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research update

Reversing raspberry decline

That’s the aimof field trials which so far indicate tissue culture plugs have excellent potential to outperformbare-root plants.

By Tamara Leigh N

Eric Gerbrandt is conducting trials to determine locally relevant growing guidelines for tissue culture plugs in raspberries.

ew trials are showing promising results for growers looking to get ahead of raspberry yield decline (RYD). The trials utilize tissue culture plugs to improve establishment of raspberry plantings in the first year and help them maintain their vigour for a longer period of time. “Part of the issue with RYD is that we are planting raspberries over and over again in the same ground,” says Eric Gerbrandt, an instructor at the University of Fraser Valley who is running the trials for the local berry industry while finishing graduate studies at the University of Saskatchewan. “Historically in West Abbotsford, we have planted raspberry on raspberry for up to 30 years on some fields. Yields are starting to decline in three to four years, as opposed to eight to 10 years in the past,” he explains.

“We’ve been seeing massive decline in the acreage of planted raspberries in B.C., and this is one of the primary issues. Farmers can’t spread out cost of establishment over as many years as they used to.”

It is standard practice in British Columbia to use bare-root plants grown in field nurseries in the United States. While the nurseries work hard to send clean material, it is almost impossible to ensure that field-grown plants are completely free of pests and disease when they arrive in Canada. One of the major concerns has been the root-rot causing water mold, Phytophthora rubi.

Pressure has been building to find solutions as the industry has come to realize that anything contributing to pest and disease build-up in the soil reduces the impact of fumigation and hastens the decline in raspberry yields. Soil-less plant materials using tissue culture offer a possible solution, using greenhouse conditions to grow essentially pest- and disease-free plants.

“Tissue culture is virtually disease-free. It goes into the field as a completely clean plant, as opposed to a nursery plant that may or may not have a small degree of pathogen,” Gerbrandt explains. “We are comparing fall and spring plantings of tissue

10 British Columbia Berry Grower • Summer 2014 culture plugs to bare-root plantings.”

Chemainus and Saanich raspberry tissue culture plugs of various sizes, planted in fall 2012 and spring 2013, were compared with standard spring-planted bare-root plants. Also compared were the effects of over-wintering the plugs in an outdoor nursery to keeping them in cold storage (-10C). Cane number, length and girth were measured at the end of the 2013 season to evaluate differences in first-year establishment.

When the combined length of all canes and total number of canes per plant, average cane height and diameter and average height and number of long (>30 cm) canes for each planting date and material combination were compared, fall plantings of 50- and 60-cell tissue culture plugs, as well as spring plantings of 50-cell tissue culture plugs, performed better than the standard spring planting of bare-root plants. Smaller 112- and 77-cell plugs were inferior to the standard. Overwintering 50-cell TC plugs in an outdoor nursery was far inferior to the use of cold storage (-10C) over the winter.

Gerbrandt is keen to see more results before making a solid recommendation to growers, but field trial results so far have demonstrated that tissue culture plugs have excellent potential to outperform bare-root plants.

There are a couple of factors that need to be taken into consideration before deciding to change to tissue culture plugs, including a difference in cost. Tissue culture plugs can cost 20 to 30 percent more than bare-root plants, but even a small increase in yield in first year or slower decline in the planting as a whole could make the initial investment pay off. The bigger concern comes from the more specialized needs of the plants themselves.

“Tissue culture plugs require closer horticultural management,” says Gerbrandt. “They are a lot more sensitive to when and how you plant them, and you have to baby them a bit. The hope is that using plasticulture will make it easier to

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