Submitted to: Mycopathologia
Publication Type: Abstract Only
Publication Acceptance Date: 10/26/2002
Publication Date: 5/1/2003
Citation: DOWD, P.F. A functional approach to more effective multigenic host plant pest resistence. Mycopathologia. 2000. p. 46.
Technical Abstract: Host plant resistance to insects and pathogens is generally recognized as desirable for growers and is environmentally benign, but numbers and methods of deployment of resistance genes remain unsettled. Examination of known resistance genes from a functional standpoint suggests that they may be more effectively deployed if genes from particular functional classes are used. Multigenic resistance is generally accepted as more stable, but the gene products originally developed by the plants having different functions may not be effectively inhibiting pests, or inhibiting them in such a manner that they need to be explored functionally to understand their role. For example, maize resistance to insects theoretically involves (based on allelochemical or protein presence and function) composition of attractive esters and alcohols, leaf color and texture, breaking down barriers to compound penetration (chitinases, lipases, proteases), degradation of protein toxins (proteases), inhibition of pest nutrition (lectins, protease and amylase inhibitors), and acute cytotoxins (ribosomal inactivating proteins). The potential activity and role of these defensive mechanisms can be better determined using unadapted insects (such as the cabbage looper). From a pharmacological standpoint, increasing the number of acute toxins may not be effective if there are penetration or stability problems; adding chitinases or protease inhibitors should be considered in these cases. Proteolytic degradation appears to affect the efficacy of fungal and plant ribosomal inactivating proteins to insects. Chitinase combined with Bt crystal protein can increase toxicity to insects overall (single dose) or on a per time basis (diet incorporation). However, single gene products may act in such a manner that multifunctional mechanisms are produced. For example, increasing anionic peroxidase activity has resulted in generally increased insect resistance in a number of plant species. Multifunctional mechanisms due to peroxidase identified so far include generation of acute toxins, nutritional stress, tougher tissues (by ca. 10 fold), and changes in volatile composition (by ca. 3 fold for some compounds) and/or color which appear to increase attractancy to beneficial insects.