One of the major problems concerning the production of food crops is the difficulty of controlling plant diseases to maintain the high quality and yield which the producer and consumer expect. For example, many fungal pathogens have developed resistance to the active ingredients of a wide range of fungicides and there is a public perception that 'pesticides' are undesirable.

At SCRI we are developing a number of approaches, through the application of biotechnology, to reducing the incidence of disease in agricultural crops. One such approach to the control of plant diseases is through the induction and enhancement of the plant's own defence mechanisms which would not involve the application of toxic compounds to plants.

Fundamental studies have helped us to understand many of the biochemical interactions occurring between plants and plant pathogens. Thus we are able to describe resistance reactions as involving not only some preformed components but more importantly, an induced response to infection which includes a 'cascade' of induced responses. These include novel antimicrobial compounds (phytoalexins), proteins, and physical barriers to penetration. This cascade of resistance factors is induced when a plant recognises that a potential pathogen is present, and compounds which are capable of triggering such responses are termed elicitors.

Detached barley leaves cv. Golden Promise sprayed with a yeast-derived resistance elicitor 24 hours before inoculation with mildew. Photograph above shows; (far right) untreated leaves; and (left) three sets of leaves treated with various yeast-derived elicitor formulations. Elicitation of resistance is not associated with any deleterious effects on the plant and the treatment on the far left shows excellent control of mildew.

At SCRI we have been studying several naturally occurring resistance elicitors including those obtained from fungi. Importantly, elicitors can be extracted from yeast which is available in large quantities as a low value product from the food and brewing industry. We believe that elicitors from yeast could form the basis of a new non-toxic crop protection system which would be environmentally benign, would enable plants to respond to infection faster than normal and prevent potential pathogens from successfully colonising the host.

Because of the unique mode of action of this control method (through induction of a cascade of resistance responses) it has the added advantage that pathogens should not develop insensitivity as they do to traditional fungicides.

There are many reports in the literature which demonstrate the concept of induced resistance in laboratory or glasshouse experiments, including biotic and abiotic elicitors, either in a pure form or as a crude mixture. Most of these elicitors have not been tested under field conditions and some have been shown to have side-effects such as phytotoxicity.

Our own work, and that of a few other groups, has shown moderate levels of efficacy of disease control in the field (for example, against cereal mildew) demonstrating the principle that induced resistance can work in the field. There have been predictions, by some, that there would be an energetic cost in the induction of resistance, but with yeast-derived elicitors we have not detected any yield loss in replicated field trials, nor have we observed any phytotoxic side effects such as yellowing, necrosis or stunting. Thus, induced resistance does not necessarily involve a 'cost' or loss in yield. The elicitors that are currently available for experimental use in laboratories are less robust than fungicides in that they are far more effective when applied prior to the arrival of the pathogen and will have an inhibitory rather than a curative effect on an existing infection.

Resistance elicitors could have a role in an integrated disease control strategy and permit a reduction in fungicide inputs. For example, they could be combined with reduced dose fungicide sprays in integrated crop management programmes either as a combined tank mix or as alternating sprays to achieve greater disease control and reduce fungicide inputs. Furthermore, because elicitors are not in themselves antimicrobial, it may be possible to integrate them with biocontrol agents thereby increasing the flexibility of disease management.

Publications on induced resistance

Induced Resistance for Plant Defence: a sustainable approach to crop protection, Eds: Dale Walters, Gary D Lyon and Adrian C Newton. Blackwell Science, Oxford, UK.

Walters D, Lyon GD, Newton AC, 2007. Induced resistance in crop protection: the future, drivers and barriers. In: Induced Resistance for Plant Defence: a sustainable approach to crop protection. Eds: Dale Walters, Gary Lyon and Adrian Newton, pp. 243-250. Blackwell Publishing, Oxford, UK.

Newton AC, Pons-Kohnemann J, 2007. Induced resistance in natural ecosystems and pathogen population biology: exploiting interactions. In: Induced resistance for plant defence: a sustainable approach to crop protection, pp. 133-142. Eds. Dale Walters, Adrian Newton, Gary Lyon, Blackwell Publishing, Oxford, UK.

Walters D, Walsh D, Newton A, Lyon G, 2005. Induced resistance for plant disease control: maximising the efficiency of resistance eleicitors. Phytopathology, 95, 1368-1373.

Lyon GD, Newton AC, 1999. Immunizing plants against pathogens: Implementing induction in Agriculture. In: Induced plant defenses against pathogens and herbivores, eds: Anurag Agrawa, Rick Karban, Sadik Tuzun, pp. 299-318. APS Press, American Phytopathological Society, St Paul, Minnesota.

Lyon GD, Newton AC, 1997. Do resistance elicitors offer new opportunities in integrated disease control strategies? Plant Pathology 46, 636-641.

Lyon GD, Forrest RS, Newton AC, 1996. SAR - The potential to immunise plants against infection. Brighton Crop Protection Conference 1996. Proceedings. Publisher BCPC. 939-946

Miller SK, Lyon GD, 1996. The ability of elicitors to induce resistance in potatoes. Proceedings 13th Triennial Conference of the European Association for Potato Research, Netherlands 1996. 462-463.

