The effect of crop size and low levels of major elements on fruit characteristics and incidence of storage pit in Sturmer apples in pot experiments

Pot experiments in sand culture with Sturmer apple trees were continued to study the effects of low levels of major elements on the storage type of bitter pit. Compared with a complete treatment, the no calcium treatment induced high susceptibility to storage pit but had no other significant effects. The other treatments had no effect on pit. Pitted fruits had a lower calcium and higher protein nitrogen content than sound fruits but there was no evidence that the level of other mineral elements was affected. Other fruit responses to low level treatment are discussed. No nitrogen and no phosphorus prevented fruit set but no magnesium and no potassium increased it. However, many of the effects on fruit cell number and levels of mineral elements in fruits may be due to competition between the fruits for limited resources rather than any direct physiological effect. Differences between years in fruit responses may be due to alternate cropping with differences in carry over of reserves or differences in level of competition between fruit and vegetative growth and caution is necessary in interpreting results.

Apple fruit cell numbers in relation to cropping alternation and certain treatments

Fruit cell numbers in a block of Jonathan apple trees with an alternate cropping rhythm were studied over the period 1955–1962. The number of cells per fruit showed a rhythm in phase with the crop level, while the percentage dry matter showed a rhythm counter to this. Seed numbers per fruit showed no rhythm. The rhythm in cell numbers proved very persistent, continuing for some years under severe thinning treatments. Against this background four types of treatment designed to affect cell numbers were imposed over the period 1957–1962: (1) Decreasing competition between fruits, by thinning by hand, by DNOC, and by NAA. (2) Attempts to increase competition, by delaying abscission with 2,4-D. (3) Attempts to stimulate cell division by kinetin plus synergistic compounds. (4) Attempts to supplement nutrition which forms the background to cell division. No significant effects resulted from the 2,4-D, kinetin, or nutritive supplements, but reducing competition by thinning, either by hand or by DNOC, resulted in an increase in cell numbers which was cumulative over several years. Thinning with NAA did not increase cell numbers. The implications of these results are discussed.

Bitter pit in the apple variety Sturmer in a pot experiment using low levels of major elements

The results of a pot experiment showing the influence of low calcium, low magnesium, and complete fertilizer on the pit incidence and mineral content of Sturmer apples are reported. Low calcium treatment resulted in high incidence of pit, low levels of calcium and high levels of potassium, magnesium, phosphorus, and nitrogen in the fruit compared to complete fertilizer and low magnesium treatments. In the ash, though the proportion of calcium was significantly lower, the proportions of potassium, magnesium, and phosphorus did not change. The difference in the characteristics examined between pitted and sound fruit in the three treatments were in the same direction as those between fruit from low calcium and complete fertilizer treatments, and the differences in calcium level were significant. The response to low calcium treatment was a much greater relative molar increase in nitrogen, potassium, magnesium, and phosphorus than the molar decrease in calcium. The evidence supports an hypothesis that the primary cause of pit is low calcium status which under water stress in the leaves and fruit induces an increase in nitrogen, respiration rate, and mineral content but gives no indication which of these causes the lesions.

Jonathon spot – Three factors related to incidence, fruit size, breakdown, and seed numbers

Observations are reported which show that: (1) There is an interaction between the disorders Jonathan spot and breakdown. There is a negative correlation between them, but the same fruits tend to be susceptible to both disorders. (2) In the absence of other disorders there is a positive intercorrelation between percentage Jonathan spot, mean fruit size, and mean seed number both within and between trees. (3) In the one fruit size group on a tree, fruits with Jonathan spot have a higher mean seed number per fruit than sound fruit, and the seeds have a greater tendency to germinate. (4) Within trees, a thinning treatment which produces fruit of differing sizes but with the same seed number does not alter the percentage Jonathan spot. Between trees, a thinning treatment which produces fruit of the same size but a differing seed number results in differing levels of Jonathan spot.

Bitter pit in the apple variety Cleopatra in Tasmania in relation to calcium and magnesium

When spray treatments were applied to half-trees of Cleopatra apples, it was shown that magnesium nitrate increased the incidence of pit and calcium nitrate decreased it. There was a suggestion that borax decreased the effectiveness of the calcium nitrate treatment. Magnesium or calcium nitrate, with or without borax, did not affect the potassium, magnesium, phosphorus, or nitrogen content of the fruit cortex. Calcium nitrate in 1959 increased the calcium content but magnesium nitrate had no effect. There was no significant difference in the content of potassium, magnesium, or phosphorus between 1958 and 1959, but the calcium content was 3.3 times as high in 1958. Pit incidence was low in 1958 and high in 1959. No significant difference in content of these four elements could be demonstrated between sound and pitted fruits. The results support the view that calcium is the critical element in pit incidence and that magnesium may play an important part.

