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Comparison of the effects of simulated fallout decay and constant exposure-rate gamma-ray treatments on the survival and yield of wheat and oats
Radiation Botany, 1971, Vol. 11, pp. 405 to 410. Pergamon Press. Printed in Great Britain.
C O M P A R I S O N OF T H E EFFECTS OF S I M U L A T E D F A L L O U T DECAY AND CONSTANT EXPOSURE-RATE GAMMA-RAY TREATMENTS ON T H E S U R V I V A L A N D YIELD OF W H E A T A N D OATS P.
J. B O T T I N O
a n d A. H . S P A R R O W
Biology Department, Brookhaven National Laboratory, Upton, New York 11973, U.S.A. (Received 17 March 1971) BOTTINO P. J. and SPARROWA. H. Comparison of the effects of simulatedfallout decay and constant exposure-rategamma-ray treatmentson the survival andyield of wheat and oats. RADIATIONBOTANY11~ 405--410, 1971.--Eight-day-old seedlings of wheat (Triticum aestivum L. em. Thell. 'Opal') and oats (Arena sativa L. 'Orbit') were subjected to xsTCsgamma radiation in two ways: ( 1)for 16 hr with constant rate exposures (CR) ; and (2) for 36 hr with changing exposure rates given as a fallout decay simulation (FDS). After irradiation the wheat was transplanted to the field, and the oats into 6-in. clay pots and placed in a screen-covered "greenhouse". Survival data were collected three times a week until no more deaths, attributable to the radiation occurred. Seed yield data from survivors were obtained at the end of the growing season. At equal total exposures, the 36-hr FDS treatment was more effective in reducing survival than the 16-hr CR treatments. The ratio of 16-hr CR/FDS LDs0's was 1.46 for wheat and 1.19 for oats. The FDS was more effective in reducing the yield only at exposures above the LDx0. The FDS exposures producing a 50 per cent reduction in seed yield (YDn0) were 1.73-t-0.29 kR for 'Opal' wheat and 1.42 -t-0.27 kR for 'Orbit' oats. The 16-hr CR YDs0 exposures were 2.264-0.61 kR for wheat and 1.514-0.22 kR for oats. In all cases, yield was a much more sensitive end point than survival, indicating that even though a crop might survive fallout exposures in some cases, no appreciable seed yield would be produced. That is, reproductive survival (seed) is more sensitive than somatic survival (plants). INTRODUCTION THE TOTAL r a d i a t i o n exposure to a p o p u l a t i o n of
plants from r a d i o a c t i v e fallout comes from b o t h b e t a a n d g a m m a r a d i a t i o n . Some investigators have s t u d i e d the r a d i a t i o n effects a n d m e a s u r e d the r a d i a t i o n doses u n d e r a c t u a l fallout conditions.(n-is) T h e y have f o u n d t h a t the ratio o f b e t a / g a m m a exposures m a y v a r y b e t w e e n 4 a n d 15:1. M o r e c o m m o n l y , however, fallout effect studies h a v e involved the less c o m p l e x situation o f e x a m i n i n g the effects o f b e t a or g a m m a r a d i a t i o n alone u n d e r g r o w t h c h a m b e r , greenhouse or field conditions. T h e b e t a r a d i a t i o n or p a r t i c l e studies have been c o n c e r n e d p r i m a r i l y with r e t e n t i o n a n d g e n e r a l effects of synthetic particles l a b e l e d w i t h b e t a emitters.(5,14.15, ~1) T h e g a m m a r a d i a t i o n studies h a v e b e e n con405 A
c e r n e d with m e a s u r i n g survival a n d yield after exposure to either u n i f o r m or v a r y i n g exposure rates, or the decreasing rate o f s i m u l a t e d fallout decay.(1-4,16-1s) O n l y very recently(-°°) has a s t u d y been c o n d u c t e d w i t h c o m b i n e d betag a m m a treatments, in w h i c h it was shown that the R B E o f these two types of r a d i a t i o n s is a p p r o x i m a t e l y 1 w h e n vegetative g r o w t h is the biological end p o i n t used. T h e c u r r e n t status of knowledge c o n c e r n i n g the effects o f g a m m a r a d i a t i o n from fallout on crop plants has b e e n r e v i e w e d recently.(19) T h e present c o m m u n i c a tion on the i m p o r t a n t crop plants, w h e a t a n d oats, is a n o t h e r in a c o n t i n u i n g series of studies c o m p a r i n g the effects o f u n i f o r m exposure-rate t r e a t m e n t s on crop plants with those of fallout d e c a y simulation treatments.
