Molecular assays reveal the presence and diversity of genes encoding pea footrot pathogenicity determinants in nectria haematococca and in agricultural soils

Aim: The aim of this study was to develop molecular assays for investigating the presence and diversity of pathogenicity genes from the pea footrot pathogen Nectria haematococca (anamorph Fusarium solani f.sp. pisi) in soils. Methods and Results: Polymerase chain reaction (PCR) assays were developed to amplify four N. haematococca pathogenicity genes (PDA, PEP1, PEP3 and PEP5) from isolates and soil-DNA from five agricultural fields with a prior footrot history. A collection of 15 fungi isolated on medium selective for Fusarium spp. exhibited variation in their virulence to peas as assessed via a disease index (DI: 0-5; no virulence to the highest virulence). PCR analyses showed that three isolates in which all four pathogenicity genes were detected resulted in the highest DI (>3·88). All four pathogenicity genes were detected in soil-DNA obtained from all five fields with a footrot disease history, but were not amplified from soils, which had no footrot history. Denaturing gradient gel electrophoresis and/or sequence analysis revealed diversity amongst the pathogenicity genes. Conclusion: The PCR assays developed herein enable the specific detection of pathogenic N. haematococca in soils without recourse to culture. Significance and Impact of the Study: Molecular assays that specifically target pathogenicity genes have the capacity to assess the presence of the footrot-causing pathogen in agricultural soils.