Characterization of Flax Germplasm for Resistance to Fusarium Wilt Caused by Fusarium oxysporum f. sp. lini

Abstract

Flax wilt is caused by the soil-borne fungal pathogen Fusarium oxysporum f. sp. lini (Fol). The best control method is to develop resistant cultivars to be grown in the field. The objectives of this study were to develop a controlled environment phenotyping method to test flax lines for reaction to flax wilt and screen a recombinant inbred line (RIL) population for reaction to flax wilt under a controlled environment and compare the observations with field evaluations at wilt nurseries. Finally, the inheritance of flax wilt resistance of the RIL population was assessed using phenotypic data from the controlled environment and field test. Four flax cultivars: Bison and Aurore (wilt resistant) and Novelty and Oliver (wilt susceptible), were inoculated with 17 Fol isolates under controlled conditions. Plants were assessed on the degree of yellowing, browning and wilting. Disease severity (DS) at 21 and 28 days after inoculation (dai) and the area under disease progress curve (AUDPC) were used to group the isolates. Isolates 65, 81 and 131 were the moderately aggressive and selected to phenotype a RIL population developed by crossing Aurore and Oliver (AO). For all isolates gradual increase in DS and AUDPC among RILs was observed. Similar observations were made in each wilt nursery. Moderate correlations were observed between controlled conditions and wilt field nursery experiments, signifying the importance of controlled condition experimental data as predictors of flax wilt resistance in the field. Inheritance of flax wilt resistance was observed to segregate in a 3:1 ratio, of susceptible to resistant. Thus, this suggested that two independent, recessive genes conferred wilt resistance to the AO RIL population. However, the phenotypic observations indicated the additive effect of minor genes. This study indicated the significance of identifying the inheritance pattern of wilt resistance in flax populations and highlights the need to locate resistance genes within the genome. This would assist in marker assisted selections (MAS) in flax breeding to reduce time and labour, and also to incorporate wilt resistant genes to develop flax cultivars resilient to Fol pathotypes.