P. J. BOTTINO and A. H. SPARROW
406
MATERIALS A N D METHODS
Young
(eight-day-old) seedlings of wheat (Triticum aestivum L. em. Thell. 'Opal') and oats (Avena sativa L. 'Orbit') in 2-in. peat pots were given the following treatments of 137Cs g a m m a radiation: (I) a constant exposure rate (CR) treatment for 16 hr; and (2) a decreasing exposure rate treatment for 36 hr given as a fallout decay simulation (FDS). Because the meristem at eight days is still below the ground the seeds are sown next to the peat pot wall in order to make attenuation by the soil negligible. The theory and facilities used for irradiation have been previously described in detail.(1,tv, is) Thirteen exposures and a nonirradiated control with 25 plants at each were used in the wheat experiment; 11 exposures and a nonirradiated control with 16 plants at each were used in the oat experiment. After irradiation the wheat seedlings were transplanted to field experimental plots covered with 12 x 12 mesh natural Saran cloth to prevent damage by birds. The oat seedlings were transplanted into 6-in. clay pots and placed in a screen-covered "greenhouse", also for protection against birds. The irradiation and field planting of both experiments were conducted in May, 1970. All plants were scored for survival three times a week until no more deaths attributable to the radiation occurred. This was an average of 45 days
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RESULTS A N D DISCUSSION
Survival data for the two crops are given in Figs. la and lb as probit plots of survival (percent of control) against exposure for the two treatments. The curves are computer-fitted lines to the actual data points. Survival. end-point values are summarized in Table 1. For both crops, the FDS treatment is much more effective in reducing survival than the 16-hr CR. For wheat (Fig. la) the ratio of 16-hr GR/FDS LDs0's is 1.46 and for oats (Fig. 1b) this ratio is 1"19.
The yield data for the two crops are given in Figs. 2a and 2b. The data are plotted as the mean weight of seeds per initially treated plant against exposure. In both cases no consistent difference
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postirradiation. Seed yield data (weight and number of inflorescences per plant) were collected after harvest in early September (1970). For low exposures the n u m b e r of plants from which seed was harvested was the same as that initially irradiated. For high exposures, where plant deaths occurred, seed weight from all surviving plants was totalled and then divided by the number of plants initially irradiated. This is termed 'seed weight per treated plant'. The average n u m b e r of seeds per inflorescence, however, was determined on a per surviving plant basis.
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FIG. I. Probit plot of survival as per cent of control vs. exposure (kR) for (a) wheat and (b) oats given a 36-hr FDS or a 16-hr OR treatment.
GAMMA-RAY TREATMENT OF WHEAT AND OATS
407
Table 1. Summary of survival and yield end points (kR 4-S.D.) for the 36-hr FDS and the 16-hr CR treatments of wheat and oat seedlings with the 16-hr CR]FDS ratios
Wheat End Point (kR+S.D.)
