File:Canadian journal of agricultural science (20343015888).jpg

Title: Canadian journal of agricultural science
Identifier: canadianjournalo02ottauoft (find matches)
Year: [1] (s)
Authors:
Subjects: Agricultural Institute of Canada; Agriculture
Publisher: Ottawa (etc. )
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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November, 1921 SCIENTIFIC AGRICULTURE 93 Diseases of the Potato P>y B. T. DICKSON, Professor of Botany, Macdonald College. (Continued) (b) Mosaic and Mosaic Dwarf. W. A. Orton first described Mosaic as a disease of potatoes from observations he made in potato fields at Giessen wliile vis- iting in (lermany, although Quanjer be- lieves that the diesase lias been kuov/ji for a long time in Europe. Orton on his re- turn found the disease to be quite prevalent in Maine in the Green Mountain variety. This was in 1912 and since that time the disease has been found in practically every potato-growing area of t,he United States and Canada. The cause of the disease is not yet deter- mined, although it is certainly a systemic disease, and it has been placed here in Group 1 because of the established fact that aphids are agents of inoculation. While the disease may be regarded as new, as compared with Late Blight for instance, it is hig^ily infectious and 'has spread with alarming rapidity. In 1919 careful estimates made in Aroostook Coun- ty, Maine, of 40 fields of Green Mountain and the same number of Bliss Triumph showed an average of 28 per cent of in- fected hills of Green Mountain and 46 per cent in the case of Bliss Triumph. In some cases the diseased plants amounted to 100 per cent. It is therefore of para- mount importance that efforts be contin- ually made to check the spread of this insidious disease. The difficulty involved lies in the fact' that t^ie potato tuber, a vegetative part of the plant, is used for seed purposes and the causal principle may be present in the tubers as a result of late infection without there being distinct signs of the disease in the foliage. Symptoms of the Disease. The disease may manifest itself in either of two ways according to the variety or according to the locality. The typical symptom from w.hic^h the name arose is the mottling of the foliage. Lighter green areas occur in the leaves and these lighter green areas may be few or numerous, they may be very small or reach t^ie size of a quarter of an inch, and in shape are usually angular. The leaflets may also be more or less ruffled or wrinkled owing to the modified growth, and where tliis is the case t,iie wrinkles are likely to obscure tiie mottling at first sight. I'he above symp- toms are typical for Green Mountain po- tatoes. It migfht be added for those readei-s who have at their disposal a microscope ihat a thin freehand section through a light green area bordered with the dark green will show, even under the low power, t;iat in the light part, the palisade tissue has not been able to develop normally. The cells instead of being from four to six times as long as wide are approximately cubical or distinctly shorter. The Irish Cobbler, on the other hand, exhibits different characteristics. Here
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Plate 3.—Plant A is healthy. Plant B is suf- fei-ing with mosaic. Note at 1 the scars left by fallen leaves and at 2 a leaf which has just dropped. mottling is not usual but instead the leaves of affected plants are extremely wrinkled and dwarfed. The leaflets are smaller, the petioles are reduced and even the haulms are dwarfed. This gives rise to a type known as Curly Dwarf in extreme cases. The Rural varieties also shoAV this group of symptoms.

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