In the material of the MRI gene bank, only imidazoline resistance was found among a group of total and selective broad-spectrum herbicides

-- Vancetovic, J, Vidakovic, M, Stefanovic, L, Simic, M

In view of the increasing need for tolerant maize genotypes to broad-spectrum herbicides, especially because of the marketing of transgenic corn resistant to herbicides (Roundup ready, Liberty link) without reliable laws regulating GMOs in Europe, we felt a need to investigate our existing germplasm variability for mutants potentially resistant to the useful broad-spectrum herbicides. Use of mutants has a few advantages in comparison with GMOs; regulation is much clearer, no special isolations are needed, and there is no danger of them being forbidden for any reason.

We chose 11 herbicides that are potentially useful in maize for the investigation (Table 1).

We made 11 bulks to sample our existing genetic variability (MRI gene bank with 5437 active accessions). Each bulk consisted of 20 kernels of each heterogeneous accession (OP variety, race, synthetic) and 10 kernels of each inbred line. Each bulk was about 20 kg in weight.

In the spring of 2001 these bulks were sown very densely (plant to plant) during an optimal sowing period, in an area of no more than 2 ares each. The first spraying with the chosen herbicides was done when the plants were at the stage of 3–4 leaves. Spraying with each herbicide was subsequently repeated 1 or 2 times because of the late emerging plants (the escapes).

Only for herbicide 9 (Pivot) were resistant plants actually found. This herbicide also had the longest period of activity (10–15 days). About 30 plants showed full resistance to Pivot, of which 6 were outcrossed to the nonresistant testers. About 40% of the resistant plants showed male sterility. Seeds from fertile resistant plants and sterile resistant plants (from the open-pollination) were collected separately.

In 2002, testcrosses of the 6 resistant plants with nonresistant testers were sown, as well as the open-pollinated seed from fertile and sterile resistant plants. Treatment was done with the Pivot herbicide, at the same dosage as the previous year. It seems that the gene(s) involved are dominant, since all treated material was resistant. Among the plants from the open-pollination of resistant sterile plants, only 1 exhibited male sterility (from a total of 60 plants in 2002), meaning that there is no correlation between Pivot resistance and some type of male sterility, as it may have seemed in the previous year. Nevertheless, sibbing was done on that 1 sterile plant, as well as selfing of testcrosses with nonresistant testers. This will allow, in 2004 (the material was planted in 2003, but a strong storm destroyed it all), investigation of the mode of inheritance of this resistance.