Oats Ratio 16-hr CR/FDS
16-hr CR
Ratio 16-hr CR/FDS
16-hr CR
FDS
FDS
LDz9 LDso LDoo
4.63 4-0-08 5'11 4-0"05 5'59 4-0"09
2.70 4-0.14 3"51 4-0.07 4"32 4-0"14
1.71 1"46 1"29
3"24 4-0"22 4.104-0.15 4"96 4-0"25
2"57 4-0.16 3"43 4-0"17 4"28 -t-0"29
1.26 1"19 1"15
YDIo YDso YDgo
0.97 4- 0.94 2.26 4- 0.61 5.80 4-0-78
1.29 4- 0.35 1.73 4- 0.29 2.92 4-0.20
0.75 1.30 1.98
0.92 4- 0.28 1.51 4- 0.22 3.15 +0.33
0.90 4- 0.36 1.42 4- 0.27 2.84 4-0.50
1.02 1.06 1.10
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FIG. 2. Log mean weight of seeds per treated plant (g) vs. exposure (kR) for (a) wheat and (b) oats given a 36-hr FDS or a 16-hr CR treatment. between the two treatments was observed at the lower exposures. However, at the higher exposures the FDS was more effective in reducing yield (see also Table 1). A measure of one of the components of yield in these irradiated plants may be made by calcularing the number of seeds per head or panicle and plotting this against exposure as given in Fig. 3. In Fig. 3a for wheat there is no difference between the two treatments at the low exposures but a clear separation occurs at the higher exposures, with the FDS being more effective than the 16-hr CR. Figure 3b gives a similar plot for oats and again only at the high exposures do
differences between the treatments occur. It is important to note that the yield response is the same even though two different yield end points were used. A similar response would be expected with weight per 100 seeds. The greater effectiveness of the FDS treatment compared to the 16-hr CR treatment has been previously reported for many other crop plants (t,l~-tg) and is probably due to the higher initial exposure rates encountered with this treatment. The greater effectiveness of high rates over low rates is well established and has good recent experimental basis.0,4,S-l°,Zg) The 16-hr CR/FDS ratios reported here, 1.46 for wheat and
P. J. B O T T I N O and A. H. SPARROW
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Fxo. 3. (a) Log mean number of seeds per head vs. exposure (kR) for wheat given 36-hr FDS or a 16-hr CR treatment; (b) log mean number of seeds per panicle vs. exposure (kR) for oats given a 36-hr FDS or a 16-hr CR treatment. 1"20 for oats, are in good agreement with those (average 1 "4) previously reported for other crops. ¢17,18) Factor differences for other treatments c o m p a r e d to the FDS have been recently published. (19) T h e absence of a difference in yield between the two treatments at the low exposures has also been noted in lettuce, barley, and another variety of wheat ('Indus').(1) T h e exact reason for this is not clear, but it could be that below a certain exposure, the d a m a g e is not great enough to bring about a significant exposurerate effect. After a certain a m o u n t of d a m a g e is induced the higher exposure rates of the FDS treatment become more effective than the 16-hr C R treatment a n d a divergence between the two treatments occurs. T h e conclusion that a certain a m o u n t of d a m a g e has to be induced before an exposure-rate effect occurs m a y also be drawn from the exposure-rate experiments of others. (4,8-10) Further support for this m i n i m u m d a m a g e requirement comes from the finding that the differences between the two treatments occur only at exposures high enough to cause some plant deaths. Therefore, it could be the plant deaths primarily in the FDS treatment which bring about the differences at the higher exposures. For both crops the point at which the
response to the two treatments begins to diverge was very near the FDS LD10, 2"70 k R for wheat and 2.57 k R for oats. W h e n seed yield is calculated on the basis of the original n u m b e r of plants as it is done here, sharp decreases in seed yield response would be expected to occur at or near exposures where plant deaths begin to occur. It should also be noted that no stimulation in seed yield occurred at the low exposures for these two crops. I n fact we have yet to observe any stimulation of seed yield by low exposures in any of the cereals studied thus far. A s u m m a r y of the survival and yield data for both crops is given in Table 1. I n the case of survival the greater effectiveness of the FDS over the 16-hr C R is evident for all end points. W i t h yield, however, the differences are not so evident. I n fact differences between the two treatments a p p e a r only at or above the YDs0. I t is also important to note that yield is a b o u t twice as sensitive an end point per R than survival. Exposures which would reduce survival by 50 per cent reduced yield by 90 per cent or more. This means that even though a crop survives an exposure to fallout radiation it would not necessarily give an appreciable yield. At first glance our results would not seem to agree with those on wheat a n d oats of DAVIES,
