GRAVY-EYE, OR MATTERYEYE, IN POTATOES.

Pukekohe & Waiuku Times, Volume 6, Issue 282, 8 June 1917, Page 1

GRAVY-EYE, OR MATTERYEYE, IN POTATOES.

Bacterial Outbreak in Pukekohe District.

By E. Waters, Biology Section. (From " The Journal of Agriculture.) For many years the occurrence of bacterial potato-disease has been reported from various potato-growing districts throughout New Zealand, but as a rale the attacks have not been '" sufficiently widespread to occasion any great concern. In these comparatively mild forms of attack the disease has frequently not especially attracted the attention of growers, or, if so, it has in many cases been associated by them with the ordinary soft-rotting of tubers, -the appearance of which will be familiar to many. Moreover, bacterial disease of potatoes in its early stages, showing as it does little outward sign of the disorganisation within the tubers, would often pass unnoticed. In these circumstances seed-potato growers will have frequently left the obviously rotten ones on the land and gathered amongst the good seed a small or large proportion of affected sets Or, again, the seed may have been harvested before the disease had managed to make such outward manifestation of its presence. Such infested seed has undoubtedly been bought and sold tor some years, and the brownish ring appearing when the tubers are cut prior to sowing has been often wrongly attributed to the somewhat similar-looking diseases variously known as " lust," " internal brown-spot," etc. Considering how little attention is often given to the selection of seed, is is a matter of considerable surprise that certain bacterial troubles have not become widespread. It was apparently thought that the general New Z«aland conditions were unfavourable to their spread. This, howeyer, so far as one particular potato-growing district in the vicinity of Pukekohe, near Auckland, is concerned, has been shown to be incoirect In that district great damage has recently been occasioned by a bacterial disease popularly known as " gravyeye," or " matteryeye>" agreeing very closely in general characteristics with the American black-rot of potatoes (Bacillus Bolanacearum , l. In 1916 the attention of, certain Pukekohe pota:o-seed growers was attracted to damp portions of their lafid where the piants had wilted and the tubers had been damaged. Such portions, so far as they could judge, however, were discarded Thus for several years at least the disease has been distributed in the seed and has recurred in subsequent crops over an increasing area, but only in small proportions. Not until about the close of the last potato season just concluded did the trouble come to assume the form of a serious epidemic, The season was an exceptionally wet one, and accompanied by considerable heat. The conditions evidently favoured the disease, which promptly exceeded its usually limited bounds and destroyed a number of crops to the extent of from 10 to 75 per cent, according to the wetness of the land, the proportion of diseased tubers in the seed, and the time at which the resultant crops were harvested. The area affected probably exceeds 300 acres. The cost of raising this area according to local practice would be not less than £IO,OOO, while the value of its yieldjestimated at 2,400 tons, would at recent rates be £28,000. FEATURES IN PUKEKOHE METHODS AND THEIR BEARING UPON THE DISEASE. The following preliminary observations and suggestions are made after a personal examination of the affected crops and their surroundings : Seed.—Gamekeeper and Northern Star are the main varieties used, and the growers are loath to plant other than locally raised seed, largely for the following reasons: (1) The strains of these varieties in their possession are uniform and apparently true to name. (2) In this environment their superiority to heavier-cropping varieties in the matter of " blight " (Phytophthora infoatans) resistance commends them. (3) They are vigorous types, and said to be not especially susceptible to frost. (4) Gamekeeper and Northern Star seed which has been brought into the district has created distrust, owing to the mixed character of the crops it yielded or by reason of its apparent unsuitability to the different surroundings. (5) Seed of these and, in fact, of otner varieties from the South Island is by no means commended by lucal experience. Doubtless the experience of . growers is weighty evidence in favour of the high esteem in which local seed is held throughout the dis'.rict. Nevertheless it should cer tainly be called to mind that in using local seed almost exclusively for many years there is a grave danger of perpetuating and distributing potato troubles and of favouring an epidemic of any disease that once obtains a footing. Thjs has undoubtedly been one of the main contributory faetois iu the case of the present outbr< ak It was noted, for instance, that the ciops grip An in various pb.ee-, hut all from the same sewlgruW' r's output, very often yielded a similar proportion of affected plants. In one case a certain grower's sots were found, roughly, to yield 5 to 10 per cent, of affected plants, while in the

