Wheat (Triticum aestivum L.) is the cereal of choice in most countries and is the principal food crop of the world. Wheat among the cereals, is the main staple diet in Pakistan. Wheat is self pollinated crop, the natural variation is very low in wheat crop. As such the genetic variation is required for its improvement. The genetic variation may be obtained through selection in the available natural resources, introduction of exotic germ plasm, hybridization and induced mutations.
Ionizing radiation (Gamma rays, X-rays) seem to be especially useful in changing simple inhirited characteristics in highly developed genic systems. Undesirable alterations in other characters are easily handled in mutation breeding programmes because the mutant lines are so similiar to the parent variety that few back crosses will restore the desired background genotype. The commulative effect of the small variations have made mutations an important force in the evolutionary changes that plants have undergone. Groski et al. (1987) reported that in M2, the number of tiller plant-1 and the number of spikes plant-1 showed significant differences with various doses of gamma irradiation. Hassan et al. (1988-a) studied the effect of gamma rays and sodium azide on wheat variety sonalika. Higher dose of gamma rays delayed maturity whereas higher concentration of sodium azide induced earliness. Sodium azide treatment resulted in more reduction in number of tillersr plant-1, number of spikelets spike-1 and length of the spike. Ayub et al. (1989) concluded that the effect of radiation was depressive and the magnitude of depression varied with the strength of irradiation dose. Most of the effect was restricted to M1 generation and only little amount was transmitted to the following generation. This reveals that the effect is genotypic in nature, which is transmitted from generation to generation. Zhu et al. (1991) noted that considerable variation was induced in heading date, plant height, fertile spike plant, number and weight of grain plant-1 in two different wheat varieties due to radiation. Wang-Guixue et al. (1995) irradiated the seeds of wheat varieties 77-Zhong-2882 and 79-P-17 with 137Cs gamma rays and CO60 gamma rays, respectively, at 20-40 KR to study their effects on the inheritance of heading data, plant height, number of tillers and other characteristics. Results showed that both irradiation sources had similar significant effects on heading data and plant height. Mutants with good characteristics were obtained form variety 77-Zhong-2882 irradiated with 30 KR. Lapochkina (1998) reported that the use of pollen irradiated at dose of 0.75 and 1.5 KR increase yield in hybrid plants in comparison with control. Perez-Talavera et al. (1999) concluded that radiography is a rapid and non-destructiv method which offers the possibility of predicting the field behaviour of irradiated material. In view of the above mentioned aspects, the present research project was undertaken to study the effects of gamma irradiation in wheat and to evaluate the possibility of using this physical agent as a source of creating new hereditary changes regarding different morphological and agronomic characters.
MATERIALS AND METHODS
The present research project was carried out from late October 2001 to early
May 2002 at the research area of Department of Plant Breeding and Genetics,
Faculty of Agriculture, Gomal University, D.I.Khan. The varieties used in this
study are given as follows.
||Inqilab - 91
||Daman - 98
Pure dry seeds of the above three wheat varieties were obtained from Agriculture
Research Institute Ratta Kulachi, Dera Ismail Khan. The seeds were irradiated
with 10,20,30 and 35 Krad doses of gamma rays from CO60 gamma source
at the Nuclear Institute for Food and Agriculture (NIFA), Tarnab, Peshawar.
One lot of seeds of each variety was kept as untreated control. Hence there
were four irradiated seed lots and one control, totaling five treatments for
each variety. The experiment was Lay out in R.C.B.D with Split plot arrangement
having four replications. The experimental plot size was kept at an area of
360.0 m2. Each replication was divided into three blocks and each
of the block in turn was sub divided into five sub plots with an area of 6 m2
each. The distance between the adjacent rows was 30 cm while the plant to plant
distance within a row was 10 cm. The three cultivars were allocated at random
to main plots (blocks) while four levels of gamma radiation plus control were
allocated to sub plots at random in each block. A basic dose of 55-28-0 kgs
per hectare N.P.K was applied. A full dose of phosphorous in the form of D.A.P
was applied to the field before sowing while half of the nitrogen was supplemented
at sowing time and remaining half of the nitrogen with second irrigation. The
irradiated seeds along with control were sown on October 29, 2001. Normal agricultural
practices for raising the wheat crop were followed uniformally for all the treatments.
