TAKE-ALL DISEASE IN WHEAT.

New Zealand Journal of Agriculture, Volume XX, Issue 3, 20 March 1920, Page 137

TAKE -ALL DISEASE IN WHEAT.

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R. WATERS,

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THE often disastrous effect of the disease here dealt with upon the wheatfields of certain of the Australian States has well merited the adoption there of the name “ take-all.” In England, France, and Germany it has been sufficiently serious to demand the careful attention of those interested in the conservation of wheat. The disease was reported in 1916 as not then known to be prevalent in the United States of America ; since then, however, it has been reported in fresh localities there. So far as New Zealand is concerned, the descriptions of experienced growers indicate that takeall has been present for many years. Although this season traces of it have been seen in widely separated portions of the Canterbury District, and the damage from its attack has been very considerable in a few isolated cases, it has not yet become particularly serious. Nevertheless, the future possibilities arising from the neglect of this affection are such as to call for the immediate adoption of all available means of control.

CAUSE OF THE DISEASE.

The take-all condition in New Zealand is characterized by the presence amongst typically affected wheat of a microscopic fungus comparable to, but in the incipient stages less evident than, the mould frequently, growing upon stale bread. Under favourable environmental conditions, particularly those of warmth and dampness combined, this fungus is capable of vigorous growth upon wheat, of the production of spores (too small to be seen by the naked eye), and of spreading to other wheat-plants in the immediate vicinity. The scientific name of the fungus is Ophiobolus graminis Sacc., the characteristic fruiting or sporing structures of which have recently been definitely identified in New Zealand. (Figs. I, 2, 3.) Other fungi, some of which have not yet been reported in New Zealand, are said to produce like effects abroad, and in some parts of the world it has not yet been possible to attribute take-all to any specific organism. Seeing, however, that Ophiobolus is the fungus commonly associated with the take-all condition in New Zealand, and that it is widely and definitely accepted as the cause of take-all elsewhere, it is presumed that this fungus is parasitic, until such , time as definite inoculation experiments shall have proved, or disproved its pathogenicity in the Dominion. - . ' . ? / .

EFFECTS.

At various stages in the growth of wheat the fungus penetrates, discolours, and disorganizes the tissues of the roots and of the culms at ground-level. At these parts, late in the season, it produces a blackish weft of mould-like growth, easily seen by . the naked eye. (This “ mould ” remains on the stubble after harvest, giving rise to the spores that may infect succeeding wheat crops.) The fungus appears to hinder the flow of sap to the parts above, to arrest the growth, and to finally^ result in the death of the roots, culms, leaves, and ears, the last three bleaching a dull ashy white in the sun. Later the heads and even the rest of such plants may become bespattered as if with soot - the effect of another fungus common on dead wheat. In all cases the grains are diminutive, often entirely useless. 7 Affected plants occur commonly in roughly circular or oval patches. The patches are up to several yards in diameter, and consist, at about the end of January., of a thin crop of stunted -white or sooty-looking plants easily pulled out of the ground. The surrounding healthy crop is taller and of a bright-yellow colour in the straw. Again, affected and healthy plants may be intermixed and of similar height, the colour of the former readily distinguishing them. .

SIMILAR EFFECTS FROM OTHER CAUSES.

The effects upon' a wheat crop of “ creeping ” grasses, such as florin (Agrostis spp.), twitch or couch (Agropyron repens), and creeping-fog (Holcus mollis), might possibly be confused with the general appearance of take-all injury. . In many districts these grasses may be seen spreading thickly through the ground in more or less circular patches in which the wheat becomes stunted, the head being much smaller than usual. Unlike take-all patches, which consist of dead plants bleached white, the wheat in these weed-ridden patches at the end of last January was

usually green in the culm, leaves, and head, and grains of moderate size were formed. Wheat thus affected commonly remains greener than the surrounding unaffected crop, which at the same time will have more or less turned a bright yellow. This-type of damage seems just as common at present as that caused by take-all. Again, stunted wheat patches to be distinguished from take-all are to be found in depressions waterlogged after sowing, and on places said to be affected by grass-grub (Odontria zealandica). In all cases the occurrence of the dark “ mould ” at the base of the culm —particularly between the leaf-sheath and the culmdistinguishes towards the end of. the season the take-all condition.

PERPETUATION AND SPREAD OF THE DISEASE.

No reliable information is at hand as to when and how take-all was introduced into New Zealand, but there seems little doubt that it has been in the Dominion for a number of years. However profitable or unprofitable it may be, it is well known that in the absence of this fungus healthy wheat has frequently been produced on the same land for many years in succession. With weather conditions unfavourable to the fungus comparatively healthy wheat might even be raised on land 1 previously carrying an infected crop. The presence, however, of but a small proportion of infected plants means that the fungus will remain in the field on the stubble after harvest. Here it will eventually produce its spores, any subsequent cultivation or trampling by stock serving as a means of distributing the disease—at least, within the same paddock. Hence, with moisture and temperature suitable to the fungus, a succeeding wheat crop would be -much more affected than the previous one — fact, might be a failure. All badly diseased plots recently examined in Canterbury had been preceded by one or more wheat crops, among which in most cases growers could recollect having observed the same but less pronounced symptoms of the disease. No instance could be found of the rapid spread of take-all from crop to crop through.the air like rust — though to a comparatively very small extent this manner of spreading is not inconceivable ; in fact, seed sown on uninfected land was seen to produce an unaffected crop even in places where such land adjoined an area carrying a badly infected crop. On the other hand, the planting of wheat on previously infected land resulted in the most serious damage that was met with, and, in my opinion, the perpetuation of the parasite is mainly due to this practice in dealing with infected areas. It is difficult to say exactly how the fungus is transferred to previously uninfected land. Stock or the wind possibly carry infected fragments from one paddock to another; but, whatever the means may be, there is no doubt that certain plants other than wheat are capable of “ nursing ” the fungus should it be carried to areas that have never been devoted to this particular crop.

