**1. Introduction**

Wheat is one of the most important cereal staple food crops in the world, both in terms of food production and for providing the total amount of food calories and protein in the human diet [1]. It is believed that bread wheat originated in south western Asia from where it spread to other regions of Asia, Europe, Africa and America [2]. Wheat has adapted itself to diverse climatic conditions and, as such, is grown over a range of altitudes and latitudes under irrigated, severe drought and wet conditions. The global demand for wheat is projected to rise by 60% by 2050 because of the increase in the world's human population and changing livelihoods.

Wheat production has been threatened by unexpected abiotic and biotic stresses due to abrupt environmental changes or movement of pathogens. The monoculture of modern wheat cultivars with low genetic diversity has resulted in pathogen resurgences, which threaten wheat supplies [3].

Biotic stress in plants is caused by several living organisms namely fungi, virus, insects, nematodes, arachnids and weeds. Unlike the stresses caused by environmental factors i.e. abiotic stresses (heat and drought), the biotic stress agents directly affect the host growth and development by depriving them of nutrition resulting into reduced plant vigor and in extreme cases, even death of the host. From the agricultural context, biotic stress has major contribution in pre as well postharvest losses. Of the nearly 200 diseases and pests that have been documented, 50 are considered economically important because of their potential to damage crops and affect farmers' incomes [4]. Among biotic stresses, pathogenic fungi represent a significant challenge to wheat production globally. The major diseases in wheat involves stripe rust, stem rust, leaf rust, powdery mildew, head blight etc. Historically, yellow rust has caused and is presently causing significant and severe losses in susceptible wheat cultivars worldwide [5]. The major insect-pests attacking wheat are aphid, hessian fly, green bug and borers etc.

In this chapter, the major diseases and pests detrimental to wheat crop along with the molecular basis of stress resistance will be discussed. Moreover, the remarkable global milestones being achieved along with some important tools and prospects for mitigating with these economically important diseases and pests will be focused.
