O efeito alelopático do óleo neem (Azadirachta indica A. Juss) sobre a germinação e crescimento de plantas de alface ( Lactuca sativa L.)

Abstract

The present study arises from an informal conversation with a farmer in which he reported that when mixing the leaves of neem trees (Azadirachta indica A. Juss) with cattle manure for use in the domestic orchard, the plants that received this mixture were more vigorous and less susceptible to attack by disease. Chemical inputs currently represent a significant financial cost to agriculture as well as triggering numerous contamination problems for ecosystems and humans. As a substitute for conventional agriculture, alternatives such as agroecology and organic food production have been sought. Following this precept, organic agriculture makes use of different extracts and vegetable oils as a way to boost production, either in the control of diseases and insects, or in improving the vigor and development of plants. Among the options are products derived from neem ( Azadirachta indica A. Juss ), which have been used in the ecological pest management. However, there are few studies showing the allelopathic effects of neem on germination and growth of plants such as lettuce. The objective of the present study was to evaluate the allelopathic effect of different doses of Dalneem ne neem oil ( Azadiracthta indica A. Juss ) diluted in distilled water on the germination and growth of lettuce plants ( Lactuca sativa L .) , cultivating Four Seasons of the Bionatur marca brand cultivated in different experimental systems. Three experiments were carried out. The first experiment in the laboratory, the effect of different doses (0 ml / L, 1 ml / L, 10 ml / L, 20 ml / L, 30 ml / L, 40 ml / L) was evaluated by initial screening. Neem oil on germination of lettuce seeds. In this experiment no significant changes of the neem oil were observed on the germination of lettuce seeds. Thus, a larger number of doses of neem oil (0; 0,001; 0,05; 0,1; 0,5; 1; 5; 10; 15; 20) mL of the oil / L of distilled water). In this screening, no significant changes of the neem oil were observed on the germination of lettuce seeds, although an increase in the fresh mass of the lettuce seedlings was observed at the dose of 0.5 mL / L of neem oil. From these experiments the doses (0 ml / L, 1 ml / L, 10 ml / L, 20 ml / L, 30 ml / L, 40 ml / L) used in experiments 2 and 3 were selected, the effect of neem oil on the growth of lettuce plants cultivated in trays and in pots was evaluated. In the experiments in trays and in pots, the oil of neem, in the different concentrations, was applied to the substrate with the aid of a graduated pisseta. The plants remained under treatment for 25 days. In the plants with 35 days, the chlorophyll index was evaluated using the chlorophyll meter. At the end of the experiments, the plants were collected, washed, and the root and shoot length were evaluated with the aid of a digital caliper, the fresh mass with the aid of an analytical balance and the dry mass after complete oven drying at 65ºC also recorded in analytical balance. In addition, aerial part samples were macerated with potassium phosphate buffer, centrifuged and the supernatant was used to determine the concentration of soluble proteins. The data were submitted to analysis of variance and the means were compared by the Tukey test with significance of 5% of probability. When cultured in trays, neem oil applied at the dose of 1 ml / L induced an increase in shoot length, but at doses of 30 ml / L inhibited the growth of this organ in lettuce plants. The same inhibitory effect was also observed at the same doses for root growth. When lettuce plants were grown in pots, significant changes were observed only in shoot length. At the dose 1 ml of neem oil the shoot length was 14% higher when compared to the control treatment, although in the larger doses (30 and 40 mm / L of Neem oil) significant reductions were observed in the length of the aerial part of the plants of lettuce. Chlorophyll indices were not affected by the application of neem oil. In addition, an increase in protein levels was observed when lettuce plants were treated with 20 ml / L of neem oil. Therefore, the results of the present study suggest that neem oil does not affect germination, but affects the growth of lettuce plants and can be used in the management of spontaneous plants.