Variation between apple fruits and its relation to keeping quality. III. Between-season variation in relation to seasonal climate

Studies were made of seasonal effects on ripening changes and disorder incidence in different varieties of apples in Tasmania for the 10-year period, 1933-1943. Most of the changes associated with ripening, namely, ground colour change, acid loss, starch conversion, soluble solids accumulation, softening, and respiration rise did not necessarily keep pace with each other and responded differently to seasonal variation, but there appeared to be a constant relation between firmness and acid level. In the final analysis, seasonal variation in the level of disorders was mainly related to differences in mean fruit size and when the size factor was held constant between seasons the differences remaining were relatively small. In the case of pit, some of these remaining differences could be accounted for by differences in relative maturity but in the case of breakdown, relative incidence between seasons was not related to relative maturity. There was an association of early blossoming with low incidence of pit and breakdown independent of later differences in seasonal climate. The results support the theory that low temperatures in the months prior to harvest increased susceptibility to breakdown.

Variation between apple fruits and its relation to keeping quality. II. Between-tree variations due to cropping factors

Storage trials and chemical tests of fruit from individual trees of plots of apple varieties Cox and Cleopatra were made. Samples from each tree were picked on the same dates each year and treated in three ways: composite samples from 100 fruits of separate zones within the fruit were examined for acid and soluble solids content; samples of 25 fruits, at progressive stages of maturity, were examined for pressure, ground colour, starch conversion, total acid, and soluble solids of the mid-cortex region; and samples of 200 fruits were stored at 32-340°F for 10 weeks followed by 3 weeks at room temperature. The mean fruit size and total number of fruits per tree were found and from the latter over a 10-year period a crop index was developed. The data were given statistical treatment. Results from samples picked at successive maturities from light-crop and heavy-crop trees showed that up to a late stage of maturity light-crop fruit had a larger diameter, higher acidity, earlier colour change, and later starch conversion than heavy-crop fruit; the level of soluble solids in light-crop fruit was lower in the earlier stages of maturation, but rose faster and might eventually become higher than in heavy-crop fruit. This relationship was called the simple crop pattern, and though there were differences between the different zones within a fruit, these differences remained constant during maturation. Respiration per unit fresh weight was the same for different crop levels. Results from samples picked at a standard date in several years from trees having a range of cropping levels in each year gave measures of the variables, number of fruits per tree, crop index, mean diameter, acid, soluble solids, starch conversion, pressure, colour change, and incidence of the disorders pit and breakdown. The intercorrelation of these variables in each year and the partial correlation holding mean diameter constant between trees were examined. There was a correlation of all variables (except soluble-solids level) which had the same sign consistently in all years and there was evidence that in the changes of maturation at least three groups of processes followed independent courses: acid-starch-pressure, colour change, and soluble solids. The highest correlation of the disorder pit was with mean diameter and if there was another factor in addition, the most consistent seemed to be acid. The correlation of the disorder breakdown with diameter was extremely high and there was no advantage in choosing any of the other measures to increase the value of mean diameter alone as a measure of breakdown liability. The mean fruit diameter per tree is by far the best index of the physiological behaviour of the fruit from it, being more reliable than any measure of crop in terms of numbers or any of the common chemical or physical changes associated with ripening. An explanation for this relation is suggested in terms of the mean cell size per fruit and respiration per unit protein. There was a physiological interaction between pit and breakdown, each tending to suppress the other, which emphasized the importance of a respiratory phase in the development of pit.

Variation between apple fruits and its relation to keeping quality. 1. Within-tree variation

Variation within trees of diameter, colour, firmness, starch conversion, total acid, and soluble solids of fruit was examined for branches of different aspect for four varieties of apples and at different stages of maturity for one of them. Incidence of the storage disorders pit and breakdown in Cox Jonathan spot and deep scald in Jonathan, and pit in Cleopatra and Sturmer was examined in quarter-inch size groups within trees. The data revealed that the frequency distribution of all variables except starch conversion were of the unimodal, symmetric, or slightly skew type. Starch conversion showed strong positive skewness at low values and strong negative skewness at high values, which is characteristic of variables which have defined limits. As fruit matured, variability increased, except for starch conversion, which decreased. For three varieties, but not for a fourth, the pattern of correlation between variables within branches resembled the pattern obtained by correlating the variables at different stages of maturity of fruit from one source, but heterogeneity between branches weakened the correlation for the tree as a whole. The pattern of means in relation to aspect was not necessarily the same for two adjacent trees or for the same tree at different maturities, indicating that aspect as such was not the cause of heterogeneity within a tree but that the branches behaved as organic units. Size was correlated within a tree with incidence of the disorders pit and breakdown, but while the relationship appeared to be linear over the restricted size range there was no justification for extrapolating this relationship. There was evidence of between-branch variation in disorder incidence.