M 



THE AGRICULTURAL NEWS, 



Maech 11, 1916. 



PLANT DISEASES. 



A MANGO DISEASE. 

 In the Bulletin of the Department of Agriculture of 

 Trinidad and Tobago, Vol. XIV, pp. 164-71, Mr. J. B. 

 Eorer, ]kIj-cologist to the Board of Agriculture, discusses the 

 anthraeno&e of the mango, a disease whose existence is 

 recorded in Florida, Porto Kico, Cuba and Trinidad, and 

 which probably occurs to some extent throughout the West 

 Indies. It has not, in any instance of which the present 

 writer is aware, attracted much attention in the lesser Islands, 

 though no doubt it has had some influence, there as in 

 Trinidad, in determining whether a year shall be a good one 

 or a bad one for the mango crop. 



Tlie fungus is of the Gloeosporium or Colletotrichum 

 type (a given fungus may adopt the form characteristic of 

 one or the other of these genera, according to circum-stance.-^), 

 and the author adopts the view that G. ma 7u/ if erne, the name 

 given to the fungus on the mango, is synonymous with 

 C. aloeosporioides, applied to the form on citrus and other 

 fruit trees. 



The fungus attacks flowers, leaves, and fruit. On the 

 flowers and flower stalks the fungus appears in spots, and 

 leads to the blackening and dropping of a proportion or all 

 of the flowers. It is in this way that most eftect is pro- 

 duced on the crop. On the leaves, spots and sometimes 

 holes are produced, which begin as minute black dots and 

 increase to a diameter of J or ,;, of an inch. "S'oung fruits 

 may be attacked and drop in large numbers, older fruits 

 become spotted with black, or streaked, and their keeping 

 tjualities are greatly reduced. 



Infection experiments with pure cultures resulted in the 

 copious production of the various forms of the disease on 

 the inoculated plants, while the controls remained nearly or 

 quite unatt'ected. 



Considerable interest attaches to the spraying, storage, 

 and shipping experiments conducted over several years in 

 Trinidad, the results of which are collected in the paper 

 under review. 



In 1912 trees of nine varieties bordering a road in the 

 Experiment Station were made the subject of an experiment on 

 the effect of Bordeaux mixture, twenty-one being sprayed and 

 fifteen left as controls. The former received three ajiplications 

 in February, three in March, and one in May. Febru- 

 ary and March were dry months, .so that the general 

 mango crop was an excellent one, but the ettect of the treat- 

 ment w;i) nevertheless shown in a much heavier crop im the 

 .sprayed than the unsprayed trees, especially the more suscep- 

 tible varieties. The fruit was moreover very much improved 

 in appearance. In 1913, though the weather was again not 

 such as to favour any very serious manifestation of the 

 disease, the beneficial results were even more noticeable, and 

 were seen in the foliage as well as in the fruit. 



The shipping of sprayed and unsprayed fruit to England 

 and the United States has revealed an improved keeping 

 (juality as a result of the treatment. Fruit of the .lulie 

 variety, kept for a month iu cold storage in I'ort-of -Spain, 

 deteriorated much more quickly after removal in tlie (Mse of 

 unsprayed than of sprayed examples. 



\V. X. 



WATER LOSSES FROM PLANTS AND 

 SOIL. 



A lengthy paper on transpiration appears in the 

 Journal of Agricultural Research, United States Department 

 of ^Igriciilture, \o\. V, No. XIV. The paper has special 

 regard to transpiration rate on clear days as determined by 

 cyclic environmental factors such as radiation, air by 

 temperature, and wind velocity. By way of introduction it is 

 stated that the great diflferences exhibited by the various 

 plants in water requirement, that is, in the water transpired 

 in the production of a unit of dry matter, are of profound 

 economic importance in the agricultural development of 

 regions of limited rainfall, and an understanding of what 

 gives ri.se to the greater etticiency which some plants possess 

 in the use of water is highly desirable in the selection and 

 breeding of plant strains adapted to dry land agriculture. 

 This problem led the writers of the paper under notice to 

 undertake a series of transpiration measurements with 

 a view to determining, so far as possible, the relative 

 influence of various environmental factors on the transpiration 

 of diff'erent plants. To this end simultaneous automatic 

 records were obtained of the solar radiation intensity, the 

 depression of the wet bulb thermometer, the air temperature, 

 the wind velocity, and the evaporation from the free-water 

 surface. The paper under notice deals with the transpiration 

 response of plants to these factors, on clear days. 



Composite graphs are presented showing the mean hourly 

 transpiration rate for each of the plants considered, together 

 with the mean hourly values of the radiation, air temperature, 

 wet bulb depression, and wind velocity for the transpiration 

 period, and also the mean hourly evaporation rate. On the 

 basis of the form of the curves, the transpiration graphs may 

 be grouped into two classes having characteristic features. It 

 should be mentioned here, that in this investigation only crops 

 that grow in temperate climates were dealt with, with the one 

 exception of sorghum. This however does not detract from 

 the scientific interest of the results. The cereals showed 

 a marked change in the sloj)e of the transpiration graph in 

 the forenoon unaccompanied by corresponding changes in the 

 environmental factors. On the other hand, the forage 

 plants gave little or no indication of such a change. This 

 flattening of the graphs in the case of the cereals appears to 

 be due to some changes in the plant, resulting in 

 a reduction in the transpiration rate below what would be 

 expected from the form of the curves during the early 

 morning hours. 



The paper concludes with a statement a.s to the form 

 shown by the curves representing the cyclic factors. The 

 radiation grai)hs are practically symmetrical wiih respect to 

 noon. The air temperature and wet bulb graph.* are very 

 similar in form, since the latter can be determined from the 

 former on days in which the humidity of the air is not 

 changing. The transpiration graphs usually rise and always 

 fall in advance of air temperature. 



It is shown finally that radiation, air temperature, and 

 wet bulb depression are correlated with transpiration approx- 

 imately to the .same degree. If the environmental factors 

 are considered as independent, their relative influence on 

 transpiration may be determined by the method of least 

 squares. 



