Plant Propagation
Virus Indexing
Viruses cause a decline in plant vigor and fruit production. They can be transmitted by insects, nematodes, on pollen, or in certain propagation practices.
To offer our customers the best quality, disease free stock, it is necessary to start our production program with indexed virus free plant material. We have instituted our own program to test all foundation stock for virus. "Indexing" is a means of detecting virus, usually by physically transmitting it from an infected host plant to a sensitive indicator plant.
Strawberry plants are indexed by grafting a leaf from a test plant onto an indicator plant. Depending on the visual symptoms expressed by the indicator, we can tell if any virus is present in the plant tested.
ELISA Testing
Raspberries are indexed by sap inoculation and leaf grafting onto different indicator plants as well as by an ELISA test in our laboratory. ELISA is a very sensitive indexing method in which an enzymatic color reaction indicates that a virus is present in the test plant. Every stock plant that is used for propagation in our facility is tested in this manner. Meristems from these virus-free plants are then used to begin the tissue culture process. If the stock plants are found to be infected, we have equipment to heat treat and eradicate the virus from the affected plants.
Tissue Culture
Tissue culture is a means of producing whole plants from pieces of plant tissue. This is possible because each cell contains the genetic material necessary to regenerate an entire plant. Our program begins by cutting a section (as little as 1 mm in length) from the growing point or "meristem" of a stock plant. For this reason, the process is often referred to as meristem or tip culture.
Each year we cut hundreds of these meristems to produce thousands of plants in our laboratory which will be sold directly as Tissue Culture Plants or used as foundation stock in our nursery plantings. Through tissue culture, we can produce many plants from a few virus-indexed stock plants and can thereby offer you the cleanest product possible.
In the Laboratory
First, we excise the growing points or meristems from indexed virus-free strawberry, raspberry, and blackberry stock plants. These meristems are placed on an agar-based growth medium in test tubes under sterile conditions where, after 10 - 12 weeks, each meristem develops into a plantlet. This is known as Stage I in the tissue culture process.
As the growing medium is changed we can force a STAGE I plantlet to develop side shoots and multiply into a small "clump" of plantlets. In STAGE II (or the multiplication stage), these "clumps" are separated into single plantlets and transferred onto fresh medium. These in turn, will multiply and the process is continued until we have produced the desired number of plantlets.
All transfer work is done in a sterile environment under laminar flow hoods. In between transfers the jars are stored in a controlled environment growth chamber, subject to 16 hours of light per day and a constant temperature of 72° F.
In the Greenhouse
From the lab, these plantlets are taken to the greenhouse for STAGE IV. We root our plants in greenhouse propagation houses, therefore eliminating STAGE III (rooting in culture in the lab). In the greenhouse, plants are set into soilless medium and grown in high humidity under careful observation where they will form roots. In 8 - 12 weeks they will have developed a strong root system that will enable them to survive and grow in the field.
Some of these tissue cultured plants will be sold directly to the customer as green, growing plants or as dormant "plugs" from our cold storage at 28° F.
We also use these tissue cultured plants in our own field as clean, virus-free foundation stock for nursery production.
Field Production
The primary benefit of our tissue culture/virus indexing program is the production of disease free, highly vigorous plant stock.
When we set these plants in our nursery and sell the daughters, our sales product is a plant which has less exposure to the environment as that of a traditionally propagated plant. This lessens the possibility of reinfection of virus or other disease, and the plant is much closer to the original stock plant in terms of generations away from the breeders original stock plant.
To ensure the plants remain healthy, tissue culture plants are planted into fumigated soil. Throughout the season, fields are well maintained; consistent irrigation, pest control and fertility keep the plants at an optimum level of growth right up until harvest. The healthier the plants are in our fields, the better they will perform for you.