Induction of Resistance to Crop Diseases

Abstract

Development of cultivars with genetic and transgenic resistance to com-bat crop diseases is beset with formidable problems. As an alternative approach to enhance the levels of resistance of cultivars with desirable agronomic attributes, induction of resistance in such cultivars has been considered as a feasible strategy of disease management. Intensive research efforts have been directed to understand the molecular mechanisms of two principal types of induced resistance viz., systemic acquired resistance (SAR) and induced systemic resistance (ISR). As in the case of genetic resistance, the natural disease resistance (NDR) mechanisms are activated by the biotic and abiotic inducers of resistance to diseases. Growth promotion by rhizobacteria in crop plants and consequent yield increases has been shown as an additional advantage, in addition to the protection of crops offered by these biotic inducers against crop diseases. Hence, the acceptability of this approach by the growers and the general public is clearly foreseen, in contrast to the genetically modified (GM) crop products. Furthermore, this approach is ecofriendly and safe, as the development of resistance in microbial pathogens to inducers is unlikely. The possibility of combining this approach with other disease management strategies has been indicated in certain pathosystems. The usefulness and limitations of developing cultivars with genetic resistance by conventional breeding methods have already been discussed (Volume 3, Chapter 3). Although the possibility of employing genetic engineering techniques to generate disease resistant plants appears to be bright, major research efforts are confined only to a few crops such as tobacco, tomato, potato and rice. Furthermore, con-sumer acceptance and environmental safety requirements have placed formidable obstacles on the utility of this approach. Under these conditions, inducing resistance to disease(s) in the existing cultivars with high yield potential and quality using biotic/abiotic inducers of resistance appears to be a practical approach that can be applied to all crops. Furthermore, this approach does not involve the introduction of any foreign gene expression in susceptible plants. This approach has been demon-strated to be as safe as the use of cultivars with genetic resistance, since the same mechanisms are activated in both genetically resistant plants and susceptible plants with induced resistance.