Development,evaluation and genetic analysis of sulfosulfuron herbicide resistance in sorghum

Herbicide tolerant varieties in combination with herbicide seed treatments can be used to manage Striga. However, there are no herbicide resistant sorghum varieties in Kenya. The objectives of this study, therefore, were to develop sulfosulfuron resistance in sorghum, to determine the level of resistance in resultant herbicide tolerant mutants, and to determine the genetic inheritance of herbicide tolerance in sorghum. Five ethyl methane sulphonate (EMS)-derived sulfosulfuron tolerant mutants (designated hb6, hb8, hb12, hb56, and hb462) were identified and selfed to M4 generation. Varying rates of sulfosulfuron, either as a spray or seed coat, were applied to determine the level of tolerance of the mutant lines. Mutant lines were also crossed with the wild-type Seredo and among themselves to determine mode of inheritance. Results showed that the susceptible wild-type Seredo was killed at the lowest herbicide rates of 0.5 g ha^-1 and 1 g ha^-1 sulfosulfuron. Dry matter from the spraying and seed coating experiments showed mutants to be up to 170 times more resistant to sulfosulfuron than the wild-type. The LD₅₀ values indicated a general trend of hb46 > hb12 > hb462 ~ hb56 > hb8 for level of tolerance under both spraying and seed coating experiments. The F₂ progeny of mutant X wild-type crosses segregated in a 1:2:1 fashion for resistant, intermediate, and susceptible, indicating semi-dominant inheritance. Intercrosses between mutant lines did not segregate for resistance in the F₂ generation indicating the same mutation could be responsible for the tolerance in all five mutants.