USE OF MOLECULAR MARKERS IN BREEDING FOR OLIGOGENIC DISEASE RESISTANCE

In several plant species, genetic maps have recently been developed for restriction fragment length polymorphisms (RFLPs). Together with isozymes, they offer alternative solutions to many breeding problems. This review deals with the current and potential uses of molecular markers in breeding for oligogenic resistance traits. In the first part, segregation analyses and analyses of near‐isogenic lines are collated with respect to the mapping of resistance genes. Also, various types of populations are compared for the amount of information obtained in segregation analyses. In the second part, theoretical and numerical results are presented dealing with the number of individuals required for marker‐facilitated selection of a resistance gene in a backcross program. Both the use of a single marker and a marker bracket are considered and the influence of the following parameters is investigated: (a) recombination frequency between the resistance gene and marker(s), (b) size of backcross families, (c) number of backcross generations, and (d) number of carriers of the resistance gene to be recovered in the final backcross generation. The results provide information with regard to the optimum design of marker‐facilitated selection programs and the required expenditures compared to direct selection of the resistance trait. In the third part, applications of molecular markers are discussed with respect to (1) advantages of marker‐facilitated selection for resistance genes under a variety of special circumstances, (2) pyramiding of resistance genes, (3) selection against the genetic background of a donor parent, and (4) their use as a starting point for chromosome Walking. Copyright © 1990, Wiley Blackwell. All rights reserved