Natural Inducers of Plant Resistance to Insects

Abstract

Many environmental factors may affect herbivore/ plant interactions by increasing the level of resistance or susceptibility of the plant to the herbivore. Among the factors with a demonstrated capability to induce changes in levels of resistance are temperature, solar radiation, water stress, soil fertility, insecticides, herbicides, fungicides, growth regulators, pathogen infection, weed competition, and previous or concurrent herbivore attack. Most chemical factors, responsible for the resistance of plants to arthropods studied to date, have involved the genetically controlled, injury-independent accumulation of metabolites with allomonal activity.A completely different plant defense strategy has been demonstrated for many pathogens for which phytoalexin accumulation is the result of a post-challenge response.The aforementioned environmental factors, including pestrelated injury, can induce de novo synthesis and accumulation of compounds with allomonal properties (phytoalexins) or change the relative concentration of both nutrient and non-nutrient compounds.The focus in this paper is on the post-infestation induction of resistance by arthropods, in a manner up until recently known to result only from pathogen infection. The insect-resistance role of phytoalexins is discussed and reference is made to other possible natural sources of inducers of resistance.Antiherbivory in plants has been ascribed mainly to the presence of physical defenses or to the injury-independent accumulation of secondary metabolites that have allomonal

Detrimental effect of rutin on Anticarsia gemmatalis

“…The importance of chemical compounds in the natural (constitutive) resistance is recognized since the fifties, although their use has been little considered (Kogan, 1986). Identification of chemicals responsible for plant defense and their role in the interactions with insects can help the breeders in the development of cultivars resistant to pests (Hedin, 1986).…”

“…(Kubo & Hanke, 1986). Although the chemical importance of those substances has been recognized since early fifties, their use by the breeders has been little considered (Kogan, 1986). The identification of those substances, and their role in the plant-insect interactions, can help geneticists to keep them in the descending generations, to constitute part of the arsenal of plant defense.…”

Does a vascular fungus of tomato induce a defence response or a change in host plant quality that also affects the oviposition of spider mites?

“…Host plant quality is affected by Fusarium by plugging of the xylem vessels and by the production of toxic metabolites, resulting in drought and nutrient stress of the leaves. This mechanism is not an example of induced resistance as defined by Kogan and Paxton (1983 ), although according to the definition of Karban and Myers (1989) the results presented by us would still fit the term induced resistance. Our drought stress experiments clearly showed a negative relationship between severe drought stress (20% PEG) and the performance of T. urticae as found by others (e.g.…”

“…Their definition does not distinghuish between a modification in host plant quality and changes in defensive allocations. In contrast, Kogan and Paxton ( 1983 ) define induced resistance as an active defense based on physical and/or chemical barriers and elicited by a pathogen (or a non-pathogenic factor). The latter definition is generally accepted among plant pathologists.…”

Resistência de variedades de algodão ao curuquerê do algodoeiro Alabama argillacea Hubner (lepidoptera: noctuidae)

“…Em virtude da necessidade de controle deste inseto, alguns produtores buscam técnicas alternativas; assim, a resistência de plantas a insetos é uma tática de controle desejável, uma vez que é compatível com outros méto-dos e frequentemente exibe efeitos sinérgicos com inseticidas e com inimigos naturais (Kogan, 1986;Santos & Boiça Junior, 2001;Azevedo et al, 2002).…”