G A M M A - R A Y T R E A T M E N T O F W H E A T and OATS (s,7) who f o u n d for b o t h crops t h a t exposures o f 2.0 k R at e a r l y vegetative stages resulted in early d e a t h of the plants. W e have found no deaths at 2-0 k R for either crop or t r e a t m e n t . This a p p a r e n t difference can be e x p l a i n e d h o w e v e r b y the h i g h e r exposure rates in D a v i e s ' experiments. D a v i e s ' exposures were given at 2 8 - 3 0 R / m i n , while o u r 16-hr C R exposure is 2"1 R / m i n for 2"0 kR. T h e m u c h h i g h e r rates in D a v i e s ' e x p e r i m e n t s m o r e t h a n e x p l a i n the lower survival levels in his e x p e r i m e n t s c o m p a r e d to the present studies. W e , in o u r experiments, h a v e shown the g r e a t e r effectiveness of high rates over low rates, o)
Acknowledgements--Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission and the Office of Civil Defense, Department of the Army, Washington, D.C. under Project Order No. DAHC20-70-C0376, Work Unit 3133E (contracting office technical representative Dr. D. W. BENSEN). This report has been reviewed by the Office of Civil Defence and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Office of Civil Defense. The authors wish to thank BRENDA FLOYD,PAMELASILIMPERIand J. BRYANTfor assistance with the irradiations and data collection. We thank Dr. NEAL JENSEN, Dept. of Plant Breeding, Cornell University, for supplying the seed. The assistance of Mr. K. H. THOMPSONwith statistics and Miss SUSANS. SCHWEMMERfor critical comments on the manuscript are also acknowledged. REFERENC2ES 1. BOTTINO P. J. and SPARROW A. H. (1971) The effects of exposure time and rate on the survival and yield of lettuce, barley and wheat. Radiation Botany U , 147-156. 2. CLARK G. M., RoY R. M., BAKER D. G. and BUNTING W. R. (1965) Simulated fallout studies in conifers--a preliminary report. Health Phys. U , 1627-1636. 3. CLARK G. M., CHENG F., RoY R. M., SWSANEY W. P., BUNTING W. R. and BAKER D. G. (1967) Effects of thermal stress and simulated fallout on conifer seeds. Radiation Botany 7, 167-175. 4. CONSTANTINM . J . , KILLION D. D. and SIEMERE. G. (1971) Exposure rate effects on soybean plant responses to gamma irradiation. In, Survival of food crops and livestock in the event of nuclear war. Proc. Symp. held at Brookhaven Natl. Lab., Upton, N.Y., September 1970, sponsored by the
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OCD, USAEC and USDA. AEC DTIE 700909 (in press). 5. D A H L ~ R. C. (1971) Prediction ofradionuclide contamination of grass from fallout-particle i'etention and behavior. In, Survival of food crops and livestock in the event of nuclear war. Proe. Syrup. held at Brookhaven Natl. Lab., Upton, N.Y., September 1970, sponsored by the OCD, USAEC and USDA. AEC DTIE 700909 (in press). 6. DAvms C. R. (1968) Effects of gamma irradiation on growth and yield of agricultural crops. I. Spring sown wheat. Radiation Botany 8, 17-30. 7. DAVIESC. R. (1970) Effects of gamma irradiation on growth and yield of agricultural crops. II. Spring sown barley and other cereals. Radiation Botany 10, 19-27. 8. HALLE.J. andBEDFOaDJ. S. (1964) Acomparison of the effects of acute and protracted gammaradiation on the growth of seedlings of Viciafaba. I. Experimental observations. Intern. o7. Radiation Biol. 8) 467--474. 9. KmEBSJ. S. and LEONG G. F. (1970) Effect of exposure rate on the gastrointestinal LDs0 of mice exposed to 6°Co gamma rays or 250 kVp X-rays. Radiation Res. 42, 601-613. 10. McCRORY G.J. and GRUN P. (1969) Relationship between radiation dose rate and lethality of diploid clones of Solanum. Radiation Botany 9, 27-32. 11. RHOADSW. A., PLATr R. B. and HAgVEY R. A. (1969) Radiosensitivity of certain perennial shrub species based on a study of the nuclear excavation experiment, Palanquin, with other observations of effects on the vegetation. USAEC Div. Tech. Info. Extension, Oak Ridge, Tenn. CEX-68.4.42 p. 12. RHOADSW. A., PLAIT R. B., HARVEY R. A. and ROm~EY E. M. (1969) Ecological and environmental effects from local fallout from Cabriolet. I. Radiation doses and short-term effects on the vegetation from close-in fallout. USAEC Div. Tech. Info. Extension, Oak Ridge, Tenn. PNE-956. 65 p. 13. RHOADSW. A., RAGSDALEH. L., PLATT R. B. and ROMNEY E. M. (1971) Radiation doses to vegetation from dose-in fallout at project Schooner. In, Survival of food crops and livestock in the event of nuclear war. Proc. Symp. held at Brook_haven Natl. Lab., Upton, N.Y., September 1970, sponsored by the OCD, USAEC and USDA. AEC DTIE 700909 (in press). 14. ROMNEYE. M., LINDBEROR. G., HAWTHORNEH. A., BYSTROM B. G. and LARSON K. H. (1963) Contamination of plant foliage with radioactive fallout. Ecology44~ 343-349.