Hoeing was done two times to control weeds. The experimental plot was irrigated
at suitable intervals avoiding the crop with water stress. The harvested bundles
of each sub plot for each treatment were labeled. These were kept separate and
dried. Each bundle was hand threshed. Maximum 10 plants at random were selected
from each sub plot for each treatment for observing the effects of radiation
on the following morphological and agronomic characters.
||Days taken to heading.
||Plant height (cm)
||Number of tillers plant-1
Germination percentage was calculated by multiplying the number of grains germinated
with 100 and was divided by the total number of grains sown. For survival percentage,
25 seedlings were selected in each sub plot 10 days after the germination, the
survival percentage was recorded by employing the following formula:
Days taken to heading was determined by counting the days from date of sowing
to the time of 50% ear emergence in each sub plot. For the plant height, 10
selected plants from each sub plot measured at maturity in centimeters from
the soil surface to the tip of spike. For the number of tillers plant-1,
ten selected plants in each sub plot were counted by uprooting the plants at
Statistical analysis: The data so collected for various morphological characteristics was statistically analysed on Split polit Design for the analysis of variance as suggested by Steel and Torri (1980), while the effects of radiation doses and their varietal response were compared by Duncans new multiple range test.
RESULTS AND DISCUSSION
Germination percentage: According to data (Table 1)
the differences in the mean values due to gamma doses were highly significant.
The data revealed that the range of mean values for radiation doses was 21.19
to 91.76 for germination Percentage. The lowest germination percentage (21.19)
was recorded for 35 Krad dose and the highest germination percentage was recorded
for control. A significant decrease in germination percentage was observed with
an increase in the gamma rays doses. All the values with respect to various
doses differed significantly from one another. The mean values due to varieties
for germination percentage were non-significant and the values were in the range
of 57.29 for Raj 58.70 for Inqilab-91 and 60.33 for Daman-98 respectively. The
effects of interaction between doses of gamma rays and varieties were non-significant.
The values recorded for interaction-ranged form 20.75, to 94.50, 21.25 to 93.00
and 21.75 to 87.79 for Inqilab-91, Daman-98 and Raj respectively. The highest
dose of gamma 35 Krad had most adversely affected the germination percentage.
The decrease in the mean values due to 35 Krad dose was computed as 78.04, 77.15
and 75.43% for Inqilab-91, Daman-98 and Raj, respectively as compared to their
|| Effects of gamma rays on survival percentage of wheat varieties.
||Effects of gamma radiation on days taken to heading in wheat
|| Effects of gamma radiation on plant height (cm) in wheat
||Effects of gamma radiation on number of tillers per plant
in wheat varieties
|Any two means sharing the same letters are not significantly
different according to Duncans New Multiple Rang Test. Capital letters
indicate significance at 5% Probability level.
These results are in agreement with those of Hassan et al. (1988-a)
and Zhu et al. (1991).
Survival percentage: According to data (Table 2) the differences in the mean values for survival percentage due to gamma rays doses were highly significant. The range of mean values for radiation doses in ascending order were 29.15 to 98.72 for survival percentage. The mean values of radiation doses showed the lowest percentage (29.15) of survival due to 35 Krad dose in Raj and decrease was computed as 69.15% as compared to 94.50% survival of control. Generally a significant decrease in survival percentage was observed with an increase in the radiation intensity and the decrease was inversely related to the intensity of gamma rays doses. The maximum survival percentage was observed in the control of all the varieties.
