FRUIT DISEASES

Dominion, Volume 28, Issue 100, 22 January 1935, Page 10

FRUIT DISEASES

Attack Planned Upon Bitter-Pit SCIENCE TO LEND AID Authorities in England Render Assistance New Zealand experts aye planning a determined attack this year upon bitterpit, which in spite of numerous investigations in different parts of the world remains a major source of wastage in certain varieties of apple. A comprehensive study of the disease is to be made by the Plant Research Station and Cawthron Institute, working in full co-operation. For some time past a thorough search has been made of all references in the literature dealing with the disease, and in this connection valuable assistance has been given by the Imperial Bureau of Fruit Production. Application to the bureau for information resulted in workers in New Zealand receiving a complete bibliography of everything written on the subject, together with summaries of tlie conclusions reached by workers in all parts of the world When it is realised that the search conducted by the Imperial Bureau of Fruit Production traversed practically the whole of the fruit research literature of Europe for some years past, and involved the translation of reports published in many European languages, the practical significance of Imperial coordination can be readily appreciated. Threefold Groupings. I With the aid of overseas assistance on these problems, workers in New Zealand will now .be able to proceed with their tasks, feeling at least they have some knowledge of what lias been done and 1 is being done in other parts of the world along similar lines. As a result of careful deliberation, it was decided to endeavour to group in some effective way the various diseases which are more or less loosely termed bitter-pit. The position is by no means clear. These diseases have often very much in common, and’ yet possess distinctive characteristics which necessitate their grouping separately. For the purpose of the present Investigation three-fold grouping has been decided upon, under the following nomenclature:— (1) Bitter-pit, which is characterised by its appearance on fruit only after picking, and particularly in cool store. (2) Blotchy cork, which appears in the form of pits on fruits toward the end of the growing season. In Blotchy cork the pits do not increase in size once the fruit is picked. (3) Corky pit, which groups the diseases to which the names poverty pit, crinkle, internal cork, etc., are applied. Tliis trouble appears only on apples while they are on the tree. It usually makes its appearance early in the season, and does not increase after picking. Work In Nelson District. Investigations have already commenced on corky pit in certain parts of the Nelson district, where the disease appears in an acute form. Dr. J. D. Atkinson, of the Research Orchard staff, has been delegated specially to undertake a series of prescribed treatments of affected trees, to ascertain what influence various nutritive materials exert upon fruit development and the incidence of corky pit. The work involves special root studies and soil examinations, and in the latter Dr. Askew, Mr. Rigg and Mr. Chittenden, of the Cawthron Institute staff, are cooperating. In addition, further trials are being arranged in the orchards of the Cawthron Institute. At the same time a survey of the affected localities is being followed up in collaboration with officers of the Horticulture Division, so that a very complete attack on corky pit will be made this year, and the new knowledge gained during the season should throw considerably more light upon the character of this serious disease. It has already been found to occur in young fruits very shortly after the fruit is set. and appears to develop in more serious form with the progress of the season. Value of Late Picking. Many theories of the origin of bitterpit have been advanced, but so far none of these can be accepted as proven, writ<»- Dr. J. Barker, of the Low Temperature Research Station, Cambridge, in the bibliography sent to New Zealand. He states that for certain varieties of Australian. New Zealand and American apples, there is good evidence that the liability to develop bit-ter-pit in storage diminishes with increasing maturity at the time of picking and for the Cleopatra apple of Western Australia, picking at a certain stage of maturity appears to be a practicable method of decreasing rhe losses from bitter-pit. With other varieties, however, such as the Cox’s Orange Pippin of Tasmania and New Zealand, later picking may bring with it a danger of increased low temperature breakdown in types of Cox’s susceptible to this trouble, and the usefulness of late picking will thus probably be restricted to fruit which is not susceptible to rhe breakdown. In general. Dr. Barker observes, it is probably safe to say that the value of late picking in diminishing losses from bitter-pit has not yet been sufficiently tested commercially, probably in large measure because of the difficulty of providing the grower with a simple method of judging maturity. A reliable index of maturity is in fact an urgent requirement both for research and commercial use, and the development of new tests ofomaturity and further trials of tlie new ones, including that of respiration. are essential features of research programmes. £