Importance of Blind Seed Disease in Ryegrass

New Zealand Journal of Agriculture, Volume 75, Issue 6, 15 December 1947, Page 595

Importance of Blind Seed Disease in Ryegrass

By

W. L. OSBORN,

Assistant Instructor in Agri-

culture, Timaru.

’T’HE germination capacity of seeds is an im- •*> portant consideration to farmers and merchants alike, and with the development of a small-seeds export trade it has become of great importance to New Zealand. Blind seed disease, causing low germination in ryegrass seed crops, therefore has been receiving increasing attention. A - general survey of present knowledge of the disease and the investigations being carried out on the problem is given in the following article.

"CARLY records show that ryegrass seed was unreliable in germination capacity 25 years ago. Even then in certain seasons crops gave seed of extremely low germination, but the reason was not discovered until 1932. Since then the main facts about the disease have become widely known, but research workers are still seeking economic methods of prevention and cure.

A fungous growth, now commonly known as “blind seed disease,” was isolated and determined as the cause of the low germination of otherwise apparently-sound, wellharvested perennial ryegrass seed by Neill and Hyde, working at Palmerston North. Since their discovery the disease has been _ isolated in other countries, including

England, Scotland, Wales, Ireland, Sweden, North America, Tasmania, and Victoria, and on grass seeds other than perennial ryegrass—among them short-rotation and Italian ryegrass, tall fescue, meadow fescue, chewings fescue, rye, and darnel.

Economic Importance

In New Zealand the economic importance of blind seed disease is considerable because primary production depends largely on the grassland type of farming. With the English ryegrasses the chief pasture species sown for the establishment and ' regeneration of grasslands throughout the country, large quantities of high-quality seeds have a ready market within New Zealand. Until recently the export trade in small seeds has flourished, with an increasing demand for high-quality New Zealand seeds from various countries. Ryegrass seed produced in New Zealand in the 1945-46 season exceeded 1,500,000 bushels, of which about a quarter was exported (Tables I and II).

However, the low germination of some ryegrass seed has become a problem to farmers and merchants alike. At its peak Certified Pedigree perennial ryegrass seed of high germination sold for more than £2 a bushel whereas for the low-germinating lines there is little or no sale. Throughout New Zealand seed firms are holding stocks of ryegrass seed that has a germination below 40 per cent., and some lines are as low as 5 per cent. To have harvested these lines, machine dressed the seed, and stored it for some time in seed stores has cost farmers consider -

able time and money. In a bad year blind seed disease may involve . the farmer in considerable financial loss. Seed. crops may be . proved worthless and, as well as the cost involved, there is the loss of production from highproducing ryegrass swards during the season and probable damage to the pastures in the process of letting them go for seed. /

Unfortunately, the higher-producing, more persistent strains of the ryegrasses now available under the certification scheme of the Department of Agriculture are more susceptible to the blind seed fungus. Farmers who pay the very high prices for these seeds are more anxious to receive some return in the form of profitable seed crops. Blind seed disease is now so widespread in the seed-producing districts that farmers do not expect to secure high-germination crops every year.

To maintain an export trade

high quality, moderate price, and a reliable and consistent supply are essential. With blind seed disease prevalent in New Zealand’s major seed-growing districts those conditions cannot be fulfilled. With embargoes now in operation an improvement in the quality and reliability' of seeds and a reduction in,their cost become even more important. Thus the menace of blind seed disease in decreasing the value of New Zealand’s rye-

grass seed crops has become of vital importance to the industry and is being investigated by a large number of research workers in this country.

Description of Disease

The blind seed fungus (Philea temulenta) affects only the seed and does not damage the, ryegrass plant. It grows through the tissues of the newlyformed seed and eventually kills it. It is not the only cause of low germination in a line of seed, but it has been found to be by far the most im-

portant in perennial, Italian, and shortrotation ryegrass.

The so-called “blind seeds” may not differ outwardly from healthy germinating seeds. A proportion of infected seeds, if infected after they have reached normal size and development and with ripening halting the progress of the fungous growth, are quite normal in size and colour, and until the outer husks or paleae are removed it is not possible to detect the damage or symptoms of the disease. However, seeds infected earlier, at flowering time, if they develop at all are small arid shrunken, and the embryo of the seed is usually atrophied or withered away.

