THE AGRICULTURAL NEWS. 



July 19, 1913. 



FUNGUS NOTES. 



A NEW DISEASE OF THE CASTOR 



PL.ANT. 



An interesting account of a new (lisea>e of the castor 

 oil plant (Ririniis cnmniti/iis. L.) is contained in tlie Mi'inoirs 

 of the Dep<i>tme»t of AfjricuUiin- in India, Vol. V, No. 4. 

 The paper in question deals almost entirely with the 

 morphological ami cultural characters and parasitism of the 

 causal fungus, liut such of the information as is thought 

 likely to bi3 of interest to the general reader has been 

 summarized in the following article. 



USES OF TIIK CA.sTOl; Oil. PL.VNT. 



The author (,J. F. Dastur, B.Sc), who is first assistant 

 to the Imperial Mycologist, begins with a discussion of the 

 economic importance of the castor oil plant. It is observed 

 that oil from the seed i.s in great demand commercially 

 owing to its value in the manufacture of Turkey red, and 

 because of its medicinal properties. Castor oil is also used 

 for illumination purpo.'^es and as a lubricant; it is employed 

 for dressing tanned hides and skins; castor oil Cfike is an 

 important constituent of manures; whilst finally, the plant 

 itself is cultivated in Assam, for feeding the erisilkworm 

 on its leaves. Incidentally it may be mentioned that 

 a beginning has been made with a view to growing the 

 plant for this latter purpose in the West Indies. 



FUNiirs DISE.VSK.S 01'' TUB 1>L.\NT. 



The castor oil plant is, on the whole, remarkably free 

 from pests and diseases The most widely distribute<l 

 perhaps is the leaf rust. In India, an Alternaria and a Cercos- 

 pora have been found on the leaves and are at present under 

 investigation; but the most important disease in India, and 

 one which has for years caused considerable damage is that 

 induced by Fhiitophthora 2MrasUira, nov. spec. 



PnYTOI'HTHORA .VXD WEATHEU CONDITIONS. 



A characteristic feature attendant on the outbreak of 

 this disease is the fact that it has been found appearing 

 every year, at Pu.sa, about the end of June, after the rains 

 have set in. In 1912, it appeared as early as June on 

 account of the frequent showers received during April and 

 May. The disease disappears by the beginning of September, 

 at the end of the rains. It is therefore largely controlled by 

 weather conditions. 



.^PI'KAllANCE Ot- WSEASEl) TISSUE. 



The fungus in question both destroys seedlings and attacks 

 lenves of older plants. The first indication of the disease is 

 the appearance of a roundish patch of an unhealthy dull green 

 colour on both the surfaces of a cotelydon. The disease 

 spreads from the leaf to the petiole, thence to the .stem and 

 growing point, killing the seedlirg. In older plants the disease 

 in the field is localized on the leaf blade. As the diseased spot 

 gets older, it turns yellowish and then brown. On the under 

 surface of the leaf, in a more or less advanced stage, there may 

 be seen by the aid of a lens a sparse white web of threads 

 originating from the unhealthy green-coloured portion of the 

 diseased spot. These are the long and nnbranched fiuit 

 stalks of the fungus, measuring from about 100 to .'lOO 

 microns in length. The mycelium within the tissues is both 

 intracellular and intercellular. Wherever an intracellular 

 hypha passes through a wall there is invariably a constriction 

 of the hypha. Haustoria are very scarce. When a diseased 

 petiole or stem is cut transversely, the ring of fibro vascular 



bundles becomes prominent by its black or brown colour on 

 account of the fungus in the vessel. Internal sporangia 

 have often been observed in the tissues of leaves, stems and 

 fruits Sexually produced spores (oospores) were not found 

 in nature, but as will be mentioned later, were readily detected 

 in pure culture. 



AKTUK lAl. I.ML(Iii>.\ \M IH SWAKMSPOKES. 



In the investigation under consideration a large number 

 of experiments were carried out to discover to what extent 

 the fungus is an active parasite. Before pure cultural 

 inoculations were made, either a portion of a diseased leaf 

 was placed under moist conditions on a healthy plant, or 

 spores were obtained from a diseased portion, grown in a petri 

 dish and the swarm-spores placed on healthy leaves. When 

 the fungus was taken in culture, swarm-spores (zoospores), 

 suspended either in distilled water or in sterilized tap water, 

 were invariably used for the various inoculations. The 

 etiect of inoculation was clearly perceptible within twenty four 

 hours by the inoculated area taking a dull unhealthy green 

 colour. Sporangia were produced in about forty eight hours 

 after inoculation, when the inoculated leaf was kept moist by 

 occasionally spraying it with water. 



FACTS CONCERNING PENETi; ATION. 



From the infection experiments it was found that 

 the germ tubes of the zoospores penetrate the leaf three 

 to five hours after they are sown on it. The penetration 

 takes place on either of the surface-i and is not 

 accomplished necessarily through a stoma. They may 

 even break through the upper wall of the epidermal cells 

 or penetrate between the cell walls I of two neighbouring 

 cells. An interesting matter in connexion with the.se inocu- 

 lation experiments was the employment of Klebahn's 

 method when that of putting a drop of water containing 

 freshly discharged zoospores, failed. 



ki.ep.ahn'.s method. 



In Klebahn's method the stems of joung plants are 

 surrounded by a jacket of distilled water, containing motile 

 zoospores in a glass tube about 4 inches long and -I'-inch 

 broad, the lower end of which is plugged by a rubber cork cut 

 into two equal halves and having a central board ju.st big 

 enough til enable the two halves to surround the stem in a water- 

 tight manner without injuring it. The lower end is waxed; 

 the u[iper end is kept open. Successful inoculations were 

 obtained by this method without any wound being made, and 

 the young plants wilted in four days. Plants three to six 

 months old, however, remained quite healthy, owing mainly 

 to the resistance offered by the cuiicularized epidermis (hard- 

 ened skin). 



AKTIFIOIAl, INFECTION OF FLOWERS AND FKUIT. 



A most interesting feature of this work was the dis- 

 covery of the fact that castor oil flowers — particularly the 

 male flowers— take the inoculation in a day, turning brown 

 and then black. The fungus also causes the iruit lo rot. 

 Inoculations on dried fruit invariably fail. Though in the 

 laboratory, fruits and flowers are so virulently attacked, in 

 nature they have been found to be entirely immune. The 

 cause of this is attributed solely to the climatic condi. 

 tions prevalent at the time of fruiting under ordinary field 

 conditions. In other words, the fungus cannot make head- 

 way in dry weather. 



\ ITALITY OF l'Ai;.\SITE IX THE .SOIL. 



The final set of experiments in regard to inoculations 

 concerned the question as to whether the disease can be 



