| Results and Discussion Plant Height : The data in Table 1 shows that irradiation generally decreased plant height, being significant at 5% and 1% level at all doses for varieties Wisconsin Supremo and Kenya Hunter. The different responses to radiation by varieties No.43 and Kenya Plume on the one hand and varieties Wisconsin Supremo and Kenya Hunter on the other indicate varietal responses displayed by wheat varieties due to their polygenomic constitution. Under 35 kR Wisconsin Supremo was the most adversely affected and No. 43 the least, a fact which may lead to the assumption that for certain characters, mutations with a deterimental effect occur more frequently. The co-efficient of variation, heritability and genetic advance was enlarged in all the radiation treatments. The maximum reduction in height was given by variety Wisconsin Supremo at 35 kR. The lowest mean height is given by Kenya Hunter at 45 kR, which is 92.80 cm. There is evidently considerable scope for selection for shorter straw following radiation. Similar plant height reductions by different radiation doses have been observed earlier (GOUD et al. 1969 ; KRISHNASWAMY 1967; RAJPUT 1974 ; and VIGLASI 1968). Reduction in plant height is desirable for the evolution of lodging resistant varieties provided yield is not affected. Clum Diameter : The character for culm diameter displayed negative response to radiation, but no dose relationship with the character could be detected (Table 2). This trend of general deterioration in the diameter of culms is indicative of the frequent occurrence of polygenic mutations. The co-efficient of variation, heritability and genetic advance was increased in all the varieties due to irradiation. GREGORY (1968) reported an increase in variance in irradiated populations without appreciable change in mean values indicating that mutations for polygenes occurred equally in plus and minus direction. Similar results were also reported by SHAHANI (1969) for culm diameter in wheat. Decrease in culm diameter is liable to lead to lodging and irradiation is therefore less promising here; nevertheless there is considerable induced variation and rare mutants giving thicker straw may be present. Days to Heading : It could be observed from the results (Table 3) that heading was hastened due to radiation treatments. Data reveal varietal responses to irradiation Variety Wisconsin Supermo was comparatively less affected for the initiation of spikes, while on the contrary, variety No. 43 displayed greater susceptibility to radiation showing maximum response of 10.18 days earliness with 45 kR treatment. There was a significant decrease in the mean values of treated populations as compared to control. Highest genotypic co-efficient of variation was observed in 35 kR of variety Wisconsin Supremo with (93.79%) heritability and (17.89%) genetic advance. These results agree with those of MACKEY (1960) and YAMAGATA (1964), who reported earliness in heading date due to X-ray treatment in cereals. Earliness in heading is somewhat valuable in the areas where winter is mild and short, and as such it is necessary to evolve early maturing varieties of wheat to conform to the requirements of grain development. Seed Index : Seed index data (Table 4) and analysis of variance (Table 5), show that all the effects are highly significant against error (M.S.). The variety and treatment interaction was also highly significant. The treatment sum of squares has been split, firstly with a component for the difference between treated and control, and secondly into its linear and quadratic components of dosage. The analysis shows that both linear and quadratic components are significant at 1% level. The treatment effect was, however, not significant against interaction (M.S.). This shows that varieties by and large reacted differently under different doses. Irradiation has slightly increased the seed index of all four varieties and at all dosages. Similar results were also reported by RAJPUT (1974) with mung beans. The results of these radiation studies are therefore promising. In three important characters of height, earliness and grain weight there are fairly consistent changes in the required direction in all four commercial varieties of wheat. (Recived March 15, 1975) |
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