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The ‘phloem necrosis’ virus disease of tea in Ceylon II. Field observations and effect on yield
Author(s) -
Bond T. E. T.
Publication year - 1944
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1944.tb06742.x
Subject(s) - biology , phloem , yield (engineering) , acre , toxicology , horticulture , agronomy , botany , metallurgy , materials science
After a brief discussion of the methods and accuracy of diagnosis of the ‘phloem necrosis’ disease in the field, the results of plot records taken over a number of years are presented. These are compared with the figures supplied from estates for the removal of non‐productive diseased bushes, which is undertaken as a routine measure of control and regeneration of affected fields. Taking all the evidence together a frequency of at least 25% diseased bushes is suggested for the aggregate acreage of tea above 6000 ft. At lower elevations no reliable estimate is possible. Despite the pronounced effect on individual bushes there appears to be no general tendency for the yield of affected estates to decline. Two estates, believed to be representative, are dealt with in which a decline in yield occurred from 1929 to 1930, followed by a recovery some 4 or 5 years later. The fields judged to be most heavily affected in each of the two properties, respectively, show a decline in yield relative to the estate as a whole, not exceeding 19 1b. made tea per acre per annum, which is only 33% of the mean yield during the last 10 years. The great variability in individual bush yields is stressed, and the conclusion is drawn that the elimination of unproductive bushes and their replacement by supplies of a type which, so far, has remained unaffected (although possibly ‘carrying’ the virus) will more than counteract the effect of the continued and gradual deterioration of the necrotic bushes remaining. The distribution of diseased bushes in the field is irregular, and records from observation plots have mostly given positive results on examination by Cochran's geometric series ‘aggregation’ test and the X 2 test for ‘neighbour infection’. The rate of spread of the disease in the different areas is highly variable, and doubling of the incidence of infection may occur in periods ranging from 3 1/2 to less than 1 year. Two ‘rogueing’ experiments are described, the results of which lend further emphasis to the importance of bush‐to‐bush spread. The course of the disease in these experiments has been expressed by means of the Verhulst‐Pearl logistic curve, whence it appears that complete rogueing of all ‘necrotic’ and ‘suspected’ bushes at 6‐monthly intervals has reduced the rate of spread to about one‐third of the value for the unrogued plots.