Alelopatia é a influência de plantas sobre outros organismos por meio de compostos por elas
produzidos e lançados no meio. Algumas espécies da família Myrtaceae apresentam
evidências de propriedades alelopáticas. Eugenia dysenterica DC., conhecida como cagaita, é
frequentemente encontrada no Cerrado sentido restrito. Os objetivos desse estudo foram
quantificar os efeitos alelopáticos de extratos aquosos foliares de cagaita na germinação e no
crescimento de gergelim (Sesamum indicum L.) e de rabanete (Raphanus sativus L.), e
verificar se a atividade alelopática dos extratos tem interferência do pH e da secagem das
folhas antes do preparo dos mesmos. Para tal, os extratos foram preparados a partir de folhas
maduras frescas e secas. A secagem ocorreu em estufa (50 oC /24h). Em ambos os casos as
folhas foram trituradas e solubilizadas em água a 5% (p/v) com diluição para 1% e 3%. Os
efeitos do pH do extrato foram verificados através de tratamentos com o pH original do
extrato (4,7) e tratamentos com o pH ajustado para 7,0. Para a germinação, foram utilizadas
placas de petri com 10 sementes de gergelim/rabanete contendo 6 mL dos extratos (suas
diluições) e água como controle, com três repetições por tratamento. Houve acompanhamento
diário por 5 dias. Para os experimentos de crescimento nos extratos, foram utilizadas
sementes pré-germinadas em água. Após cinco dias as plântulas tiveram suas partes aérea e
radicular medidas e características morfológicas registradas. Os experimentos foram
conduzidos em câmaras de germinação a 25oC (rabanete) e 30oC (gergelim), com fotoperíodo
de 12h. Os resultados mostram que a germinabilidade e o tempo médio de germinação de
ambas as espécies-alvo não foram afetados pelos extratos, independentemente do pH e da
secagem ou não das folhas. Quanto ao crescimento, a parte radicular foi a mais afetada para as
duas espécies, apresentando redução em seu comprimento 82% (gergelim) e 87% (rabanete),
escurecimento radicular em todas as plântulas em contato com o extrato, redução do número
de plântulas com pêlos radiculares (73% e 90% - gergelim e rabanete, respectivamente) e com
raízes laterais (30% e 70% respectivamente). O ajuste do pH para 7,0 não alterou o potencial
alelopático do extrato. O extrato proveniente de folhas secas promoveu maior efeito inibitório
no crescimento radicular 85% (gergelim) e 86% (rabanete) que o de folhas frescas (69% e
80% respectivamente).
Allelopathy is the influence that compounds produced by plants and released into the
environment produces on other organisms. Some Myrtaceae’s species have shown some
allelopathic property. Eugenia dysenterica DC., popular known as cagaita, is very common in
the Cerrado sentido restrito. The objectives of this study were 1) to quantify the allelopathic
effects of leaf aqueous extract of cagaita on the germination and growth of sesame (Sesamum
indicum L.) and radish (Raphanus sativus L.) seedlings and 2) to verify if the allelopathic
activity of the extracts are influenced by its pH and by the drying of the leaves before
preparing them. Aqueous extracts were prepared using fresh and dry adult leaves. The leaves
were dryed at 50o C for 24h. In both cases the leaves were grinded and dissolved in water at
5% (w/v) with posterior dilution to 1% and 3% for the experiments. The effects of pH of the
extracts were verified through treatments keeping the original pH value (4,7) and treatments
with pH adjusted to (7,0) with NaOH. To test the effects on germination, Petri dishes with 10
seeds of sesame/radish each containing 6 ml of the extracts (1 and 3%) were employed, water
was the control. Three replications by treatment were conducted. Germinated seeds were
counted everyday for up to five days. To test the effects on seedling growth, seeds previously
germinated in water were employed. They were disposed in 15cm petri dishes with 10 mL of
the extract to be tested. Water was the control. All the experiments were carried out in B.O.D.
chambers at 25oC (radish) and 30oC (sesame), with photoperiod of 12h. After five days, the
seedlings had their aerial and root parts measured and morphological characteristics were
recorded. The results show that the germinability and the average time of germination of both
targeted-species were not affected by the leaf extract of cagaita, irrespective of its pH and the
drying of the leaves. However, the seedling growth was affected by the extracts. For both
species the root parts showed to be more sensitive to the extracts than the shoot parts,
showing a growth inhibition of about 82% (sesame) and 87% (radish), when compared to the
growth in water. Both sesame and radish seedlings incubated in the extracts presented a
reduction of the number of seedlings with root hairs (73% and 90% - sesame and radish,
respectively) and with lateral roots (30% and 70% respectively). These effects were not
affected by the pH adjustment. However, extracts prepared with dry leaves promoted a higher
inhibitory effect on root growth 85% (sesame) and 86% (radish) than the fresh leaves one
(69% and 80% respectivetly).
