Common waterhemp resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was first reported in northeast Kansas in 2001. The objective of this research was to determine the inheritance characteristics of the protox-resistance trait. Resistant and susceptible common waterhemp were screened for resistance and inbred lines were developed using full-sib mating for three generations in the greenhouse. After the third generation, resistant and susceptible plants were crossed in a male and female reciprocal manner creating 57 F1 (first generation) lines. A proportion of the F1 progeny was screened for resistance and the remaining progeny were used to create F2 (second generation) and backcross (BC) lines. Approximately 500, 400, and 1400 F1, BC, and F2 progeny, respectively, were treated with 105 g ha−1 of lactofen when plants reached the 8-node growth stage. Visual injury ratings were determined at 14 days after treatment and based on a scale of 0 = no injury and 100 = mortality. A plant was considered to be resistant when visible injury was less than 50%. Approximately 91 and 93% of F1 progeny from susceptible female × resistant male and resistant female × susceptible male crosses, respectively, were scored as being resistant. There was no evidence of reciprocal differences or segregation in the F1 indicating the resistance trait is dominant and contained in the nucleus. F2 progenies supported a 3:1 genetic ratio and BC progenies supported a 1:1 ratio using a Chi-squared goodness-of-fit test. These results indicate resistance to protox-inhibiting herbicides is determined by a major dominant nuclear gene.
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Vol. 111 • No. 3