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Pierluigi (Enrico) Bonello, The Ohio State University, Department of Plant Pathology; James T. Blodgett, Daniel A. Herms, |
Pine trees and their diseases are much more important to the nursery industry than is often realized. The wholesale value of the nursery industry in the United States was $3,096,723,000 in 1998 (USDA 1998). Pines are the fourth largest selling species in nursery sales, with 30,068,000 plants produced annually for a total value of $108,840,000 (USDA 1998). Once pines are placed in the landscape and achieve ages of approximately 15 to 18 years, their values exceed $200 per tree, or a total estimated landscape value of approximately $6 billion.
In Ohio, the nursery/ornamental industry is estimated to have a value of $2.4 billion. Wholesale production of ornamental plants in Ohio exceeded $500 million in 1999, accounting for 12% of total agricultural production in the state, and making it Ohio's fourth leading agricultural commodity behind corn, soybeans, and milk (Randall etal., 2000). Additionally, cash receipts for Ohio's landscape and garden center industries exceeded $1.5 billion dollars in 1996 (Rhodus, 1997).
Pines suffer major losses from plant diseases and insect pests. Historically, pesticides have been widely used to manage these problems of ornamental plants. For example, more than 27 million U.S. households used pesticides in 1989 to control pests of lawns, trees, and gardens (Raupp, Koehler, and Davidson, 1992). Because pesticide use can create risks to human health, the Food Quality Protection Act is restricting their use. This has increased the need for the development of alternative pest management strategies. In fact, the Ohio Nursery and Landscape Association (ONLA) rates the development of new and alternative IPM techniques and environmentally safe pesticides as the two top horticultural research needs.
Although plant disease resistance has been recognized as an ideal strategy for managing pests of ornamental plants and shade trees for many years, little progress has been made in the deployment of disease-resistant ornamental plants, or in understanding their resistance mechanisms (Herms, in press; Raupp, Koehler, and Davidson, 1992). If host-pest interactions were better understood in ornamental trees, it would be possible to manipulate them to minimize pest problems while reducing pesticidal inputs (Herms, Akers, and Nielsen, 1984). However, few studies have investigated these interactions in any detail.
Pines are affected by numerous diseases, particularly those caused by fungi, that often severely limit their ecological, environmental, and commercial value (Harrington and Wingfield, 1998). Some diseases also predispose trees to insect infestations. Thus, there is a clear incentive to minimize the negative impacts of fungal diseases on the health and productivity of pines in managed situations. A better understanding of the basic physiological and biochemical processes that influence the outcome of host parasite interactions in pines, and how these are affected/modulated by environmental variables, can contribute significantly to this objective. Systemic induced resistance can protect plants against both insects and pathogens. This is one reason why we are studying this approach to resistance in pines.