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Inheritance of Tolerance to, and Agronomic Effects of, Difenzoquat Herbicide in Spring Wheat

USDA-ARS
Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108

M. Elakkad

Soil Science Dep., Univ. of Minnesota, St. Paul, MN 55108

^* Corresponding author.

The herbicide difenzoquat (1,2-dimethyl-3,5-diphenyl-1 H-pyrazolium) has been widely used to control wild oat (Arena fatua L.) growth in wheat (Triticum aestivum L.). Different wheat genotypes have been found that are susceptible and tolerant to difenzoquat. Our objectives were to determine the inheritance of tolerance, and the effect of difenzoquat on agronomic traits in spring wheat. Two tolerant (T) and two susceptible (S) spring wheat cultivars crossed in all combinations (reciprocals bulked) to produce six populations. Four hundred sixty-two F₂ derived F₄ lines were evaluated for herbicide injury when treated at 2x (twice) the recommended rate. Three classes of injury level (tolerant, intermediate, and susceptible) were recognized. From one of the four T x S populations, 10 lines for each class were selected. These lines and their parents were exposed to 0, 1x, and 2x rates of difenzoquat for 2 yr, and agronomic traits and herbicide injury were measured. In the genetic study, lines from each of the T x S populations exhibitedifferential herbicide reactions, while the lines within the T x T and S x S populations did not differ. All T x S populations, individually and combined, fit a 3:1 ratio suggesting a single dominant gene for tolerance. However, lines with intermediate tolerance were found, indicating that other genes may modify the expression of tolerance. In the agronomic study, when untreated, the tolerant, intermediate, and susceptible lines did not differ for yield, plant height, or days to head. The 1x and 2x rates had no apparent effect on agronomic traits of lines in the tolerant class. The intermediate lines yielded 92 and 80% of their untreated check at the 1x and 2x rates, respectively, while the susceptible lines yielded 69 and 51% as much grain as their untreated check in these treatments. Since no deleterious effects of tolerance were found, its incorporation into susceptible genotypes should pose few problems.

Contribution from USDA-ARS and Minnesota Agric. Exp. Stn. Journal Article No. 15 592. Research in part supported by a grant from Minnesota Wheat Research and Promotion Council.

Received for publication October 20, 1987.