i8 97 . 



GARDENING. 



59 



Miscellaneous. 



fl LILY BULB DISEASE. 



During the past year a destructive 

 wave of fungoid disease almost com- 

 pletely ruined the crop of lily bulbs raised 

 in |apan for exportation to Europe. The 

 first indication of this disease received at 

 Kew was through Messrs. Tozer Bros. 

 & Co , of Graeechurch street, who sent a 

 large number of diseased bulbs lor exami- 

 nation. These bulbs formed part of a 

 consignment received from Japan in 

 November last, consisting of S48 cases, 

 containing 73,050 bulbs of Lilium specio- 

 sum (Thun ), album and rubrum. Out of 

 this number only 250 bulbs arrived in a 

 saleable condition, the whole of the 

 remainder being more or less rotten and 

 worthless. At a later date the same firm 

 received a second consignment of 37,000 

 very large bulbs of Lilium aurutum and 

 out of this quantity only -l-.OOO were 

 saleable. Similarly diseased bulbs received 

 from Japan were afterwards sent to Kew 

 lor examination from other sources. 

 Finally a quantity of bulbs obtained 

 through an agent from Japan, for plant- 

 ing at Kew, contained a large percentage 

 suffering from the same type of disease. 

 The bulirs received for investigation 

 showed every stage of disease; in the 

 earliest condition, the base of the bulb is 

 alone discolored and somewhat soft; this 

 discoloration and softening of the tissues 

 graduallv spread from the base, until 

 finally, in the most advanced stage, every 

 part of the bulb is of a brownish color, 

 and sufficiently soft to admit of being 

 readily crushed into a pulpy mass between 

 the fingers. 



Microscopic examination revealed the 

 presence of slender, continuous, hyaline, 

 branched hyphse traversing the tissues in 

 every direction; the cell-walls are never 

 pierced, but gradually dissolved, and it is 

 only at the last stage of the disease that 

 the starch grains become irregularly 

 corroded and gradually dissolved. So 

 long as the epidermis of the bulb-scales 

 remains intact there is no trace of myce- 

 lium or fructification on the surface, but 

 when the tissue is reduced to a soft pulp, 

 or when a diseased bulb is cut open, the 

 broken surface is within twenty-four 

 hours covered with a dense snow-white 

 mycelium, which within three days be- 

 comes studded with numerous clusters of 

 fruit, resembling to the naked eye minia- 

 ture pins with round black heads The 

 occurrence of this particular form of fun- 

 gus on every bulb examined suggested 

 that it might possibly be in some way 

 associated with the disease, and subse- 

 quent cultures and inoculations proved 

 this surmise to be correct. The fungus 

 grows readily as a saprophyte the spores 

 germinating and forming the characteris- 

 tic superficial white flocose mycelium, 

 which within a week bears an abundance 

 ot fruit, or such varied culture media as 

 prune juice, sterilised potato, decoction of 

 bulb scales, etc. In one experiment four 

 spores weie sown in a 5 percent, solution 

 of cane-sugar in water in a Petri dish, and 

 at the end of six days the entire surface of 

 the liquid was covered with the fungus in 

 a fruiting condition. When spores were 

 sown in a hanging-drop along with a 

 very thin section of lily bulb-scale, it was 

 observed that the germ-tubes could not 

 tnter the tissue through the epidermis, 

 but that they entered readily at those 

 points where the cells were not protected 

 by the epidermis. 



A set of experiments was also carried 

 out, using healthy lily bulbs, some of 



which were furnished by Messrs. Tozer, 

 for inoculation. For the purpose of 

 dsetroying stray fungus spores the bulbs 

 were immersed for a quarter of an hour 

 in a 1 per cent, solution of corrosive sub- 

 limate. The bulbs were afterwards placed 

 in wide-mouthed flasks filled with steri- 

 lized tap-water containing a 5 per cent, 

 solution of cane-sugar, the base of the 

 bulb being immersed in the liquid; finally, 

 the entire bulb was covered with a sheet 

 of cotton wool soaked in a 1 per cent, 

 solution of corrosive sublimate, the cotton 

 wool being tied round the neck ol the 

 flask. When the roots were about an 

 inch long an attempt at inoculation was 

 made as follows: The numerous cultures 

 of the fungus furnished a large supply of 

 spores, which were tested and found to 

 germinate readily. These spores were 

 collected with a wet camel's-hair brush 

 and washed off into a small amount of 

 sterilised water in a flask until it became 

 discolored by the quantity of spores 

 present; this was the inoculating mate- 

 rial. A quantity of this spore-carrying 

 water was added to the water in which 

 two of the bulbs were growing, care be- 

 ing taken not to injure the roots; the 

 inoculating liquid was also deposited 

 freely between the scales of the two bulbs, 

 which were then covered with sterilized 

 cotton wool as before. The water in 

 which two other bulbs were growing 

 was inoculated as above, but the roots of 

 the bulbs were broken off. Finally. 1 per 

 cent, of salicylic acid was added to the 

 water in which two more bulbs were 

 growing, a copious supply of the inoculat- 

 ing water added, the roots of the bulbs 

 broken off, the bulbs replaced, and, as in 

 the otherinstances, protected with cotton 

 wool. 



