Virus Indexing

  • Viruses cause decline in plant vigor and fruit production
  • Viruses are transmitted by insects, nematodes, pollen and certain propagation practices
  • To produce the best quality planting stock, it is necessary to begin with indexed virus free plant material
  • Indexing is a means of detecting virus

Methods of virus indexing at Nourse Farms

Indicator Plants

  • Indicator plants are so called because they express virus infection visually by exhibiting strong symptoms in their leaves and/or growth habit
  • Indicator plants are a good general virus screen because they detect the presence of virus in your plant but not necessarily which virus
  • Nourse uses sap inoculation and grafting techniques to virus screen their stock plants on indicator plants


  • ELISA stands for enzyme-linked immunosorbent assay
  • ELISA is a laboratory test that uses antibodies made to specific plant viruses and an enzymatic color reaction to detect virus in the plant
  • ELISA is more sensitive than indicator plantsELISA  tests are specific for each individual virus unlike the general virus detection of indicator plants


  • PCR stands for polymerase chain reaction
  • PCR tests are laboratory tests that detect the presence of plant viral DNA or RNA in the stock plant
  • PCR tests are more sensitive than indicator plants and like ELISA tests, each PCR test is specific for an individual virus

Tissue Culture

Tissue culture or micropropagation is a method of propagating plants from the tiny growing points or meristems in the buds or shoot tips of a plant. This process is possible because each cell contains the genetic material necessary to regenerate an entire plant.

There are four stages of tissue culture propagation:

Stage I - Under sterile conditions in the laboratory, the growing point of the plant, such as a shoot tip or bud, is excised from the stock plant and placed into a simple growth medium where it develops into a tiny plantlet.

Stage II - The stage I plantlet is transferred into a different growth medium containing plant hormones that will encourage the plantlet to produce more plantlets. In this stage, the number of plantlets is increased through a series of transfers to fresh medium. This process continues until the desired number of plantlets is produced.

Stage III - The stage II plantlets are transferred to another different medium that will prepare them for transfer to a greenhouse environment.

Stage IV - The stage III plantlets are removed from stage III medium and planted in a greenhouse where they root and acclimate to the greenhouse environment.

Greenhouse Production

  • Stage IV plantlets are rooted, acclimated, and grown on to a field–ready plug plant.  This process takes 8 – 12 weeks.
  • These plug plants are the foundation stock for our strawberry and raspberry nurseries.  Certain raspberry plug plants are also sold directly to the customer.
  • Our plug plants are finished off as either dormant plugs, hardened – off green plugs or nursery – matured plants.
Lab at Norse Farms
Greenhouse at Nourse Farms
Field Production at Nourse Farms
Field Production
Packhouse at Nourse Farms