**7. Sources of biotic stress resistance in wheat**

Wheat belongs to the kingdom Plantae and family Poaceae. It is a long day and a self-pollinated crop. The bread wheat (*Triticum aestivum*) genome is one of the most challenging plant genomes to study. It is highly repetitive (~85%) and approximately 15.4–15.8 Gbp in size, which is five times larger than the human genome [102]. The genus Triticum contains 10 species, out of which six are cultivated and four are wild. Hexaploid wheat (*T. aestivum*) genome (2n = 6x = 42) encompasses A, B and D sub-genomes which is advantageous for providing useful genetic diversity for crop improvement. There are three ploidy levels in *Triticum* and *Aegilops* (encompassing cultivated wheats and their progenitors) genera with 2n chromosomes 14, 28, 42 and the basic chromosome x = 7 in all the species. Other genera of Poaceae such as Secale, Hordeum, Dasopyrum, Agropyron, Elymus, Leymus, Elytrigia, and Thinopyrum are also important for introgression of useful variability into cultivated wheats. On the basis of their genomic constitution, the wild relatives of wheat can be classified into primary, secondary, and tertiary gene pools [103, 104]. These gene pools are affluent source of genes for disease and pest resistance, mitigating abiotic stresses and micronutrient enrichment in wheat. These three gene pools of wheat as sources of resistance can be described as follows: *Breeding Wheat for Biotic Stress Resistance: Achievements, Challenges and Prospects DOI: http://dx.doi.org/10.5772/intechopen.97359*

