{{Short description|Physiological plant disorder}} {{Distinguish|Bitter rot of apple}} 220px|thumb|Bitter pit in the 'Summerred' cultivar thumb|right|Signs of bitter pit beginning on one apple, lower left '''Bitter pit''' is a disorder in apple fruits, now believed to be induced by calcium deficiency. It occurs less commonly in pears. The disease was probably first reported in Germany where it was known as ''Stippen''.<ref name="Jaeger">Jaeger, G (1869) Uber das Peliz oder Stippinwerden Kernobstfrucht. Illus. Monash obst u-Weinbau 16: 16 : 318–319.</ref> 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.<ref name="Cobb">Cobb, N.A. (1895). Diseases of plants and their remedies. 11. Bitter Pit of apples. Agric. Gaz.N.S.W. 6 : 859–861.</ref> 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.<ref>{{cite web|title=Market Diseases of Apples, Pears, and Quinces: Bitter Pit|url=http://postharvest.tfrec.wsu.edu/marketdiseases/bitterpit.html|website=postharvest.tfrec.wsu.edu|access-date=10 April 2018|archive-url=https://web.archive.org/web/20150505054533/http://postharvest.tfrec.wsu.edu/marketdiseases/bitterpit.html|archive-date=5 May 2015|url-status=dead}}</ref>

== 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.<ref name="McAlpine">McAlpine, D. (1911–1916). Bitter Pit investigations. Rep 1–5 Govt. Printer. Melb. Aust.</ref><ref name="Carne">Carne, W. M. (1948). The non-parasitic diseases of apple fruit in Australia. CSIR. Bull. Aust. No. 238</ref><ref name="Bunemann">Bunemann, G (1972)—. Annotated bibliography on bitter pit of apples. Berlin Tech. Univ. Bibliogr. Ser. No 2.</ref><ref name="Martin">Martin, D. (1961). Bitter Pit 1935–1959. Int.Refrig. Annex 1961 Bull 1. 155–159</ref><ref name="Little Holmes">Little, C. R., and Holmes, R. J. (2000). Storage for apples and pears. Institute for Horticultural Development Victoria. 528pp</ref>

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.<ref name="DeLong">DeLong, W. A. Variations in the chief ash constituents of apples affected by Blotchy Cork. Plant Physiol. 11:453–456</ref><ref name="Garmen Mathis">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</ref><ref name="Askew">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</ref>

==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.<ref name="Garmen Mathis"/> 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.<ref name="Jackson">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.</ref> 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.<ref name="Wills">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.</ref> 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.<ref name="Scott Wills 1977">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</ref><ref name="Scott Wills 1979">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.</ref> 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.<ref name="Scott 2011">Scott, K. J. (2011). The control of Bitter Pit of apples with postharvest application of calcium chloride. YouTube video</ref><ref name="Scott 2012">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.</ref> 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.<ref name="Scott 1980">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</ref><ref name="Scott 1985">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.</ref> 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.<ref name="recomm">Anon. (2000). Bitter pit of apples Fact Sheet Ontario Ministry of Agriculture; Anon. (2013). Apple fruit disorders related to calcium deficiency. Penn State Univ.</ref> 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|date=September 2023}}

==References== {{reflist}}

{{Commons category|Bitter pit}}

Category:Physiological plant disorders