Life Cycle of Fungus

-s Infected seeds that have fallen to the ground from the seed heads or have been sown remain dormant during the following winter. During the early summer when temperature and moisture conditions are favourable the fungus revives and produces the next

stage in the form of a mushroom growth (or apothecium) from the seed and protruding 1 above the surface of the ground. These white, saucershaped mushrooms about gin. in diameter, developed on a short, white, cylindrical stalk, can be found readily in ryegrass paddocks during November and December if the ground surface is examined carefully. Under humid conditions they have a life of eight to fourteen . days, but they . shrivel. in a few hours if exposed to direct sunlight. With age their colour darkens to a cinnamon brown.

Spores Infect Seed Heads

The mushrooms produce spores which, when ripe, are forcibly ejected and shoot upward for considerable distances to be carried by air currents to the flowering heads of ryegrass plants. These spores (called ascospores) mature in succession, so that their discharge may last for > several days, and in that time several million spores, may be ejected from one mushroom. As many as seven of these mushroom growths have been found growing from the one blind seed. . Ryegrass heads become infected either by flying spores from within the crop or by wind-borne spores from outside sources of infection such as neighbouring paddocks.

Further Stage of Infection

The fungus attacks and penetrates the young seed and develops a further stage, which again produces millions of spores, this time enveloped in slime. The slime is readily soluble in water, so that spores (now called conidia) are carried and spread by rain or dew drops to other heads to produce the secondary infection of the disease.

Seeds infected earlier in their development from the mushroom ascospores either fail to complete their development or are small and light, so are likely to be removed in the

machine dressing process. The secondary infection, however, takes place nearer to the ripening stage and the size and weight of diseased seeds may be quite normal. These blind seeds cannot be removed during the machine dressing of.the line, and, being dead,, remain in the dressed seed to give a lower percentage of germination to the line J a whole ..'_ , , , . The disease is difficult to detect in the field, but in the laboratory it is possible to obtain a clearer picture of the damage to the seeds. Seeds are peeled of the outer husks and under strong light and magnification are examined for embryo, development and signs of the disease. A check can be made by placing peeled seeds in drops of water or staining solution and recording the presence of the slime ; spores under a microscope. c '

Pre-harvest Testing With the spread of blind seed disease throughout the seed-growing districts, and with the great variation in its seasonal incidence, it has become of vital importance to the farmer to know whether areas of ryegrass seed are worth harvesting. By knowing extent of blind seed infection ,in his crops the farmer can decide whether to harvest, whether to wait or a white clover crop in preference to the ryegrass, and which crops are the most valuable and should receive his attention first. If given the information in time, the farmer is able to decide ; whether to make hay 'of his seed crop or to risk harvesting it. Therefore, in the pre-harvest testjng service for blind seed disease in ryegrass crops the Department of Agriculture gives the farmer a service supplying valuable infor-

mation and guarding him against financial loss. Very often the grower has to arrange for a contractor’s header to complete the harvesting of his paddock, and that cash outlay can be saved if the crop -is proved of low germinating capacity and little saleable value. Finally, on the pre-harvest test report the stage of maturity of the sample is given.

Sending in of Samples

As in the past, the Department of Agriculture will set up stations for the pre-harvest testing of ryegrass seed at Christchurch and Timaru in the coming season to provide a free service for farmers. Care should be taken in the collection of samples for this service. The sample required is about 300 individual heads of ryegrass (a good handful), and it should arrive in as fresh a condition as possible, taken just before mail collection and wrapped carefully in several rolls of newspaper. The collection of the . heads needs particular care, as a representative sample is essential for an accurate estimate of the probable germination capacity of the crop. The best method is to walk right across the paddock taking two or three heads at a time and collecting a large bundle from which is selected a fully representative handful to be sent forward. Cut the stalks, tie the bundle with string, and attach a label showing the origin of the sample, preferably the paddock’s registered number and letter.

At the testing station at least 100 heads of ryegrass are; taken from a sample and one or more seeds on each is examined for the disease, giving a percentage of infection. By adjusting this to the stage of maturity and probable advancement of the disease up to final harvesting, some indication of the probable germination of the seed harvested is possible. The farmer receives the report' a day or two later by telephone, telegram, or letter giving him the proportion of diseased seeds, the stage of maturity of the sample, and the probable germination of the crop when harvested if the sample is of a late enough stage of maturity to allow of a reliable estimate.

