Systemic Acquired Resistance and Induced Systemic Resistance in Conventional Agriculture

common bean (Phaseolus vulgaris L.), rice (Oryza sativa L.), and Arabidopsis thaliana (L.) Heynh., demonstraPlants possess a range of defenses that can be actively expressed ting that SAR was conserved across diverse plant famiin response to pathogens and parasites of various scales, ranging from microscopic viruses to insect herbivores. The timing of these defense lies and was effective against a broad range of viral, responses is critical and can be the difference between being able to bacterial, and fungal pathogens (reviewed in Sticher et cope or succumbing to the challenge of a pathogen or parasite. Sysal., 1997). temic acquired resistance (SAR) and induced systemic resistance (ISR) Additional interests in the biological control of soilare two forms of induced resistance; in both SAR and ISR, plant borne diseases of plants led to the serendipitous discovdefenses are preconditioned by prior infection or treatment that reery of another form of induced resistance associated sults in resistance (or tolerance) against subsequent challenge by a with the colonization of plant roots by certain plant pathogen or parasite. Great strides have been made over the past growth promoting rhizobacteria (PGPR), referred to as 20 yr in understanding the physiological and biochemical basis of induced systemic resistance (ISR) (reviewed in van SAR and ISR. Much of this knowledge is due to the identification Loon et al., 1998). ISR is distinct from SAR in several of a number of chemical and biological elicitors, some of which are commercially available for use in conventional agriculture. However, key physiological and biochemical phenotypes that are the effectiveness of these elicitors to induce SAR and ISR as a practical best defined in A. thaliana (Knoester et al., 1999; Pietmeans to control various plant diseases is just being realized. In this erse et al., 1996, 1998; Ton et al., 1999, 2001; van Wees review, we first briefly summarize the fundamentals of ISR and SAR, et al., 1997). Results of lab and field studies show that, for which a number of critical reviews already exist. We then examine like SAR, ISR is effective against a broad range of the efficacy of SAR and ISR in published field-based studies. We diseases caused by viruses, bacteria, and fungi (Murphy place special emphasis on the benefits, drawbacks, and future considet al., 2000; Nandakumar et al., 2001; Niranjan Raj et erations for the improved use of chemical and biological elicitors al., 2003; Raupach and Kloepper, 1998, 2000; van Loon of induced resistance in conventional agriculture; this includes the et al., 1998; Wei et al., 1996; Zehnder et al., 2001). potential to exploit genetic variability within populations of crop species to improve the utility of SAR and ISR in the field. Over the last 20 yr, research on SAR and ISR using model systems has furthered our understanding of the molecular basis of induced resistance and promoted the P researchers have known for over 100 yr that development of synthetic elicitors and PGPR formulaplants can be preconditioned against diseases caused tions for use in conventional agriculture (see reviews by a variety of parasites. Initially, the debate was over by Benhamou and Nicole, 1999; Hammerschmidt and the serological basis of what was then referred to as Kuc, 1995; Kessler and Baldwin, 2002; Kessmann et al., acquired physiological immunity (reviewed in Chester, 1994; Leroux, 1996; Lucas, 1999; Lyon et al., 1995; 1933a, 1933b). It would take another 60 yr before Ross Sticher et al., 1997; van Loon et al., 1998; Walling, 2000). (1961a, 1961b), from results of experiments using ToThe future use of SAR and ISR to control crop pests bacco mosaic virus to sensitize tobacco (Nicotiana tabain conventional agriculture seems promising. Since syncum L.) against subsequent “challenge” inoculations of thetic elicitors and PGPR strains, in general, do not Tobacco mosaic virus on infected leaves or on distal exhibit any direct antimicrobial activity, unlike tradiuninfected leaves, would clearly articulate the concepts tional pesticides, they provide a way to control disease of localized acquired resistance and SAR, respectively. without asserting direct selective pressure on pathogen Cruikshank and Mandryk (1960) extended this concept populations. In addition, the use of synthetic elicitors to a nonviral pathogen in field-grown tobacco plants and PGPR strains seems to be environmentally benign using stem injections of Peronospora tabacina (D.B. relative to current pesticides. These characteristics make Adam, also referred to as P. hyoscyami de Bary f. sp. SAR and ISR, and other forms of induced resistance, tabacina) to trigger SAR against subsequent inoculations an attractive approach for managing crop pests in a of the same pathogen, the causative agent of blue mold sustainable manner within the scope of a conventional of tobacco. These landmark studies led to the developagriculture system. ment of the classic SAR models during the 1980s in other plants, such as cucumber (Cucumis sativus L.), Systemic Acquired Resistance and Induced Systemic Resistance Gary E. Vallad, Dep. of Plant Pathology, Univ. of California–Davis, c/o U.S. Agriculture Research Station, 1636 E. Alisal St., Salinas, Induced resistance is a physiological “state of enCA 93905; Robert M. Goodman, Dep. of Plant Pathology and Gayhanced defensive capacity” elicited by specific environlord Nelson Institute for Environmental Studies, Univ. of Wisconsin, mental stimuli, whereby the plant’s innate defenses are Madison, WI 53706. Received 22 Oct. 2003. *Corresponding author potentiated against subsequent biotic challenges (van (rgoodman@facstaff.wisc.edu). Loon et al., 1998). This enhanced state of resistance is Published in Crop Sci. 44:1920–1934 (2004). © Crop Science Society of America Abbreviations: ISR, induced systemic resistance; PGPR, plant growthpromoting rhizobacteria; SAR, systemic acquired resistance. 677 S. Segoe Rd., Madison, WI 53711 USA