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P. J. B O T T I N O and A. H. S P A R R O W
15. SCHULZ R. K. (1971) Survival and yield of crop plants following beta irradiation. In, Survival of food crops and livestock in the event of nuclear war. Proc. Symp. held at Brookhaven Natl. Lab., Upton, N.Y., September 1970, sponsored by the OCD, USAEC and USDA. AEC DTIE 700909 (in press). 16. SmMeR E. G., CONSTANTINM . J . and KILLION D. D. (1971) Effects of acute gamma radiation on plant development and grain yield. In, Survival of food crops and livestockin the event of nuclear war. Proc. Symp. held at Brookhaven Natl. Lab., Upton, N.Y., September 1970, sponsored by the OCD, USAEC and USDA. AEC DTIE 700909 (in press). 17. SPARROWA. H., FLOYDBRENDAand BOT'nNO P.J. (1970) Effects of simulated radioactive fallout buildup and decay on survival and yield of lettuce,
18.
19.
20.
21.
maize, radish, squash and tomato. Radiation Botany 10, 445-455. SPARROW A. H. and PUGLIELLI LEANNE (1969) Effects of simulated radioactive fallout decay on growth and yield of cabbage, maize, peas and radish. Radiation Botany 9~ 77-92. SPARROW A. H., SCHWEMMER SUSAN S. and BOTTmO P.J. ( 1971 ) The effects of external gamma radiation from radioactive fallout on plants with special reference to crop production. Radiation Botany 11, 85-118. WITHERSPOON J. P. and CORNEY KATHLEEN A. (1970) Differential and combined effects of beta, gamma and fast neutron irradiation of soybean seedlings. Radiation Botany 10, 429-435. WITHERSPOONJ. P. and TAYLOR F. G. JR. (1969) Retention of a fallout simulant containing 1~4Cs by pine and oak trees. Health Phys. 17, 825-829.
C O M P A R I S O N OF T H E EFFECTS OF S I M U L A T E D F A L L O U T DECAY AND CONSTANT EXPOSURE-RATE GAMMA-RAY TREATMENTS ON T H E S U R V I V A L A N D YIELD OF W H E A T A N D OATS P.
J. B O T T I N O
a n d A. H . S P A R R O W
Biology Department, Brookhaven National Laboratory, Upton, New York 11973, U.S.A. (Received 17 March 1971) BOTTINO P. J. and SPARROWA. H. Comparison of the effects of simulatedfallout decay and constant exposure-rategamma-ray treatmentson the survival andyield of wheat and oats. RADIATIONBOTANY11~ 405--410, 1971.--Eight-day-old seedlings of wheat (Triticum aestivum L. em. Thell. 'Opal') and oats (Arena sativa L. 'Orbit') were subjected to xsTCsgamma radiation in two ways: ( 1)for 16 hr with constant rate exposures (CR) ; and (2) for 36 hr with changing exposure rates given as a fallout decay simulation (FDS). After irradiation the wheat was transplanted to the field, and the oats into 6-in. clay pots and placed in a screen-covered "greenhouse". Survival data were collected three times a week until no more deaths, attributable to the radiation occurred. Seed yield data from survivors were obtained at the end of the growing season. At equal total exposures, the 36-hr FDS treatment was more effective in reducing survival than the 16-hr CR treatments. The ratio of 16-hr CR/FDS LDs0's was 1.46 for wheat and 1.19 for oats. The FDS was more effective in reducing the yield only at exposures above the LDx0. The FDS exposures producing a 50 per cent reduction in seed yield (YDn0) were 1.73-t-0.29 kR for 'Opal' wheat and 1.42 -t-0.27 kR for 'Orbit' oats. The 16-hr CR YDs0 exposures were 2.264-0.61 kR for wheat and 1.514-0.22 kR for oats. In all cases, yield was a much more sensitive end point than survival, indicating that even though a crop might survive fallout exposures in some cases, no appreciable seed yield would be produced. That is, reproductive survival (seed) is more sensitive than somatic survival (plants). INTRODUCTION THE TOTAL r a d i a t i o n exposure to a p o p u l a t i o n of