Accuracy of Estimates

Occasionally these pre-harvest estimates of germination , are higher or lower than those obtained on the final purity and germination certificate based on the machine-dressed seed. In such cases many factors may be involved.

First, the sampling may have been at fault and the sample may not have been truly representative; with the secondary infection spread by dew or rain, a handful taken together from one spot may have been heavily diseased, whereas a yard away there might have been a healthy area.

Secondly, the estimates are ' reliable within reasonable' limits if the cutting and threshing, of the seed proceed without much delay; if an infected crop is exposed to prolonged wet weather or. heavy dews before or during harvesting, and the drying out of the seed is thereby delayed, the final germination may differ considerably from the estimate. Thirdly, if infection occurs at an early stage and diseased seeds are small' and light, they may be lost in dressing, thus giving a higher final germination. Finally it is well established that blind , seed disease is not the only cause of low germination in- ryegrass' seed. Other causes may not be as important, but sprouting of seeds, mechanical injury in threshing or dressing, and excessive heating of seed may all contribute to the loss of vitality and death of seeds. Where such factors operate the final germination capacity may differ from the estimate given on the pre-harvest test reports, which, however, have been proved in the main reasonablyaccurate forecasts.

Factors Concerned in Disease

It is widely recognised that the germinations of ryegrass crops vary widely with the seasons. Present knowledge of the problem . points to the following main factors being involved in the fluctuating incidence of the disease: —

1. Weather conditions, especially the rainfall between flowering and harvesting, are the principal factor contributing to the spread of the disease. There is a significant correlation between summer rainfall (DecemberJanuary total) and the average germination of perennial ryegrass seed in South Canterbury, i Usually North Island dry-summer x areas produce crops of higher germination than' the wet-summer areas in the south. .

2., Growth conditions, which of course are related ..to the climatic conditions, are another important factor.

3. Harvest year or age of the stands: First-harvest areas have a higher germination average than older areas, which may be more particularly the result of their greater vigour and growth.

4. Harvesting conditions: Early harvesting under dry conditions with more rapid completion of the task aids the control of the disease.

The relative importance of primary and secondary infections is not yet known, but more light is expected to be shed on this aspect by the intensive study of the problem now being organised.

Previous Research

In 1932 Neill and Hyde, working at Palmerston North, ' worked out the general history and life cycle of the blind seed fungus and first attributed low germination in perennial ryegrass to this cause. In 1939 they produced

a comprehensive account of the problem and in 1943 a further treatise, In their earlier report they described a'similar fungus growth that is of no importance in its effect on the seed or germination capacity, but by producing similar mushroom growths can easily be mistaken for the _ blind seed fungus. This fungus, called Lolium fun- / gus No. 2, produces apothecia on leaf sheaths and dead stalks of ryegrass, whereas the blind seed fungus grows from seeds only. Also in this report is the statement that producing resistant strains is the best method of overcoming the disease problem. Gorman, also working in Palmerston North in a series of experiments, the results of which were published in 1945, determined yields and germination of ryegrass 1 sown with different types of clovers. In those experiments the lowest germinations ’ were from ryegrass crops sown without clovers and the highest from crops sown with the highest-quality Certified Pedigree . white clovers, though the yields of .the latter crops were low. At a meeting of the Blind Seed Com- , mittee in Wellington last April reports ■

of research carried out since the previous meeting in 1941 were discussed. Experimental work suggested at the previous meeting had been carried ,out to the extent permitted under wartime conditions and had followed the following main lines of investigation: j Breeding of resistant strains; growth conditions; „ TT . 3 - Use of sprays and du » 4 - Use of manures; ■, 5- Surveys of the incidence of the disease and factors concerned; 6. Experimental trials to increase knowledge of the disease. . .. c . , Improving pedigree strains The Grasslands Division of the Department of Scientific and Industrial Research has developed the improved Pedigree strains of perennial, Italian, and short-rotation ryegrass, which are all susceptible to the blind seed fungus, However, Rose and Corkill found that susceptibility to the disease was significantly lower in plants from four Southland old-pasture lines than in plants of the Certified Pedigree strain, They also proved that resistance and

susceptibility to the disease were inherited and that crosses from resistant plants showed 41.8 per cent, higher germination than the susceptible plant crosses. The resistant plants, however, were greatly inferior to the Certified strains in general production and persistency.

