THE AGRICULTURAL NEWS. 



FEBEtTAEY 18, 191L 



FUNGUS NOTES. 



THE SECRETION OF POISONS BY FUNGI. 



It has been known for some time that eertain fungi 

 possess the power of secreting various poisons from the tips 

 of their hj-phae. These poisons kill the cells of the host in 

 their immediate neighbourhood, somewhat in advance of the 

 tips of tlie hyphae, which subsequently in the course of 

 their growth, reach these dead cells, and feed on them in 

 a saprophytic manner. 



A good example of this is the secretion of oxalic acid by 

 the hyphae of the Botrytis st^ige of species of Sclerotinia. 

 These fungi attack tulips, lilies, and various other host 

 plants. They are partly saprophytic, but are enabled 

 to live practically as parasites bj' means of this character. 

 Very many fungi give rise to crystals of calcium oxalate, appa- 

 rently as a w;iste product, these crystals either being stored 

 inside the hyphae of the fungus, or being formed on the out- 

 side of the hyphal wall. It would seem that, in the case of 

 Botrytis, calcium is either not absorbed to the same extent, 

 or is used for some other purpose, so that the acid which is 

 formed, as in several other fungi, is not neutralized, and, 

 consequently, is secreted. In this case, however, it serves 

 a useful purpose, since it kills the cells of the host plant and 

 enables the hyphae to attack them, the latter being unable to 

 penetrate living cells. 



A much more remarkable instance of this secretion of 

 poison is furnished by a fungus known as Stereiim piirpuyeum. 

 This causes a disease known as silver leaf, affecting plums, 

 peaches, apples, pears, laburnums and the Portugal laurel. 

 Some recent work on this fungus, by Mr. Spencer Pickering, 

 has been published in the Twelfth Repm-f of the Jrobiini 

 Ex/'erhnoiial Fntii Farm; a short account of this paper ap- 

 pears in the (ranieners' Chronicle, Xo. 1246, November 12, 

 1910. The mycelium of the fungus lives in the branches, 

 only, and does not appear to extend to the leaves. It secretes 

 a poison, however, which is carried to the leaves of the 

 host plant by way of the wood and the leaf veins; this is 

 produced in sufficient quantities to a\use a material alteration 

 in the appearance of the leaves, namelj-, to turn their colour 

 from green to a silvery or ashen grey. The yield of infected 

 trees is much reduced, and eventually branches are killed, 

 and the trees slowly die. Death does not always occur, how- 

 ever, as infected trees sometimes recover, at any rate so far 

 as to be free from the silver leaf symptoms. The cause of 

 the silvery colour is the sep;iration from one another of the 

 surface cells of the leaf, so that spaces are formed which 

 are filled with air. These cause the silvery appearance, t>n 

 the same principle as the white coleur of pounded ice is 

 produced: among the particles of this, air is entangled. In 

 the case of the leaf, between the adjacent cell walls of two 

 healthy cells is a p<irtion known as the middle lamella, which 

 binds the two together: this is dissolved by the substance 

 secreted by the mycelium of the Stereum, and thus the silvery 

 apjtearance is brought about. 



The middle lamella is composed of a substance known as 

 calcium pectate, which can be destroyed by acids. This 

 suggests that, possibly the poison secreted by the fungus is 

 oxalic acid as in the case of Botrytis. If this is so, a dress- 

 ing of lime, or of calcium niti-ate, might prevent to some 



extent the damage inflicted on the leaves, since these sub- 

 stances, if absorbed by the roots and present in the water 

 carried in the wood, would neutralize the acid, with the 

 formation of calcium oxalate. 



Sttreum purpureum is a wound parasite, and its spores 

 gain an entrance only through wounds. Consequently, soft- 

 wooded varieties of the plants mentioned are usually found 

 to be more susceptible to the disease than the hard-wooded 

 varieties, since the former are more easily injured. The 

 fructifications are formed on the surface of dead branches only, 

 and it is not until this stage is reached that a diseased tree is 

 capable of infecting others in its vicinitj-. 



Another fungus which possesses this power of secreting 

 a poison is the wither-tip fungus of citrus trees, C-jlhtotri 

 chum i/lotosporioidef, found in Florida and other places. It 

 kills the young twigs and branches, which it attacks by 

 means of the poison. As in the case of Stereum, the poison 

 is also carried in the wood to the leaves, which are turned 

 yellow. 



The power possessed by some fungi, of killing parts of 

 their host situated at some distance from the actual invading 

 mycelium, may possibly furnish an explanation of the cause 

 of more than one disease at present but little understood. 



THE GREEN MUSCARDINE FUNGUS OF 

 FROG-HOPPERS. 



In the Proceetiiny^ of the Agricultural i^ocieti/ of Trini- 

 dad and Tobago, Vol. X, pp. 467 to 482, appears a second 

 short pajier by Korer on the green muscardine fungus of 

 frog-hoppers in Trinidad. The first paper by the same author 

 on this subject is referred to in the Agricultural News, 

 Vol. IX, p. 350. 



The fungus has been identified by Dr. Roland Thaxter 

 of Harvard as Metarrhi.ium anisopliae, Sorokin. It is iden- 

 tical with a species frequently found in Russia and France. 

 In the former country it attacks the cockchafer of wheat, 

 Atiisoplia austriaca; in the latter it has occurred on silk 

 worms. It has also been found on a weevil {Cleo7ius puncti- 

 ventris) that attacks sugar beets, and has been observed on 

 several other insects in different countries. 



The fungus is a somewhat peculiar one, which has been 

 given a number of different names, and has been placed in 

 many different genera, but at present is usually consigned to 

 a speciallj- created genus of its own. 



Such infection experiments as have been undertaken, 

 both in the field and in the laboratory, have led to the belief 

 that it may be possible to employ it as a means of assisting 

 in the control of the frog-hopper in Trinidad, though former 

 experiments in Russia with the cockchafer of wheat were not 

 successful on a field scale. The chief difficulties to be over- 

 come are the provision of a sufficient!)- large number of spores, 

 and their distribution throughout the fields. Rorer appears 

 to think that it will be jjossible to produce the spores in the 

 quantity required, and that their distribution can be effected 

 by either of two methods. The first means is the employ- 

 ment of a machine such as is used for distributing dry 

 insecticides and fungicides. This would blow a cloud of spores 

 into the air, and these wciuld be distributed over the field by 

 the wind. The other means is by catching a large number 

 of adults with light traps at night, inoculating them with 

 the fungus, and setting them free the next day. 



It seems probable that as the frog-hoppers are most 

 active in the rainy season — the time most favourable 

 for the growth of the fungus: this may render of consider- 

 able value the means of controlling the insects, 



