Rust of Linseed and Linen Flax: Life Cycle and Control

New Zealand Journal of Agriculture, Volume 85, Issue 2, 15 August 1952, Page 123

Rust of Linseed and Linen Flax: Life Cycle and Control

LINUM rust (Melampsora Uni Ehrenb.), a . disease of linseed and linen flax, was first recorded in New Zealand by Cunningham in 1927 (l), since when it has occurred to a greater or less extent each season, In 1947-48 a rust epidemic in Canterbury seriously threatened the survival of the linseed and linen flax industries. Since then they have recovered, the area in linseed being over 30,000 acres in the 1951-52 season. Further expansion is expected as farmers learn more about the crop, but rust still remains a serious annual hazard. Recent surveys and research have suggested ways in which the danger can be lessened. These control methods depend on a knowledge of the different stages in the life cycle of the rust fungus, and in this article these stages and the control methods are described by I. A. M. Cruickshank, Plant Diseases Division, Department of Scientific and Industrial Research, Auckland, '

THE life cycle of linum rust has four distinct stages, all of which occur on cultivated and wild species of Linum. The first obvious signs of rust in a crop are orange pustules or uredosori (illustration at right). This phase may be observed from early summer to late autumn on crops, and on volunteer plants and wild flax throughout the year. Minute orange, spores are produced continuously from the pustules for several weeks at the rate of several millions each day. Uredospores may infect other plants in the stand or they may be carried many miles by air currents to other crops of linen flax or linseed. The time required from infection for the production of fresh uredospores is 10 to 12 days. Thus every 10 to 12 days throughout summer this short cycle repeats itself and the rust fungus multiplies rapidly. However, crops are susceptible only while green and growing vigorously; once they change colour they become resistant to further infections. In late summer the second or teleutosorus stage appears as black pustules on stems previously infected with the orange phase. This is the over-wintering stage. In early spring (September - October) teleutospores making up the black pustules germinate and produce minute colourless spores which are shot into the air. If these spores alight on a flax leaf or ■stem they penetrate the tissues and there develop the third or pycnidial stage.

Pycnidia appear as minute, pin-point spots in small orange areas on leaves and stems in early spring. They produce large numbers of sticky spores and are an important phase of the sexual cycle of the fungus. A few weeks after pycnidia have appeared the fourth or caemosoral stage develops from the mixing of spores ,or fungous threads of two pycnidia, Orange powdery spores are formed by caemosori and are spread in the same way as uredospores, and the life cycle is complete. . , , The first and second stages are most readily observed and cause directly the most damage. The third and fourth stages, although not conspicuous, are equally important, as they not only assist survival of rust from one season to the next, but may also play a part \ n development of new and more damaging races of rust. Recent studies have shown that there are a f least 12 races of this rust fungus in New Zealand, and that most of them are widely < spread throughout districts where linen flax and linseed are grown. This information is being used in the breeding and selection of new rust-resistant varieties of both crops. The time new varieties may remain resistant after they are released depends on many factors. One of the most important is the ability of rust to produce new races which will attack them. This largely depends on the abundance and distribution of the third and fourth stages of the life cycle, and indirectly on the amount of volun-

teer linseed, linen flax, and wild Linum growing through winter. Surveys made during spring for the last 4 years in North Canterbury and South Canter- , bury have shown the presence of large quantities of Australian flax (Linum marginale A. Cunn.) (illustrations at left and on next page) growing alongside roads and railways and on waste land. Plants in 1 many instances were heavily infected with rust in both uredosorus and teleutosorus stages. They were also commonly infected with two other diseases of Linum,

namely pasmo (Sphaerella . linorum Wollenw.) and browning (Polyspora Uni Laff.). As L. marginale grows throughput the year, it is a serious carrier of rust and other diseases from one season to the next. Native flax (L. monogynum Forst. F.) has also been found infected with rust, but this species is not as common as L. marginale, being confined to coastal areas. The surveys have also shown the presence of rust-infected volunteer linen flax and linseed plants in fields sown with these crops the previous season. The practice of sowing down grass with linseed crops has an important bearing on this problem, as the growth of volunteer plants through the oilowing . winter may remain • unchecked. Equally dangerous is the practice of sowing linseed “seconds” with autumn . greenfeed crops. If plants from this source become infected with rust, they, are a serious menace to the folio wing, season’s spring crops. This was well illustrated in 1948, when the autumn crops of 1947 spread large amounts of rust to the following season’s spring sowings and a rust epidemic was experienced. The practices mentioned would be less dangerous if such areas were heavily fed off through winter and again in • early spring. Observations have shown that where this has been done few linseed plants survived. However, because of different seasonal feeding requirements, it is almost impossible to guarantee sufficiently heavy grazing to eliminate all linseed plants. Control of Rust The ideal method for controlling rust is the growing of resistant varieties. Varieties at present grown have been shown to be much more rust-resistant than those grown before 1947 (2). Further selections of even more resistant types within these varieties have been made and it is hoped to release two lines for field trials in 1953. A

