CONTRIBUTIONS FROM THE WISLEY LABORATORY. 595 



CONTRIBUTIONS FROM THE WISLEY LABORATORY. 



XIX. — Leaf Blotch in the Potato ' President.' 



By A. S. Horne, B.Sc, F.G.S., F.L.S. 



In a former paper in this Journal I described as "Leaf Blotch"* 

 a disease of the potato ' President ' in Scottish crops grown from 

 Continental seed tubers. It will be recalled that many of the plants 

 in the field crop were dwarfed ; the foliage curled, turned yellowish 

 green, or yellow, and became blotched ; and that these bad plants 

 produced either very small tubers or none at all. 



It is clear that a condition of this kind in a variety is one that 

 needs urgent and careful study, since considerable loss might be ex- 

 perienced through using it — the greater the proportion of bad plants 

 in a field crop, of course, the smaller the total yield and the smaller 

 the return on the total outlay incurred for " seed " and labour. 

 Accordingly investigations were at once commenced (1911). Tubers 

 from good plants and bad plants respectively, obtained from Dunbar, 

 were planted at the Chelsea Physic Garden and the South-Eastern 

 Agricultural College, Wye, and it was found that not only did tubers 

 from bad plants (always of small size) give rise without exception to 

 bad plants, but tubers from good plants gave rise to a certain number 

 of bad plants at both Chelsea and Wye. The bad plants at both 

 Chelsea and Wye almost exactly resembled those I saw in the potato 

 fields near Edinburgh and Dunbar, but the fungus, Macrosporium 

 solani, which appeared on the foliage of the Scots plants was absent 

 from those grown in the above-mentioned English localities. With the 

 details of these earlier experiments the present Report is not concerned. 



The first account of this pathological condition in the potato 

 1 President ' appeared in the Society's Journal, and the investigation 

 has been continued at Wisley, since the problem promises to prove 

 of exceptional interest and importance, and indeed gropes, as it 

 were, at the very root of a great deal of what is known as potato 

 disease. 



The work carried out at Wisley includes : 



(a) Experiments with seedlings raised from seed saved at Dunbar 



(b) Experiments with tubers. 



Whilst examining bad foliage obtained from Scotland in the 

 autumn of 1910, indications of the activities of insects were discovered ; 

 accordingly, the writer, at that time engaged in research at the Imperial 

 College of Science, South Kensington, sought the advice of Professor 

 H. Maxwell-Lefroy, and succeeded in obtaining his co-operation 

 with the object of attempting to determine the part played by insects 



Horne, A. S., " On Potato 1 Leaf Blotch ' and ' Leaf Curl ' " {Jour. R.H.S. 

 xxxvi. (1911), p. 618). 



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