plants from r a d i o a c t i v e fallout comes from b o t h b e t a a n d g a m m a r a d i a t i o n . Some investigators have s t u d i e d the r a d i a t i o n effects a n d m e a s u r e d the r a d i a t i o n doses u n d e r a c t u a l fallout conditions.(n-is) T h e y have f o u n d t h a t the ratio o f b e t a / g a m m a exposures m a y v a r y b e t w e e n 4 a n d 15:1. M o r e c o m m o n l y , however, fallout effect studies h a v e involved the less c o m p l e x situation o f e x a m i n i n g the effects o f b e t a or g a m m a r a d i a t i o n alone u n d e r g r o w t h c h a m b e r , greenhouse or field conditions. T h e b e t a r a d i a t i o n or p a r t i c l e studies have been c o n c e r n e d p r i m a r i l y with r e t e n t i o n a n d g e n e r a l effects of synthetic particles l a b e l e d w i t h b e t a emitters.(5,14.15, ~1) T h e g a m m a r a d i a t i o n studies h a v e b e e n con405 A
c e r n e d with m e a s u r i n g survival a n d yield after exposure to either u n i f o r m or v a r y i n g exposure rates, or the decreasing rate o f s i m u l a t e d fallout decay.(1-4,16-1s) O n l y very recently(-°°) has a s t u d y been c o n d u c t e d w i t h c o m b i n e d betag a m m a treatments, in w h i c h it was shown that the R B E o f these two types of r a d i a t i o n s is a p p r o x i m a t e l y 1 w h e n vegetative g r o w t h is the biological end p o i n t used. T h e c u r r e n t status of knowledge c o n c e r n i n g the effects o f g a m m a r a d i a t i o n from fallout on crop plants has b e e n r e v i e w e d recently.(19) T h e present c o m m u n i c a tion on the i m p o r t a n t crop plants, w h e a t a n d oats, is a n o t h e r in a c o n t i n u i n g series of studies c o m p a r i n g the effects o f u n i f o r m exposure-rate t r e a t m e n t s on crop plants with those of fallout d e c a y simulation treatments.
P. J. BOTTINO and A. H. SPARROW
406
MATERIALS A N D METHODS
Young
(eight-day-old) seedlings of wheat (Triticum aestivum L. em. Thell. 'Opal') and oats (Avena sativa L. 'Orbit') in 2-in. peat pots were given the following treatments of 137Cs g a m m a radiation: (I) a constant exposure rate (CR) treatment for 16 hr; and (2) a decreasing exposure rate treatment for 36 hr given as a fallout decay simulation (FDS). Because the meristem at eight days is still below the ground the seeds are sown next to the peat pot wall in order to make attenuation by the soil negligible. The theory and facilities used for irradiation have been previously described in detail.(1,tv, is) Thirteen exposures and a nonirradiated control with 25 plants at each were used in the wheat experiment; 11 exposures and a nonirradiated control with 16 plants at each were used in the oat experiment. After irradiation the wheat seedlings were transplanted to field experimental plots covered with 12 x 12 mesh natural Saran cloth to prevent damage by birds. The oat seedlings were transplanted into 6-in. clay pots and placed in a screen-covered "greenhouse", also for protection against birds. The irradiation and field planting of both experiments were conducted in May, 1970. All plants were scored for survival three times a week until no more deaths attributable to the radiation occurred. This was an average of 45 days
99.9
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J
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RESULTS A N D DISCUSSION
Survival data for the two crops are given in Figs. la and lb as probit plots of survival (percent of control) against exposure for the two treatments. The curves are computer-fitted lines to the actual data points. Survival. end-point values are summarized in Table 1. For both crops, the FDS treatment is much more effective in reducing survival than the 16-hr CR. For wheat (Fig. la) the ratio of 16-hr GR/FDS LDs0's is 1.46 and for oats (Fig. 1b) this ratio is 1"19.
