1V4 



THE AGRICULTURAL NEWS. 



May 23, 1914. 



FUNGUS NOTES. 



TWO TOMATO DISEASES. 



Two impoi-tant tomato diseases have recently been 

 cjramined by the Mycologist to this Department on plants 

 ^rown in Barbados from American seed. 



The first is the well-known leaf mould disease due to 

 €lados2Jorium fit! turn, Cke. The fungus develops principally 

 on the under side of the leaves, where it produces indefinite 

 greyish patches, which later become smoky brown. The spots 

 chow through to the upper surface, where they are yellowish 

 at first, then become brown as the invaded tissues die. On 

 the under side the fungus is easilj- seen through a pocket lens 

 ID tlie form of closely set dense tufts of the conidiophores. 

 The conidia are elliptical, somewhat elongated, very variable 

 in size, mostly one-septate, but sometimes two- or three-septate. 



The disease was first described from specimens obtained 

 io South Carolina in 1883, since which time it has become 

 generally known in the L^nited States and has become 

 common in Europe, It was first recorded in England in 1887. 



It is found to be capable of causing great damage to 

 plants grown under glass if ventilation and drainage are not 

 good, and in America is sometimes troublesome in the open 

 sir in damp weather. L^^nder the dry conditions which 

 generally prevail in certain of the West Indian islands it is 

 not likely to be of much account, but in wetter seasons and 

 in the islands with more abundant rainfall it may recjuire 

 treatment. Tt c.<in be fairly successfully controlled by 

 spra)ing with -1 4 50 Bordeaux mixture about once a fortnight, 

 especially if this is started at an early stage. 



The second disease afi'ects the fruits, and is described by 

 numerous American authors under the name of blossom end 

 tot. It appears in the green fruits, usually when they are 

 lalf- or three quarters grown. It almost invariably affects 

 the tissues around the end of the tomato opposite to tlie stalk, 

 tence its popular name. The first appearance is in the form 

 of a watery spot, which later becomes black. It tends to 

 develop in a circle lound the point where the carpels meet, and 

 may remain rather small or cover the whole end of the fruit. 

 Owing to the growth of the unafi'ected parts, the spot soon 

 becomes considerably sunken and the end of the fruit may 

 be quite flattened. A longitudinal cut through the fruit 

 shows that the rot is of a dry nature and often is quite 

 shallow. This latter character appears to vary according to 

 the age of the fruit when first attacked, apparently because 

 the causal organism depends upon the supply of starch, which 

 is abundant when the fruit is green but is dissolved in the 

 process of ripening. Hence the spread of the disease is 

 arrested by that process. In accordance with this, ripe toma- 

 toes are very much less susceptible to the disease. A late 

 infection produces a very shallow depression. 



Investigations as to the nature and identity of the 

 organism causing the disease have been numerous and long- 

 continued, and the results have been the subject of much 

 dis|:iute. 



There is usually, and at a fairly early stage, an abun- 

 dant development of fungi in the spots, and species of 

 Macrosporium, Alternaria, Cladospcrium and Fusariura were 

 each described by earlier investigators as originating the 

 disease. 



In 1900 Y. S. Earle (Alabama Experiment Station 

 Bulletin 108) published the results of a study of the disease. 

 After a description of the development and character of 

 the spots corresponding with that given above, he continues: 



'In the early morning drops of .sticky exudation were 

 observed on the spots of half grown rotten fruit. These were 

 found to be swarming with bacteria, which were found 

 abundantly within the diseased tissues. Sound green 

 tomatoes under a beU jar were inoculated with a pure culture 

 prepared from the exudate. In all cases they showed signs 

 of rot within twenty-four hours. When agar containing 

 the germs was smeared on the surface of sound tomatoes, na 

 rotting took place even after a number of days. The disease 

 cannot be contracted through the flowers, as in the case of 

 pear blight. The stigmas of many open flowers were 

 smeared with cultures of the germ without inducing a single 

 case. In no case were inoculations successful where the 

 fruit was less than one centimeter in diameter. It prows on 

 ripe tomatoes, but less readily than on green ones. It seems 

 to be strictly aerobic' 



Miss Elizabeth H. Smith carried out an investigation 

 on the subject in the years 1902-4 (Massachusetts Agricul- 

 tural Experiment Station Technical Bulletin 3, 1907). During 

 the first year she found a species of Fusariura closely associ- 

 ated with the disease and apparently able to give rife to it, 

 but in the following year this was absent in a large number 

 of cases and a bacterium was isolated from the spots which 

 was capalile of producing the disease. Dr. George E. Stone, 

 who directed Miss Smith's experiments on the bacterial rot, 

 published in 1911 (Bulletin 138, Massachusetts Agricultural 

 Experiment Station) his conclusions after sixteen years' obser- 

 vations on the disease. He regards the disease as being of 

 bacterial origin and the fungi as of secondary importance. 

 He states that imperfect moisture conditions tend to make 

 the tomatoes coarse, ill-shaped and fissured at the blossom 

 end, thus offering favourable conditions for the entrance of 

 the bacteria. Other conditions, such as insufficient atmos- 

 pheric moisture and too much sunlight also favour the 

 disease. 



Examination of the Barbados specimens showed that in 

 the earlier stages the diseased tissues were fall of bacteria, 

 while no fungus hyphae were found at that stage. There 

 was an exudation, from the skin covering the spots, of 

 yellowish drops of fluid filled with bacteria. Needle 

 puncture inoculations with this fluid produced exactly 

 similar diseased areas on sterilized healthy green tomatoes 

 of separate origin, beginning with a watery spot plainly- 

 discernible in about twelve hours, and full of similar 

 bacteria. Cultures on nutrient agar showed small round 

 compact yellow colonies. Circumstances did not permit of 

 the investigation being pursued further, but the observations 

 and exi)eriments so far as they went were in close accord 

 with those of Earle. 



The remedial laeasures adopted were designed to 

 prevent as far as possible irregularities in water-supply and 

 excessive transpiration. The surface of the soil was made 

 as loose as possilile and covered with a thick mulch of 

 leaves; light shade was provided overhead, and the plants 

 thoroughly watered in the early morning. Although the 

 weather conditions underwent no change, the spread of the 

 disease was quickly arrested, so that the measures may be 

 taken as having proved successful. Spraying with Bordeaux 

 mixture is not recommended. 



It may be noted that during a recent visit to Antigua 

 the Mycologist found that an experimental plot of tomato 

 plants of which the first crop of fruit was still green was 

 infected throughout with this disease. 



