Rice physical defenses and their role against insect herbivores.

Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.