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The stem rust resistance gene Sr31, transferred from rye (Secale cereale) into wheat (Triticum aestivum L.) imparts resistance to all the virulent pathotypes of stem rust (Puccinia graminis f. sp. tritici) found in India. Wheat genotypes including carriers and non-carriers of the Sr31 gene were analysed using arbitrary primed polymerase chain reaction (AP-PCR). AP-PCR markers viz. SS30.2 580(H) associated with the Sr31 gene and SS26.1 1100 associated with the allele for susceptibility were identified. Linkage between the markers and phenotypes was confirmed by analysing an F 2 population obtained from a cross between a resistant and a susceptible genotype. The markers were tightly linked to the respective alleles. Both the AP-PCR markers were converted into sequence characterized amplified region (SCAR) markers, viz. SCSS30.2 576 and SCSS26.1 1100 respectively. The markers were validated in two more segregating populations and 49 wheat genotypes. Using both markers it was possible to distinguish the homozygous from the heterozygous carriers of the Sr31 gene in the F 2 generation. The markers developed in this study can be used for pyramiding of the Sr31 gene with other rust resistance genes and in marker-assisted selection.

Genetic variation is the mainstay which plant breeders require to produce new and improved cultivars. The opportunity of obtaining novel traits exists through induction of mutations. Induced mutations have played a signifi cant role in meeting challenges related to world food and nutritional security by way of mutant germplasm enhancement and their utilisation for the development of new mutant varieties. A wide range of genetic variability has been induced by physical and chemical mutagens. In the past several decades, induced mutations have contributed immensely to the development of improved varieties in several crop plants. Cellular and molecular biology tools have led to enhanced effi ciency of induction, detection and deployment of mutations. Till date, 3,218 mutant varieties have been released worldwide. More than 60 % of offi cially released mutant varieties are from Asia with China, India and Japan topping the list. The mutant varieties developed and released in major crops have been cultivated by farmers in large areas and have resulted in increased food production, thus contributing to food security. In this chapter, various aspects of mutation induction, applications and examples of successful use of induced mutants in crop improvement programmes are presented.