Effect of recurrent mutagen seed treatments on mutation frequency and combining ability for forage yield in pearl millet (Pennisetum americanum (L.) K. Schum.)

The effects of 3 cycles of recurrent seed treatment with thermal neutrons (TN), ethyl methane sulfonate (EMS), and diethyl sulfate (DS) on mutant frequency and combining ability in pearl millet (Pennisetum americanum (L.) K. Schum., formerly P. typhoides) were studied for eleven years. TN seed treatments gave the highest percentages of M₁ striped plants, the lowest percentage of M₁ selfed seed set, and the highest M₂ frequency of chlorophyll-deficient seedlings of the mutagens tested. Combining a low dose of EMS or DS with high and low TN treatments generally increased these effects. Normal lines, which looked like the controls, selected from lines subjected to 3 cycles of mutagen treatment, were compared with controls in 3 × 3 or larger Design II hybrid matings in 9 × 9 forage-yield trials. The 1,637 singlecrosses between normal lines from mutagen treatment failed to exceed the 825 control singlecrosses in average forage yield or highest forage yield. These results suggest that pearl millet has many specific-yield genes, none of which exerts a very great effect on yield. Genetic variances estimated from the Design II diallels were not significantly altered by mutagen seed treatment. EMS treatments increased the percentage of non-additive genetic variance over that in the control and TN treatments, but the failure of any of the 486 hybrids from EMS lines to outyield the best control hybrid suggested that these variance estimates might not be significant. The study suggests that attempts to improve the combining ability of inbred lines of pearl millet by mutagen treatment without several cycles of recurrent selection are not likely to succeed.