It is hoped to breed a strain with the desirable characteristics of the present Pedigree strain , but still having the resistance 'to blind seed. Such work can be regarded only as long term, and as nothing is yet known of the cause of this resistance it is . too early to forecast the final result of this breeding programme. No such comparable research has been carried out with Italian or short-rotation ryegrass, but plans are being prepared for similar investigations .in these grasses, in which the lower infection usually experienced in the field is probably the result of . later flowering, when the weather is less favourable to the blind seed infection and the shorter period between flowering and ripening..

Trials with sprays and dusts have been carried out -at various ' centres, treating seed before sowing and plants at’and after the flowering stage. The usefulness of fungicides still requires further investigation, though colloidal sulphur sprays and copper oxychloride dusting of the plants have given significant and promising increases in germination. ,

Nitrogenous manures have also given increased yields and germinations when applied at the equivalent rates of 1, 2, or 4cwt. of sulphate of ammonia to the acre. Their value lies in increasing the growth and vigour of the crop. . . ■

Surveys, have been .carried out in Hawke’s Bay and South Canterbury, and r Lincoln College has also been collecting data. Much valuable information has been collected, but the surveys are not yet completed. Trials to study methods of infection have been laid down by over-sowing paddocks with infected seeds, and results have given further proof that the heavier the crop the higher the germination. , The germination of seed sown bears no significant relationship to the germination of seed harvested, as shown by surveys of seeds of the same origin harvested in different districts. There is, however,, correlation between ger-, mination percentages and seasonal conditions in individual districts.

Further research on the time for which the fungus lives in the seed was carried out in 1938. Low-germinating lines from each of the 1936, 1937, and 1938 seasons were tested in the laboratory and in the field. The fungus was still alive in the 1938 and 1937. seed but not in the 1936 seed. It would appear that the fungus lives in the seed for well over a year, but that after longer storage it dies. Sowing old seed therefore might assist in the control of the disease.

Hot water treatment of seed has been found by Northern Ireland workers, Calvert and Muskett, to kill the fungus. Treating seed for 30 minutes in water at 50 degrees C. consistently eliminates infection and, if the treated seed is dried thoroughly immediately after treatment, they report no danger of \ impaired germination. This treatment is no more. than a

disease killer and does not improve the germination of the line of seed. The treatment, which needs special equipment and great care, is no guarantee that the subsequent crop will be free , from blind seed, as wind-borne spores from headlands or adjacent paddocks may easily infect the,crop. Future Research Realising the economic importance of ,this problem, research programmes are being accelerated by the Divisions concerned and will be along the following lines: — 1. Mycological studies are to be continued to determine the significance of the primary and secondary infections and related facts.

2. Breeding programmes for resistant strains of perennial, Italian, and shortrotation ryegrasses are to be continued by the Grasslands Division, Department of-Scientific and Industrial, Research. . ' .

3. Field studies on infections and sampling techniques are to be undertaken by the Seed-testing Station. .

4. A Dominion-wide survey is to be carried out by the Fields Division of the Department of Agriculture to cover as many crops as possible,' collecting data on crop management,, fertilisers, growth conditions, weather conditions, and harvesting conditions, and correlating these with crop yields' and final germinations. '

5. Widespread field trials are to be carried out by the Department of Agriculture to study intercultivation of crop and depth of sowing, seed treatments, fertilisers, closing dates, bottom growth in crops, grazing management, and sprays and dusts.

Summary . Blind seed disease has taken a very serious toll of New Zealand ryegrass seed crops during the past few difficult seasons. Especially in certain districts it has caused considerable financial loss to farmers, as well as accentuating the high prices of Certified ryegrass seeds. Considerable research work has already been carried out on the problem, knowledge of the disease is increasing, and vigorous research is planned for the future. . ?

