YELLOW-LEAF DISEASE IN PHORMIUM TENAX.

Manawatu Herald, Volume XLI, Issue 2022, 30 August 1919, Page 1

YELLOW-LEAF DISEASE IN PHORMIUM TENAX.

A RECENT INVESTIGATION,

(N.Z. Journal of Agriculture l .)

During the last year or two the occurrence and spread of the socalled yellow-leaf disease in New Zealand flax (phonniura tenax) has caused grave concern for the flaxmilling industry. Apart from attention given to the matter by the Department of Agriculture, the New Zealand Faxmillers’ Association commissioned Dr. L. Cockayne, E.R.S., to make a special investi-' gallon of the disease, possible methods of control, etc. Dr. Cockayne has made two reports on his work to the association.' The first re-

port, prepared in May of last year, was chiefly of an interim character; the second one, of recent date, closes the investigation for the time being. It may be noted here that the occurrence of yellow-leaf in the principal flax areas has very markedly diminished during the past few months, the improvement much exceeding what might be expected normally in autumn and winter. Hence the position is considerably eased from the economic aspect. The following extract from Dr. Cockayne’s first report describes the disease and discusses related factors: — NATURE AND PROGRESS OE THE DISEASE.

Flax-plants ■ suffering from yel-low-leaf are apparently to lie recogni.sod at a glance by the presence of more or less bright-yellow leaves, which contrast distinctly with the ordinary healthy green leaves. The word.“apparently” is used advisedly, since healthy plants have frequently a few yellow leaves, such being leaves dying naturally. The yellowing of the leaf in an affected plant is in fact but a secondary symptom, the cause of which is that the roots supplying the plant with water have decayed, if (he upper half of a leaf of a healthy plant be so bent that its water-supply is cut off it finally assumes exactly the same bright-yellow colour as seen in plants affected by yellow-leaf. t

The real trouble is (he decaying of the roots, which if new roots cannot lie put forth in sufficient quantity will quickly lead to (he death of the plant —first of all the leaves turning yellow and then becoming brown and withered, while finally the stem rootstock becomes rotten.

There appears to be every grudation between much-stunted moribund plants and those where one cannot deeide whether thoy are truly alTeeted at all. Many plants appear splendidly healthy notwithstanding the presence of more or less typical /yellow leaves, In 'other eases yellow leaves are numerous and the plants obviously unhealthy, c or plants may have been s,o bad that most of the fans have died out, and yet there may be one or two perfectly healthy fans with long- green leaves; or, again, a whole flax-bush-may-have completely died out. There are apparently quite heallhy bushes, however, which contain many erect dead leaves that almost certainly arc yellow leaves turned brown. As there are many llax-bushes of this kind it is almost certain that they have been badly affected and have recovered. Recovery after yellowleaf is believed in by all whom I have questioned on the subject.

Where a fan is badly affected it can be readily pulled out of the ground. Such a fan may show the outermost leaves brown and dried up, the next leaves quite yellow, the next more or less yellow from the apex downwards or on the margins, but the young centre-leaf of the fan will bo green. There will be many quite rotten roots, but a few short roots an inch or two long will have been developed, and if these are able to lengthen and -branch the plant may be able to exist, but for a considerable time its growth will be extremely slow. From the above it follows that even when yellow-leaf does not immediately cause death it leads in many eases, should the plant eventually recover, to a stunted growth which forbids for some years the leaf reaching a size fit for the stripper.

According'’ to those conversant with badly affected areas, yellowleaf appears all of a sudden and. develops rapidly. Thus Mr W. White, of Tane, showed me an area where almost every plant was affected which had been quite healthy twelve months before. Also I was shown a ‘badly affected area, cut, twelve months before, which had only -been diseased for the last three months. Other examples could be cited. In all cases recently cut affected tlax shows no trace of yellow-leaf on its new leaves. This does not prove the plants to have recovered; rather is the healthy growth correlated with the fact that the short roots already mentioned are able • to supply sufficient water for the

needs of the reduced leaf-surface as a whole, while., the loss of water by evaporation from the smaller area of leaf-surface is much less than had been the case in that of four-year-old plants at the time of cutting. The following are extracts from Dr. Cockayne’s later report: — GENERAL. This report is concerned chiefly with the behaviour of a number of carefully chosen plants, growing naturally under more or less different conditions, especially of moisture in the soil, in the flax areas of Miranui and Ashlea (Manawatu). Plants of every degree of health were selected for observation from such as were extremely healthy and vigorous to those which were stunted and almost dying. The plants

were labelled during the concluding days of February and the beginning of March, 1918, and notes were taken as to their condition. Subsequently the marked plants were examined at intervals of not less than three months, so that changes in their condition could be ascertained.

