H ead of d ep artm en t: H. R ønde K ristensen (until 31st July) A rn e Thom sen (acting from 1st August) Scientific staff:
Je n s Begtrup: Electron microscopy
B en t Engsbro: Viruses o f agricultural plants; production o f healthy nuclear stocks of potatoes
M o rte n Heide: Serological diagnosis methods
Niels Paludan: V iruses o f vegetables and ornamental plants (herbaceous); production o f healthy nuclear stocks
A rn e Thomsen: V iruses of fruit trees, soft fruit and woody ornamental plants;
production o f healthy nuclear stocks
The primary work o f the department is development o f reliable and preferably fast and cheap methods of diagnosis, investigations o f transmission and spread o f virus diseases, analyses of virus m olecular biological structures and importance (including extent and influence on growth and yield) and finally the department provides knowledge about methods of preventing and controlling (e.g. thermotherapy and establishment of meristem cultures, etc.) virus diseases.
V iru s diseases in a g ric u ltu ra l p lan ts (Bent E ngsbro)
Diseases of cocksfood, maize, pea, beet and barley were investigated in collaboration with the advisory service and through observations in the fields and corresponding tests.
A survey of the extent o f cocksfood mottle is being made and possible differences between cocksfood cultivars investigated.
Many winter barley fields were examined for barley yellow mosaic and Polym yxa gram inis.
Beet fields were observed for Rhizom ania and for Polym yxa betae.
V irus in woody p la n ts (A rne Thom sen) Populus
Investigations concerning virus infection in Populus have been performed. Poplar Mosaic virus (PMV), Tobacco necrosis virus (TNV) and an unknown virus were isolated in infected plants, virus sym ptom s are observed on several cases, but tests showed that also
P opulus plants without symptoms are infected.
Virus diseases in fruit bushes (Arne Thomsen)
Attacks o f arabis mosaic virus were found in cultivated Sam bucus nigra yellow-spotted leaves.
Also Sambucus nigra wild growing and naturally infected with arabis mosaic virus was found.
Raspberry
Attacks of raspberry leaf curl virus was found in a crossing without name o f raspberry.
The plant material showed shortened shoots with curled and yellowing leaves. The indexing was made by grafting to Rubus henryi. No serological reaction to raspberry ringspot virus was found.
Virus diseases in ornamental plants (Niels Paludan)
D ipladen ia sanderi belongs to the A pocyn aceae family and is an attractive flowering pot plant o f commercial interest in Denmark. To improve the culture, selection w as carried out among 38 different clones collected from Australia and Denmark.
Virus symptoms, mainly mosaic in the leaves were registered during the selection. Typical mosaic symptoms were seen in all the clones.
Infection trials were carried out in order to find suitable indicator plants and plants for propagation, mainly within the families Chenopodiaceae, Papilionaceae and S olanaceae.
Local lesions appeared only in N icotiana m egalosiphon and only when virus-infected sap from N icotiana plants were used as inoculum.
Systemic symptoms appeared constantly in N icotiana bentham iana as a chlorotic mosaic and distortion o f young leaves.
In the Papilionaceae family, mainly latent infection occurred. Spinach and Catharanthus roseus were both symptomless as well.
Physical properties. Virus-infected sap from N icotiana benthamiana was used. The virus survived for 10 minutes at 65°C, but not at 75°C for 8 days at 20°C, but not for 16 days, and a dilution end point at 1:10'5.
Virus diagnosis using electron microscopy. Sap from virus-infected N icotiana benthamiana w as used for suspension samples. Both flexuous poty-like virus particles named Dipladenia mosaic virus (DMV) and TM V particles were observed.
The DMV was further diagnosed against 54 antisera to poty-viruses using the ISEM technique. Only one reaction was achieved to one o f three antisera used against bean yellow mosaic virus (BYMV). However, cytological investigations carried out by Dr. D.
Lesemann showed that the DMV is not related to BYMV.
Aphid transmission. Successful transmission o f DMV was carried out with M yzu sp ersica e feeding for 15 minutes on infected Catharanthus roseus. DMV was transferred to the Catharanthus roseus as a latent infection and to Trifolium repens causing brown streaks along the veins.
The presence o f two viruses has been demonstrated in Dipladenia showing mosaic symptoms - a poty-virus which has not yet been identified, and a TMV reacting both with the tomato and the tobacco strains.
K alanchoe blossfeldian a
K alanchoe plants often show conspicuous leaf symptoms resembling virus attacks.
Many different virus particles have been found in diseased plants, probably associated with the developed symptoms, but so far only one latent virus has been sufficiently diagnosed.
With the results achieved this year, a strain of tomato bushy stunt virus (TBSV) causing chlorotic spots and vein clearing in two cultivars, has been diagnosed in Kalanchoe blossfeldiana.
The Kalanchoe virus found is serologically most closely related to the type strain o f TBSV and based on sym ptom s in indicator plants closest to the pepper strain of TBSV.
The Kalanchoe virus is apparently a new strain of TBSV (K alanchoe strain), the K alanchoe plant being a new host for the TBSV.
This is the first description o f TBSV occurring in Denmark.
Occurrence of viruses in recirculated nutrient solutions
The risk o f spreading viruses through contaminated w ater has become greater in recent years due to the development o f new growing systems, such as soilless cultre and recirculated nutrient solutions.
In order to investigate this new situation a survey was made o f the occurrence o f viruses in recirculated nutrient solutions from Danish nurseries.
Virus was found in the recirculated nutrient solution from 4 o f 8 nurseries investigated, and in 11 out o f a total o f 91 selected samples.
The following viruses were diagnosed: Tobacco mosaic, tobacco necrosis, tomato bushy stunt and potato virus X. Virus was transferred to indicator plants (Chenopodium quinoa) either from concentrated and/or from non-concentrated samples.
Virus diseases in ve£etables (Niels Paludan)
Iceberg lettuce tested for resistance to lettuce big vein virus (LBVV)
The big vein resistant cultivars ’Sea Green’, ’Thom pson’, ’Pacific’ and lines from Dr. E.
J. Ryder, Salinas, California and the commercial cultivars ’Cavalloria’, ’N abucco’,
’Pennlake’, ’Saladin’ and ’T ires’ without known resistance w ere used for infection trials in the open during spring and autumn.
To achieve infection, young plantlets were placed for 24 hours in a recirculating nutrient solution together with virus-infected lettuce plants containing Olpidium brassicae.
The autumn experiment also included healthy plantlets planted in contaminated and non- contaminated soil, respectively.
All cultivars and lines showed different degrees of chlorotic vein banding. The plants with symptoms showed strong visible symptoms, first as vein clearing and later as vein band with curly leaves, independent of the cultivar.
The most promising cultivars/lines with fewest plants showing symptoms, with the highest weight and the best trade value were ’Pacific’, 83-1016 and 83-1019.
Thus the most valuable material for cultivation was found among the resistant cultivars/lines.
When infected with LBVV the resistant cultivars/lines had a longer incubation period. This explains the better quality and growth of this plant material.
New virus attacks 1987 (Niels Paludan)
Re-circulated nutrient solutions from 8 nurseries using the ebb-flood system:
Potato virus X
Tobacco necrosis Chenopodium strain Tobacco necrosis strain A
Tom ato bushy stunt virus, type strain TM V strains: tomato, tobacco, MDG
F. ZOOLOGY DEPARTMENT, Jørgen Jakobsen