CLUB-ROOT.

Otago Witness, Issue 3215, 27 October 1915, Page 12

CLUB-ROOT.

Club root has been common enough in various parts of New Zealand amongst swede crops, particularly during the past season. Mr A. H. Cccicayne, of the Department of Agriculture, in writing upon this subject, says, inter alia: “ihe organism caus.ng this disease is not a true fungus, but is placed in a separate group known as ‘ the slime fungi.’ ffhis group of extremely lowly-organised life possesses certain characters that superficially resemble those characteristic of the true fungi. On the other hand, many of the features of their life history so closely approximate to those of certain of the lower animals that biologists are even yet in doubt as to which great kingdom of organisms—plant or aniin'd“~the slime fungi should be classed in. Ihe life-history of club-root was first described by the Russian plant pathologist VVoronin in the year 1878, and he named the causative organism ‘Plasmodiophora brassicas.’ On examining an affected, but not yet decayed, root many large cells will be seen containing a brownish mass of semi-fluid consistency. These masses, which are not enclosed by any special envelope, are capable of movement, and assume various shapes. They feed on the food materials elaborated by the plant, and their presence causes a great development of abnormal tissue that results in the knots and swellings so characteristic of the disease. After a certain time the brownish semifluid mass ((called a ‘plasmodium’) within the giant cells breaks up into an immense number of spherical sports, each encased in a thick protective envelope. The diseased portions now rot away, and the spores arc liberated in the soil. After a period of rest the wall of the spore splits, and a naked mass of protoplasm emerges and swims about in ttie soil-water. Tuis mass of protoplasm, termed a ‘swarmspore,’ is apparently able to penetrate the more delicate parts of the root, probably by way of the root-hairs, and finally comes to rest in a normal cell. Enlargements of the invaded root then occurs. It is thus seen that in order for a crop to become infected it is necessary for spores to be present in the ground. These spores are apparently capable of retaining their vitality for many years. —Plants Affected.— “Club-root attacks only plants belonging to the turnip family (Cruciferse), and in New Zealand lias been reported as occurring on the following cultivated members of the group;—Cabbage, cauliflower, Brussels sprouts, rape, mustard, swede turnip, soft turnip, radish, and wallflower. The disease is also often found on the roots of certain weeds belonging to the same family, amongst which may be esiDecially mentioned Shepherd’s purse (Capsella bursa-pastoris), wild turnip (Brassica campestris), American cress (Barbarea praecox), hedge-mustard (Sisymbrium oflicinate), and pepperwort (Lopidium niderale). It is probable that certain other cruciferous weeds assist in the perpetuation of the disease in New Zealand. —The Effect of Acid Soils.— “A very noticeable feature with regard to club-root is the fact that its prevalence as a serious disease did not take place in Europe until the modern use of artificial fertilisers became general. .Since that period it has been abundantly proved that the use of artificial manures of an acid nature increases .the ravages of club-root. It has been shown that acid-soil conditions are far more favourable for the development of club-root than are those of neutral or alkaline soils. Tin's fact is of the greatest importance, as on it rests the whole principle of controlling club-root by chemical means. -—Methods of Control.— “In the control of club-root it is extremely important to note that the contamination of the soil over large areas from comparatively small centres of infection can easily take place. So far as field crops are concerned, these are generally fed off in situ, and stock feeding on diseased crops carry away large numbers of the spores on their feet when driven on to fresh fields. As for spores in faecal matter, it is doubtful if they retain their vitality after passing through an animal. For my part, I am convinced that the greater part of soilcontamination takes place through the stock feeding on disease crops and being transferred to fresh ground. It would appear to be a good practice to try and limit this method of spread as much as possible, and not to transfer stock that have been feeding on diseased crops to land that will be required for turnip or swede growing for some years at least. I know that this will not be practicable in many cases, but whenever such a procedure is feasible it should be carried out. Paddocks that have carried a diseased crop should bo limed if possible, and if this cannot be done the area should not be sown with a cruciferous crop for at least three years. Any crop that is not a cruciferous one can be grown with perfect safety, so that, excluding the growing of the turnip family on affected naddocks need not seriously affect the rotation practised. It has also been shown that affected land sown to pasture in which clover, especially red clover, plays an important part appears to become free from the disease more quickly than when little clover is used. From this is indicated the fact that leguminous crops should be grown on affected ground. “Liming is universally looked upon as the greatest safeguard that can bo secured against the attacks of club-root. Lime in the carbonate state (ground limestone) ia now generally preferred to burnt lime; but the dressing necessary for badly-affected land is large, as much as seven tons per acre having been advocated; smaller amounts of from one and a-half tons to three tons, however, have given good results in many parts of the world. It la important to remember that in regions

whore club-root is prevalent the liming of the ground should be done in the autumn previous to the sowing of the seed; the beat results, in fact, have been secured with n heavy liming two seasons before a cruciferous crop was grown The fact that acid artificial fertilisers appear to greatly increase the development of club-root should not be overlooked, and whenever it is feasible basic manures should be substi tuted. The effects of basic slag in restraining the excessive development of club-root in many parts of the North Island has been most marked —Comparative Immunity Among Swede Varieties. — “So far as swedes are concerned, there appears to be a great variation in the comparative immunity of certain varieties over others. It is generally stated that Superlative is almost immune, and certainly many crops of this variety have escaped while others in the immediate vicinity have become seriously affected. Other varieties that often appear to be extremely resistant to attack are Magnum Bonurn, John Bull, Elephant, and its doss ally Crimson King. But there does not seem to be any variety that is completely immune from attack, and one variety that more or less escapes ono season may in the next become seriously affected. This has been particularly noticeable with regard to Superlative; but in this case probably the forms now susceptible are different strains from those previously resistant.”