Phytotoxic effect of Pinus Elliottii extracts on invasive plants from agricultural cultivation systems.

Abstract

Among the factors that lead to low rural productivity, weeds are responsible for 34% of the reductions in agricultural incomes. The increase and uncontrolled use of agrochemicals such as glyphosate is increasingly requiring less-harmful alternatives to the human health and environment that ensure weed control and food security. This study, therefore, investigated a property called allelopathy encountered in the pine species Pinus elliottii, in order to evaluate the bioherbicidal potential of its allelopathic effect on invasive plants from pre- and post-emergent agricultural cultivation systems. Initially, the aqueous extracts obtained from Pinus elliottii needles were diluted in different concentrations and models according to the test to be performed. To simulate a post-emergent system, the extracts were applied to young individuals of Conyza bonariensis and Cyperus rotundus, both species of weeds. Subsequently, samples of the roots and aerial parts were collected and subjected to moisture and metal analysis. Acid digestion occurred in a microwave oven with the samples from each set previously dried to measure the amount of sodium (Na) and potassium (K) by flame photometry. With regards to the pre-emergent system, the interference of Pinus elliottii in germination and seedling formation factors of the Bidens pilosa species was analysed. In addition, the extracts were subjected to the analysis of organic compounds and acute ecotoxicity through tests with Artemia salina nauplii. The post-emergent test demonstrated a similarity in the phytotoxic effect of Pinus elliottii and the reference herbicide glyphosate, by reducing the humidity of the roots and aerial parts, which increases Na and decreases K contents, suggesting a metabolic imbalance in the plant that causes its death. The pre-emergent test revealed that the 16% extract (m/v) caused 100% inhibition in Bidens pilosa germination and the 8% extract demonstrated statistical significance by interfering in the delay and formation of seedlings and germination. Regarding ecotoxicity, Pinus elliottii indicated LC₅₀ equals to 2000 ppm of the 16% extract, falling within the limit of toxicity that determines LC₅₀ < 1000 ppm for toxic substances. Therefore, Pinus elliottii extracts revealed efficiency in both pre- and post-emergent systems and guaranteed toxicity within approved environmental standards, which serves as evidence of its promising phytotoxic potential and use as a bioherbicide.