case of another line of seed the crops in almost every case yielded a very high percentage of disease. Occasionally, however, certain factors would upset these results. Thus early harvesting of the 1917 autumn crop was shown to save considerable infection in a crop the seed of which had elsewhere given very bad results. On the other hand, particularly damp patches were seen to accentuate bacterial disease in crops from seed that elsewhere had yielded only a small percentage of affected tubers.

Concerning seed obtained outside Pukekohe, there are to be seen several examples of lately introduced seed producing in diseased areas crops up to the time of writing free from contamination. In one case, moreover, in which the seed was obtained from Feilding, the crop promised to be perfectly satisfactory in its yield per acre. This instance naturally suggests that local growers might well employ such a crop for seed, or, better still, obtain as far as possible seed of the same strain at Fielding for sowing at least a portion of their land during the coming June.

While on the subject of seed, it must be strongly emphasisad that a local seed-grower would follow an exceedingly short-sighted policy if he himself sowed or sold as seed (even at high rates) any tubers known to be effected with bacterial disease. Particularly would this bo so if such seed were used in his own district; but none the less would the district's reputation suffer if tho seed were sold to outsidors. Potatoes showing the presence of the disease wore found bagged up on one or two farms, presumably for seed. Such tubers should be burnt. On the other hand, buyers of seed would be well advised (as a precautionary raeesure only) to treat all the local seed with suspicion. The earlier-harvested crops in general are reported to be much less diseased than the later ones. Purchasers should always ascertain whether or not the seed under offer was derived from an in'ectod source, and only that from reputedly clean crops should be entertained. Samples properly representing the line offered should also be rigorously examined before purchasing. The tubers should be cut in half and allowed to stand for an hour or ?o. If by then tho characteristic dark ring or dark points develop upon the cut surfaces the line should bo avoided.

The planting of whole seed has been suggested in order to make use of the skin, which is the natural means of protection for the inteiior against bacte-ia, but it would be better to cut all sets (at least of Pukekohe seed) at the stem end and ascertain whether or not they are diseased tha r i risk tho chance of using whole tubers that may be affected.

Fertilisers.— Generally speaking, Pukekohe growers are liberal in the application of aitificial fertilisers, 15 cwt. per acre not infrequently being used, and bonedust being the most favoured form. Potash, at present high in price and almost impossible to obtain, would be of great advantage when it becomes practicable to employ it, as potassic fertilisers appear to reduce the effects of bacterial diseases iu potatoes. Proprietary mixtures containing nitrogenous fertilisers should be avoided. In connection with bacterial disease, lime also is often of doubtful value.

Crop Kotations.—The practice in Pukekohe is unique, but in keeping with favourable climatic conditions of the locality. According to the weather, a spring crop is sown often about June or July, and is lifted about October or Novembor. Seed saved from this crop is regarded as highly suitable for the autumn crop, which is often sown the following December or January and gathered in in March cr April. Tlie land thereafter may bo put down to grass, or may be similarly cropped with potatoes in the succeeding year. By some the growing of onions and a few other crops is also introduced into their rotation.

