Write the role of molecular markers for crop improvement giving example for biotic stress.
Answers
Plants being sessile in nature encounter numerous biotic agents, including bacteria, fungi, viruses, insects, nematodes and protists. A great number of publications indicate that biotic agents significantly reduce crop productivity, although there are some biotic agents that symbiotically or synergistically co-exist with plants. Nonetheless, scientists have made significant advances in understanding the plant defence mechanisms expressed against biotic stresses. These mechanisms range from anatomy, physiology, biochemistry, genetics, development and evolution to their associated molecular dynamics. Using model plants, e.g., Arabidopsis and rice, efforts to understand these mechanisms have led to the identification of representative candidate genes, quantitative trait loci (QTLs), proteins and metabolites associated with plant defences against biotic stresses. However, there are drawbacks and insufficiencies in precisely deciphering and deploying these mechanisms, including only modest adaptability of some identified genes or QTLs to changing stress factors. Thus, more systematic efforts are needed to explore and expand the development of biotic stress resistant germplasm. In this chapter, we provided a comprehensive overview and discussed plant defence mechanisms involving molecular and cellular adaptation to biotic stresses. The latest achievements and perspective on plant molecular responses to biotic stresses, including gene expression, and targeted functional analyses of the genes expressed against biotic stresses have been presented and discussed.