414 



THE AGKIUULTUKAL NEWS. 



Decembee 29, 1917. 



PLANT DISEASES. 



BACTERIAL DISEASES OF TOMATOES 

 IN ST. VINCENT. 



WILT. — During the recent visit of ihe writer to St. Vincent 

 some attention was given to a wilt di.sease of tomato plant", 

 ■which was found to be occurring in beds of hybrid tomatoes 

 (Ponderosa x Native), and in a row of the variety Earliana 

 from American seed, grown by Mr. S. C. Harland at the 

 Experiment Station, Kingstown. The symptoms of the 

 affected plants, the appearance of the associated bacterium 

 under the microscope and on agar cultures, and its virulence 

 when inoculated into healthy plants, leave no reason to 

 doubt the identity of the disease with the wilt due to 

 Bacterium (Bacillus) solanaceariim, Erw. Sni. 



This disease is very prevalent in the Southern United 

 States, and prohibits the growing of tomatoes over large 

 tracts of country. A closely similar, probably identical, 

 affection has been reported i many countries of the Old 

 World. Several other members of the natural order 

 Solanaceae, especially cgg-plact, potato, tobacco, and Datura 

 spp , are liable to serious diseases produced by the same 

 organism. The whole series has been grouped together 

 Tinder the name of Brown Rot of Solanaceae, and very fully 

 treated in Vol. 3 of E. F. Smith's monumental treatise 

 'Bacteria in relation to Plant Diseases.' 



So far as the records of this Department show, the 

 disease has only been previously reported in the Lesser 

 Antilles on one occasion, on tomatoes from Union, St. Lucia, 

 in January 190-i. 



The outstanding character of the affection on tomatoes, 

 as seen in St. Vincent, is the wilting, usually sudden, of the 

 ■whole plant, which has just the appearance which would 

 be produced by severing the b"" of the stem from the roots. 

 No preliminary browning of leaves or stems was observed. 

 When the bacterium was artificially introduced into a single 

 stem, wilting above the point of the inoculation took place in 

 from two or three days to a week, while backward infection 

 proceeded only slowly. 



Since wilting of the same type is produced by Fusarium 

 disease, and would ensue from any other cause which cut off 

 the supply of water through the stem, it is necessarj- for the 

 purpose of a field diagnosis to have some further evidence of 

 the presence of this particular disease. Confirmation fairly 

 satisfactory for this purpose may be obtained by cutting 

 across the stem at intervals with a clean sharp knife. When 

 the region of infestation is reached the woody ring in the 

 stem is found to be di.scoloured brown, and in a short time 

 dirty white or brownish beads 6f bacterial ooze collect on 

 the ends of the cut vessel.". In the region of serious 

 infestation this discharge is copious enough to be quite 

 apparent to the naked eye. The pith may or may not be 

 discoloured; the principal seat of the disease is in the vascular 

 'issues, from which circumstance, when the infestation of 

 any section of the stem is complete, the wilting of all parts 

 "f the plant btyond that section follows. 



There seems to be no evidence of varietal resistance 

 given in connexion with the published studies of this disease. 

 Solanuiit mammonim is reported frtmi Porto Rico to be 

 resisten', and the suggi stion has been made to use it as 

 a stock for grafting tomato and egg-plant. At the St. Vin- 

 cent station natural infection occurred to a considerable 

 extert in American varieties of the I'onderosa type (which 

 includes Earliana), The type with small round fruits, 

 lOtimion ill theso' inlands and reputed to be native, proved 

 fully suscfptible to inoculations. A bed of F2 hybrids 

 between Ponderosa and Native was witli few exceptions des- 



troyed when in full bearing. It is very much open to doubt 

 whether the survivor^ were really resistent to the disease^ 

 in view of the known lessening of susceptibility to infectioa 

 in matured plants. From whatever circumstance arising, 

 some of the plants did resist artificial infection at this stage, 

 and cuttings were taken from the survivors for further trial. 

 A batch of hybrid seedlings, inoculated through needle pricks 

 when a few inches high, succumbed in five days, showing at 

 the point of introduction of the bacterium an infestation which 

 was greatest in the protoxylem and the immediately adjacent 

 cortical parenchyma. 



The plants in which natural infections occurred were 

 transplanted seedlings, in some cases very widely spaced, and 

 the distribution of the diseased plants was of a sporadic type. 

 In one rather clo.se-planted row of Earliana several scattered 

 plants died when coming into fruit without infecting their 

 neighbours. The failure of attacked plants was completed 

 at one stroke, and the indication given by this feature was 

 confirmed in all the cases examined by the finding of the 

 most severely affected sections at or near the base of the stem, 

 and in one or more of the principal toots. 



It seems on the whole most likely that infection had 

 proceeded from the soil, probably, in some cases examined, 

 through wounds made by removing basal shoots. The possi- 

 bility remains, however, that wounds kept moist by nearness 

 to the soil may have been more susceptible to infection from 

 the pruning knife than those higher up, and it is somewhat 

 easier to conceive of the knife becoming contaminated than 

 the soil in some of the cases noted, where no Solanaceous 

 plants appear to have been grown in recent times. 



According to E. F. Smith, it seems probable that the 

 organism is strictly a wound parasite. He has shown that it 

 may be transmitted by insects, and is inclined to attach great 

 importance to the action of nematode worms in opening the 

 way for root infections, regarding their presence as prohibit- 

 ive of tomato growing in infected soil. The St. Vincent 

 plants did not show any obvious signs of the presence of 

 nematodes. The further precaution on which most depen- 

 dence must be placed, according to the author quoted, lies 

 in avoiding even trifling injuries to the roots in transplanting. 

 For this reason, if the seed cannot be germinated in situ, the 

 transfer must be made with great care while the seedlings 

 are still small enough to make the avoidance of injury 

 possible. It is also obvious that infectious may be easily 

 made in pruning. A branch may be infested for a pirfe of 

 its circumference Avhile not yet showing signs of wilt, s,nd 

 the cutting of it will smear the knife with large numbers 

 of the cau.sative bacteria. It would be safest to avoid 

 pruning altogether when infected plants are known to be 

 present. 



It should be noted in conclusion, that it is reported from 

 North Carolina and from Sumatra that ground nuts gr.)wn 

 on infested soil have proved susceptible to the attacks of 

 ISiicteriu in fohinacea rum. 



BACTERIAL FRUIT ROT. Attempts to infect tomato 

 fruits with Bact. so/nnacear^un resulted in slight local 

 injuries which developed no further. This is in agreement 

 with the results of previous investigators. There was presi'nt, 

 however, at the Experiment Station, fairly well distribu ed, 

 but not during the period of my observations causing mare 

 than moderate losses, a bacterial rot of the fruit of a very 

 swift and decisive nature. Bacteria which invade injuries', 

 and cau.'e ripe rot of the tomato, as of other llesliy fruits, 

 are not at all uncommon, but the one in question was distin- 

 guished by its ability to cause very destructive effects in 

 fruit of any age, and ranging frnm the small 'native' to the 

 large fruits of- Earliana. Its outstanding character was iliQ 



