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Abgeschickt von Peter Corkhill am 30 April, 2004 um 06:20:07
This seems a good name to use for the condition shown in the attached photograph and it is my enemy number one. Suddenly, in spring while a seemingly healthy plant is in full growth, one or more shoots just fall over. They look fine in the evening but the next day they are down and dying. The compost is neither too wet not too dry and the condition affects seedlings and adult plants alike often hitting the ones that seem to be doing well and striking so rapidly there is no time to take preventative action on an individual plant basis.
I recently read an account of a disease called Peony Wilt in an old RHS magazine caused by the organism Botrytis paeoniae that sounds a very close parallel. Stems collapse if the infection is low down and the organism is closely related to Botrytis cinerea, the common grey mould. The organism produces resting structures in diseased tissue called sclerotia and these remain in the soil or compost over winter when they germinate and infect the stems but they can also just be blown in on the wind so they are pretty much everywhere. Recommended treatment is to promptly cut off affected parts even is this means cutting below ground to ensure no sclerotia are left in the plant and grow Peonies on a fresh site as there is no information on how long the sclerotia can remain in the soil. No chemical controls are available to home gardeners in the UK.
I feel sure my Cypripedium wilt is also caused by a Botrytis infection too. Grey mould is very common in our damp Atlantic climate and turns up in greenhouses on many species of other plants without fail each autumn however well they are ventilated. The problem seems worse in greenhouse culture perhaps because plants outside just have the spores washed away by heavy rain or is it that the higher greenhouse temperatures encourage germination of the spores at a more critical time? I notice that if we get a day or two of unseasonably high temperatures in spring just as the shoots are elongating rapidly then I get problems much worse than if the weather remains cool and damp. An earlier posting by Carl Hardwick suggests the problem can be avoided by dipping pots in water at this critical time so that only the lower half of the compost gets wet. This is only practical with small collections in individual pots.
A closer inspection of the affected plant in the photograph shows telltale streaking at the stem base just above ground level indicating all is not well. Perhaps this should have alerted me to take action with a fungicide before the stems fell over but when I tried this in the past I didn’t think it made a difference to the outcome.
Another depressing snippet in an RHS magazine titled “doomed plants” tells that researchers at Reading University and Horticulture Research International have recently discovered that fresh Primula and Cyclamen seeds can already be infected with Botrytis even before the seed is sown. Sally Barns found that leaves from young and healthy-looking plants were often infected by Botrytis cinerea. Using genetic fingerprinting she proved that it was common in all parts of healthy-looking commercially grown Primula and Cyclamen, even in the roots and that only one clone of the fungus was present in the whole plant. The team was able to confirm that this infection originated in the seed. When seeds were treated with a suitable fungicide the researchers were able to grow plants that remained disease free all their lives.
From this we can imply that cutting off parts of an affected Cypripedium plant may not get rid of any infection but that plants can have the disease all their lives without showing symptoms if growing conditions are optimal and only show the disease if stressed by other factors. Also, we know that some seedpods of Cypripediums are so badly contaminated with mould spores that they cannot be sterilised by normal means for micropropagation. But why should getting rid of seed infection in Primulas impart lifelong protection? Unless perhaps another protector organism infects them – it certainly looks that way.
How do we focus the minds of these boffins on real problems i.e. the way to impart lifelong protection from fungal attack to Cypripediums? I heard that research along these lines was being carried out at one of the Canadian Universities some years ago but never subsequently heard any firm results. It would be really frustrating if the answer already lies gathering dust on some distant shelf where student thesis are stored.
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