Cracking is a physiological disorder that describes the splitting of the outer skin (epidermis) of the tomato fruit. Two kinds of cracks occur in tomatoes. Radial cracks are deep, V-shaped splits that begin at the stem end and radiate toward the blossom end. Circular cracks are a series of concentric rings that appear between the stem end and the shoulders of the fruit.
Tomato fruits crack in response to environmental conditions that encourage rapid fruit growth or expansion, such as wide fluctuations in moisture or temperature. For example, when the epidermis cells have “hardened” during a slow growth period, excess water encourages rapid growth that can cause the skin to split. Also, hot daytime and cool nighttime temperatures can result in expansion and contraction of the fruits, leading to the development of cracks. Finally, high nitrogen and low potassium levels have been linked to fruit cracking.
Some tomato varieties resist cracking better than others. Highly susceptible tomatoes develop cracks while the fruit is still green; crack-resistant varieties show no signs of stress in the green stage until they start turning red. Ripe tomatoes tend to develop circular cracks if they remain on the vine too long.
Cracking is affected by several genes, and because different genes control each type of crack, it is difficult to breed crack-resistant varieties. However, researchers have found that plum tomatoes and small, globular tomatoes such as ‘Marglobe’ and ‘Heinz’ are more resistant to cracking than cherries and large varieties such as your ‘Better Boy’. Other crack-resistant tomatoes include ‘Daybreak’, ‘Jet Star VF Hybrid’, ‘Pink Girl VFT Hybrid’, and ‘Monte Carlo VFN Hybrid’, ‘Mountain Fresh VF Hybrid’, ‘Mountain Spring VFF Hybrid’, and ‘Spitfire VFFA Hybrid’.
This week’s Q&A is excerpted from the July/August 2004 issue of Horticulture.
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