A TRANSMISSIBLE VIRUS DISEASE OF THE EASTER LILY
Authors: OGILVIE LAWRENCE 
Published: February 2008

Summary.

A summary is given of the history of the Bermuda Easter lily (Lilium longiflorum var. eximium Baker), known to the trade as “Lilium Harrisii.”
It is known that about 1893 “a peculiar sickness” appeared in the lily fields of Bermuda, which caused a very marked decline in the yearly amount of bulbs exported from the Colony.
Subsequent to 1919 a resuscitation of the industry has taken place, and especially in recent years, when the chief cause of its failure has been ascertained.
A summary of the methods of cultivation in Bermuda is given.
Theories as to the cause of the disease were put forward by Woods, Bishop, and others. It is shown that there were two types of disease, one resembling a mosaic, the other characterised principally by very marked stunting and downward curling of the leaves. The latter is here dealt with.
Photographs taken in the United States Department of Agriculture greenhouse at Washington in 1915 show clearly examples of the disease. The disease came prominently to the notice of the writer in 1925 when certain aspects of it suggested that it was a virus disease. It was called “yellow flat” by the grower who first observed it.
The general appearance of a plant grown from an infected bulb is a flat rosette or cylinder. The leaves are very markedly curled downwards and are slightly chlorotic in colour, but without streaks or spots.
In current season infection the leaves which are mature at the time of infection do not show the symptoms. The young leaves show considerable twisting besides curling.
Plants from affected bulbs do not show the symptoms till about 4 weeks after coming above ground.
Transmission experiments are described in which positive results were secured by the use of Aphis gossypii Glover. Experiments with the following were unsuccessful: Aphis Ogilviei Theob., Macrosiphum gei Koch., Neotoxoptera violae Perg., and Pseudococcus citri Risso. Attempts at mechanical transfer were also unsuccessful. There is no evidence that the disease is carried in the soil.
Aphis gossypii is described. Its biology is discussed. It is parasitised by Lysiphlebius (Aphidius) testaceipes Cress, and attacked by certain Coccinellids, larvae of Syrphids, etc.
Spread of the disease takes place mainly early in the season.

Affected plants occur in patches in the fields, the average number of infected plants round a bulb‐infected plant being about 15.It appears that the disease is transmitted to the scales and side shoots of affected plants.Affected plants begin to die down about flowering time, about two months before healthy plants.The root system is affected and is attacked by secondary organisms, fungi and the bulb mite.Bulbs from affected plants are flat, small and compact, and resemble bulbs of poor types of Lilium longifiorum.There is a marked tendency to splitting of the bulbs, so that in successive years smaller and smaller bulbs are produced. Amongst weeds or in shady situations the affected plants are not so markedly stunted.Plants from affected bulbs seldom produce flowers. In current season infection the number of flowers is considerably reduced, the flowers twisted and blistered and the pedicels turned stiffly downwards.

In the writer's opinion recovery from the disease never occurs.
At temperatures of about 70° F., under greenhouse conditions, the internodes are often lengthened and the leaves twisted rather than curled.
The disease has been observed on “Lilium formosum” and “Lilium giganteum” and apparently occurs in Japan. It is apparently not connected with any virus diseases of other plants occurring in Bermuda.
Similar symptoms brought about by other causes are described.
The disease was probably introduced into Bermuda from Japan about 1893, either direct or via the United States.
The means of control recommended are roguing, spraying with contact insecticides, and clean cultivation.

The official inspection carried out by the Government since 1925 has already reduced the disease to a practically negligible quantity.19. The disease is compared with other virus diseases. It is apparently the first virus disease of bulbous plants to be fully described.