Potato Stocks Research Articles

Testing seedling potato stocks for specific horticultural factors under controlled conditions

Testing seedling potato stocks for specific horticultural factors under controlled conditions

Studies on Aphides Infesting the Potato Crop: Ii. Aphis Survey: Its Bearing Upon the Selection of Districts for Seed Potato Production

Summary.1. A comparative study has been made during 1928–1933 of the aphis infestation at successful seed potato producing centres, where there has been no increase in virus infection among the stocks, and also at unsuccessful centres, where the increase in virus infection has been large and rapid.2. The technique developed for this study—one which is applicable for an aphis survey of prospective seed potato producing areas—is given. Identification, in the field, of the different species of aphides infesting potato is desirable in such a survey, and descriptions, with photographs, are presented.3. Ecological notes on the development of the aphis infestation show that M. persicae—the species that is generally responsible for the spread of virus diseases among potatoes—hibernates as apterae in considerable quantity on winter Brassicae, particularly savoys. These plants constitute the main source of alate spring migrants in most rural districts. The main migration of alatae takes place, normally, in early June, and, in North Wales, is largely from the east. Alatae are not common during July and August and do not increase until the late September migration from potatoes.4. The index figure of infestation at centres in which there was a rapid increase in virus diseases among the potato stocks always exceeded 100 M. persicae per 100 leaves, and attained such numbers as 1000 individuals per 100 leaves. At centres where there has been no increase in virus infection, the index figure of infestation has not exceeded 20 M. persicae per 100 leaves. The period at which this index figure should be obtained is important, and, with certain exceptions, mid‐July proved to be the most satisfactory. It is essential that the figure should be an index of the intensity of the initial infestation of alatae from outside Bources and their subsequent spread, and should not be simply an index of the rate of reproduction of aphides within the field.

VIRUS DISEASES IN RELATION TO COMMERCIAL SEED POTATO PRODUCTION

SUMMARY Under a scheme, begun in 1927, and supported by a special grant from the Ministry of Agriculture since 1928, an attempt is being made to test the value of certain localities in North Wales for the production of seed potatoes. Evidence is produced to show that out of fifteen farms originally selected for this purpose, eight have maintained their stocks without increase of virus diseases, three have shown only a slight increase, whilst four have been discarded from the scheme. Replicated yield trials at the College Farm proved that seed mixed from these eleven farms was equal to Scotch “stock” seed, and the value of this Welsh seed was confirmed by trials in a number of Welsh counties in which it was tested against ordinary T.S. Scotch seed. Concurrently with this, a study has been made of the aphid population on the potato crops at these centres, which has led to the following conclusions: The absence of increase of virus diseases, and of leaf‐roll in particular, at the more successful centres is not due to the scarcity of aphides, nor to the absence of known vectors of the diseases, such as Myzus persicae. Neither can it be attributed to the non‐infective condition of the aphid vectors present at these centres since representative samples, taken from potato crops, transmitted leaf‐roll to healthy plants under glass. With one exception no transmission occurred with any of the species of aphides when taken from apparently healthy plants in a partially diseased crop. In samples taken from leaf‐roll plants transmission only occurred when they included Myzus persicae. The accumulated data suggest that the maintenance of health in potato stocks is influenced not merely by the relative abundance of aphides, but rather by the relation between the date of maximum infestation and the stage of maturity of the foliage. The more successful centres, each year, showed either a delayed maximum infestation and/or the foliage was cut down earlier than at the less successful centres. The relative movement of aphides within the crops at the different centres is certainly of importance, but this is conditioned by many factors which are still under investigation.

The Maintenance of Healthy Stocks of Potatoes in England

1. An attempt to maintain the health of a stock of Scotch seed Majestic in England is described.A small stock of seed obtained direct from Scotland was split up into three equal portions A, B, C, which were grown isolated from each other and all other potatoes for three years (1927–9).A. Remained unrogued.B. Had all plants showing virus disease symptoms rogued out and the requisite seed saved from the remaining plants when mature.C. Had a similar quantity of seed saved from ostensibly healthy plants when immature.2. In a final chequer board yield trial fresh Scotch “stock” seed, which can be assumed to be above the average of ordinary Scottish seed, beat stocks A, B and C significantly. There was no significant difference in the yields from the stocks obtained by the two methods B and C and both stocks beat the mature unrogued stock A significantly.