Markers of plant resistance to nematodes: classical and molecular strategies

Abstract

One of the most effective, economical and environmentally safe methods to reduce crop yield losses from diseases is to use pathogen-resistant cultivars. The challenges of classical approaches for rating host suitability for phytonematodes are presented and critical factors influencing phenotypic expression of the resistance are considered. An accurate identification of both plant genetic background and pathogens is necessary for an exact measurement of pathogen/host compatibility. Scientists with expertise in plant nematology should collaborate with plant breeders and molecular biologists to investigate new sources of resistance and their effectiveness, the nature of resistance traits and their inheritance, and the probability of DNA recombination during cycles of cultivar improvement. Specific molecular markers of plant resistance to nematodes should be determined for unique pathogen/host systems to rate resistance/susceptibility to the most economically important nematode families, which would save effort, time and money. Such markers may also be represented by enzymes with promise for use as genetically-based biochemical markers for screening breeding lines with potential for nematode resistance. More sensitive, rapid and accurate electrophoretic methods, such as those that are possible with miniaturized and automated equipment, should further facilitate identification of desirable markers. At present, more investigation is needed for effective transfer of cloned genes into susceptible plant species to integrate resistance to nematodes that have a broad host range. While tightly linked markers must be identified and used to monitor introgression, analysis of the chromosomal region concerned should be made to explore any unexpected linkage drag. The comparative value of molecular markers and consideration of the most up-to-date strategies of gene transfer for nematode resistance are also reported.