30 



THE AGRICULTURAL NEWS. 



January 21, 1911, 



FUNGUS NOTES. 



THE BUD-ROT DISEASE 

 IN INDIA. 

 I'AltT II. 



OF PALMS 



SPREAD OK iN'FiiCTioN (Continued). Insect.s and birds 

 are probably responsible for a larger share in the spread of 

 the disease than are air-ljorne spores. The reiiroductive bodie.s 

 of this particular parasite are comparatively large, and could 

 onl}' be carried by large insects. Two kinds of beetle, which 

 are sufficiently large for the pur[)ose, occur commonly on palms. 

 These are the rhinoceros beetle and the palm weevil. Scor- 

 pions may also be concerned in this method of distribution. 

 Birds are common on the tops of palm trees and might con- 

 ceivably carry j)0rtions of the mycelium and sporangia on their 

 feet. The beetles, however, are more important, since they 

 penetrate to the heart of the crown, and probably emerge from 

 the pupal stage within the decaying mass which originally 

 formed the crown of diseased trees. Neither of the two 

 methods mentioned up to the present is likely to be nearly 

 as important as the last, namely the agency of man. 



As has been stated above, the Palmyra palm in particular 

 is of great value on account of the numerous uses to which 

 iits parts can be put. In order to obtain the leaves, climbers 

 ascend the trees frequently and remove the outer leaf sheaths, 

 exposing the inner soft ones. Now, it has already been pointed 

 out, that masses of mycelium often occur between consecutive 

 sheaths, portions of which might adhere to a climber's knife, 

 or his person, and infect the ne.xt healthy tree on which he was 

 iWorking. Besides the mycelium itself, all kinds of small 

 pieces of infected material would be conveyed in this way. 

 Two facts indicate that this method of spread is the most 

 usual. In the first place, there is evidence that in some 

 localities the disease has followed definite lines of communi- 

 cation; in the second, cocoa-nuts which are but rarely attacked 

 are but seldom climbed. 



THE CAUSATIVE FUNGUS. This belongs to the most 

 primitive group of the fungi — the Phycomycetes — (see Agri- 

 ciiltiira/ iV'cics, Vol. IX, i)p. 94 and 1 10), and is a memlier of the 

 genus Pythium, which is closely allied to Phytophthora. The 

 mycelium of the fungus may form a mass on the surface of 

 the diseased spots, but naturally, the i)art of it which is 

 respon.sible for the damage is that occurring within the tissues 

 of the host. The mycelium itself is unable to penetrate the 

 cells but occurs in the inter-cellular spaces, while the hyphae 

 can push their way between adjoining cells. The fungus obtains 

 its food-supply by means of haustoria. These are small finger- 

 like processes, either straight or bent, which are given otf from 

 the hyphae; they possess the power of dissolving cellulose 

 and penetrating the cells of the epidermis and parenchyma. 

 They are, however, unable to enter the lignificd vessels 

 of the vascular bundle.', or the fibrous cells. The mycelium 

 itself consists of a continuous branched tube which- is 

 only divided up by cross walls in the neighbourhood ' of 

 the reproductive organs. These are of two kinds: sporan- 

 gia borne terminally on the main hyphae, or on long or .short 

 lateral branches, and resting spores which may lie formed 

 terminally on large hyphae, or in an intercalary position. 



The sporangia are typically pear shaped, lieing attached 

 by the broad end, and having a small protrusion or pajjilla at 

 the narrow end. Germination may take j)lace in four ways, 

 two of which are intermediate between the two extremes. 

 The first method is that typical of the genus, by means Of 

 whicli it is separated from that of Phytophthora. In this 

 case, the apex of the papilla swells up into a vesicle po.ssess- 



ing a very thin wall into which the protoplasmic contents of 

 the .sporangium pass in a uniform ma.ss. Here the mass 

 segments into a number of biciliate, free-swimming zoo- 

 spores (see Agrindtuf'tl Jfews, Vol. IX, p. 94), \\hich 

 Ijreak through the wall of the vesicle and escape. In 

 some cases, for various reasons, some of the zoospores fail 

 to escape, but instead germinate inside the sporangium; 

 when their germ tubes reach the sporangial wall, they 

 penetrate it by means of a cytase such as is excreted 

 by the haustoria. In the last form of germination, the 

 zoospore formation is entirely done away with, and the un- 

 opened sporangium puts out one or several germ tube.s, as 

 does an ordinary conidium of one of the higher fungi. The 

 zoospores them.selves, when liberated, swim for about an hour, 

 then come to rest, round themselves off, and put out a germ- 

 tube, which may cause a fresh infection. 



The resting spores are spherical, thick-walled and 

 yellowish when old. They germinate and form a tube whose 

 growth is always limited by the production of a terminal 

 .sporangium. Itesting spores are most commonly produced 

 in dry weather; sporangia when the air is moist. 



It is probable that infection, either by means of portions 

 of mycelium or of sporangia, usually takes place through the 

 stomata. In a few instances, hyphae have been observed 

 running in the cuticle of the epidermal cells, but they have 

 hardly ever been found traversing the cell cavity. 



A curious feature of this fungus is the power which it 

 pos.sesses of entering into a dormant condition, particularly in 

 dry weather. It was observed that a sudden reappearance 

 of the disease would occa.sionally occur in a village in which 

 all the attacked trees bad been most carefully destroyed some 

 time previously. The distribution of these cases was often 

 such as to preclude the possibility of their having been 

 infected from the trees which had lieen destroyed. The facts 

 could only be explained on the suppo.>ition that the trees had 

 been attacked for some time, but that after a certain stage 

 the fungus had become dormant during several months, and 

 had then recommenced its activities, and completed the 

 destruction of the terminal bud. 



PREVENTIVE MEASURES. .\ most caiefully organized 

 campaign has been instituted to prevent the spread of the 

 disease, and to reduce its virulence in the infected area. 



In order to do this, arrangements were made to ins[)ect 

 as far as po.ssible every tree in the district, and to destroy all 

 the diseased palms. The inspection has to be repeated every 

 few months, as new cases continually arise and have to be 

 destroyed as soon as possible. This necessitates the employ- 

 ment of a definite staff' of officials, and the expenditure of 

 considerable sums of money. This expenditure seems to be 

 thoroughly justified by the results so far obtained, especially 

 when it is n'lnembered that the spread and increase of the 

 disease might mean the financial ruin of a very large district. 



The destruction of the trees is conducted as follows. 

 A palm climber ascends the diseased tree and cuts off the top, 

 which is then completely burned. The leaves arc usually 

 sufliciently dry to burn easily without other fuel. The pole 

 of the tree is permitted to stand. 



The similarity of the symptoms of this disease to 

 those of bud-rot in Ceylon is interesting (see Agricultural 

 News, Vol. I.\, p. 2.54), and it may po.ssibly prove, as is stated 

 above, that some of the Eastern forms of bud-rot are due to 

 this organism. In any case, it is satisfactory to learn that 

 the cause of this disease is definitely known in one country, 

 and that the general evidence is fully substantiated by infec- 

 tion exfjeriment.s' with the causative fungus, which were suc- 

 cessful in every case, and were conducted with material that 

 was, in tnost cases, microscopically pure. 