breeding programme for rust resistance in the linseed variety Golden Viking and the linen flax variety Liral Crown, initiated in 1949 by the Crop Research Division of the Department of Scientific and Industrial Research, is progressing favourably. The farmer himself has power to reduce greatly the chances of a recurrence of severe rust epidemics. Measures listed below will reduce spring infections and at the same time reduce the risk of new races of rust developing. 1. Eradication of wild flax alongside roads and railways adjacent to farms. Pulling and destruction of these plants before they set seed is the best method of removal. They are readily recognised when they come into flower (see illustration above). 2. Eradication of volunteer linen flax and linseed plants from cropping land by autumn ploughing and working and from pastures by heavy winter and spring grazing. 3. Sowing of spring crops of linen flax and linseed as early as practicable within the limits of the locality and season, preferably not later than the end of October. Late resowing in November is inadvisable. 4. Practising a 3- or 4-year crop rotation. - 5. Dusting of seed before sowing with a fungicidal seed dressing. References 1. "Transactions and Proceedings of the New Zealand Institute", vol. 58, pp. 47-50, "Fifth Supplement to the Uredinales and Ustilaginales of New Zealand”, by G. H. Cunningham (1927). 2. "New Zealand Journal of Science and Technology”, vol. 31, No. GA, pp. 54-57, "Resistance of Linseed and Linen Flax Varieties to Flax Rust (Melampsora Uni) in New Zealand”, by I. A. M. Cruickshank (1950).

“The Grass Crop”: William Davies

TO many people “ecology” is merely another scientific term, the significance of which can be appreciated only by scientists. That this thought is fallacious is shown in “The Grass Crop”, a book of over 300 pages. The author demonstrates that to farmers, research workers, and extension workers an ecological approach to the study of grassland is essential. He shows, by argument based on wide observation and experiment, the extent to which good grassland husbandry throughout the world is based on an appreciation of the interdependence of the soil, climate, plants, and animals (including humans). To establish certain principles, example, and argument he does not always follow conventional “grassland” lines. For instance, penguins on the coast of the Falkland Islands are used as one example of the extent to which the animal factor can change a type of vegetation. The book is based on two main themes: First, there is the ecological theme, which answers many “why” rather than “how” questions about grassland. This theme should be of interest to everyone interested in grassland, as it deals mainly with principles which may be converted to practice in many areas. Second, there is the advisory theme, in which advice is given principally to farmers in Britain on matters such as pasture establishment, management, use of strains of pasture plants, and seed production. In the preface the author states that he is writing for the intelligent rather than for the academic person and that he uses argument rather than 1 numercial data. For this reason the research worker will find little in the way of figures with which he can compare his own results. This, however, is compensated for to some extent by a comprehensive bibliography of over 600 papers, many by the author. Mr. Davies is a keen advocate of the policy of ploughing up old and poor grassland and resowing to short-term pastures. He estimates that 65 per cent, of Britain’s permanent grassland is poor and that if this land were adequately utilised, production from it would be trebled. A parallel argument could well be applied to many of New Zealand’s older pastures.

The book states that for a long time it was assumed that grass would grow only in its season and could not be made to alter its ways. Recent research which has been and is being put into practice shows that this assumption is wrong. For example, by the use of various species and strains of pasture plants the production period of pasture can be changed to the farmer’s advantage. Autumn-saved pasture and break feeding carry growth well into winter. “Early bite” is provided by the stimulation of growth with nitrogenous fertiliser out of the bag, by the holding of autumngrown cocksfoot, and by the use of cereals and cruciferous crops. The importance of the biotic factor to hill (or marginal) lands is pointed out. Hill country should be the rearing ground not only for animals but also for humans. ' Such land reclamation pays not the generation that does the work but the generation that follows. Among the many points of interest dealt with are the following: That in general depletion and erosion can be cured by the better use of pasture and livestock; that in research observing results is often easy, but ascertaining causes may be difficult and time absorbing; that without the application of research “we may not have held out on the food front in 1942-43”; that, the . problem of national grassland is one of maintenance rather than one of improvement; that the treatment applied to a type of vegetation determines its character and composition; that there is no experimental evidence to show that herbs have any value in adding to animal output from pastures; that the greatest problem in tropical grassland research is that there is no appropriate legume. When the wide range of territory and subjects covered is considered the paucity of illustrations is surprising. Of the objectionable but übiquitous hat, matchbox, and ruler, the lastnamed has been chosen to grace an illustration used on the dust cover and as the frontispiece. Good and 'ample illustrations not only make a book such as this more informative but also more readable; nine illustrations only do not do justice to the book. —S.H.S. E. and F. N. Spun Ltd., London, 265.