In addition to examining the marked plants, some attention was paid to the general condition of the flax while certain of these not examined by mo previously were visited. Thanks also to an important investigation I am carrying out for the Department of Agriculture, I have travelled extensively through the South Island and had an opportunity of seeing phormimu tenax growing in many localities and under diverse surroundings.

It must not be forgotten that this report, so far as it concerns the marked plants, deals only with experiences of fourteen months, a lime altogether 100 brief to enable any definite statements to be made; therefore the conclusions at the end of the report cannot be looked upon as final. Nor, have I been concerned with the diesase as a disease; my investigations have been directed rather towards attempting to ascertain the conditions of soil and climate favouring or restraining yellow-leaf, and also by means of marked plants to gain some fairly accurate knowledge as to the progress of the disease during a period of fourteen months.

In my former report Hie View was pul for 111 Hial yelluw-leaf was not clue either to a fungoid or a baeterial disease, hut that it was ‘‘caused Ity the roots of the (lax being exposed in winter 'to an excess ol stagnant water, and in summer Id too great dryness." Moreover, I stated that, “even ft it is eventually proved that yellow-leaf is caused by a fungus or a bacterium, a faulty

environment for the flax-plant may probably be an important factor in inducing the disease.” Since these statements were put forth the facts dealt with under the next head make it abundantly clear that these statements must be considerably modilied. ' FURTHER FACTS REGARDING THE ENVIRONMENT OF AFFECTED PLANTS AND THE CAUSES OF THE YELLOWLEAP. Daring the spring and early summer of 1918-19 yellow-leaf so rapidly increased imthe Manawatu flax areas that there could be no longer any doubt as to the affection being an infectious disease of some kind or other, which'most probably would be either fungoid or bacterial. This statement is strongly supported by the fact that throughout the South Island, with hardly an • exception, there is more or less yel-low-leaf. Nor are the diseased plants confined to milling areas, or even to swamps. On the contrary, they occur amongst plants of dry stations at all altitudes up to the altitudinal limit of the plant; indeed, there is possibly no situation where the flax-plant can live secure. Notwithstanding what is said m the lasi paragraph, flax-plants of a wet station are apparently far more liable to become affected than are those of drier positions. Also, I. do not know whether plants growing with their roots in pure running water are ever attacked. The flax area, of Mr Brown, at Waikanae, is an instructive case. This area had entirely escaped the trouble until about the month of September, 1918, when it broke mu. in the wettest part of the area and spread rapidly. In December, 1918, I paid a visit to this swamp. At that time but feAV plants in that splendid flax where the soil is comparatively dry, near the high road,, were affected—so few, indeed, that hardly any yellow-leaf was apparent when walking along the load. In a wet hollow near the sandhills the position of affairs was strikingly different. There, in places, was a veritable epidemic, perhaps onethird of the-plants being diseased. In company with Air Brown I also visited that area of magnificent flax (Iladlield’s) between Waikanae and Paraparaumu, where we noted one diseased plant, and. that very slightly affected. As a general rule I have seen very little badly diseased flax when the plants grew naturally under dry conditions. Disease there may be, it: is true, but generally it is negligible. As for the cause of the disease, a fungus has been isolated by Mr R. Waters, in the laboratory of the Biologist to the Department of Agriculture, Weraroa, and pure cultures prepared for inoculation experiments. Such have to he conducted with the greatest W, and, of necessity, considerable time must elapse before definite conclusions can he reached. Also, the fungus dealt with may not he the one causing the disease; nor must it lie forgotten that when the actual organism causing the disease is discovered, it it be fungoid or bacterial, science has yet no remedy for such a trouble.’ The plants to be cured are m.’l in the orchards, gardens, or even fields, where spraying is practicable, hut (hey occur in dense masses inf'-gd with dying leaves, tall { »- ri iss it mav bo, or other weeds of flax areas. Nor is it foliage amenable to spraying which is attacked, but the roots far-spreading beneath the soil. The report then deals with the general progress of the disease as shown l.v the marked plants, gives detailed results of the final examination of those plants, and recounts several specific eases of remarkable recovery among them. A history is given of a small flax area from the time of eniting up to a period of fourteen months; .also the history ol a. number of marked plants of a badly diseased area, from the lime of cutting up to a period of fourteen and fifteen months. The report proceeds as follows: ■ THE QUESTION Off RACES Off PHORMIbM TENAX WHICH AiRE PROOF AGAINST YELLOW-LEA ff. When it is considered that out of 147 healthy plants more than one-half never took the disease for a period of considerably more than fourteen months, although plants on all sides of them were affected, the question of their immunity from the disease at once arises. These plants were quite healthy at the time of marking; many gave every proof that they had been healthy for months. Can such immunity be accidental? The answer- to this question, bearing in mind the teachings of science, must- be in the negative. It stands out clearly, then, that in some of these healthy plants there is the best material available at the present time for raising a race incapable of contracting yellow-leaf.-Such a race, once segregated', would be of great monetary value. Nor does the work of producing such a race appear to me of extraordinary difficulty. Such v ork, however, is not suited for a private individual; there is no patent law with regard to plants. Such a work should be undertaken either by the State or by such a body as the Flaxmillers’ Association. But the latter might well hesitate iirview of the uncertainty still existing- regarding the spread of yellow-leaf, the favourable opinion of this report notwithstanding. If the yellow-leaf, however, prov-' es to be not so hurtful as it once promised to be, the. quest for a race

