282 A M E R I C A N P O T A T O J O U R N A L

Reviews of Recent Literature Parker, W. H. and H. Bryan--Lord Derby Gold Medal Potato

Trials 1928. Jour. Nat'l. Inst. Agr. Bot. 2: 162-169, 1929.

The Lord Derby Gold Medal potato trials are designed by the Gold Medal committee which is composed of Ormskirk farmers and representatives of the National Institute of Agricultural Botany to test new varieties of potatoes immune from wart dis- ease. Nine entries were made in ]928 and in view of the fact that some of the varieties were known to mature early and others late two trials were a r ranged~an early bulkin~ trial for the reputed first earlies, and an ordinary yield trial for the later varieties. The committee considered that the commercial value of a first early variety was dependent on its capacity to produce at an early date a large bulk of marketable potatoes. Epicure, on account of its popularity was selected for control or check purposes, and NineW-fold was used as a second control. All plats were planted with sprouted cut sets. Only three vari- eties were entered. MacKelvie's 440 and 520 and Macbeth's Castle. They were rated by the committee in the order given. In the main crop yield anc~ maturi ty trials six varieties were entered-- The Baron. Cherry, Claymore, Electron. Incomer and Inverness Favorite, Great Scot. Majestic and Kerr's Pink were used as con- trols. Kerr's Pink, Incomer and Cherry were found of practically the same maturi ty; Inverness Favorite and Claymore are earlier than Kerr's Pink and later than Majestic. Electron was classed with Majestic and The Baron as earlier than all three controls. Brief comments are made regarding the desirable attributes of the tubers of each variety.

~ W . STUART.

Eden, T. and Fisher, R. A.--Studtes in Crop Variation. VI. Experiments on the Response of the Potato to Potash and Nitro- gen. Jour. Agr. Sci. XIX part 2, April 1929.

These experiments runing through 1925 and 1926 at the Rothamsted Station in England were designed to study the effect on potato yields of different sources of potash used in equivalent acre applications of actual potash. Low grade potash manure salt was compared with no potash, with sulphate of potash and with muriate (chloride) of potash. A marked response to potash was shown both years. In 1925 the depressing effect of the chloride form found in the low grade manure salts was not clearly shown, whereas in 1926 by a reorganization of the experiment affording more replicatiorts, this effect was well demonstrated. There was no significant difference in yield between the muriate and the sulphate forms of potash used in either year. The authors discuss the importance of plot technique as affecting

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precision of results. They recommend a system known as Lat in squares wherein the number of plot replications shall be equival- ent to the number of t rea tments studied.

- -E . V. HARDENBURG.

Goss, R. W.mThe rate of spread of potato virus diseases in Western Nebraska. Jour. Agri. Res. 39 (1) :63-74. 2 fig. 1929.

This is an example of the sort of detailed and complex records necessary to yield precise information on how fast , how far, and at what stage of the season potato virus diseases spread. Pre- sumptive conclusions regarding the agents of transmission are also drawn. Knowledge of this sort is essential to the develop- ment of effective practices and regulations in the production of disease-free potatoes yet, in the words of the author, "It is im- possible to forecast the amount of spread in one locality f rom the results of investigations conducted under different environ- mental conditions." This detailed information is a t present avail- able for but few seed potato localities. In the present study the method was followed of laying out a plot with known~ heal thy plants and a few specially located diseased plants to serve as sources of infection; the exact pat tern of the plot is then re- peated each year, the progeny of any hill occupying the same relative position as the parent hill.

The results may be summarized as follows: The mosaic dis- eases, mild and rugose, were t ransmit ted in but small amounts (~/~% in four years) and no spread occurred in two of these years. Spread of mosaic was correlated with the presence of aphids. From an initial infection with leaf roll of under 1%, there was an increase to about 10% in four years, with slight spread each year. Since aphids were not present every year, it is believed t h a t other insects were involved in leaf roll t rans- mission. Spindle tuber increased from 1% to over 40% in four years. In each year late-season infection, which was not evi- dent in the plants or tubers but was detected by a greenhouse index test , occurred to an important extent. In the years of greatest spread aphids were present, but as spread occurred each year, other insects--grasshoppers and possibly plant bugs - - were agents of transmission. However, not even spindle tuber, among the four virus diseases studied, spread across more than three or four rows ( leaf roll spread only to a distance of three hills f rom infected plants) in the four years the plot was main- tained. Along the row spread was more rapid in the case of spindle tuber, most of the plants in rows with infected plants contract ing the disease a f te r two or more years ' exposure.

- -F . WEISS.