The frequent cropping of potatoes on the same land is a well-known reason for the perpetuation of disease, and it would be especially inadvisable in cases where tho bacterial disease had made its appearance. The custom is to dig the crop aud gather the good tubers, leaving the noticeably bad ones on the ground. It is impracticable to recover and burn all affected parts of tho plants ; thus the land is liable to be a source of danger to subsequent potato crops for two or three years. Under dry, cool conditions ii is, of course, possible that potatoes could again immediately be grown on infected land and yield only a small proportion of damaged tubers : but, considering the cost of ( raising this crop, tho risk is too great to t..ko wherever it can possibly bo avoided. Spraying and Dipping —Bordeaux spraying for fungoid <iis- asos is regularly carried out in the di-triot. Seeing, however, that the bacteria rapidly leach internal parts, both Bordeaux squaring and clipping are of littlo avail fur this part ciihtr disease. There is some foundation for thinking that tho bacteria giiin easy access ;it those pi.■< ••.-. wheio insects liavo laid bain internal tissues, b'or this reason llm inclusion ol 1 lb to I.lib el a reliable brani) of arsenate of h a i per •">(> gallons of Bordeaux mixture voii'd i.f-s.st in the control of bit ng-ii sects, uu l imne particularly of the grub of t'ae potato moth (Geltchia operculellaj, which was noted in encumous numbers about bacterially infested plot-". Tho burning of as much of tho remains as possible ;

moulding up so as to cover'well the developing tubers ; rapid bagging and protected storage, to avoid mothinfestation, also should be continued. This is advisable if only on account of the injury of which this grub is capable, but incidentally for removing one of the suspected causes of the spread of bacteria in growing as well as in harvested potatoes. More frequent spraying and retreatment, according to the demands of wet weather, may be suggested as improvements on the practice occasionally adopted. Drainage.—Some of the potato plots received in places the drainage of adjacent higher levels, or were themselves naturally or artifically not provided with the means for quickly disposing of surplus water after heavy rains. Here the bad effects of excessive rain had continued for a longer period, and were demonstrated in the diseased condition of the crops. The planting of small but particularly wet patches in a plot might well be omitted while liability exists to the attack and spread of bacterial disease. Not always, however, did disease follow apparently wet conditions, for an excess of water is not in itself sufficient to produce disease. This crop itself, crop-remains, or plants allied to the potato must also be present; moreover, the temperature, and doubtless other physical, chemical, and physiological conditions of which at present we have little or no knowledge must all be sufficiently favourable to the organism at the time when it is ready to attack. Only in these circumstances is infection accomplished ; but when the bacteria are present each essential condition is perfect for them, then it is that au epidemic occurs. Tho organisation and practical cooperation of local growers, buyers and sellers is required, if only for the purpose of substituting suitable or harmless crop-environments for avoidable hnetena-favouring conditions. This should at least avert the recurrence of epidemics and finally control effectively or perhaps stamp out the disease throughout the district.

Harvesting—With a little practice a difference can frequently be seen at a glance between bacterially affected tops and those attacked by " blight." Tho loaves of the former wilt something liko tho latter, but tho stems discolour brown and bond over, remaining for some time moist and supplo—unlike " blighted " plants, the haulms of which commonly continue for some time straight, upright and more or loss green. With this in mind, a grower could do really good work by carefully lifting cut, bagging and burning any odd plants he noticed, thus reducing tho liability of contaminating healthy ones. A number of diseased patches were noted, suggesting contagion wbero a diseased plant had contacted healthy suirounding ones. The bacteria may also be carriod in the air from the centres of infection Tho consensus of local opinion is that tho effects of the attack this year were first observed towards the end of February or the beginning of March. This was supported by the fact that, as far as could bo ascertained, the disease was not noticed in crops gathered about that time—the later ones suffering. The spring crops should certainly bo watched, despite the popular belief in their comparative immunity ; and from a little before the above time onward the autumn crops should be closely ob erved. If the elimination of odd plauts becomes too laborious aud fails to arrest the disease, then the lifting of them all, even if a little on the green side, may save a considerable reduction iu the tofal yield. Moisture on the tubers when bagged and dampness in the store, like excessive soil-water, favour matteryeye. When possible, the sowing of spring and autumn crops at dates enabling the latter to be early harvested may prove to be a good precaution. In some cases this has been done unwittingly with good results