H.—34

Influence of Rootstock and Intermediate Scion on Core-flush in Granny Smith Core-flush is generally the most serious disease of Granny Smith apples in cool storage. It occurs much earlier than other diseases and very often is quite noticeable by mid-September. Much of the fruit of this variety comes from trees which have been reworked from some other variety, and it has been suggested that these intermediates might influence the susceptibility of the Granny Smith to core-flush, especially if the intermediate variety is itself susceptible to this disease. It was also thought that different rootstocks might have some influence on the disease. A postal survey was made of the Nelson and Hawke's Bay districts to ascertain the range of intermediate scion varieties used, and samples wore collected from trees that had been worked over from the most important of these intermediates. These were Cox's Orange Pippin, Delicious, Dougherty, Dunn s Favourite, Jonathan, Stunner, King David, London Pippin, Reinette du Canada, Statesman, and Washington. All these were themselves worked 011 to Northern Spy rootstock. In the Nelson district Granny Smith has also been worked direct on to the following rootstocks : Northern Spy, Large's Seedling, Ivory's Double Vigour, and East Mailing types XII and XVI. The results indicate that both intermediate and rootstock can influence the severity of scald in the scion variety, Granny Smith. The most striking results were obtained with the fruit from trees worked 011 to Reinette du Canada. These samples had the least core-flush of all the double-worked types, and this was true of fruit from both Nelson and Hawke's Bay. Intermediates which are themselves susceptible to core-flush gave variable results uncorrelated with their inherent susceptibility. In illustration of this, the following table gives typical percentages of core-flush with the susceptible varieties Dunn's and Statesman as intermediates. Data for the best of the intermediates, Reinette du Canada, are given for comparison :—

The two values quoted for Statesman from Nelson are of interest in that the higher percentage was recorded from trees that had been treated with boron to remedy a deficiency of this element in the soil. As regards the direct effect of rootstock, the worst core-flush (83 per cent.) was found when Granny Smith was worked direct on to Northern Spy stock. This is particularly unfortunate, because the majority of the trees in Hawke's Bay are of this type. The best results were from trees in which the variety was worked direct on to East Mailing rootstocks. Type XVI gave slightly better results (22 ner cent.) than type XII (25 per cent.). An interesting feature of the experiment was the way in which the intermediate varieties imparted some of their physical characteristics to the fruits of Granny Smith. This was particularly noticeable in colouring when the intermediate variety was a coloured type such as Dougherty or Delicious. Shape was also liable to be modified, the most noticeable example being the tallness imparted by King David. This work is being continued during 1945. Effect of Fertilizers on Cold-storage Quality of Apples Cox's Orange Pippin.—Nitrogen (N), when used alone, continues to increase breakdown and fungous losses, but when it is balanced by the inclusion of phosphate (P) and potash (K) in the manurial programme the storage quality of the fruit is equal to that of untreated control fruit. Superficial scald and storage pit were not influenced to any appreciable extent by manurial treatment. This season, for the first time, there was a divergence between the effects of ammonium sulphate and dried blood as sources of nitrogen. Ammonium sulphate gave rather less satisfactory storage quality in respect of breakdown and fungous disease. Dunn's Favourite.—'The season was characterized by an almost complete absence of severe breakdown m this variety, even after prolonged storage. Though N alone had little effect on breakdown or fungus and none on wilt, it substantially lowered the storage quality, chiefly through a sharp rise in superficial scald. PNK fruit kept almost as well as the untreated, except for a very slightly higher incidence of scald. An experiment dealing with the rate of application of ammonium sulphate clearly showed the effect of Non scald development. Fruit from trees receiving 0, 2, and 4 lb. showed respectively 1, 10, and 27 per cent, of scald of commercially significant intensity. The trees were carrying good crops and, as has proved usual in such cases, N had no influence on the incidence of fungus or commercially significant breakdown. Similar results were obtained in a liming test, in which an increase in nitrogen status of the trees had been brought about indirectly by lime through better growth of leguminous cover-crops. Delicious— The PNK fruit was again in every way equal in storage quality to the untreated control fruit, but this year, for the first time, the use of N by itself gave a slightly inferior result, manifest as a small rise in fungus and superficial-scald percentages. Jonathan — The variety stored exceedingly well this season, and even on long storage there was virtually no Jonathan-spot. In a trial in which all trees received a basic dressing of P and K, a high N application (4 lb. ammonium sulphate per tree) increased susceptibility to fungus and breakdown. With a more moderate application (2 lb.) the storage quality was as good as that of the no-nitrogen control. In another trial in which a basic treatment of P and N is supplemented by potash in one set of plots, the K-treated fruit continued to show a greater resistance to breakdown and fungus, and also proved more resistant to superficial scald.

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Intermediate. Nelson Fruit Hawke'sBayFruit Core-flush. Core-flush. Per Cent. Per Cent. Dunn's .. .. .. .. 69 25 Statesman .. .. '' \ 74 Reinette du Canada .. .. 20 21