The yield data for the two crops are given in Figs. 2a and 2b. The data are plotted as the mean weight of seeds per initially treated plant against exposure. In both cases no consistent difference
l
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postirradiation. Seed yield data (weight and number of inflorescences per plant) were collected after harvest in early September (1970). For low exposures the n u m b e r of plants from which seed was harvested was the same as that initially irradiated. For high exposures, where plant deaths occurred, seed weight from all surviving plants was totalled and then divided by the number of plants initially irradiated. This is termed 'seed weight per treated plant'. The average n u m b e r of seeds per inflorescence, however, was determined on a per surviving plant basis.
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FIG. I. Probit plot of survival as per cent of control vs. exposure (kR) for (a) wheat and (b) oats given a 36-hr FDS or a 16-hr OR treatment.
GAMMA-RAY TREATMENT OF WHEAT AND OATS
407
Table 1. Summary of survival and yield end points (kR 4-S.D.) for the 36-hr FDS and the 16-hr CR treatments of wheat and oat seedlings with the 16-hr CR]FDS ratios
Wheat End Point (kR+S.D.)
Oats Ratio 16-hr CR/FDS
16-hr CR
Ratio 16-hr CR/FDS
16-hr CR
FDS
FDS
LDz9 LDso LDoo
4.63 4-0-08 5'11 4-0"05 5'59 4-0"09
2.70 4-0.14 3"51 4-0.07 4"32 4-0"14
1.71 1"46 1"29
3"24 4-0"22 4.104-0.15 4"96 4-0"25
2"57 4-0.16 3"43 4-0"17 4"28 -t-0"29
1.26 1"19 1"15
YDIo YDso YDgo
0.97 4- 0.94 2.26 4- 0.61 5.80 4-0-78
1.29 4- 0.35 1.73 4- 0.29 2.92 4-0.20
0.75 1.30 1.98
0.92 4- 0.28 1.51 4- 0.22 3.15 +0.33
0.90 4- 0.36 1.42 4- 0.27 2.84 4-0.50
1.02 1.06 1.10
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FIG. 2. Log mean weight of seeds per treated plant (g) vs. exposure (kR) for (a) wheat and (b) oats given a 36-hr FDS or a 16-hr CR treatment. between the two treatments was observed at the lower exposures. However, at the higher exposures the FDS was more effective in reducing yield (see also Table 1). A measure of one of the components of yield in these irradiated plants may be made by calcularing the number of seeds per head or panicle and plotting this against exposure as given in Fig. 3. In Fig. 3a for wheat there is no difference between the two treatments at the low exposures but a clear separation occurs at the higher exposures, with the FDS being more effective than the 16-hr CR. Figure 3b gives a similar plot for oats and again only at the high exposures do
differences between the treatments occur. It is important to note that the yield response is the same even though two different yield end points were used. A similar response would be expected with weight per 100 seeds. The greater effectiveness of the FDS treatment compared to the 16-hr CR treatment has been previously reported for many other crop plants (t,l~-tg) and is probably due to the higher initial exposure rates encountered with this treatment. The greater effectiveness of high rates over low rates is well established and has good recent experimental basis.0,4,S-l°,Zg) The 16-hr CR/FDS ratios reported here, 1.46 for wheat and
P. J. B O T T I N O and A. H. SPARROW
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Fxo. 3. (a) Log mean number of seeds per head vs. exposure (kR) for wheat given 36-hr FDS or a 16-hr CR treatment; (b) log mean number of seeds per panicle vs. exposure (kR) for oats given a 36-hr FDS or a 16-hr CR treatment. 1"20 for oats, are in good agreement with those (average 1 "4) previously reported for other crops. ¢17,18) Factor differences for other treatments c o m p a r e d to the FDS have been recently published. (19) T h e absence of a difference in yield between the two treatments at the low exposures has also been noted in lettuce, barley, and another variety of wheat ('Indus').(1) T h e exact reason for this is not clear, but it could be that below a certain exposure, the d a m a g e is not great enough to bring about a significant exposurerate effect. After a certain a m o u n t of d a m a g e is induced the higher exposure rates of the FDS treatment become more effective than the 16-hr C R treatment a n d a divergence between the two treatments occurs. T h e conclusion that a certain a m o u n t of d a m a g e has to be induced before an exposure-rate effect occurs m a y also be drawn from the exposure-rate experiments of others. (4,8-10) Further support for this m i n i m u m d a m a g e requirement comes from the finding that the differences between the two treatments occur only at exposures high enough to cause some plant deaths. Therefore, it could be the plant deaths primarily in the FDS treatment which bring about the differences at the higher exposures. For both crops the point at which the
