Production of Clubroot Standards Using a Recombinant Surrogate to Overcome Natural Genetic Variability

Clubroot is caused by the obligate pathogen Plasmodiophora brassicae. The organism targets root hair cells for entry and forms spores in numbers so large that they eventually develop characteristic galls or clubs on the roots. Clubroot incidence is rising globally and impacting the production of oil seed rape (OSR) and other economically important brassica crops where fields are infected. P. brassicae has a wide genetic diversity, and different isolates can vary in virulence levels depending on the host plant. Breeding for clubroot resistance is a key strategy for managing this disease, but identifying and selecting plants with desirable resistance traits are difficult due to the symptom recognition and variability in the gall tissues used to produce clubroot standards. This has made the accurate diagnostic testing of clubroot challenging. An alternative method of producing clubroot standards is through the recombinant synthesis of conserved genomic clubroot regions. This work demonstrates the expression of clubroot DNA standards in a new expression system and compares the clubroot standards produced in a recombinant expression vector to the standards generated from clubroot-infected root gall samples. The positive detection of recombinantly produced clubroot DNA standards in a commercially validated assay indicates that recombinant clubroot standards are capable of being amplified in the same way as conventionally generated clubroot standards. They can also be used as an alternative to standards generated from clubroot, where access to root material is unavailable or would take great effort and time to produce.