Characterization of Flax Germplasm for Resistance to Fusarium Wilt

Fusarium wilt of flax (Linum usitatissimum L.) caused by Fusarium oxysporum f. sp. lini (Fol) is an economically important disease that can result in severe yield losses. Due to the pathogen’s ability to survive in soil for long periods, it is essential to identify fusarium wilt resistant flax varieties. The objectives of the study were to phenotype and compare a recombinant inbred line (RIL) population of flax in a controlled environment and in field wilt nurseries. Disease reaction of a subset (160) of RIL lines developed from cultivars ‘Aurore’ (moderately resistant) and ‘Oliver’ (susceptible) was assessed under controlled environment conditions to two Fol isolates. Disease severity was determined and the area under the disease progress curve (AUDPC) was calculated. The population varied in response from resistant to highly susceptible, indicating that resistant to wilt was probably polygenic. Twenty-eight days after inoculation, 14% and 5% of the RILs were severely wilted (scores of 8 and 9, with isolates 131 and 81, respectively). Plant height was negatively correlated with AUDPC (r 2 = -0.13155 for 131 and r 2 =-0.29841 for 81). Similarly, in the field in wilt nurseries, at Saskatoon and Morden, evaluation of the full set of 200 RILs, the disease reaction varied from resistant to susceptible, with 21% and 42% of RILs severely wilted (rated 8 and 9) at each site at the green boll stage. The results from the two locations were significantly different, although moderately correlated (r 2 =0.6127). The 160 RILs in controlled environment inoculated with isolates 131 and 81 showed a higher correlation for disease severity at 28 days after inoculation, with the wilt nursery in Saskatoon (r= 0.40028 and r 2 =0.38046) as compared to Morden (r 2 =0.33016 and r 2 =0.21140) at green boll stage. Differences in environmental and experimental conditions (such as seeding date) at the two locations, as well as different Fol strains in the soil combined with the subjectivity of the grading system may explain the differences between locations.