Cell size, total and protein nitrogen, and preclimacteric respiration have been studied for light and heavy crop fruit of certain Tasmanian-grown apple varieties. Differences in size of fruit from light and heavy crops have been shown to be due mainly to differences in cell size rather than in cell number. Respiration per cell, protein nitrogen per cell, and cell volume were closely intercorrelated but respiration per unit protein is greater in light crop fruit than in heavy crop.
Fruits harvested from Granny Smith trees known to be affected to varying degrees by apple green crinkle virus were held in cool store for five months before analysis for their total nitrogen and protein nitrogen contents. Fruit seed number, cell number, and dry matter content were also determined. There tended to be a greater incidence of superficial scald in fruit from infected trees. Fruits from infected trees were smaller, had a higher dry matter content, a greater proportion of protein nitrogen to total nitrogen, and fewer cells than those picked from healthy trees. Within infected trees the total nitrogen content decreased as the severity of fruit crinkling increased. The results are discussed in relation to effects of the virus on yield, the physiological status of infected trees, and a consideration of the likely storage disorders to be encountered in fruit from healthy and infected trees.
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.
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.
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.
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