Bitter pit

Not to be confused with Bitter rot of apple.

Bitter pit is a disorder in apple fruits, now believed to be induced by calcium deficiency. It occurs less commonly in pears.

Bitter pit in the 'Summerred' cultivar

Signs of bitter pit beginning on one apple, lower left

The disease was probably first reported in Germany where it was known as Stippen.^[1] It was also known as "Baldwin spot" and "blotchy cork" in North America. The name "bitter pit" was first used by Cobb in Australia in 1895.^[2] The disease has been shown as non-pathological and is now known as a disorder. When it occurs on the tree, it is known as "tree pit"; it may also occur in storage, when it is known as "storage pit".

Symptoms

The affected fruit have dark spots, about ½ cm diameter, which occur on the skin or in the flesh or both. The cells in the spots are dead (necrotic), and turn brown-black.^[3]

Causes

Early reports indicated that the disorder was affected by climate and growing conditions. Dry weather before harvest seemed to increase the condition. Light crops, heavy use of fertilizers, large fruit and early harvesting increased the condition. Fruit that were free of bitter pit at harvest were often severely affected after a short period of storage. Bitter pit has been widely reviewed over many decades.^{[4][5][6][7][8]}

The disorder became a major problem for exports from the Southern Hemisphere to Europe. The breakthrough in control came with the discovery in North America that the mineral calcium was low in affected fruit. This was confirmed elsewhere.^[9][10][11]

Control

Several decades of research in several countries with many cultivars showed that moderate levels of bitter pit could be controlled with the spraying of the trees with calcium chloride or calcium nitrate during the growing season.^[10] However, in the southern hemisphere where highly susceptible fruit had to be harvested early for export to Europe, the problem remained. An attempt to increase the calcium content by applying calcium after harvest had resulted in severe injury to the fruit.^[12] Export of susceptible apples from New Zealand was under threat and new methods for controlling bitter pit were investigated. While it was shown that bitter pit was reduced as calcium levels rose, it was not possible to determine a minimum level of calcium that would ensure that the disorder was controlled.^[13] The most effective treatment found for closed calyx fruit was to submerge the fruit in the calcium chloride solution and to apply a vacuum and immediately rinse in water.^[14][15] This overcame the injury problem and gave much better control of the disorder. The vacuum treatment was commercialized in New Zealand for the Cox's Orange Pippin cultivar in 1978, and was used for several years.^[16][17] However the treatment was expensive and could not be used for open calyx cultivars.

A simpler treatment was developed in Western Australia and was adopted in Australia and in New Zealand. This involved dipping the fruit in the calcium solution and rinsing in water after about 36 hours.^[18][19] This treatment has been confirmed by independent workers and has generally been adopted in Australia and New Zealand. Postharvest dipping in a calcium solution has been recommended in some other countries where bitter pit is severe.^[20] However the problem of fruit injury does not seem to have been addressed.

It appears that bitter pit can generally be reduced by using good horticultural practices. Usually spraying throughout the growing season with a calcium salt is also necessary for moderately susceptible cultivars. It is more difficult to control storage pit in highly susceptible cultivars as field spraying may not be able to apply sufficient calcium to the fruit. Improved control can be obtained by also dipping the fruit in a 2–3 per cent calcium chloride solution after harvest and rinsing the fruit in water after about 36 hours.^{[citation needed]}

References

1. Jaeger, G (1869) Uber das Peliz oder Stippinwerden Kernobstfrucht. Illus. Monash obst u-Weinbau 16: 16 : 318–319.
2. Cobb, N.A. (1895). Diseases of plants and their remedies. 11. Bitter Pit of apples. Agric. Gaz.N.S.W. 6 : 859–861.
3. . postharvest.tfrec.wsu.edu. Archived from the original on 5 May 2015. Retrieved 10 April 2018.
4. McAlpine, D. (1911–1916). Bitter Pit investigations. Rep 1–5 Govt. Printer. Melb. Aust.
5. Carne, W. M. (1948). The non-parasitic diseases of apple fruit in Australia. CSIR. Bull. Aust. No. 238
6. Bunemann, G (1972)—. Annotated bibliography on bitter pit of apples. Berlin Tech. Univ. Bibliogr. Ser. No 2.
7. Martin, D. (1961). Bitter Pit 1935–1959. Int.Refrig. Annex 1961 Bull 1. 155–159
8. Little, C. R., and Holmes, R. J. (2000). Storage for apples and pears. Institute for Horticultural Development Victoria. 528pp
9. DeLong, W. A. Variations in the chief ash constituents of apples affected by Blotchy Cork. Plant Physiol. 11:453–456
10. Garmen, P., and Mathis, W. T. Studies on mineral balance as related to Occurrence of Baldwin Spot in Connecticut. Conn. Agric. Expt. Sta. New Haven Bull. No 601
11. Askew, H.O., Chittenden, E.T., Monk, R.G., and Watson, J. (1960). Chemical investigations on bitter pit of apples. 11. N.Z. Agric.Sci.3. 141–168
12. Jackson, D.J. (1962). The effects of calcium and other minerals on the incide of bitter pit in Cox’s Orange apples. N.Z. J. Agric. Res. 5 : 302-9.
13. Wills, R.B.H., Scott, K.J., Lyford, P.B., and Smale, P. E. (1976). Prediction of Bitter pit with calcium content of apple fruit. N.Z. J. Agric. Res. 19 : –513-519.
14. Scott, K. J., and Wills, R. B. H. (1977). Vacuum infiltration of calcium chloride: A method for reducing bitter pit and senescence of apples during storage at ambient temperatures. HortScience. 12 : 71–72
15. Scott, K.J., and Wills, W.B.H. (1979). Effects of vacuum and pressure infiltration of calcium chloride and storage temperature on the incidence of bitter pit and low temperature breakdown of apples. Aust. J. Agric. Res. 30 : 917–928.
16. Scott, K. J. (2011). The control of Bitter Pit of apples with postharvest application of calcium chloride. YouTube video
17. Scott, K. J. (2012). Postharvest Horticulture. A scientist’s Life Work. A bibliography held in the National Library of Australia and the State library of New South Wales. 205 pp.
18. Scott, K. J. Hardisty, S. E. and Stafford, L.A. (1980). Control of bitter pit in early picked Granny Smith apples from Western Australia. CSIRO Food Pres. Quart. 40 : 29–32
19. Scott, K. J. O’Loughlin, J. England, B. and Roberts, E. A. (1985). Effects of water rinses after calcium chloride dips, with and without additives on control of bitter pit of apples. Aust. J. Agric. Res. 36:305–313.
20. Anon. (2000). Bitter pit of apples Fact Sheet Ontario Ministry of Agriculture; Anon. (2013). Apple fruit disorders related to calcium deficiency. Penn State Univ.

 

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