MAPPING QUANTITATIVE TRAIT LOCI (QTLS) FOR RESISTANCE TO GIBBERELLA-ZEAE INFECTION IN MAIZE

The basic prerequisite for an efficient breeding program to improve le vels of resistance to pathogens in plants is the identification of gen es controlling the resistance character. If the response to pathogens is under the control of a multilocus system, the utilization of molecu lar markers becomes essential. Stalk and ear rot caused by Gibberella zeae is a widespread disease of corn: resistance to G. zeae is quantit atively inherited. Our experimental approach to understanding the gene tic basis of resistance to Gibberella is to estimate the genetic linka ge between available molecular markers and the character, measured as the amount of diseased tissue 40 days after inoculation of a suspensio n of Fusarium graminearum, the conidial form of G. zeae, into the firs t stalk internode. Sensitive and resistant parental inbreds were cross ed to obtain F1 and F2 populations: the analysis of the segregation of 95 RFLP (restriction fragment length polymorphism) clones and 10 RAPD (random amplified polymorphic DNA) markers was performed on a populat ion of 150 F2 individuals. Analysis of resistance was performed on the F3 families obtained by selfing the F2 plants. Quantitative trait loc i (QTL) detection was based either on analysis of regression coefficie nts between family mean value and allele values in the F2 population, or by means of interval mapping, using MAPMAKER-QTL. A linkage map of maize was obtained, in which four to five genomic regions are shown to carry factors involved in the resistance to G. zeae.