At the end of six weeks the two bulbs 

 whose roots were not destroyed appeared 

 to be quite healthy; they were then 

 planted in soil, and are still growing and 

 show no indication of disease. The two 

 bulbs with broken roots showed signs of 

 disease at the end of three weeks after 

 inoculation, and at the six weeks period 

 the disease had extended nearly halfway 

 up the bulb from the base. After being 

 cut open the same kind of fungus showed 

 itself on the surface that has been de- 

 scribed as occurring on the bulbs received 

 from Japan. The companion bulb was 

 also diseased, and in about three months 

 was soft and rotten, and covered with 

 the fungus in a fruiting condition. The 

 two bulbs with broken roots that were 

 growing in water containing 1 per cent, 

 of salicylic acid remained quite healthv, 

 made fresh roots, and are still living. 



Numerous experiments were made with 

 other kinds of bulbs, and it was found 

 that the fungus refused to grow on onions, 

 however much mutilated. On the other 

 hand, daffodil bulbs are very susceptible 

 to the disease; if the roots are broken or 

 a wound made in the bulb and afterwards 

 powdered with the spores, the disease 

 showed itself wkhin a few days, 

 and was in due course followed by 

 the characteristic fruit of the fungus. It 

 was invariably found that however 

 much bulbs were mutilated and then 

 inoculated with fungus spores, sub- 

 mergence for a few minutes in a 1 per 

 cent, solution of salicylic acid or corrosive 

 sublimate prevented the disease; in other 

 words, all fungus spores coming into con- 

 tact with the above-named solutions are 

 destroyed, whereas the vitality of the 

 bulbs thus treated is not at all aft'ected. 

 Dr. Halsted has described* a somewhat 

 similar disease, called "soft rot," as at- 



V'\\ Jersey Agricultural (mII,-^,- E\pi'ri mental 

 Station, liulletiu No. 76. 



tacking the sweet potato in the United 

 States. The fungus this disease (Rhizo- 

 pus nigricans, Ehrh.) is closely allied to 

 the species under notice causing the lily 

 bulb disease. 



In addition to the kind of fungus fruit 

 already described, a second form, of sex- 

 ual origin, called a zygospore, is present 

 in the genus Rhizopus; several large, spin v 

 zygospores were found in the matted 

 mycelium present on bulbs in the last 

 stage of decay, and presumably belong to 

 our fungus. Zygospores differ from the 

 minute spores already described in requir- 

 ing a somewhat lengthened period of rest 

 before they germinate, by this means 

 tiding the fungus over that period of the 

 year not suitable for its growth, and 

 germinating when favorable conditions, 

 climatic and otherwise, return. During 

 this period of rest the zygospores remain 

 in the soil, or attached "to the substance 

 on which they were produced. The 

 minute spores previously described pos- 

 sess the capacity of germination the mo- 

 ment they are mature, and enable the 

 plant to extend its area of distribution; 

 and as these spores are produced very 

 quickly and in immense numbers, it can 

 readily be understood how rapidly the 

 disease spreads when once introduced 

 into a given locality. The fungus causing 

 the lily bulb disease, although allied to 

 Rhizopus nigricans, is quite distinct from 

 this and every other known species. 



SUMMARY. 



The lily bulb disease is caused by a par- 

 asitic fungus called Rhizopus necans. 

 The funguscannot penetrate the unbroken 

 tissues of the bulb, but gains an entrance 

 through wounds, more especially broken 

 roots. The amount of evidenceforthcom- 

 ing indicates that the bulbs are not dis- 

 eased until after they are removed from 

 the ground. The spores of Rhizopus 

 necans are killed by a short immersion in 

 a 1 percent, solution of corrosive subli- 

 mate or of salicylicacid. Neither of these 

 substances has any injurious effect on liv- 

 ing bulbs, provided they do not remain 

 in the liquid for more than fifteen minutes. 

 PREVENTIVE MEASURES. 



The fungus is by no means confined to 

 lily bulbs for its food, but as experiments 

 have proved, can live on a great variety 

 of dead or decomposed substances; it n ay 

 also occur as a parasite on other plants 

 than lilies in Japan, as it readily attacks 

 and destroys daffodil bulbs. Judging 

 from the enormous amount of injury 

 caused, it would appear that the fields 

 where the lilies are grown rr ust be sat- 

 urated with the fungus, growing indis- 

 criminately on various substances, and 

 attacking the lily bulbs along with other 

 things, as a matter of course. If practic- 

 able, entirely new localities should be 

 selected for the work. Even if this were 

 done, great care would have to be exer- 

 cised, so as not to introduce the fungus. 

 The spores are readily conveyed from one 

 locality to another in the soil on tools, 

 cart wheels, shoes, clothing, etc., in addi- 

 tion to being carried by wind or animals. 

 An important point to remember is not 

 to allow vegetable rubbish of any kind 

 to accumulate, and all diseased bulbs 

 should be burned and not allowed to 

 remain on the ground, otherwise the zyg- 

 ospores that form on such old decaying 

 bulbs would start the disease the follow- 

 ing season. As little injury as possible 

 should be done to the roots of the bulbs 

 when they are removed from the ground, 

 and the bulbs should be allowed to 

 "sweat" before they are packed for ex- 

 portation. If the fungus is known to be 

 present when the bulbs are being pre- 



