Bioassay Of Herbicidal Activity Of Synthetic Tenuazonic Acid

Alternaria alternata (Fr.) Keissler is a pathogen of Crofton weed (Eupatorium adenophorum), one of the malignant weeds in the world. It has potential to be developed into a mycoherbicide for biocontrol of Crofton weed. Phytotoxin AAC-toxin produced by the fungi is the main factor that can cause the disease on crofton weed. The previous studies have shown that the main components of AAC-toxin is tenuazonic acid (TeA). Due to the low content of TeA in A. alternata and high cost in AAC-toxin obtained by submerged fermnetation pathway, only the way for this problem is to synthesize TeA with good herbicidal activity. But TeA has lots of isomers in different condition, it’s necessary to systemically evaluate herbicidal activity of synthetic TeA in order to confirm the exact ingredient which has as the same structure and biological activity as biosynthetic AAC-toxin. Hence, the following studies were performed to evaluate the herbicidal activity of synthetic TeA compound. At the same time, it will also provide some theoretical support for the commercialization of TeA as a bioherbicide.By using the intact leaf puncture assay and pannikin assay, it’s evaluated that effect of two adjuvants in the case of separated-or mixed-use on weed control efficacy. Results showed the adjuvants gradually enhanced the herbicidal activity of TeA as the concentration of the adjuvants increased. But low level of concentration has no obvious effect on the herbicidal activity, while mixed-use of JFC and laurocapram at concentration of over0.4%is the optimum to enhance the bioactivity of TeA. However, as the concentration increased to a higher level, the adjuvants themselves could do harm to the target. The increasement of herbicidal activity of TeA results from the damages which the adjuvants produce directly. So mixed-use of JFC and laurocapram at concentration of0.4%is the optimum to enhance the bioactivity of TeA.25%TeA formulation was made utilizing the optimum adjuvant group. The evaluation of the weed control efficacy and the safety of crop were done by experiments of the pannikin bioassay and field trials. Results of the biometrics indoor indicated that the25%TeA AS has good herbicidal activity to all applied weeds including gramineous and broadleaf weeds. According to evidence of the field experiments, the total stem control efficacy of25%TeA AS at the concentration of1125g ai./hawas up80.5%after14days. In the case of1500g ai./ha, weed control efficacy of whole plant after14days and total fresh after14days is87.7%and90.0%, respectively. There was insignificant difference in control efficacy of25%TeA AS towards Digitaria sanguinalis (L.) Scop. Echinochloa crusgalli (L.) Beauv, and Amaranthus retroflexus L., which is well consistent with result of the pannikin bioassay. Aftre7days of application at the concentration of1125g ai./ha and1500g ai./ha, the injury rate of25%TeA AS to crop cotton is16.3%and25.2%, respectively. However, the injury rate of all concentration treatment showed a clear lowering after application for14days. For application of1500g ai./ha, the injury rate decreased to15.3%. Based above results,25%TeA AS at concentration of1500g ai./ha may be recommended to apply in the cotton fields since the dose is the most suitable to weed control efficacy and cotton safety.