Studies on genetic variations in a sorghum variety irradiated with cobalt 60 (CO~(60))

摘要

Genetic variability was created in a common sorghum variety SK5912 (SAM-SORG 17) using gamma-ray irradiation from Cobolt 60 (Co~(60)) source. The M_0 seeds were grown in the off-season of 1985/86. This was bulk harvested and planted as M_1 bulk in 1986. In 1986, ninety (90) M_2 single seed selections were made as single plants selected based on height, yield and disease resistance. These were advanced to M_3 in 1987, out of which 34 M_4 family selections were harvested, threshed and evaluated for 3years. The seeds from each family were divided into three equal portions for three years evaluation (1989, 1990 and 1991) in a randomised complete block design (RCBD) at the Institute for Agricultural Research, northern Nigeria. Data were collected on 22 characters, (i) eight panicle characters, (ii) eight leaf characters, and (iii) six stem (culm) characters. Coefficients of variability (C.V) were higher for panicle characters than for leaf and stem characters. They ranged from 1.65 percent for days to 50 percent flowering to 4.15 percent for grain weight per spikelet. Broadsense heritability estimates were high for most panicle characters (45 percent) while they were moderate for both the leaf and stem characters (40 percent). The mean squares for all characters except for grain weight per spikelet were highly significant in a combined analysis. There were high and significant correlations (r=>0.5) between the lengths of first and second leaf sheaths (r=0.689) and also the lengths of internodes (r=0.652, 0.628 and 0.634). Highly significant but negative correlation was found between length of first leaf sheath and width of spikelet (r=-0.840) in 1991. Variance components from the combine analysis showed that genotypic variance was high for all characters except for protein percentage and weight of spikelet. All other characters had lower genotypic variances than their respective phenotypic and error variances. Principal components extracted from the combine correlation matrix showed high variability in leaf and stem characters than in the panicle characters. Internode length and leaf sheaths length load significantly (SEL=0.417, i.e., standard error of significant loading) on the first factor in the individual years as well as in the combined. Plotting of the first two factors of all the years (F_1 and F_2) in a common scale showed that internode length and leaf sheath length were clustered together in one quadrant; grain weight per panicle, grain weight per spikelet, days to 50 percent flowering and width of spikelet were also clustered together, indicating a close relationship between these characters and that these characters could be selected together in order to improve sorghum yield.