Blossom-end rot has a "physiological" cause; it is due to a lack of calcium. It is not caused by insects, fungi, bacteria, or any other pathogens. It is not a disease.
Worldwide. Wherever tomatoes are grown.
Mostly a problem of tomato, although eggplant, capsicum and watermelon are also affected.
The first sign of the disease is a clear or light brown area - often said to look 'water-soaked' - at the blossom end of the fruit, which eventually becomes dark brown or black, dry, sunken and leathery (Photos 1&2). Blossom end rot occurs at any time when plants are flowering and fruiting, but it is more common on the first fruit. Sometimes, fungal moulds grow on the surface of the rot after it has dried, and they are mistaken for the cause.
Blossom end rot is caused by a lack of calcium in the plant. This may mean that there is not enough calcium in the soil, or that it is present but the roots cannot take it up. Calcium is important in the growth of cell walls. It is especially important in rapidly developing parts of plants, such as the fruits. If there is not enough calcium, cells die and tissues rot; as seen here in the fruits.
There are several reasons why fruits show signs of blossom end rot. These are:
Symptoms of blossom-end rot first appear when the fruits are one-third to one-half full size, and still green. Not only are the fruits unsightly, and they may have moulds growing on the black areas, but also they ripen prematurely, and are inedible. They are neither fit for the market or home use. Losses can be severe, up to 50%.
Look for black areas of rot at the blossom end of developing fruits, especially on the first formed trusses; look to see if the rots are covered in fungal moulds.
The most common cause of blossom-end rot is erratic watering so that the plants get too little or too much water.
Varieties differ in susceptibility to blossom end rot, with plum or pear shaped varieties being the more susceptible.
AUTHORS Suzanne Neave & Grahame Jackson
Photo 2 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty. Limited, Canberra, Australia.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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