COLLAR-ROT OF PEAS.

New Zealand Journal of Agriculture, Volume XXX, Issue 4, 20 April 1925, Page 250

COLLAR-ROT OF PEAS.

INCIDENCE OF THE DISEASE

W. D. REID,

Biological Laboratory, Wellington

During the past four or five years a disease — now locally known as collar-rot — become common in the pea crops of New Zealand,, but- apparently it was not until the 1924-25 season that it reached sufficient importance to warrant inquiry from seed merchants and growers. Evidence supplied by farmers indicates that the extent of diseased crops fluctuates from year to year, but the amount of damage which occurs during any season shows the necessity for a thorough investigation into the cause. Although the occurrence, of- an unhealthy condition of some crops has been known for some years, it was not until October, 1924, after an examination .of a Wellington-grown crop of garden-peas which was suspected of being diseased; that a preliminary investigation was begun. Later, in November, specimens of affected plants were received from Marlborough and the Hutt Valley (Wellington), and inspection of

the crops grown for the vegetable-market and the seed trade shows that in New Zealand the disease is widespread. From these samples and from the crops examined it is known that the disease is present in the districts of Dunedin, north and south Canterbury, Marlborough, Nelson, and the- Hutt Valley. This wide distribution means a considerable variation of soil and climatic conditions, but • under no circumstances has the trouble been totally absent, although certain factors, which will be discussed in a subsequent paper, tend to lessen or increase the virulence of the disease. Similar diseased crops have occurred in other countries, particularly “ stem-blight of peas ” in the United States (i), but the literature available does not indicate clearly either the distribution or the importance of the disease. SURVEY OF PEA-CROP AREAS. In the early part of the season —October and November last survey of some of the pea-crop areas was undertaken, particular attention being paid to the crops of Marlborough, one of the important pea-grow T districts in New Zealand. In this area and Canterbury the bulk of the crops are for seed ’ purposes, whereas the crops of Dunedin, Nelson, and the Hutt Valley are mainly grown for the vegetable-market; but in all cases the early symptoms of the disease are similar, notwithstanding differences in soil, climate, and methods of sowing. The first signs of any variation from the normal growth is a yellowing of the culm, a condition which is considered by the growers as being due to excessive soil-moisture. This diseased appearance may occur at any time during the life of the plant, but it is most noticeable and more prevalent in the early spring, when the plant has attained to a height of 3 in. to 8 in. Although heavy and continuous rain or drought may give rise to this sickly nature of the crop, the condition, if disease is present, always persists after a return to normal soil-moisture content has been attained. Death of 'the plant does not necessarily occur, but the growth is seriously retarded, so much so in some cases that the total seasonal growth does not exceed 6 in. In some crops all the plants may be badly affected, while in others the seriously diseased plants may be confined to large or small areas throughout the. fields but in all the crops examined, comprising many examples of apparently healthy and diseased crops of the previously mentioned districts, the disease has been present. The extent of the disease . may vary in effect from almost total destruction of the crop, as far as ultimate seed-yield is concerned, to an amount which is only noticeable by a detailed examination. Inspection of the spring growth of the yellowed pea-plants showed that the. roots and basal portion of the stems were decayed, a feature which has given cause for the local name collar-rot. Such plants are readily withdrawn from the soil, owing to the absence of healthy secondary roots. This decay, generally of a brown colour, may only affect the epidermal tissue of the root, but where conditions favour the" growth of invading organisms the vascular system may be destroyed. In the first case the growth of the plant may not be appreciably retarded, but in the second, where the connection between the root and shoot may be completely rotted off, wilting of the plants results. Where the disease has not materially affected the conductionvessels (the central core) the plant is often able to put forth a fresh

root-system, by which a moderate growth is obtained, but the life, growth, and usefulness of the new roots are subject to attack under the same conditions which influence the life of the original roots. The tap-root and secondary roots, when diseased, are destitute of roothairs, and the root-nodules generally abundant on leguminous plants

