DAS AND H. K . JAIN

variety C. 306. This stability of C . 306 may be attributed to the presence of templaterelatively stable to the inhibitor or not accessible to it at the concentration used .Suppose we can assume that in the present experiment AD acts by restricting the flowof gene products by inhibiting the synthesis of RNA dependent on nuclear DNA asdemonstrated in other systems, then the highly adapted genotype of C. 306 is able tomaintain the flow of its gene products in a relatively efficient way as compared to othervarieties in the presence of AD .Recently JAIN and DAS (1970) studied nucleic acid synthesis in wheat varieties dif-

fering widely in their adaptation after growing them at different temperatures : 20 °C,30'C and 38T . Following the treatment of tritiated thymidine they studied quantita-tively the synthesis of DNA at different thermal agitations . It was observed that thehighly adapted variety showed a remarkable stability in DNA synthesis at differenttemperatures . On the other hand, poorly adapted varieties failed to do so . Their ob-servations thus suggest that constancy in the synthesis of DNA under different environ-mental conditions may be an important attribute of a well adapted genotype . If thisshould be so, it is not difficult to appreciate why the highly adapted genotype like C .306 shows a remarkable phenotypic stability against the treatment of AD . The highlyadapted variety C. 306 in this experiment can grow relatively efficiently in the presenceof AD. Its DNA synthesis is not affected adversely as compared with that of othervarieties . It would thus appear that the presence of stable template may be a charact-eristic feature of a well adapted genotype .

REFERENCES

ALLARD, R. W. & BRADSHAW, A. D., 1964. Implications of genotype - environmental interactionsin applied plant breeding . Crop. Sci ., 4 : 503-508 .

BROWN, B. 1963 . Cellular differentiation in the root . S.E.B . Symposia, 17 :1-17 .CASPERSON, T., FERBER, S., FOLEY, G. E., KILLANDER, D . & ZETTERBERG, A ., 1965. Cytochemical

evaluation of metabolic inhibitors in cell culture. Expl . Cell Res 39:365-385 .FINLAY, K. W. & WILKINSON, G . N ., 1963 . The analysis of adaptation in a plant breeding program-me. Aust . J. Agric . Res ., 14: 742-754 .

GRIFFING, B. & LANGRIDGE, J . 1963 . Phenotypic stability of growth in the self-fertilised species,Arabidopsis thaliana . Statistical genetics and plant breeding NAS-NRC Publ . 982 : 368-390 .

JAIN, H. K. & DAs, P. K., 1970. Nucleic acid synthesis and adaptation in wheat . Wheat Inf. Serv .30:22-23 .

REICH, E. 1964. Actinomycin: Correlation of structure and function of its complexes with purinesand DNA . Science 143 :684-689 .

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