Herbicidal compound screening

1. A method for identifying an herbicidally-effective composition that comprises a first compound and a second compound and confers plant cell lethality, the method comprising:

a. transforming a first non-transformed plant with a recombinant polynucleotide that comprises an inducible promoter and a toxic regulatory sequence to produce a transformed plant, wherein:

the toxic regulatory sequence encodes a toxic regulatory polypeptide that is capable of conferring cell death in the transformed plant when the polypeptide is expressed in the transformed plant;

the toxic regulatory sequence is under regulatory control of the inducible promoter that is activated by an induction factor exogenously applied to the transformed plant, and activation of the toxic regulatory polypeptide in the transformed plant is increased in response to the induction factor; and

in the absence of activation by the induction factor, the toxic regulatory polypeptide does not kill the transformed plant;

b. establishing a level of the induction factor exogenously applied to the transformed plant that activates the inducible promoter, wherein the level is sufficient to induce expression of the toxic regulatory polypeptide to an extent that is sub-lethal to the transformed plant;

c. exogenously applying to the transformed plant a first compound from a pool of test compounds, wherein the first compound lacks herbicidal activity when applied alone to a control plant, to identify a co-herbicidal first compound that is herbicidal to the transformed plant in which a sub-lethal level of the toxic regulatory polypeptide is expressed; and

d. exogenously applying to a second non-transformed plant the co-herbicidal first compound and a second compound obtained from the pool of test compounds to identify a potentiating factor that acts in combination with the co-herbicidal first compound in the herbicidally-effective composition to confer plant cell lethality in the second non-transformed plant.

2. The method of claim 1 , wherein the induction factor is a chemical or environmental treatment applied to the transformed plant.

3. The method of claim 1 , wherein the method further comprises step:

e. determining effective amounts of the exogenously applied co-herbicidal first compound and the potentiating factor applied to the harmful or unwanted plant that are sufficient to confer plant cell lethality.

4. The method of claim 1 , wherein the herbicidally-effective composition is applied to a harmful or unwanted plant and application to the harmful or unwanted plant results in cell death in the harmful or unwanted plant or a part thereof.

5. The method of claim 4 , wherein the herbicidally-effective composition is applied to a growth area of a harmful or unwanted plant or a part thereof and said application to the growth area kills or retards growth of the harmful or unwanted plant or the part thereof relative to the control plant.

6. The method of claim 4 , wherein the harmful or unwanted plant is a monocot plant.

7. The method of claim 4 , wherein the harmful or unwanted plant is a dicot plant.