Apical necrosis

 (blossom-end-rot)

• Symptoms :
  • moist lesions appearing at the end of the fruit, at or near the pistillate attachment. Diffuse at first, they turn brown and gradually spread thereafter (figure 1).
  • broad brownish to black weathering at term, more or less concave and well defined, of rather dry consistency (figures ).
  • sometimes essentially internal browning of some seeds and of a more or less significant portion of the placenta located in the pistillate part of the fruits . It may happen that this internal lesion takes on the appearance of a corky fibrous mass. This internal necrosis would correspond to a little evolved or attenuated form of classic apical necrosis.

• Cause(s) : This condition is linked to a lack of calcium in the distal part of the fruit following a lack of absorption of this element by the roots or its insufficient transport via xylem. Several parameters can explain these two situations:
  • a real calcium deficiency or an antagonism of this element with other elements of the soil or the nutrient solution (NH ₄ ⁺ , NO ₃ ^- , Mg ⁺⁺ );
  • high salinity induced by insufficient watering or high electrical conductivity of the nutrient solution, limiting calcium absorption;
  • heavy sweating;
  • too rapid growth of plants and fruits;
  • a root system that is naturally limited or following the development of lesions of biotic origin (root bioaggressors) or abiotic (poorly prepared soil, mutilating tillage for the roots, root asphyxia, etc.), this reducing water absorption and calcium (see topic Root asphyxia );
  • Insufficient or badly distributed irrigations causing excessive fluctuations in soil moisture.

In addition to these previous factors, apical necrosis manifests itself particularly during and following hot and dry climatic periods.

• Diagnostic clues :
  • physiological disorder commonly observed in all types of culture, especially in those irrigated by furrowing, flooding, or among amateur gardeners using a garden hose;
  • manifests itself at all stages of fruit development, but it occurs especially when the latter have reached one-third or one-half of their maximum size;
  • the affected tomatoes are often the first formed, which ripen more quickly;
  • various micro-organisms, secondary invaders, can be responsible for rot.

• Possible confusion :

• Remedies :
  • Ensure maximum comfort for plants;
  • Ensure optimal hygrometry in shelters and limit plant transpiration as much as possible (whitewashing or sprinkling of roofs);
  • Avoid subjecting plants to hot, dry wind;
  • Ensure fertilization (avoid excess, particularly nitrogen) and optimal calcium intake;
  • Above ground, enrich the nutrient solution with PO ₄ H _{2 ^-} and Cl ^- , these two elements favoring the absorption of calcium;
  • In the soil, maintain an adequate level of phosphorus , especially at planting, and a soil pH between 6.5 and 6.8;
  • Avoid salinities excessive
  • Cultivate less susceptible varieties ;
  • Carry out regular stripping in order to maintain a good balance with the fruit load;
  • Mulch the soil to maintain a more constant humidity;
  • Avoid mutilating roots during soil maintenance operations.