Lyon GD, Reglinski T, Forrest RS, Newton AC, 1995. The use of resistance elicitors to control plant diseases. Aspects of Applied Biology. Physiological responses of plants to pathogens 42, 227-234.

Lyon GD, Reglinski T, Newton AC, 1995. Novel disease control compounds: The potential to 'immunize' plants against infection. Plant Pathology 44,407-427.

Miller S K, Lyon GD, 1995. Assessment of the ability of elicitors to induce resistance to P. infestans in potato. Proceedings of EAPR meeting "Phytophthora 150", Dublin, September 1995. Edited by L.J. Dowley, E. Bannon, L.R Cooke, T. Keane and E.O'Sullivan. Published by Poole Press Ltd Dublin and Teagasc, Carlow, Ireland. Abstract p 370-371

Newton AC, Reglinski T, Lyon GD, 1995. Resistance elicitors from fungi as crop protectants. M. Manka (ed), Environmental biotic factors in integrated plant disease control 419-422. Proceedings 3rd Conference of the European Foundation for Plant Pathology, Poznan, Poland.

Reglinski T, Lyon GD, Newton AC, 1995. The control of Botrytis cinerea and Rhizoctonia solani on lettuce using elicitors extracted from yeast cell walls. Journal of Plant Diseases and Protection 102, 257-266.

Reglinski T, Lyon GD, Newton AC, 1995. Induction of plant defence mechanisms for crop protection. Proceedings of the 10th Biennial Australasian Plant Pathology Society Conference, Lincoln University, NZ, 28-30th August 1995. Abstract number 57, page 48.

Reglinski T, Lyon GD, Newton AC, 1995. Stimulating the plant "immune system" using resistance elicitors. HortResearch 1995 Technical Updating Seminars, Pest and diseases; problems and solutions. Ruakura Research Centre, Hamilton, NZ, 29th May, 1995. p54-59.

Newton AC, Reglinski T, Lyon GD, 1994. Resistance elicitors from fungi as crop protectants. In: Environmental biotic factors in integrated plant disease control. Proceedings of the third meeting of the European Foundation for Plant Pathology, Poznan, Poland. Abstract p74.

Reglinski T, Lyon GD, Newton AC, 1994. Induction of resistance mechanisms in barley by yeast-derived elicitors. Annals of Applied Biology 124,509-517.

Reglinski T, Newton AC, Lyon GD, 1994. Assessment of the ability of yeast-derived resistance elicitors to control barley powdery mildew in the field. Journal of Plant Diseases and Protection 101, 1-10.

Lyon GD, Reglinski T, Newton AC, 1993. Assessment of the potential to use phytoalexin elicitors as a crop protectant. In, Mechanisms of plant defense responses. (Eds B.Fritig and M.Legrand). Kluwer Academic Publishers, Netherlands. 452.

Newton AC, Lyon GD, Reglinski T, 1993. Development of a new crop protection system using yeast extracts. Home-Grown Cereals Authority Project Report No. 78. pp41.

Newton AC, Reglinski T, Lyon GD, 1993. Development of a novel crop protection system using yeast derived resistance elicitors. Abstracts 6th International Plant Pathology Congress, Montreal, Canada. 217.

Reglinski T, Lyon GD, Newton AC, 1993. Lettuce: A non-toxic crop protection system for lettuce (and other vegetable crops). Horticultural Development Council project report PV/FV135.

Reglinski T, Newton AC, Lyon G D, 1993. Assessment of the potential to use phytoalexin elicitors as a crop protectant. Proceedings of the Crop Protection Conference in Northern Britain 1993. 361.

Lyon GD, Reglinski T, Newton AC, 1992. Assessment of the potential to use phytoalexin elicitors as a crop protectant. 2nd Conference of the European Foundation for Plant Pathology, Strasbourg, France. Abstract P136.

Lyon GD, Newton AC, Reglinski T, 1991. A novel system for controlling plant disease. SCRI Annual Report for 1990. 68-69.

Newton AC, Reglinski T, Lyon GD, 1991. Elicitors of resistance: durability and specificity. In, Integrated control of cereal mildews: virulence patterns and their change. Ed. J. Helms Jorgensen. Riso National Laboratory, Roskilde, Denmark. 295-302.

Newton AC, Reglinski T, Lyon GD, 1991. The use of non-toxic elicitors to enhance resistance in cereals. Proceedings of the 6th International Barley Genetics Symposium, Helsingborg 1, 647-649.

Lyon GD, Newton AC, Reglinski T, 1990. Pathogen control by defence mechanisms. The Grower, March 15, 25-26.

Reglinski T, Newton AC, Lyon GD, 1990. Effectiveness of elicitor-active yeast cell wall components as a novel crop protectant. Proceedings of the Crop Protection Conference in Northern Britain 1990, 213-218.

Reglinski T, Newton AC, Lyon GD, 1990. Yeast cell wall components as a novel crop protectant. Proceedings of the Crop Protection Conference in Northern Britain 1990, 402 (abstract).

Reglinski T, Newton AC, Lyon GD, 1990. Elicitor-active yeast cell wall components as a novel crop protectant. British Crop Protection Council monograph No.45. Organic and low input agriculture, 231-234.

Newton AC, Lyon GD, 1988. Enhancement of barley mildew resistance using yeast cell wall extracts. Barley Newsletter 32, 117-119.