Nitrogen Metabolism During Storage in Relation to the Breakdown of Apples. I. Changes in protein nitrogen level in relation to incidence

Protein nitrogen content was followed in fruits of four apple varieties during cool storage under conditions designed to induce different rates of water loss. Increase in protein nitrogen content during cool storage did not appear to be related to the development of breakdown. High nitrogen level in the fruit, high relative humidity in the storage atmosphere, and advanced maturity at harvest all increased susceptibility to breakdown, but only the first of these factors influenced the protein nitrogen level. An inverse relationship between percentage water loss and breakdown incidence was demonstrated.

Protein Nitrogen Content and Phosphorylative Activity of Apple Fruits During Ripening and Senescence

Respiratory activity, protein nitrogen content, and rate of esterification of infiltrated 32p have been followed during ripening and senescence at 20�0 in detached fruits of five apple varieties.

The interrelation of susceptibility to breakdown, cell size, and nitrogen and phosphorus levels in Jonathan apple fruits

A block of Jonathan apple trees were treated for 4 years as individual tree plots with nil, nitrogen, nitrogen + phosphorus, and nitrogen + potassium applied as sprays during two periods, either in spring before bud differentiation or after bud differentiation in mid January. The treatments had no effect on the levels of phosphorus or potassium in the fruit. Spring applications had no significant effect on the nitrogen content, but summer applications a marked one, though there was no evidence of a cumulative build-up or any effect on cell number per fruit. These increases in nitrogen content were accompanied by small increases in breakdown level, but only when an inherent seasonal susceptibility existed. Only a diminishing proportion of the additional nitrogen was incorporated into the protein fraction, and the preclimacteric respiration rate was not affected significantly by the increase in protein. Except for percentage dry matter, there was a wide variation in the values between trees of the variables, which permitted a multiple regression analysis. The regression of breakdown and cell volume was positive and highly significant in all years. Except for the year of very low incidence, there was a significant positive relationship between breakdown and nitrogen level, and a consistent negative relationship between breakdown and phosphorus level which was significant in the years of high breakdown incidence. No relationship could be shown between breakdown and potassium. Similar results were obtained by using a percentage fresh weight or percentage dry weight basis for the nitrogen, phosphorus, and potassium contents, or by using actual values or a log (x + 1) transformation for the variables, though there were some advantages in using the latter. The results suggest an important physiological interaction between breakdown and cell volume, nitrogen, and phosphorus.

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.