Discovery of 4-(2-phenylethynyl) benzoic acid as a potential potent chemical pruner

Rocketing labor cost is a major challenge threatening agricultural sustainability and food security worldwide. The replacement of manual pruning of horticultural plants with chemical pruning has long been a goal for saving cost and reducing virus spreading. Here, guided by the structure-function relationship of allelochemical benzoic acid derivatives, we have identified 4-(2-phenylethynyl)-benzoicacid (PEBA) as a highly bioactive compound. PEBA arrested tomato seed germination at a concentration as low as 0.5 μM, and effectively suppressed lateral branching at 10-100 μM. In field conditions, a foliar spraying of 25 μM PEBA altered tomato plant architecture by repressing emergence and elongation of lateral buds, without significantly affecting plant growth and final fruit yield. Moreover, PEBA could also inhibit seed germination in cereals, albeit at a lower efficacy. The application of 500 μM and 750 μM PEBA profoundly curbed preharvest sprouting in wheat and rice. Acute toxicity analysis using silkworm and Trichogramma chilonis revealed that PEBA posed a low risk of toxicity. The persistence analysis further indicated that residue levels of PEBA in various plant organs were very low following applications. The inhibitory effect of PEBA on tomato seed germination was associated with the suppression of GA1 accumulation and reactive oxygen species generation, while its effect on lateral bud outgrowth were related to perturbations in the plant hormones and the modulation of genes involved in secondary metabolism and those encoding ABC transporters. Collectively, our findings demonstrate the potential of PEBA as a potent plant growth regulator with significant value for chemical pruning.