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GENETIC VARIATIONS AND ROSETTE RESISTANCE IN EARLY GENERATIONS OF GROUNDNUT (Arachis hypogaea L.) VARIETIES IRRADIATED WITH GAMMA RAYS
Abstract:
Seeds of groundnut, Arachis hypogaea L. were treated with gamma rays. Two sets of irradiations were performed. The first set consisted of irradiating five varieties (two early maturing, SAMNUT 14 and 18, one medium maturing, UGA-7, and two late maturing, SAMNUT 21 and 10) at 10, 35, 45, and 50 krads with cobalt 60(C60 ) source. An F2 population, Ex RM12 (derived from an Ex-Dakar X RMP 12 Cross) was used as control in the set. Only lOkr treated plants survived for all the varieties, these were evaluated for increased variability, agronomic performance and for resistance to groundnut rosette disease at M2 and M3 populations. The second set of Irradiation was done at lower doses 15, 20, 25, 30 and 35kr with 0 dose serving as control using the 5 varieties. Varieties survivity under all these lower doses and were evaluated in M1 and M2 populations as the first set. These varieties were grown under two field conditions: rosette and rosette free. Results indicate wide ranges and coefficients of variability for the characters studied. Population means showed significant differences in performance of irradiated populations and control within each variety for the characters measured. Effects of doses produced more detrimental changes in the M2 than in the M2. Increases in yield and components were seen within varieties for the lower doses 15kr, 20kr and 25kr than at higher doses 30 and 35kr especially at M2. Significant (P= 0.05) effects were record for the doses used and for the varieties planted. Interaction of varieties and doses were not significant. Estimates of genetic variance were large in the populations, interaction variance were negative or small. Abnormally high broad sense heritability estimates were obtained for the M2. Positive and highly significant (P=0.01) correlations between yields and its components were recorded in M2 except between one hundred seed weight and shelling percentage. Effects of the mutagenic agents on the varieties were similar on rosette infested and rosette free fields. The irradiated populations of each variety showed variations in their reactions to disease infections. The performance of irradiated populations compared with control indicated that doses 15, 20 and 25kr generally produced more beneficial, significant changes in plants while dose lOkr was not too far from the control and dose 30 and 35kr produced more detrimental effects on characters studied. Selections from M3 and higher generations of populations irradiated with 15, 20, and 25kr may produce higher yielding and disease (rosette) resistant mutants.
GENETIC VARIATIONS AND ROSETTE RESISTANCE IN EARLY GENERATIONS OF GROUNDNUT (Arachis hypogaea L.) VARIETIES IRRADIATED WITH GAMMA RAYS
