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Show DISEASES OF POTATO Problems of Increasing Importance Im-portance to Agriculture. No Trouble Has Caused Greater Difference Dif-ference of Opinion as to Nature and Cause Than "Leaf-Roll" Symptoms Vary Greatly. (By N. ORTON.) No plant disease in this generation has been the subject of such general discussion as that known in Germany as the "Blattroll-krankhelt," herein named "leaf-roll." None has arouBed greater difference of opinion as to its nature and cause, and no other malady Df plants is today receiving so much in- Comparison of Healthy and Diseased Hills of Same Varieties. vestigation by skilled pathologists as this. Possibly no disease which has appeared since the forties presents a greater menace to potato culture. The literature on leaf-roll has become so voluminous that few will undertake to peruse all the contributions. Leaf-roll is a disease characterized by an upward rolling of the leaves, by a decreased yield of tubers, and by transmission of the diseased condition condi-tion through ubers planted. Its symptoms symp-toms vary so much in detail that they can be most clearly outlined by separate sepa-rate treatment. The rolling of the leaves is the most constant and conspicuous symptom of this disease. The leaflets curl or roll upward on their midrib, often assuming assum-ing a nearly tubular shape, and giving a plant a starving appearance. This rolling is sometimes restricted to the upper leaves, while irt other cases all or nearly all of the leaves may exhibit It. This type of roll is distinct from the curly-dwarf condition, but a very similar roll may be induced by other causes. The color of the foliage changes with the advent of leaf-roll, but these Solor symptoms vary greatly, from cases where the leaves assume an unhealthy, un-healthy, light-green color to those marked by pronounced yellowish, reddish red-dish or purplish tints. The effect of leaf-roll on the plant Is to check development. There is a lessening or cessation of growth. The shoots remain short and the leaves Upper Illustration Shows Yields of Healthy and Diseased Hills Caused by Curly-Dwarf. Lower Illustration Shows Yields of Diseased and Healthy Hills Caused by Leaf-Roll. stand more upright. There is, however, how-ever, no such shortening of stems and leaf ribs as occurs in curly-dwarf, with its resultant deformation of the plant The duration of life of the plant it shortened by leaf-roll. This is a rela tive matter, since the leaf-roll cases may die earlier, as would be expected of sick plants. The true leaf-roll is inheritable. The tubers from diseased plants produce diseased progeny, as a general rule. This affords a means of distinguishing from the genuine leaf-roll those temporary tem-porary conditions which give rise to a similar appearance of the plants. All those who are best acquainted with the trouble agree as to the results re-sults of planting diseased seed stock. This point is one of capital importance in the control of the disease and of great interest in its bearing on the nature of the disease. That leaf-roll is not communicable from diseased to healthy plants is the conclusion to be drawn from all available evidence. |
