A.S. LARIK1)
Sind Agriculture College, Tandojam, Pakistan
Introduction
The use of ionizing radiation is now an acceptable tool to supplement conventional breeding methods with field crops. The extensive literature on the production of varieties resulting from screening irradiated material for desirable deviates has been summarized by GAUL (1965) and VIGLASI (1968). It is now of interest to explore and examine the possibilities of the practical application of induced mutation through different mutagens applied in different doses.
Many workers (ABIDI and BALUCH 1969; BHATIA and SWAMINATHAN 1962; D'AMATO et al. 1964; DONINI 1968; GAUL 1965; GOUD 1967; KUMAR 1972; KRISHNASWAMY 1967; RAJPUT 1974 and YAMAGATA 1964) have attempted to assess radiation induced variation in quantitative characters and have reported significant improvements in these characters.
The present paper reports the results of M2 studies on plant height, culm diameter, days to heading and seed index.
Materials and methods
Seeds from M1 generation of four cultivars of Triticum aestivum L.; namely Wisconsin Supermo, No. 43, Kenya Plume and Kenya Hunter were received through the courtesy of the Department of Botany and Plant Breeding, College of Agriculture, Tandojam, Pakistan. Two hundred and forty seeds from each of three radiation treatments (25, 35 and 45 kR) and 60 seeds for the control for each of the cultivars were sown in plots uniformly treated. Sowing was done in four blocks, by dibbling single seed per hole at 30 cm intervals in rows 3.6 m long and 30 cm apart. Every block consisted of 75 rows, of which 60 were sown with treated seeds and 15 with the respective control.
Data collected on individual plants in the M2 generation for four characters, viz. plant height, culm diameter, days to heading and seed index were analysed according to a one-way classification for each variety and treatment separately. The mean values of all the treated populations for character and varieties were compared with the respective control means by using t test.
The total phenotypic variance (gamma2t) calculated from the treated plants for each character was partitioned into an environmental variance (gamma2e) and radiation induced genetic variance (gamma2g) by subtracting the variance of the control plants from the variance of treated plants.
% heritability was calculated from (gamma2g/gamma2t) x 100
The estimates of the expected genetic advance at 5% selection intensity was based on the relation suggested by JOHNSON et al. (1965) where
Where K=2.06 at 5% selection differential. The genetic advance was expressed as a percentage of the means for the purpose of comparison. For the seed index (1000 grain weight) three random samples were drawn from each treated and control seed bulks, and an analysis of variance made.