Title: Photosystem II-inhibitors play a limited role in sweet corn response to 4-hydroxyphenyl pyruvate dioxygenase-inhibiting herbicides Authors
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2014
Publication Date: June 24, 2014
Citation: Choe, E., Williams, M., Boydston, R.A., Huber, J., Huber, S.C., Pataky, J.K. 2014. Photosystem II-inhibitors play a limited role in sweet corn response to 4-hydroxyphenyl pyruvate dioxygenase-inhibiting herbicides. Agronomy Journal. 106:1317-1323. Interpretive Summary: HPPD-inhibiting herbicides mesotrione, tembotrione, and topramezone are applied with PSII-inhibitors such as atrazine in sweet corn production in order to improve the weed control. Given sweet corn sensitivity to HPPD-inhibitors, this research broadens the understanding of sweet corn growth and yield response to the combination of HPPD- and PSII-inhibitors. Field experiments were conducted in Illinois and Washington, the major processing sweet corn production regions in the U.S. Results confirmed that topramezone was safest across sweet corn hybrids and PSII-inhibitor combinations. For the other herbicide combinations, we found that the mutation in cytochrome P450 alleles is the main cause of sweet corn sensitivity. Addition of atrazine, the most common PSII-inhibitor applied in sweet corn, did not change crop sensitivity to HPPD-inhibiting herbicides. The impact of this research is that it quantified risk of crop losses from herbicide combinations commonly used in U.S. sweet corn production.
Technical Abstract: Postemergence (POST) application of 4-hydroxyphenyl pyruvate dioxygenase (HPPD) inhibitors in combination with a photosystem II (PSII) inhibitor, such as atrazine, is common practice in sweet corn production. Given the sensitivity of sweet corn to HPPD-inhibiting herbicides, the objective of this work was to determine the extent to which cytochrome P450 (CYP) genotype and PSII-inhibitors affect crop sensitivity to HPPD-inhibiting herbicides. Greenhouse experiments were used to identify PSII-inhibitors that were least injurious as measured by leaf bleaching when combined with the HPPD-inhibitors, mesotrione, tembotrione, and topramezone. Subsequently, HPPD-inhibitors were tested individually with PSII-inhibitors atrazine, or bentazon, or alone in field experiments on all three CYP genotypic classes; hybrids homozygous for mutant CYP alleles (cypcyp), hybrids homozygous for functional alleles (CYPCYP), and heterozygous hybrids (CYPcyp). In both greenhouse and field experiments, leaf bleaching within one week of herbicide application increased when a PSII-inhibitor was combined with an HPPD-inhibitor; however, the relatively low level of injury was short-lived. Adding atrazine to POST applications of mesotrione, tembotrione, or topramezone – at a 2X use rate – in sweet corn did not increase risk of yield loss from these HPPD-inhibitors. The synergistic effect on weed control between certain PSII- and HPPD-inhibitor combinations reported previously does not hold true regarding sweet corn sensitivity to these herbicides. Topramezone was the safest HPPD-inhibitor, regardless of PSII combination, for all CYP genotypes. Mutant CYP alleles, namely CYPcyp and cypcyp hybrids, are the main cause of sweet corn sensitivity to mesotrione, tembotrione, and other CYP-metabolized herbicides; therefore, breeding efforts to eliminate mutant CYP alleles should remain a high priority.