414 



THE AGKICULTUEAL NEWS. 



December 16, 1916. 



PLANT DISEASES. 



AFFECTIONS OF LIME SEEDLINGS. 



Mr. AV. liobson, Curator, iVIontserrat, recently forwarded 

 for examination specimens of lime seedlings attacked by 

 a fungus in a manner different from that of the damping-ott' 

 fungus familiar in citrus seed beds. In this case the disease 

 affects the tips of young plants 2 or 3 inches high. One 

 or two of the youngest expanded leaves suddenly turn 

 yellow over a part or the whole of their surface, and the 

 growing point is infested and killed. 



A small amount of loose, white mycelium develops 

 externally on the affected parts, and the tissues are found to 

 be infested with freely branching hyphae, coarse and 

 irregular, and of gorged appearance. 



The fungus is one of the downy mildews (Peronospo- 

 raceae). The few sporangia seen were more or less detached, 

 and the genus could not be ascertained. The nature of the 

 disease is characteristic of this group, especially of the genus 

 Phytophthora. to which this fungus most probably belongs. 



The seedlings in* question occurred in two beds which 

 for part of the da.y are shaded by the surrounding trees, and 

 on the most shaded parts all the seedlings have died. The 

 appearance of the disease is to be accounted for by these 

 conditions of damp and shade, accentuated by the abnormally 

 heavy rains which fell during the period in which the affection 

 came to notice. It does not seem probable that any direct 

 measures of control will become necessary. 



The damping-off di.sease of lime seedlings referred to in 

 the first paragraph above, which is a more or less regular 

 feature of nurserj* work in Dominica and St. Lucia, has 

 caused inconvenient losses this year at Reunion in the latter 

 island, owing to the anfortunate occurrence of heavy rain.s- 

 after the successive sowings. Mr. A. J. Brookes, Agricultural 

 Superintendent, in response to a request for information as to 

 the incidence of the affection, forwarded the following notes. 



'Provided few showers fall between the time the seeds 

 germinate up to the time they are about 4 inches in height, 

 large batches can be succe.ssfully raised without the fungus 

 ap[)earing. 



'To prndiice sufiicient seedlings to raise 70,000 strong 

 plants we have to sow in batches for the necessary succession, 

 and we invariibly get hit by the fungus in the batch which 

 should be ready for planting in July and August. If we get 

 heavy rain oq certain days with hot dry intervals of a few 

 days betwc'-r. we are still all right, but if a light shower falls 

 on each day or three days in succession, the fungus rajjidly 

 attacks over the whole area at the same time. 



•This year we had a very bad season, rain falling about 

 two weeks too soon for the safety of the seedlings, and the 

 .successive sowiugs, made every week so as to strike a dry spell 

 sooner or late:', woic attacked, and heavy dustings daily and 

 •sometimes tv/it.e daily with sulphur and lime had to be made 

 to keep the disease .in control. This remedy is very effective 

 if the rains arc not continuous. 



'Once the .seedlings become wood}' they are safe. This 

 stage is reached .vlien they are about .3 or 4 inches in height.' 



Th(> fungas concerned has not been identified owing to 

 failure .so fir in obtaining it in a fruiting condition. The 

 specimens e~ainined have hyphae which are freely septate, 

 and the dist'ase bts no relation to that from Montserrat 

 described jibove. 



A DISEASE OF ALFALFA. 



Mr. Eobson forwarded in August specimens of diseased 

 alfalfa grown in Montserrat from seed of the Grimm variety 

 obtained from St. Croix. At the time of writing the plants 

 were from 1 foot to 18 inches in height, and were flowering. 

 They did not promise to be of any more vigorous a type than 

 those tried many years ago, the cultivation of which was 

 abandoned. 



The lesions found in the large supply of spirit material 

 examined have constant characters. They occur as black 

 spots encircling the stems just above the crown for a distance 

 of about half an inch. The cortex at this place becomes 

 infested with stout, freely septate, much branched hyphae, 

 which mostly follow a longitudinal course. The cortex is 

 rotted off down to the woody cylinder, which is externally 

 discoloured but not, so far as was seen, much invaded. Above 

 the lesion a thick cushion of callus commonly forms, which 

 may send out abundant adventitious roots, showing that the 

 fungus is probably limited in its action to the neighbourhood 

 of the surface of the soil. The roots do not seem to be at 

 all affected. 



No trace of fruitifications could be found, nor any 

 evidence indicating the systematic position of the fungus. 

 The evidence seemed to exclude insect complicity in the 

 formation of the lesions. 



THE SMALL ROSELLINIA ON CACAO. 



A description is given in the current number of the 

 West Indian Bulletin (Vol. XVI, No. 1 ) of an unidentified 

 species (referred to as C) of llosellinia found on cacao in 

 Grenada and St. Vincent and on immortel in St, Lucia, 

 A letter from the Director of the Royal Botanic Gardens, 

 Kew, has now been received enclosing a memorandum by 

 Miss E, VL Wakefield discussing the identity of this 

 fungus. It is stated that the species does not agree with 

 any one of which material exists at Kew, and conse- 

 quently all the published descriptions have been carefully 

 compared. The only known species to which it can be 

 referred with any probability from the description only, is 

 a. paraguayends, Starb,, which was described from San 

 Tomas, Paraguay, in 1904. With this it agrees fairly well. 

 There are a few minor points of difference, which may 

 however be merely individual variation.s. On the whole, 

 the agreement is so close that without having seen material 

 of R. paraguayensis it would be unsafe to regard the West 

 Indian form as distinct. 



In view of this information it would seem that, pending 

 a comparison of actual specimens should that become possible, 

 the name may be adopted for purposes of reference to this 

 fungus in departmental communications. 



W.N. 



The paper dealing with sulphur on alkali soils appearing 

 in Soil Science for September 1916 is of interest in regard to 

 'gall patches" on the soils of Antigua. It is suggested in this 

 paper that sulphur might be used to reclaim alkali soils instead 

 of sulphuric acid previously proposed. There are vast areas of 

 land in which carbonates and bicarbonates of sodium are 

 pre.sent in sufficient amount to interfere partially or completely 

 with profitable crop production. It is hoped that experiments 

 will be undertaken with sulphur as a means of reclaiming 

 land which now contains an excess of these carbonates and 

 bicarbonates. 



