Inheritance of Fusarium wilt resistance in flax

Fusarium wilt (FW) caused by the facultative fungal saprophyte Fusarium oxysporum f. sp. lini (Fol) is a major disease affecting flax production. Cultivation of FW-resistant cultivars mitigates effects of the disease and is a requirement for variety registration. Understanding the genetic inheritance of FW resistance will facilitate the development of resistant varieties. In this study, the inheritance of wilt resistance against western Canadian isolates was studied in F8 recombinant inbred lines (RILs) of a cross between cultivars Aurore (moderately resistant) and Oliver (susceptible). Seventeen Fol isolates were collected from across western Canada and tested for differences in the severity of FW on both parental lines and two check lines under controlled environment conditions. Three of the 17 isolates that caused moderate disease severity were selected to screen the RIL population. The segregation of the RILs for FW resistance was determined under controlled conditions and in field wilt nurseries. A 3:1 ratio of susceptible to resistant RILs was observed with two F. oxysporum f. sp. lini isolates, indicating FW resistance was conditioned by two independent recessive genes. Cluster analysis of disease severity data identified two major clusters of phenotypes in the RIL population, in accordance with the 3S:1 R ratio. High heritability of FW resistance was observed at the late flowering stage, indicating a high level of genotypic variation contributing to phenotypic variation.