Plants have inherent defense mechanism that protects against their predators and pathogens. Their inability to move is largely completed by defensive adaptations that help plants to survive and reproduce successfully. One of the most important defensive mechanisms is the production of secondary metabolites. These metabolites are chemical substances which are not involved in the normal process of photosynthesis of plants. They are also known as allelochemicals, and they can influence the behavior, growth or survival of herbivores. Allelochemicals act as toxins of herbivores and in some cases also reduce cell wall digestibility.
Some external structural characteristics on the stem and leaves (prickles, spines, thorns etc) discourage herbivores in a very large extent. These mechanical defence mechanisms deter, injure or kill the Grazer. Some defensive substances such as wax, lignins, resins, etc. are released on the epidermis of plants and prevent herbivores to feed on them. Apart from that, the by sensitive touch sensitivity is another example of plant defense mechanism.
Herbivores form a main link in the food chain, because they are the source of energy for ranking higher in the food chain organizations. Plants are the only source of food for herbivores, and this has led to the Coevolution of adaptations that help them acquire their food, irrespective of the mechanisms of defence in plants. Some of these adaptations are:
synthesis of enzymes that can reduce the effect of the secondary metabolitesexistence of internal symbiotic bacteria, fungi, or protozoa which help to break down the cellulose plant so that it can be digested by herbivoremechanical as butterflies incisors adaptations to help eat soft leaves.Among these adaptations, manipulation of the host is the most important mechanism by which herbivores feed on plants in a better way. According to recent research conducted by Renato Almeida Sarmento and his team, invasive spider mite Tetranychus evansi, manipulates its host (tomato), by interfering with signaling pathways involved in his defense mechanism [1].
The primary hosts for t. evansi are solanaceous crops such as tomatoes, potatoes, tobacco etc. These mites puncture the leaves while feeding, yellowing or whitening of the leaves. Subsequently, the leaves fall to the bottom and in a serious crisis, the plant dies. The study by Sarmento, suggests that t. evansi, manipulates the host defense mechanism by removing the induction of signalling routes jasmonic acid and salicylic acid involved in the defenses of the plant in the tomato plant. Salicylic acid and jasmonic acid play a vital role in plant immunity. Spider mites reduce levels of inducible defense compounds and volatile substances (for example, protease inhibitors) which play a crucial role in the defence of plants.
Crops such as tomatoes and potatoes are a widespread around the world use. Control of pathogens affecting these cultures is an essential area of research. The result of research by Sarmento, offers a better understanding of the plant-herbivore interactions. It opens the door for further research in two directions:
Biological control of Tetranychus evansi at an affordable price to the farmer.Develop crop varieties that are able to fight against manipulation by herbivores.Reference:
[1] R. Sarmento Lemos F et al. A herbivore that manipulates the plant defense. Ecol Lett. 14 March 2011 (3): 229-236.