response to the two treatments begins to diverge was very near the FDS LD10, 2"70 k R for wheat and 2.57 k R for oats. W h e n seed yield is calculated on the basis of the original n u m b e r of plants as it is done here, sharp decreases in seed yield response would be expected to occur at or near exposures where plant deaths begin to occur. It should also be noted that no stimulation in seed yield occurred at the low exposures for these two crops. I n fact we have yet to observe any stimulation of seed yield by low exposures in any of the cereals studied thus far. A s u m m a r y of the survival and yield data for both crops is given in Table 1. I n the case of survival the greater effectiveness of the FDS over the 16-hr C R is evident for all end points. W i t h yield, however, the differences are not so evident. I n fact differences between the two treatments a p p e a r only at or above the YDs0. I t is also important to note that yield is a b o u t twice as sensitive an end point per R than survival. Exposures which would reduce survival by 50 per cent reduced yield by 90 per cent or more. This means that even though a crop survives an exposure to fallout radiation it would not necessarily give an appreciable yield. At first glance our results would not seem to agree with those on wheat a n d oats of DAVIES,
G A M M A - R A Y T R E A T M E N T O F W H E A T and OATS (s,7) who f o u n d for b o t h crops t h a t exposures o f 2.0 k R at e a r l y vegetative stages resulted in early d e a t h of the plants. W e have found no deaths at 2-0 k R for either crop or t r e a t m e n t . This a p p a r e n t difference can be e x p l a i n e d h o w e v e r b y the h i g h e r exposure rates in D a v i e s ' experiments. D a v i e s ' exposures were given at 2 8 - 3 0 R / m i n , while o u r 16-hr C R exposure is 2"1 R / m i n for 2"0 kR. T h e m u c h h i g h e r rates in D a v i e s ' e x p e r i m e n t s m o r e t h a n e x p l a i n the lower survival levels in his e x p e r i m e n t s c o m p a r e d to the present studies. W e , in o u r experiments, h a v e shown the g r e a t e r effectiveness of high rates over low rates, o)
Acknowledgements--Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission and the Office of Civil Defense, Department of the Army, Washington, D.C. under Project Order No. DAHC20-70-C0376, Work Unit 3133E (contracting office technical representative Dr. D. W. BENSEN). This report has been reviewed by the Office of Civil Defence and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Office of Civil Defense. The authors wish to thank BRENDA FLOYD,PAMELASILIMPERIand J. BRYANTfor assistance with the irradiations and data collection. We thank Dr. NEAL JENSEN, Dept. of Plant Breeding, Cornell University, for supplying the seed. The assistance of Mr. K. H. THOMPSONwith statistics and Miss SUSANS. SCHWEMMERfor critical comments on the manuscript are also acknowledged. REFERENC2ES 1. BOTTINO P. J. and SPARROW A. H. (1971) The effects of exposure time and rate on the survival and yield of lettuce, barley and wheat. Radiation Botany U , 147-156. 2. CLARK G. M., RoY R. M., BAKER D. G. and BUNTING W. R. (1965) Simulated fallout studies in conifers--a preliminary report. Health Phys. U , 1627-1636. 3. CLARK G. M., CHENG F., RoY R. M., SWSANEY W. P., BUNTING W. R. and BAKER D. G. (1967) Effects of thermal stress and simulated fallout on conifer seeds. Radiation Botany 7, 167-175. 4. CONSTANTINM . J . , KILLION D. D. and SIEMERE. G. (1971) Exposure rate effects on soybean plant responses to gamma irradiation. In, Survival of food crops and livestock in the event of nuclear war. Proc. Symp. held at Brookhaven Natl. Lab., Upton, N.Y., September 1970, sponsored by the
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