Evaluation of tissue culture-derived methomyl resistant cms-T lines

We have previously reported the recovery of many plants resistant to methomyl following in vitro selection using 6-8 month old callus derived from normally sensitve cms-T inbreds and hybrids (MNL 61: 59-60). Field tests were conducted this past summer using first (R1) and second (R2) generation progeny from regenerated plants (R0). Lannate (whose active ingredient is methomyl) was applied at 1.12 lbs/A, twice the rate recommended for sweet corn, before evaluation. Results indicate a maternal mode of inheritance for the methomyl resistance trait. All methomyl-resistant plants were also male-fertile and HmT toxin resistant. Segregation for resistance and sensitivity was seen among ear-to-row progeny from some self- and cross-pollinated R0: 4/21 rows from sensitive R0 and 3/69 rows from resistant R0. None of the R2 examined showed segregation in the field. The N- and T-cytoplasm checks were uniformly resistant and sensitive, respectively. Test crosses indicate that restoration of male-fertility was not due to a novel or newly activated dominant cms-T restorer gene.

Regenerated plants were also recovered from callus cultured for 14-16 months. Many (19/31 or 61%) methomyl-resistant R0 were obtained from non-selected control callus. Only 2% of the plants regenerated from callus 6-8 months in culture showed such spontaneous resistance. This result suggests that prolonged time in culture increases spontaneous resistance and concurrent reversion to male-fertility. Not all genotypes responded similarly, suggesting an effect of nuclear background on frequency of these traits.

Analysis of phosphorylation by mitochondria isolated from resistant R1 and R2 and N-cytoplasm checks, shows that resistant mitochondria are unaffected by the addition of 1mM methomyl. Mitochondria isolated from sensitive R1 and R2, and T-cytoplasm checks, show over a 70% decrease in their phosphorylation activity in the presence of ImM methomyl. These results suggest that the tissue culture-derived resistance may arise from an alteration in the mitochondrion. Molecular studies of mitochondrial DNA from resistant and sensitive lines are currently in progress.

A.R. Kuehnle and E.D. Earle

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

Return to the MNL 62 On-Line Index
Return to the Maize Newsletter Index
Return to the MaizeGDB Homepage