Mechanism of Plant Resistance to Insects, Weeds and Pathogens

Plants are primary producers and a food source for many heterotrophic phytophagous organisms. They are affected by different biotic and abiotic environmental stress. Insects, fungi, bacteria, viruses, nematodes, and other pests are biotic factors that significantly reduce crop productivity. Naturally, plants protect themselves from pest attacks by developing different morphological, structural, and biochemical defense mechanisms. However, our understanding of these defensive mechanisms is still limited. Hence, the objective of this paper is to review the mechanism of plant resistance to insects, weeds, and pathogens to know the relevant defense or resistance mechanisms of plants against pests. Many morphological characteristics contribute to plant resistance to insect pests. These include trichomes, surface waxes and hardness of plant tissues, thickening of cell walls and cuticles, the rapid proliferation of tissues, anatomical changes in plant organs, and color and shape of plant parts. The chemical composition of the host plant affects the behavior and adaptation of the herbivore and the host plant. These chemicals can be physiological inhibitors or nutritional deficiencies. Secondary metabolites are compounds that decrease the palatability of the plant tissues in which they are produced but have no effect on a plant's regular growth and development. Plants defend themselves against pathogens by a combination of weapons termed host resistance which is a structural and biochemical defense mechanism and they also defend from weeds by producing allelochemicals. Thus, plants have developed multiple resistance mechanisms to protect against pests. These resistance mechanisms could be an important tool for pest management by reducing the dose of chemicals used in pest control, resulting in a minimal effect of the chemicals on the environment. Also, these resistance mechanisms are compatible with other control methods that act as one of the components of integrated pest management methods to reduce the damage caused by pests.