Pre-harvest Examination of Ryegross Seed for Blind Seed Disease

New Zealand Journal of Agriculture, Volume 87, Issue 5, 16 November 1953, Page 405

Pre-harvest Examination of Ryegross Seed for Blind Seed Disease

THE Seed Testing Station of the Department of Agriculture is this year again undertaking the pre-harvest examination of samples of ryegrass for infection with blind seed disease. For this purpose a sub-station will be opened at the offices of the Department of Agriculture in Timaru from 15 December to handle samples from the South Island. This service has now been provided for a number of years and has been of considerable assistance to farmers and merchants by enabling a forecast to be made of the germinating prospects of the seed which might be harvested from any particular crop of ryegrass. Examination procedure is described by A. V. Lithgow, Officer in Charge, Department of Agriculture Seed Testing Station, Palmerston North, in the first section of this article. The section which deals with blind seed disease is by K. Cottier, Instructor in Agriculture, Department of Agriculture, Wellington.

Experience has shown that it is not worth while testing samples when they are taken from crops earlier than a week before cutting, as the disease can spread up to the time the seed is mature. The results on immature samples are not reliable, as if wet weather follows after a sample has been drawn, rapid spread of the disease may occur. In these circumstances it is recommended that a further sample be submitted to obtain an up-to-date result, particularly if the earlier sample has already shown some infection. When a grower decides to sample his paddock for testing he should draw the sample so that it is as representative as possible of the area from which it is taken. It is advisable to traverse the whole area picking a seed stalk every few paces. The sample should

comprise 400 to 500 seed heads, which should be trimmed to about lOin. in length, and a label with the sender’s name, address, and telephone number

in block letters should be attached. The date of sampling and the registered number of the area under certification (if applicable) should also be given. The sample should be wrapped tightly in several layers of paper to keep it fresh. It is important that growers should forward their samples without delay once they are collected, as samples deteriorate fairly quickly in transit. All North Island samples and those South Island samples posted before 12 December should be sent to the Seed Testing Station, P.O. Box 609, Palmerston North, and South Island samples sent after 12 December should be forwarded to the Department of Agriculture, P.O. Box 110, Timaru. The reports on the samples indicate the relative degree of infection of the seeds present in the heads and also indicate the stage of development of

the seed. For this purpose the following terms are used: — Flowering (anthers still present in half of the flowers).

Very immature' (seed half length). Middle stage (up to full length but still milky). Mature (fully developed but still doughy). Ripe (mature and dry).

Experience has shown that where the sample has been carefully taken and cutting takes place shortly afterward the pre-harvest report gives a good indication of what the final germination of the line might' be. It is not considered economic to harvest a paddock which under these conditions shows an infection of over threetenths.

Blind Seed Disease

SINCE the causative organism, of blind seed disease of ryegrass was discovered in New Zealand 20 years ago many avenues of investigation have been explored in an effort to find some means of controlling the disease. Lines of Research One line of research has been the possibility of breeding a desirable type of ryegrass which is resistant to blind seed disease. Certain strains of ryegrass were until, recently regarded as resistant, although otherwise not of a desirable type. It was thought that such resistance could be combined by breeding with the other qualities desirable in commercial ryegrass. It has now been shown, however, through more refined inoculating techniques, that the “resistant” strains are in fact highly susceptible if inoculated at the correct —when the florets are open. In the field these plants may not normally become infected, because through features associated with the length and time of flowering they escape infection. Such escape mechanisms might, of course, prove, valuable factors to incorporate into the best strain of ryegrass. Control through the use of fungicidal treatments has also been investigated. Sprays and dusts applied at flowering time have given a measure of control, but the best control achieved has not

been sufficient for it to be considered a worthwhile, economic treatment. Nitrogenous fertilisers have been shown to be an efficient means of increasing seed yields, but there is no evidence that nitrogenous fertilisers will affect the incidence of blind seed disease. Farm management methods have also been investigated. There is no doubt that the time at which fields are closed for seed production has an effect not only on yields, but on germination. Germinations as well as yields were much reduced in a series of trials when fields were closed later than the end of October. Overseas workers stress the importance of crop hygiene with this disease —the use of clean seed and the elimination of sources of infection of blind seed disease from the vicinity; that is, ryegrass in nearby paddocks, headlands, and roadsides should not be allowed to seed. In New Zealand it has been amply demonstrated that the infecting spores are present in the atmosphere for considerable periods during the flowering of ryegrass, and the dangers of air-borne infection are great, particularly in weather favourable to the development of the disease. Some trials have been conducted to investigate how closely field germinations from seed sown correspond with the germination tests normally carried out in the seed testing laboratory. Germination counts were made on a number of seed lines each of which was germinated under field, glasshouse, and laboratory conditions. The results showed close correlation. Farmers can be reassured that the laboratory figures give a reliable pointer to the maximum strike which can be expected under the best germinating conditions in the field. For three seasons (1948-49 to 1950-51) Instructors of the Department

of Agriculture have prepared information on the growing conditions of ryegrass seed crops at the time of routine inspection for certification. Subsequently the yields and germinations of machine-dressed seed from these crops were obtained. Approximately 2500 crops of perennial ryegrass and 1100 of short-rotation ryegrass were surveyed. The information was analysed in an endeavour to isolate factors affecting seed germination. The following conclusions were reached: — 1. Season and district are two of the most important factors associated with the incidence of blind seed disease. The critical period for infection is when flowering is taking place. When this period is also one of considerable rainfall, infection is likely to occur, with resultant low germination. In the survey the number of rain days in the period of flowering in districts with high resultant germination was less than half that in districts of low-germinating crops. In these cases rainfall data outside the flowering period were similar. The district effect, which is probably closely bound up with weather, was shown by the low germination obtained in most seasons in South Otago and Southland. 2. There was no strong evidence to suggest that germination was greatly affected by the vegetative condition of the crop; that is, whether the crop was heavy, medium, or thin. 3. In some crops lodging improved the germination, the difference being about 20 per cent, between upright crops and those completely lodged. This effect was more consistent with short-rotation ryegrass. 4. There was no clear indication that the amount of bottom growth in crops had any effect on germination. 5. The percentage of grass in the sward had some effect on germination; in some crops there was an increase of 5 per cent, in germination with a 10 per cent, increase of grass. 6. In practically all cases highyielding crops had better germination. This was more marked with perennial ryegrass, in which an increase of 10 bushels per acre in yield was accompanied by an increase of 5 per cent, in germination. This effect is probably correlated with some of the other factors. Many high-yielding crops were lodged, very heavy, and had a high percentage of grass in the sward. Nevertheless it is likely that efforts to increase yield of seed are also likely to result in better germination. Effects Can be Minimised Despite the wide scope of investigations to date into blind seed disease, the immediate future offers little to the farmer in practical means of avoiding the disease. If seasonal conditions are against the grower, there is little that can be done. However, the effects of the disease can be minimised by the adoption of practices that will, in most cases, give good yields of seed: Early closing, adequate fertiliser (especially nitrogenous), and saving of seed from vigorous crops. Nevertheless, some progress has been made, and investigations are being continued in the hope that the future will bring a means of combating blind seed disease more successfully than has been possible in the past.