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.

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Chitosan (CSN) and its derivatives are being exploited for their potential role in agriculture in mitigating environmental stress factors. The present study was aimed to enhance the synthesis of chitosan (CSN)-based silver nanoparticles (Ag NPs) using γ-irradiated chitosan (IR-CSN) and to study the antimicrobial activity of IR-CSN–Ag NPs. The chitosan–silver nanocomposites (CSN–Ag NPs) were prepared by employing the green synthesis method using normal chitosan (high molecular weight (MW), NL-CSN) and oligochitosans (low MW, IR-CSN). The latter was derived by irradiation with γ rays ( 60 Co) at 100 kGy dose to obtain a lower MW (approximately 25 kDa). NL-CSN and IR-CSN (0.0–2.5% w/v) were amalgamated with different concentrations of silver nitrate (0.0–2.5% w/v) and vice versa. The UV–visible spectra displayed a single peak in the range of 419–423 nm, which is the characteristic surface plasmon resonance (SPR) for Ag NPs. The physicochemical properties were assessed using different methods such as transmission electron microscopy (TEM), Fourier transform infrared (FTIR), zetasizer, elemental (CHNS) analysis, etc. The degree of Ag NP synthesis was more in IR-CSN than NL-CSN. The in vitro disc diffusion assay with IR-CSN–Ag NPs exhibited a significantly higher antimicrobial activity against Escherichia coli . Further evaluation of the antifungal activity of IR-CSN and Ag NPs showed a synergistic effect against chickpea wilt ( Fusarium oxysporum f. sp. ciceris ). The study has provided a novel approach for the improved synthesis of CSN–Ag nanoparticle composites using γ-irradiated chitosan. This study also opens up new options for the development and deployment of γ-irradiated chitosan–silver nanocomposites for the control of phytopathogens in sustainable agriculture.