At present no definite recommendations can be given for the effective prevention and control of the disease. However, in general it can be stated that the best crops for farmers to save for seed are those from the most

vigorous first-harvest areas; the vigour and vitality of those crops will withstand blind seed activity , even in a bad year. Any crop or stock management that will' increase this vigorous growth—early shutting ■ up, topdressing in spring or autumn, liming, or stimulating dense clover growth and thereby giving the grass more nitrogen—-will increase the yield of seed and also probably assist the control of blind seed. There is, however, a danger of overlodging a crop and, thus reducing the yield considerably by causing the crop to rot underneath, but only in wet seasons' is that likely , to occur.

' It cannot be too strongly emphasised that during the past few years, because of wet conditions, the disease has- been building up to a very dangerous extent. Farmers should therefore consider whether it is not worth while to adjust their seed harvests to avoid this building up as much as possible.

First-harvest areas, if they are vigorous, well-established stands, give the highest germinations. That is indicated in Table 111, which shows the average germination capacity as estimated in pre-harvest tests for blind seed disease in 1946-47 season on material of known origin. Ryegrass seed harvested with white clover is usually of low germination during bad seasons, and in the third year of a stand germinations may not be much improved. Dry conditions will greatly upset this build-up of disease, but the past few wet seasons in some districts have made continuous seeding a very risky business.

Farmers are well advised to make use of the pre-harvest testing service. Used effectively it can be of inestimable value. So that surveys and research programmes will be wider and information collected s more valuable, farmers are urged to assist by labelling carefully the origin of all samples sent in for testing. If the origin of samples is known, the final germinations of the machine-dressed seed can be checked with the estimates made on the pre-harvest test reports. South Canterbury returns collected last season are now being tabulated, and it is hoped to obtain some valuable and reliable information on the general field management necessary for high germi-

nation. The results of this survey will be made available when the final dressing ' returns have come to hand.

References . J. C. Neill and E. 0. C. Hyde: “Blind Seed Disease of Ryegrass,’’ Bulletin 27, Plant Diseases Division. ■ . ' , \ . 1

J. C. O’Neill and O. C. Hyde: “Blind Seed Disease of Ryegrass, II,” Bulletin 59, Plant Diseases Division. , ■■ '

L. W. Gorman: “Further Investigations in Blind Seed Disease of Perennial Ryegrass,” Publication 210, Grasslands Division.

I. D. Blair: “Ryegrass Blind Seed Disease,” Bulletin 210, Canterbury Chamber of Commerce.. ' . . .

E. 0. C.' Hyde: “Ryegrass Seed,” “N.Z. Journal of Agriculture,” March, 1945.

HAYMAKING HANDBOOK

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The major part of the bulletin comprises a comprehensive general study. Following this are four articles on special aspects“ Feeding Hay to Sheep,” “Covering < Haystacks with Rushes,’’ “Determining Tonnage of Stacked Hay,” and “Care of the Mowing Machine.” . .

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1944-45 1945-46 Production under , Total Certification Acreage (bushels) 1945-46 Total Total Production Acreage (bushels) Production Total under ProductionCertification (bushels) < (bushels) Total Acreage ■- ' V ‘ Total Production (bushels) Production - under Certification (bushels) Perennial .. 47,287 689,499 405,656 . . 58,345 1,032,103 550,675 Italian . . .. 17,547 389,178 221,807 21,013 507,858 284,288 Short rotation .. 300 6,150 6,150 2,500 .48,499 48,499 Totals 65,134 1,084,827 633,613 81,858 1,588,460 883,462

TABLE I: PRODUCTION OF RYEGRASS SEED IN NEW ZEALAND

, ' ' 1945 ' 1946 Exported to United Kingdom (bushels) Total exported (bushels) Exported to United Kingdom (bushels) \ Total exported (bushels) Perennial .. . ; 145,936 249,424 145,600 280,000 Italian .. .. 145,936 195,040 i 249,424 249,872 145,600 53,760 280,000 95,000 Totals .. 340,976 499.296 199,360 375,000

TABLE II: EXPORT OF RYEGRASS SEED FROM NEW ZEALAND

South Harvest South Canterbury Dunedin (per cent.) (per cent.) (per cent) First-harvest areas .. 50 79 Second-harvest areas 36 ' 46 Third-harvest areas 42, 3f

TABLE III: AVERAGE ESTIMATED GERMINATION CAPACITY AS ASCERTAINED BY PRE-HARVEST TESTS 1946-47 SEASON