Days taken to heading: According to data (Table 3), the difference in the mean values due to varietals effects for days taken to heading were 115.9, 116.10 and 119.0 for Inqlab-91, Daman-98 and Raj, respectively. It was noticed that Raj took more days to heading as compared to Inqilab-91 and Daman-98 respectively. Raj took 2.4 and 2.6% more days to heading as compared to Inqilab-91 and Daman-98. The mean values for days taken to heading due to doses, were also found to be highly significant except for 10 Krad as compared to the control. By comparing the mean values of various doses with one another, it was observed that time taken to heading was increased with the increase of radiation intensity except for 10 krad. The values noticed for various doses were ranging form 113.7 to 121.9, representing an increase of 6.7% in days taken to heading due to 35 Krad dose as compared to control. The interaction between varieties and doses was also found non significant and the values ranged form 113.00 to 118.80, 112.802 to 119.05 and 115.30 to 127.50 for Inqlab-91, Daman-98 and Raj respectively. An increase of 5.8, 6.7 and 12.2% was observed in days taken to heading for Inqlab-91, Daman-98 and Raj respectively as compared to their mean values due to 35 Krad to their respective controls. These results are quite inline with those of Hassan et al (1988-a), Zhu (1991) and Din et al. (2003) who also recorded variation in different parameters of the wheat crop.
Plant height (cm): Due to varietal effect the differences found in the mean values were highly significant. Differences recorded for plant height were in the range of 81.43 cm, 84.14 cm and 89.71 cm for Inqilab-91, Daman-98 and Raj respectively. It is evident from Table 4, that increase in the mean values of Daman-98 and Raj for plant height (cm) was 2.74 and 8.56% respectively as compared to the mean value of Inqilab-91 (81.43 cm) for plant height. Highly significant effect of various radiation doses were recorded. By comparing the mean values due to various radiation doses with one another it was found that the average plant height was decreased with increase in radiation doses except for 10 krad in Daman-91 (88.30 cm) which did not show any decrease in height but slight increase was observed in this special case as compared to its respective control. The mean values for plant height due to different radiation doses ranged between 77.18 to 92.30 (cm) and differed significantly. The maximum decrease in plant height due to 35 Krad dose was 15.12 cm by comparing the mean value due to 35 Krad (77.18 cm) to control (92.30 cm). The interaction between varieties and doses was non significant and the data obtained for effects of radiation doses on varieties indicated that various radiation doses in increasing arrangement produced gradual reduction in plant height in Inqilab-91, Daman-98 and Raj. The values obtained were ranging between 72.50 to 87.60 cm, 79.00 to 91.00 cm and 80.03 to 98.30 cm for Inqilab-91, Daman-98 and Raj respectively. The maximum reduction in plant height due to 35 krad dose in case of Inqilab-91, Daman-98 and Raj was 15.10 12.00 and 18.27%, respectively as compared to their respective controls. These results are quite inconfermity with those of Hassan et al. (1988-a) and Zhu et al. (1991).
Number of tillers plant -1: The mean values differences of tillers per plant in response to different doses of gamma rays were highly significant and the mean values shown in Table 5 ranged form 8.40 to 11.68. The highest value of 11.68 tillers was obtained due to 35 Krad while the minimum value for number of tillers (8.40) was obtained in control. The maximum increase in number of tillers plant-1 was observed due to 35 Krad dose, which was computed as 16.80% in comparison to the mean value of control. In general, the number of tillers per plant exhibited gradual increase with the increase in radiation intensity except for 35 Krad which showed slight decrease in tillers number plant-1. The difference in the mean values due to interaction between doses varieties were highly significant. The values ranged between 6.66 to 12.35, 10.05 to 13.20, 8.55 to 9.50 for Inqilab-91, Daman-98 and Raj respectively. The number of tillers plant-1 was increased in all the three varieties. The maximum increase of 46.07, 23.86 and 30.76% were noted for Inqilab-91, Daman98 and Raj, respectively. These results are in agreement with those reported by Ghafoor and Sidiqui (1976) and Wang et al. (1995).