Conservation of Endangered Plant Species in the South West

by Ros Smith

For some years, the micropropagation unit at Duchy College, Rosewarne, has been interested in using this method of propagation for conservation purposes.  Micropropagation / tissue culture is usually associated with the rapid bulking up of plant material for the commercial release of new cultivars, or has perhaps more sinister connections with, dare I mention, GM!

A few years ago Rachel Martin, the then head gardener at Trebah, approached the unit to hopefully rescue from extinction one of their rhododendrons named ‘Trebah Gem’; a plant bred there in the early 1900’s.  Following the damaging storms of 1987, their small population had been reduced to a single elderly specimen.  Attempts had been made to propagate it by conventional means but without success.  Could we help?

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Fig.1: Rhododendron shoot before treatment

After a few unsuccessful attempts, the rhododendron was finally growing in culture and was propagated successfully with young plants being returned to the garden for restocking.

The micropropagation technique, for those of you who may not have come across it, involves the growing in sterile conditions of small pieces of plant tissue that contain a bud.  Cleaned pieces of plant tissue are placed in a nutrient jelly together with plant growth hormones (one type of these hormones you may already be using to root your cuttings!).  The hormones cause the buds to develop into shoots that can then be further manipulated.  All of this process goes on in the laboratory rather than the glasshouse because of the need for cleanliness, otherwise there are cultures heaving with fungal or bacterial growths that quite overpower the plant tissue.

The successful micropropagation of ‘Trebah Gem’ illustrates to students how micropropagation is useful as a tool in plant conservation work.  Our students have the opportunity to try the technique themselves, with varying degrees of success!  It so happened that one, Bee Robson, later became involved with the cataloguing and identification of the ancient camellias and rhododendrons at Heligan Gardens.  It became apparent through her research work that many of them were original plantings brought to the gardens by Joseph Hooker in the 1850’s from his plant hunting expeditions.  Other specimens were un-named hybrids of a slightly younger age but, nevertheless, of horticultural importance and quite unique.  A pilot scheme was set up to micropropagate some of the less vigorous species in order to prevent their demise and with a generous donation from Heligan Gardens new equipment was bought to further this aim.  The impetus for success was heightened with the outbreak of the disease Sudden Oak Death (Phytophthora ramorum) in the SW.  Duchy College Rosewarne, applied for, and were granted, a licence to micropropagate infected plant material, the only micropropagation laboratory in the country to be licensed for this purpose.

Success rates for micropropagating rhododendrons and camellias were not as high as we wanted; it was proving difficult to get contaminant-free plant material with which to start the process.

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Fig.2: Single divisions taken off shoots

Dr Barry Mulholland from Duchy College was successful in gaining substantial funding from the Combined Universities in Cornwall (CUC) and other organisations to create two research posts to provide protocols for the successful micropropagation from these plants growing outdoors.  Our concentrated efforts have improved success levels markedly, but not up to the 100% we would like.  With rhododendrons we have been focussing on using young shoots, just as they emerge from the bud scales.  The problem is that many are hairy and sticky and hold on to contaminants too well.  As you will appreciate, the time span for this growth stage is very short and limits research work.  This autumn research has focussed on trying to micropropagate from floral bud tissue; in particular using the ovary wall and pedicel (flower stalk).  These tissues are generally contaminant-free being tightly covered by the immature petals and the scale leaves.  At the time of writing, this looks a promising technique for regenerating plant tissues during an otherwise barren season of the year.

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Fig.3: Cultures in the growth room

There have been some notable successes with our rhododendron conservation at Heligan.  One mature specimen was completely blown over with the gales this autumn, but we have a couple of hundred of its offspring happily growing in culture, so all is not lost!  In spring 2004, we tried unsuccessfully to micropropagate one infected with P. ramorum before it was cut back.  This spring there has been rapid regenerative growth from the roots which has been successfully micropropagated and is disease free.

The micropropagation of historic, rare or endangered rhododendrons and camellias is a free service to gardens in the SW – provided that large numbers of offspring are not required!  The old rhododendrons and camellias that provide the spring colour in Cornwall’s gardens are of great historic importance and should be conserved lest they disappear forever.

Ros Smith

If you know of any rhododendrons or camellias worthy of conserving do please contact Ros Smith at the Micropropagation Unit, Duchy College, Rosewarne.