Project R-3884

Physiological characterization of tolerance of sunflower Clearfield hybrids to herbicide imazamox (Research)

The herbicide imazamox belongs to the group of imidazolines. The herbicides from this group inhibit activity of the enzyme acetolactat synthase (ALS, EC 4.1.3.18) and thus block the synthesis of branched chained amino acids valine, leucine and isoleucine. The deficit of these amino acids disturbs protein metabolism and causes various functional disorders in treated plants. The growth of sensitive weeds stops at 10-12 hours after treatment, while tolerant plants manage to break down or inactivate the herbicide molecule. The selectivity of the herbicide imazamox to "Clearfield" sunflower hybrids is relatively high and is achieved through traditional breeding using wild-resistant form. However, treatment with the herbicide causes temporary yellowing of the younger leaves of sunflower plants. This herbicide stress intensifies when an overdose is applied as well in case the herbicide treatment is combined with unsuitable weather conditions. The recovery of plants usually lasts two or three weeks, after which a rapid growth in the absence of competing weeds allows plants to overcome the negative herbicide effect and produce high yields. Despite of the wide use of Clearfield technology, the physiological basis of sunflower plant tolerance to the herbicide imazamox is not completely understood. It is believed that it is due to the rapid metabolism of the herbicide, more effective protection from oxidative stress as well as higher capacity for repair. Clarifying these issues would help to select more tolerant sunflower hybrids as well as create opportunities to support better recovery of treated plants in cases where necessary. All this illustrates the need for further research with the following aim and tasks.

01 August 2012 - 31 May 2013