PLANT DISEASE WAR.

New Zealand Herald, Volume LXV, Issue 20087, 26 October 1928, Page 5

PLANT DISEASE WAR.

USE OF MICROSCOPE

PRODUCTION OF PURE SEED. LIFE HISTORY OF FUNGI. Working with a mieiUscope ol' high power, and growing queer-looking cultures of many forms of fungi, a group of research experts at the pathological plant research station, Pahnerston North, wages continual war against plant diseases.

The successful researches of this institution. now removed from Wellington and operating as a separate entity under the control of representatives ol the Dcpaitrnent of Agriculture, the Department of Scientific and Industrial Research, and of the Massey Agricultural College, are well known, particularly in Canterbury, where disease among cereals is fast disappearing as the result of applied lesearch results. Few people, howevei, have any idea of the manner in which diseases are investigated. Avoiding intricate technicalities, a broad explanation of this important element of science in fanning is of peculiar interest. As a preliminary to an explanation of the methods employed at the station, Dr. G. H. Cunningham, mycologist, in a recent interview, mentioned the word mycologv was derived from the Greek for fungus, and itJi use in plant research work was due to the fact that nearly all plant diseases were caused by fungi, which were really a lower fo:rm of plant life living parasitically on the liighei forms.

Elimination—Not Control. Chief of the aims of the department was the elimination, rather than the control, of disease, and to that end, determination of the nature and cause of a disease was followed by efforts to provide in commercial quantities, disease-free pedigree seed for the agriculturalist. By growing this in a clean soil and with close supervision, disease could be stamped out, and with continual caie the farmer could proceed from crop to crop "without the old fear of heavy losses. The first function of the research station, however, was *to del.erm.ine the exact character and the life history of a malignant fungus growth, study its habits, ascertain its " weak spots," and find out whether it was carried on or in the seed; whether it infected the soil, and, if so, for how long. The life history of cereal smuts, for instance, was now well known. One viricty which was carried on the seed, could be killed by steeping the seed in a solution. A second group had its existence in the seed. There different treatment was called for to kill the fungus and yet leave the seed reasonable germinating power. Always effort was directed at killing the infection at tho outset, and not toward after-care of crops which otherwise would be sure to develop in a diseased state.

Pure Seed for the Farmer. It was not suggested, of course, that all seed sown should be so treated. That would be immensely costly. Further, treated seed lusfc about 25 per cent. of its germinating power. The methods outlined were employed for the production of disease-freo nucleus lines. Once those were obtained the next task was to produce pedigree disease-free seed in bulk for commercial use. This was achieved by growing' under conditions closely regulated by experts in tho work, whoso next task was to place tho seed in the hands of commercial growers and give advice in the direction of maintaining freedom from disease. Such work could not bo done for nothing. The wheat growers and flour millers of Canterbury had co-operated in a practical manner, and now had the satisfaction of seeing disease fast disappearing from tho province.

In a darkened room, Dr. Cunningham demonstrated tho first stags of investigation. Samples of affected pollen grains, so small as to bo invisible to tho naked eye, were examined under a highpowered microscope, an essential feature of which was an electric light beam of great strength, which was "shot through" tho slide holding tho specimen, so that the enlarged imago was projected 011 to a sheet of paper 011 a desk in front of the operator. Sketching an Enlargement.

It is exactly liko a miniature cinematograph, showing a coloured film, for before examination, tho minute specimens are treated, perhaps for a fortnight, with solutions of known colour reactions which facilitate study of tho nature of tho fungus when thrown 011 the white sheet. By this form of microscopic research, too, tho investigator is enabled to trace at ease the outlines of the projected imago enlarged, to any size up to about sin. in diameter.

Included in some processes preliminary to examination by tho microscope is the embedding of samples in paraffin, which, when solidified, is cut off in strips as thin as ono 25,000 th part of an inch. The machine used for this purpose is a model of exactness. In itself this is a phase of work which requires t lie training of a man for at least six months.

The disease identified, samples of the fungus are isolated and cultures grown to study their habits. To ascertain whether the disease exists in or on tho seed, is comparatively easy. For example, in tho study of collar rot in peas, seed was externally sterilised and then placed in a culture medium under sterile conditions. When a fungus developed it was proved that it must have existed in tho seed itself.

Even when fungus was eliminated from seed it might still persist in infected soil, and so field experiments were conducted to ascertain how land could best be sterilised or how long it would have to remain before it became clean of itself. It all reverted, however, to the question of providing tno farmer with disease-free seed.

Merchants and Farmers' Part. In experiments in the growth of diseasefree and infected seed at the laboratory the greatest care is taken to ensure that results are not affected by outside contamination. Plants aro grown in closelyfitted glass frames with the logs standing in oil to prevent "carrying" insects chmbing up and perhaps gaining access to the beds. That, briefly, is an outlino of the steps taken to classify disease, study its habits and ascertain how it may best bo killed in or on seed to pave the way for the growth of pure lines for the fanner.

Much, ol course, depends upon the cooperation of agriculturalists and merchants in dealing with disease-freo seed where obtainable. Potatoes and tomatoes, suffering so much from disease in New Zealand, will receive the benefits of further early research, although in the case of the former the production of disease-free lines in largo quantities natur* ully presents considerable difficulties.