BUST IN CROP AND PASTURE.

Otago Witness, Issue 2356, 20 April 1899, Page 15

BUST IN CROP AND PASTURE.

A North Island correspondent complains fcf the recurring injury caused to grass in j the pastoral districts by rust, and inquires whether anything can be done to oheck its ravages. "We, have submitted. the question to Mr. T,.-W. jKirk,' F.L..5., Government Biologist, who kindly. replies: — " Your post card and ! specimen to hand re' grass attacked by rußt, from which, grain, grass and other graroineae suffei bo much. ■Unfortunately there is at present no means icnown for controlling this disease in past- .■ tures, the cost of applying the remedies being too great. If you will refer to page 53 | of 1894 report of this department you will j find a precis of the information available on : - this subject." # j We reprint below the portion of the report j alluded to by Mr Kirk:— RUST : (PUCCINIA GRAMMINIA). This fungus has been very prevalent in many parts" of the colony, "and has caused considerable damage to orops and pasture. It is a small parasitic fungus, common on many grasses, as well as on wheat and other grain crope. Its injurious elect* have been known in Europe for centuries.

Bust and mildew are merely different Btages in the development of the same organism. This fungus does not complete the cycle of existence on one species of plant, but passes from one host to a, different host in the various stages of development. •

.The yellow spots so frequently seen on barberry, in Europe, may be regarded ar the first stage. These spot* grow, burst the surface of the leaf, and form small red cups called jEcidium cupß; these contain innumerable spores which, when liberated, aro carried by the wind in all directions. Many fall on grain or grass plants, and if the weather be moist they soon germinate ; their germ tubes or minute rootlets enter the elomata or openings in the surface of the leaf and thence pass into the tissues of the plant. The parasites now grow rapidly, and convert large portions of the sap of the plant to their own übc Long, narrow, reddish-yel-low blotches soon appear on the host. This is another stage of the fungus. These red patches are called uredospores. They presently burst, the numerous spores are disengaged, and are scattered by the wind, passing animals, insects, oi other agencies, and are deposited On other plants of wheat, oats, rye, or certain grasses, where, under favourable circumstances, they germinate in a few hours. There is sometimes a succession of generations of this uredo form of the fungus in a season.

I now quote from Mr Whitehead's admir«ble report on the rust of wheat and other • gramineae : " Aftei a time a change comes in the colour of the spores that are produced. They j become dark-brown, and finally black. The son also turn to black-brown, and the spores then are termed teleutospores, or the final spores. This change happens as the host plants ripen, and is caußed by the process of maturing; and it is at this stage that the •fungus does tho m_Oßt mischief, oi it may evei be said its chief mischief, as the host plants require all their starch for forming seed at this period. It is well known that parasitic fungi cannot form starch like other ulants that have chlorophyll, and mus' therefore get this food from theii host plants. If there r much moisture at this time, favouring th© development of the fungue, it frequently happens that the' straw is thickly covered with the thick pustules, and the grains of corn are shrivelled because of the abstraction of the starch necessary to make them perfect. As a Tule the uredo stage, with its reddish-yellow spores, is: not particularly harmful to corn plants, unless the season is exceptionally favourable to its development. To return to tlic peculiar-shaped black pustules of the teleutospore stage : if a section of infected straw be examined, it is. found that Ihe tissues of the cells have been completely broken down by the action of the myceliun? of the fungus, and the teleutospores can be seen upon their hyphae. These teleutospores ara quite different in shape from the uredo spores, being shaped like a club, and dark-brown or blackish in , jetour. They are divided in the middle by a

wall or partition, so that they form two cells.'.' These teleutospores may be called the resting-spore stage of this fungus, for in this stage they pass the winter on infected straw 01 grass. "With the approach of mild weather these teleutospores, which have lain dormant during the winter, again show signs of life, and produce another crop of spores, which in England germinate on the leaves of the barberry, and so complete the cycle. The causes of these attacks are largely climatic, and therefore almost beyond control. As already stated, wet mild weather is favourable to the propagation of these fungus pests, but a bright sunny spell checks the development of the parasite, and gives the host a chance to regain its strength. Many mechanical applications have been devised to lessen the attacks of this pest, and some so-called infallible remedies pub-

lished; but bo far they have not proved | capable of general application. Extensive experiments are being conducted in Australia and other countries, with a view to the discovery of some cheap and effective means of restricting the ravages of rust, and of producing a strain of rust-proof wheat. 1/ a really rust-proof variety of wheat could be discovered or produced, it would certainly be a direct boon to grain-growerE and an indirect one to pasfcoraliste, by reducing the number of host plants, and so lessening the quantity of spores likely to be carried to the pastures. It has been proved that eavly sown wheat frequently escapes attack altogether, or at any rate is much less damaged than that sown latei. The obvious reason is that the plants have had time to become well established, and are therefore strong and healthy before the fungi develop, and they are consequently better able to resist invasion. Much might be done by burning rusted straw, thus destroying the resting spores, and so reducing the chances of a bad attack the following season. An effort should also be made to ascertain what plant or plants in this hemisphere take the place occupied at Home by the barberry. For it must be manifest that if the host of ( this satge can be found and destroyed the pe3t would be kept in check — that is, provided this stage ir absolutely necessary to its existence, which the experience of Australia and New Zealand seems to throw some doubt xipon.