In addition to the numerous biotic causes (pathogens and pests) that threaten greenhouse tomatoes, growers periodically have to contend with losses—sometimes substantial—due to abiotic causes.

This refers to physiopathies or physiological disorders, generated by conditions of crop stress that induce morphological or chromatic changes in the plant or fruit. This results in stunted production or low-quality berries, sometimes rendering them unsaleable.

It is important to delve deeper into these aspects because sometimes growers do not fully realize how small agronomic adjustments could increase profits without having to increase production volume. Consider the containers filled with berries discarded due to blossom end rot, cracking, puffiness, catface, blotchy ripening, etc.: by the end of the cycle, these physiopathies can account for 10-20% of the fruits actually produced but discarded. These figures—in some ways optimistic—should not be surprising, as often a large part of the discarded fruit remains in the greenhouse, on the ground, making it impossible to quantify the total weight. Therefore, recovering even half of this waste can “free of charge” increase production by 5-10%, with significant consequences for the final balance of the cropping cycle. Let’s take a closer look at these aspects in an attempt to stimulate a pragmatic approach that helps minimize the incidence of physiological disorders. In this article, we examine the three main physiopathies that directly affect the fruits, which are the commercial organs of the tomato plant:

  • Blossom End Rot (BER)
  • Cracking (Splitting)
  • Blotchy Ripening (Uneven Ripening)

lossom End Rot (BER)

Blossom End Rot (BER) is a physiopathy that affects the distal portion of the berry due to a localized calcium (Ca) deficiency. It appears as a lesion ranging in color from grayish to necrotic, rendering the fruit unsaleable (Photo 1).

BER is often not a consequence of actual Ca deficiency in fertigation but rather an imbalance between the speed of Ca translocation to the distal portion of the fruit and the speed of fruit growth itself. Therefore, it manifests primarily during hot periods when high temperatures induce rapid fruit growth.

Ca is an element that moves within the plant with water in the evapotranspiration flux. For this reason, it concentrates in areas with the highest stomatal density, i.e., the leaves (which is why Ca concentration is low in the fruits). Furthermore, within the fruit, the proximal portion (near the peduncle) always has a higher Ca concentration than the distal portion. In conditions of high temperature (T) and low relative humidity (RH), the Vapour Pressure Deficit (VPD) of the environment increases, causing greater foliar evapotranspiration which diverts water and Ca towards the leaves through the xylem vessels. Therefore, the most “explosive” combination for BER occurs precisely in conjunction with a hot and dry environment, because both the fruit grows rapidly and the leaf transpires heavily, drawing Ca away from the fruit.

To avoid or contain BER, the objective of cultural management in the greenhouse, even in the months preceding the expected heat peak, is to prevent conditions that will limit Ca absorption.

The greatest fruit sensitivity to BER extends up to the third week after flowering, which is the period of maximum cell division.

Since the causes of BER are manifold, action must be taken on multiple fronts to reduce its incidence:

 

🥬 Plant Management

  • Balanced plant (neither too vegetative nor too generative).
  • Defoliate regularly, avoiding an excessive number of leaves relative to the fruit load.
  • Reduce the fruit load (cluster pruning/thinning).
  • Do not remove BER-affected fruits from the plant until close to harvest.
  • Promote an abundant root system uniformly distributed in the substrate.
  • Absence of root diseases.

🌡️ Climate Management

  • Total shading up to 60%.
  • Average T over 24 hours < 23°C.
  • Humidify the environment.
  • Reduce window opening to retain RH in the greenhouse until 28-30°C is reached, beyond which it is still advisable to ventilate to disperse excess heat.

💧 Irrigation Management

  • Irrigation strategy that favors root oxygenation and the renewal of the circulating solution.
  • Water Content (WC) of the substrate < 80%, preferably 50-70%.
  • Absence of water stagnation at the bottom of the substrate.
  • Abundant drainage, uniformly distributed throughout the irrigation day.
  • Substrate Electrical Conductivity (EC) stably reduced during the brightest hours.
  • 2-4 irrigation interventions during the hours with low daytime VPD.
  • Irrigation water T between 14 and 24°C.
  • Substrate T max 26°C.

🧪 Nutrition Management

  • Foliar treatments with calcium chloride (Ca-Chloride).
  • Promote the renewal of the circulating solution by making 1-2 additional drainage cuts at the bottom of the substrate slab/bag.
  • Modify the nutrient balancing: reduction of potassium (K) and magnesium (Mg) in favor of Ca, increase in boron (B), elimination of ammonium.
  • Supply part of the Ca in the form of chloride.