SUSCEPTIBILITY OF OTHER SPECIES.

The extent of information under this head is not very wide or conclusive. The following plants other than wheat are recorded as

(A) Magnified somewhat over 60 diameters. Shows protruding through a portion of an affected leaf-sheath the necks of unripe perithecia and those of ripe perithecia, some expelling coils, and others masses of mucilaginous matter., ■

(B) More highly magnified. Showing a cross-section through an unripe perithecium. The body of the perithecium is immersed in the tissues of the leaf-sheath; about it, particularly at its base, are the threads of the fungus from which it arose, and within it is the mucilaginous matter, together with the asci or spore sacs, which later will be expelled through the neck that is shown protruding through the outermost tissues of the leaf-sheath.

(C) A similar cross-section, showing a coil of mucilaginous matter carrying the asci through the neck of a ripe perithecium under comparatively dry conditions.

(D) A similar cross-section, showing a mass of mucilaginous matter bearing asci similarly expelled, but under moister atmospheric conditions, which soften the mucilage and prevent coil-formation. Much moisture dissolves the mucilage completely, distributing and liberating the asci.

(E) Very highly magnified. Shows an ascus separated from a mucilaginous coil by water. Within the ascus are the long filiform or threadlike spores, and at the top of the ascus the aperture through which the spores escape at maturity.

(F) Very highly magnified. Showing two spores which have escaped from an ascus. These are the reproductive bodies of the fungus Ophiobolus graminis. [Diagrams by E. H. Atkinson.

susceptible to. the disease, and therefore as capable of perpetuating the fungus in infected land or of harbouring it on areas not devoted to wheat : Barley (Hordeum sativum) ; ' rye (Secale cereale') ; barleygrass (Hordeum murinum) ;. brome-grass (Bvomus sterilis) ; giant twitch, couch-grass, or spear-grass (Agropyron evens'). - . Red wheats, though not immune, are quoted as the most resistant kinds, while the earlier varieties are spoken of as the more susceptible.

METHODS OF CONTROL.

Various methods of combating take-all have been suggested : — i. If by cutting the stubble longer, and, if necessary, by rolling it, a fire could be run over the ground a considerable proportion of the fungus and its spores would be destroyed. Infected land so treated would be much safer, but not entirely safe, for a succeeding wheat crop. Where there is no alternative than to grow another wheat crop, on infected land this course might be adopted, together with late sowing,, so as to avoid wet conditions, which favour the fungus. Deeper tillage would also assist in avoiding excessive soil-moisture. Wheat following a . badly diseased crop is, however, a very doubtful proposition.

2. For the treatment of a few isolated patches in a paddock good results are reported from the recommendations of N. A. Cobb, of New South Wales, briefly as follows : Before harvest, when the disease is. showing, mark the patches with stakes. After the harvest and before the following ploughing apply lime to these patches, at the rate of at least . i ton per acre. As the disease is associated with excessive water in the soil the levelling-off of depressions in the ground and anything that can be done to improve the soil-drainage, such as deeper tillage, will be beneficial. ■ .

3. In considering a general line of treatment for larger areas the following points may be stated : —•

(a.) Seeing that the fungus is retained on the land after harvest,, and that its. complete destruction by fire or by the application of a chemical compound may be impracticable, such, methods as . these should in general be employed, not as in themselves sufficient, but rather assubsidiary to other methods of control. Burning, where possible, in preparation for further treatment would therefore be a sound practice.

(5.) As, moreover, the fungus cannot be immediately destroyed, in the soil, then the subsequent unhindered growth of wheat, barley, rye, barley-grass, brome-grass, or giant twitch would with suitablemoisture and warmth probably serve to maintain, if not increase, the infection of the land. Susceptible plants must therefore be rigorously suppressed by cultivation or smothering, and any tendency to waterlogging in the soil be anticipated by drainage or tillage.

(c.) As the parasite apparently depends for its existence upon the presence of a susceptible plant the complete destruction of such plants by fallowing long enough would eventually cause the fungus to perish for lack of sustenance. The cost of fallowing, however, would in most cases be prohibitive ; the alternative, therefore, is a rotation of crops.

(di) In the choice of a rotation any crop not known to be attacked may be selected, but especial preference given, where practicable, tooats and rape on account of their attributed immunity.

(g.) On land difficult to rid of twitch or other susceptible plants, prior to the establishment of temporary pasture, oats, rape, or other crop not subsequently cultivated, the use of a smothering - crop, such as autumn-sown oats and tares, is suggested.

(/.) Wheat would wisely be avoided in the rotation for at least two years.

(g.) There is a possibility of transferring the disease by means of stock, but several most valuable examples of healthy and badly diseased paddocks actually adjoining clearly show that healthy wheat can be produced on uninfected land even when it is adjacent to a badly infected paddock. ,

(A.) There is no positive evidence that the disease has been conveyed in the hairs of seed-wheat, nevertheless it would certainly be advisable to secure all seed from an undoubtedly healthy crop.

(?.) Straw stacks from badly infected areas are better destroyed by fire, more especially if there is no definite use for them.