Later seasonal examinations have shown that in those crops where the wilting was extensive in the spring the yellow condition has persisted and the growth has remained stunted. . Needless to say, the seed-production from such crops is negligible, and it is not an uncommon practice to feed them off with sheep. In addition to the above-mentioned features of the disease other symptoms appear which at first apparently have no connection with the early stages. At the time of flowering and setting of the seed — and this may occur on plants which have not shown any indication of previous wilting—dark brown and grey spots of | in. to in. in diameter appear on the leaves and petioles. On the culms occur similar blue-black oval lesions, varying , in size from -I in. in length to

areas covering the greater portion of the culm. Only where the stems are subjected to very moist conditions does the staining of these lesions penetrate far into the tissue of the stems, the usual effect merely being a darkening of the cortex. The pods are often affected in the same manner, showing grey and brown spots, varying in size from small pin-points to patches covering the greater portion of the pod, or more often being small raised disks of A in. to J in. in diameter. Where the pods are more or less covered with these spots the husk is stained internally, and the seed may have a similar brown stain. The presence of lesions on the. leaves, culms, and pods, and the staining of the seed, do not have any serious effect, if any, on the host, but the condition under which they occur and the relationship to the disease of the spring growth will be more fully discussed in a later article. ECONOMIC IMPORTANCE OF THE DISEASE. The New Zealand agricultural statistics (2) include the data regarding peas and beans under the one heading, but, assuming that the proportion of beans sown in the years previous to 1915 has not altered greatly in recent years, then the acreage of peas can be estimated by reducing the following totals by 17 per cent. : 1915-16, 9,359 acres ; 1916-17, 11,905 acres ; 1917-18, 11,685 acres ; 1918-19, 17,929 acres ; 1919-20, 14,4.16 acres ; 1920-21, 14,466 acres ; 1921-22, 12,789 acres 1922-23, 24,449 acres i 1923-24, 18,676 acres. Although a reduction of 17 per cent, of the foregoing acreages may be approximately correct in the case of the pea crops for threshing, it is doubtful if a similar reduction of the total values will give a true estimate of the value of the pea crop. Following is the estimated combined value of peas and beans for the past ten years : 1915-16, .£49,978.; 1916-17, £82,113 ; 1917-18, £125,033; 1918-19, £151,785; 1919-20, £166,188 ; 1920-21, £142,158 ; 1921-22, £135,759 ; 1922-23, £261,580 ; 1923-24, £136,045. These values and acreages do not include the crops grown for the vegetable trade, of which the Wellington City market alone consumes about £5,000 each year. Literature (2) (3) dealing with similar diseases in America and Europe does not give reliable estimates of the proportion of loss apart from stating that they are considered a serious trouble in connection with the canning industry. It is difficult to estimate the amount of damage caused by collar-rot in New Zealand, but when it is considered that all garden-pea varieties are • more or less susceptible to

the disease, which under suitable conditions may partially or completely ruin the crops, it is evident that the trouble is of decided economic importance, calling for further investigation. . Further, the loss sustained is not confined solely to those crops which are a total failure, but varies according to the virulence of the disease, so that a removal of the cause would not only obviate the complete failures, but also improve the growth and average yield of what are regarded as satisfactory crops. Results of field examinations, life-history of the casual organism, and control measures will be. dealt with in subsequent articles. LITERATURE CITED. (i.) Jones, F. R. Stems and Root-rot of Peas in the United States caused by a . Species of Fusarium. " Journal of Agricultural Research, vol. 26, pp. 459-476, 1923. . . , . . . . (2.) Statistical Report on the Agricultural and Pastoral Production of the Dominion of New Zealand, 1923 -24. ' . . .. . (3.) Van Hook, J. M. Blighting of Field and Garden Peas. Ohio Agricultural ., Experiment Station Bulletin 173, pp., 233-246, 1906. - ' - ‘