Phytotoxicity of the extracts of Lonchocarpus muehlbergianus Hassl. (Fabaceae) leaflets and galls on seed germination and early development of lettuce

Denis Coelho De Oliveira,Geraldo Luiz Gonçalves Soares,Rosy Mary Dos Santos Isaias

doi:10.1590/s0102-33062008000400020

Denis Coelho De Oliveira, Geraldo Luiz Gonçalves Soares + Show 1 more

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https://doi.org/10.1590/s0102-33062008000400020

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Abstract

Galls induced by Euphalerus ostreoides (Hemiptera: Psyllidae) cause structural and chemical alterations on Lonchocarpus muehlbergianus leaflets. Healthy and galled leaflet tissues of this plant species are rich in secondary metabolites with potential allelopathic effects. This research compares the allelopathic effects of the aqueous extracts of L. muehlbergianus leaflets and galls on seeds and seedlings of Lactuta sativa, and evaluates the chemical impact produced by a gall-inducing insect on the other trophic levels associated with it. The extracts were obtained through static maceration in distilled water (5% p/v). The treatments consisted of aqueous crude extracts and those previously filtered in polyvinylpirrolidone (PVP). After seven days, seedling height was measured, and the radicles were fixed in FAA50 for anatomical analyses. Healthy leaflet and gall aqueous extracts, and those filtered in PVP, significantly inhibited seed germination, with no significant differences between the two groups. Treatments with aqueous extracts reduced seed germination speed and vegetative axis length. Plant tissue alterations confirm the phytotoxicity of allelochemical substances present in the extracts. The differences among the treatments indicated that gall formation altered L. muehlbergianus leaflet metabolism, and this could influence the other trophic levels associated with this gall inducing-host plant system.

Highlights

Allelopathy is any direct or indirect, harmful or beneficial effect that a plant or microorganism exerts on another plant by the release of chemical compounds into the environment (Rice 1984)
For evaluation of the allelopathic potential of the aqueous extracts of healthy leaflets and galls induced by Euphalerus ostreoides on Lonchocarpus muehlbergianus, plant material was collected from 10 specimens located at the Campus Pampulha of Universidade Federal de Minas Gerais, in Belo Horizonte, Minas Gerais
The allelochemical effects of healthy leaflet extract (HLE), healthy portion of galled leaflet extract (HPGLE) and gall extract (GE) of Lonchocarpus muehlbergianus on lettuce seeds were more evident on germination speed (Fig. 3) and seedling length (Fig. 4) than on the final germination percentage

Summary

Introduction

Allelopathy is any direct or indirect, harmful or beneficial effect that a plant or microorganism exerts on another plant by the release of chemical compounds into the environment (Rice 1984). Besides the structural alterations in host plant tissues, gall inducing herbivores produce biochemical modifications, noticed either on primary or secondary specific metabolites (Hartley 1998) These metabolites, nutritive compounds and growth hormones are reallocated from the healthy tissues to the gall site (Leicht 1994; Nymam 2000) which functions as a sink. Oliveira et al (2006) demonstrated that the healthy tissues and the galls induced by Euphalerus ostreoides on Lonchocarpus murhlbergianus leaflets accumulate nutritive substances, such as starch and lipids, as well as phenolic and flavonoidic derivatives (flavones, flavonols, and flavanones) In these gall tissues, the flavonic compounds formed oxonium salts by the reaction with sulphuric acid, which did not occur in healthy tissues. The synthesis of oxonium salt precursors may be a specific response to the biotic stress induced by the endophytophagous insect

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