Cracking (Splitting)

Cracking or fruit splitting is a physiopathy that affects the berry in one or more places. The epicarp cracks either longitudinally or sometimes horizontally, resulting in juice leakage, rendering the fruit unsaleable (Photo 2).

The fundamental cause of splitting is an increase in root pressure not compensated by an increase in foliar transpiration. The fruits—which act as a water reserve organ for the plant—are “irrigated” more heavily by the water that the leaves cannot expel. This increases the internal pressure of the fruit, whose epicarp ruptures because it is not sufficiently elastic.

Growers are mistakenly led to believe that the presence of condensation or wetness on the fruits causes cracking. In reality, wet fruits may not crack, just as dry fruits may split. The solution to this dilemma lies in the balance between root absorption and foliar evapotranspiration: if foliar transpiration is inhibited by low T and/or high RH at the time irrigation begins, the fruits split. If the fruit is still cold and the ambient T has risen sharply (e.g., due to solar radiation) without a reduction in RH in the greenhouse, the water vapor suspended in the air condenses on the berry due to the difference in T between the air and the fruit (dew point). In this case, wet and cracked fruits may be observed, but only because an untimely irrigation occurred beforehand.

Fruits resulting from slow fruit set are the most susceptible to cracking, so it will be easy to observe an increase in splitting during the ripening (turning) stage. The greatest risk of slow fruit set occurs in conditions of high T or persistently high RH.

To reduce the incidence of cracked fruits, it is necessary to:

🥬 Plant Management

  • Maintain a medium-high number of leaves, implementing an efficient dehumidification strategy.
  • Maintain a medium-high number of fruits.

🌡️ Climate Management

  • Dehumidify after sunrise with gradual window opening, but without exposing the plant heads to cold external air.
  • Increase heat supply after sunrise.
  • Activate destratification systems.

💧 Irrigation Management

  • Do not irrigate before foliar transpiration has effectively started (indirectly measurable through the loss of water content in the substrate).
  • Do not finish irrigating close to sunset or when the VPD significantly reduces at the end of the irrigation day.
  • Do not heat the roots above 14-15°C when the greenhouse VPD is still low.
  • Maintain medium-high EC in the feed solution and substrate.

 

Blotchy Ripening (Uneven Ripening)

Blotchy Ripening is a physiopathy that causes non-uniform turning, leaving the berry with patches of color ranging from whitish to yellow (Photo 3). In less severe cases, the fruit can still be marketed but requires more time to complete ripening. In the most severe cases, the external symptom is accompanied by browning of the mesocarp parallel to the vessels (“grey wall”, Photo 4), thus affecting marketability.

Blotchy ripening occurs mainly during two periods of the season: Spring and Summer. In spring, it is due to the combination of an excess of large leaves, high RH (vegetative conditions), and a high K requirement due to the heavy fruit load; in this case, grey wall frequently occurs. In summer, however, it is the high T and exposure to strong solar radiation that alter the berry coloration.

Therefore, in Spring, to reduce the incidence of blotchy ripening, it is necessary to:

🥬 Plant Management

  • Avoid setting the plant to a vegetative state.
  • Regularly remove basal leaves, starting 3-4 weeks before harvest.
  • Remove 2-3 intermediate leaves to favor air circulation within the canopy.

🌡️ Climate Management

  • Avoid stagnant climate, using destratification systems and/or dehumidifying with an adequate combination of heating and window opening.

💧 Irrigation Management

  • Reduce inputs that increase root pressure (e.g., irrigations near sunrise and sunset, low EC in the feed solution and substrate, high root T, etc.).

🧪 Nutrition Management

  • Increase K supply.
  • Substitute part of the potassium nitrate (K-nitrate) with potassium chloride (K-chloride) and potassium sulfate (K-sulfate).

In Summer, however, it is necessary to:

🥬 Plant Management

  • Avoid setting the plant to a generative state.
  • Protect the fruits from solar radiation, maintaining a higher number of leaves on the plant.

🌡️ Climate Management

  • Shade appropriately.
  • Humidify when necessary to reduce the average T.
  • Cool the greenhouse as much as possible from sunset onwards, considering that, when it is very hot outside, reducing window opening allows the greenhouse not to disperse the cool, humid air generated by foliar evapotranspiration.

💧 Irrigation Management

  • Short and frequent irrigations to compensate for strong evapotranspiration and maintain sufficient leaf surface.

🧪 Nutrition Management

  • Substitute part of the potassium nitrate (K-nitrate) with potassium chloride (K-chloride) and potassium sulfate (K-sulfate).