of flax which Could not take the disease would be a legitimate cqmruer*"cial venture for the association. Undoubtedly, the future of the flax industry lies partly in increasing the areas by planting. For this purpose, as I pointed out in my last report, much poorer ground than msed at present would suffice. . SUMMARY AND GENERAL CONCLUSIONS. (1.) This report gives an account of the behaviour of certain marked flax-plants in the Asblea and Miranui flax areas during a period of fourteen months. This behaviour is considered a reliable index of the progress of events so far as yellow-leaf is concerned in the above areas for the period stated. (2.) Although some idea of the progress of the disease may be gained from the observations mentioned in (1), yet too much reliance must not be placed upon them as an indication of ivjiat may happen in the future. (3.) My former statement that yellow'-loaf is not an infectious disease is repudiated, and the opinion is advanced that it is an infectious disease probably due to fungoid or bacterial attack. (4.) My former statement that yellow-leaf is favoured by stagnant water is upheld, together with the obvious conclusion that the disease would not he nearly so had were the swamps better drained in winter and kept w etter in summer. (5.) The conclusions of (4) are supported by the distribution of yellow’-leaf in the Manawatu, at Waikanae, and near Plimmerton, in the North Island, and throughout the South Island generally, this latter knowledge being the outcome of seeing the plant under all the conditions it can tolerate. ((i.) The periodical examination of the marked plants has shown—(a) that .a great improvement is taking place at the present time; (b) that there is a great improvement in autumn and Winter, which is followed fly deterioration in spring and summer, at which latter season the flax is at its worst; (e) that a large percentage of healthy plants can remain healthy even when in close proximity to diseased plants; (d) that a flax-hush itself can 1)0 in perfect health in one part and dying out in another part, and that siicli a bush may eventually make most- excellent flax; (e) that when a portion of a diseased plant which by extension of the rootstock has gained a piece of level ground it almost always becomes remarkably healthy and rapidly makes good flax; (f) that diseased plants frequently recover, and may become quite as good as plants which have never been affected; (g) that groat fluctuations may occur during? the year, recovery being followed by disease, (his again by recovery, and vice versa; (h) that even during, (he Avorst period of the disease more originally healthy plants remained healthy than became diseased; (i) that a large percentage of healthy phials remained healthy all the lime ; -(,j) that a considerable percentage of diseased plants not merely recovered,.lint became equal to the best unaffected plants; (k) (hat very few plants die outright; (1) that a small amount of disease may he beneficial, since the removal of a few leaves leads to belter development of. (he remainder; (m) that (lie plants of an area cut when badly diseased may remain virtually free from true yellow-leaf symptoms for over a year, and eventually grow vigorously; (n) that even if

a general recovery has set in it is most likely that for some yearn there will he seasonal fluctuations; (o) that there are probably plants not liable to the disease, and that from some of the marked plants material is to hand for the selection of a race which cannot take the disease; (p) that under certain circumstances it would ho a fair business proposition for the Flaxmillers’ Association lo spend money on a race as mentioned in (o), since ills probable Unit it niffy be profitable to ctxoud the flax areas by planting.