206 



THE AGRICULTURAL NEWS. 



JtiXE 24, 1911. 





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FUNGUS NOTES. 



DISEASE OF THE ARECA PALM. 



Interesting work has been conducted recentlj- b}- 

 L. G. Coleman, il.A., Ph.D., Mycologist and Entomologist to 

 the Government of Mysore, on the diseases to which the areca 

 palm {Areca CaterJui) is subject, in that State. The first of 

 these is Koleroga or rot' disease: an account of it has been 

 piiblished in Bulletin No. II of the Mycological Series of the 

 I)eij)artni,ent of Agriculture of Mysore. The subject-matter 

 of this mj'jer is interesting in many ways, but one of the 

 main 'Aoiri'ts is that the fungus causing the disease is closely 

 relateif'tb that responsible for canker and black rot of cacao. 

 In f.nict, tlie second and more technical portion of the Bulletin 

 contains a description of the cacao fungus and of comparative 

 cross-inoculation experiments with it and with the areca nut 

 fungus. An account of the conclusions arrived at as regards 

 both is given below, as well as of the disease which formed 

 the jirimary object of the investigation. 



sv.Mi'TOMs. The areca nut is cultivated in gardens or 

 estates in the hilly regions of the State of Mysore where the 

 rainfall varies from 100 to 300 inches in the year. In the.se 

 district.*, as the monsoon commences (this is usually early in 

 July), a serious disease breaks out on the nuts and destroys 

 a varying proportion of the crop, while in severe cases the 

 whole may be destroyed. This disease is known as Koleroga, 

 but has no connexion with the Koleroga of coffee. The first sign 

 is a drop|iing of the nuts from attacked bunches. Such nuts 

 on examination are found to have lost more or less completely 

 their clear green colour. If they are in an early stage of the 

 disease, it is seen that part of the surface of the shells, usually 

 at the base of the nuts, is of a darker green colour and has 

 a water-soaked appearance: at a later stage the surface is 

 covered with a whitish mass of mycelium, e.asily removed by 

 scraping with a knife or with the finger nail. This ma.ss of 

 mycelium commences to appear on the water-soaked area at 

 the base of the nut, and gradually spreads over the whole 

 surface. Various saprophytic organisms, both fungi and 

 bacteria, quickly follow the original, causative fungus and 

 complete the destruction of the nuts. In addition to the 

 nuts, the flowers and flower stalks may be attacked: further- 

 more, the fungus I'.-.ay in rare cases spread down the flower or 

 fruit stalks into the tree and thence ui)wards into tlie terminal 

 bud; as a consequence the tree is killed In even rarer 

 cases, infection may start on the leaf .sheaths and spread 

 directly into the terminal bud, with the same result. 

 Altogether about 1 per cent, of the trees in many gardens 

 were killed in this way. 



THE FUNGUS. The disease is due to a variety of P/ii/- 

 tophlliora omnivora, which lias been provisionally named by 

 Coleman P. omnivora, var. Arccae; it lives in and between the 

 cells in the tissue of the nut. The portion of the mycelium 

 between the cells j)uts out .short, finger-like haustoria, which 

 penetrate the cells. These haustoria may lie straight or curved, 

 and are occasionally branched. As the disease progresses, 

 the mycelium bursts it < way through the epidermis in small 



tufts. These tufts then grow out, and produce the white 

 superficial covering found in mo>e advanced stages of the 

 disease. It will be remembered that a mass of superficial 

 mycelium is also produced by Pythium pahnivoriim, Butler, 

 the fungus causing bud rot of the Palmyra palm (Bomssus 

 fl(il'tllife)'), and to a less extent of cocoa-nut and areca nut 

 palms in Travancore (see Ayricultuml News, \o\. X, pp. 14 

 and 30). In some cases, the erumpent tufts of mycelium 

 give rise to sporangia borne on very short stalks, while these 

 organs are also produced on short sporangiophores among 

 the mass of superficial hyphae. They are more or less 

 lemon-shaped structures, with a blunt, hyaline projection at 

 one end. In damp conditions, under the influence of light 

 their contents are extruded through a hole formed in this 

 projection. These break up, on emerging, into 10 to 40 

 minute spores, which swim about in drops of rain-water by 

 means of two small whip-like appendages, or flagellae. After 

 swimming for some time, they come to rest and germinate, 

 the germ tube growing out until it reaches a stoma, through 

 which it enters the nut, and produces a new infection. The 

 fungus also possesses a sexual method of reproduction, by 

 means of antheridia and ongonia. The contents of the anthe- 

 ridium pass into the oogonium, and as a result a thick-walled 

 resting oospore is formed. The oospores are capable of 

 resisting drought, and it is by their means that the fungus 

 is enabled to survive from one monsoon to the next. Coleman 

 was unable to state definitely where they are produced, as 

 ho never found them on the nuts or in the soil. He believes, 

 however, that they are formed in the nuts, and also in the 

 tops of trees attacked in the bud region; while there is also 

 a possibility that ihey are produced on other plants, as infec- 

 tion experiments showed that the fungus could attack many 

 of the hosts of Phytopliihora otiuiivora, and in addition 

 young tomato plants. 



METHOD OF SPREAD. When the sun is shining between 

 falls of rain, in the monsoon, the sporangia formed on the 

 surface of a nut liberate their zoospores into the rain-drops 

 left by the last fall. This is done under the influence of the 

 sunlight, and occupies about fifteen minutes. In the dark, 

 zoospores are not liberated. Soon, another rain-cloud comes 

 up, the rain falls very heavily, and the drops are blown by 

 the strong wind. In this way drops of water infected with 

 zoospores are carried to healthy trees to leeward of the un- 

 healthy group, and the disease is spread. Insects and birds 

 may also assist, but the part played by tliem is small, as they 

 do not fly much in the wet weather. 



PREVENTIVE ME.vsuEES. The first precaution is the 

 removal and burning of all diseased nuts and branche.s, and the 

 tops of trees that have been killed. Two other precautionary 

 measures were investigated. The first consists of covering 

 the bunches of nuts, before the monsoon breaks out, with 

 S|>ecial coverings known as 'kottes', made by sewing tot'ether 

 th? bases of two leaf .sheaths. This is a practice in general 

 use and helps to prevent an outbreak, but is not of much avail 

 in stopping the spread nf the disease. The second and more 

 successful method is to spray the bunches with Bordeaux 

 mixture to which a strong adhesive has been added. 



CO.MPAEISON OF THE AREC.\ AND CACAO FUNGI. This 



fungus is so like Phytophtlwra omnivoia, to which .species the 

 cacao canker and black rot fungus were formerly referred, 

 that Coleman made a comparative investigation of the two 

 forms, and also c.irried out inoculation experiments, with both, 

 on various hosts of /'. omnironi. He f(.uud that the cacao 

 fungus possessed the peculiarity that it appeared never to 

 form antheridia, while its oogonia developed oospores without 

 any tcrtilization taking place. In consei|uence of this and other 

 characters, and of the fact that it could not attack areca nuts 



