Identification of quantitative trait loci (QTL) for resistance to Fusarium crown rot in wheat and a survey of Fusarium pseudograminearum and Fusarium culmorum in the Pacific Northwest of the U.S

Fusarium crown rot (FCR), caused by a complex of Fusarium species, of which F. pseudograminearum and F. culmorum are the most important, reduces wheat yields in the Pacific Northwest (PNW) of the U.S. by an average of 9%. The objectives of this research were to: (1) conduct a thorough survey of Fusarium spp. in 2008 and 2009 throughout 105 wheat fields in Oregon and Washington; (2) correlate FCR severity ratings in wheat to DNA extracted from infected wheat stems through the use of Q-PCR techniques; (3) develop greenhouse inoculation methods for screening for FCR resistance; and (4) map resistance to FCR in two recombinant inbred line populations with a resistant Australian hard red wheat line 'Sunco'.;Results from the FCR survey showed that four species of Fusarium were isolated into pure culture from 99% and 97% of the fields surveyed in 2008 and 2009, respectively, showing the widespread occurrence of the pathogen. Although previous efforts had been made to extract Fusarium DNA from infected stems and quantify the amount of pathogen DNA using Real Time Quantitative PCR (Q-PCR) technology, results from this study did not indicate a strong positive correlation between Fusarium crown rot severity ratings from field samples in the 2008 survey and DNA concentrations using Q-PCR.;To accurately describe Quantitative Trait Loci (QTL) for FCR resistance, it was necessary to develop a reliable inoculation method for screening mapping population lines. Optimization experiments to assess the virulence of five PNW isolates of F. pseudograminearum and to determine the best method of inoculation revealed that one Fusarium isolate was consistently the most virulent across studies. Placing millet seed colonized with F. pseudograminearum at the stem base of the seedling resulted in the most consistent virulence and differentiation between the parents of two mapping populations. Two recombinant inbred line mapping populations with the parents Sunco/Macon and Sunco/Otis were developed for the purpose of constructing a genetic linkage map for identifying QTL describing FCR resistance. Significant QTL were identified on chromosome 3BL with a LOD = 14 and LOD = 10 for the Sunco/Macon and Sunco/Otis mapping populations, respectively.