Transgenic Technology for Disease Resistance in Crop Plants

The ever-increasing demand for food production proportionate to exponential growth of global population evoked the need for applying innovative techniques for developing disease-resistant crop varieties, as the pest and pathogen attack causes considerable yield loss which in turn putts the agriculture sector and crop production in crisis. This is highly significant when the resistance conferred by conventional measures, like artificial hybridization, mutation breeding, marker-assisted selection, etc. appears to be inadequate in many cases, especially due to the evolution of new/more virulent strains/pathovars/isolates of pathogens and their unexpected host range expansion. Development of recombinant DNA technology, transgenic expression and RNA silencing strategies lead to a new era of transgenically engineered resistance in several crop species, many of which succeeded in field trials and got commercialized. Elucidation of genetic and molecular mechanisms underlying host-pathogen interactions, resistance, susceptibility and different levels of plant immune responses (PTI, ETI, HR, etc.) revealed the key genes in the host as well as pathogens that can be manipulated by transgenic approaches/techniques for conferring effective resistance. Reprogramming of phytohormonal regulatory pathways determining defence response and remodeling of molecular receptors/transcription factors involved in resistance or disease development can be brought about by transgenic methods to enhance the resistance in host plants. Targeting of conserved sequences or molecular components could provide broad-spectrum resistance in certain cases. Mining of R genes, transgenic expression of foreign R gene, etc. are other useful strategies. Potential of genome editing based on engineered nucleases like ZFNs, TALENs and CRISPR/Cas9 to precisely mutate the genomic sequence of interest can be exploited for specific targeting of the host/pathogenic genes associated with the biotic stress response. Application of all these approaches for the management of plant pathogens is discussed in this chapter.