Physiological Tomato Fruit Disorders


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December 13, 2005

While out looking at tomato fields this August, I was asked several questions by growers about various markings or misshaped fruit and the cause and possible prevention of these problems. I will list some of the more common physiological and insect-related problems with their description and causes and possible remedies as they are known. Several problems i think most people will recognize, while others are a bit uncommon. I will not list any problems caused directly by diseases of the fruit.

Blossom-end rot begins with tan, water-soaked areas at or near the blossom end of fruit, which usually enlarge and turn black and leathery (Figure 1). This malady is caused by a localized shortage of available calcium as the fruit develops. While the problem usually occurs externally at the blossom end of the fruit it may also occur internally with no visible symptoms on the outside of the fruit. There are several conditions that may increase the likelihood of blossom end rot. These include: 1. Widely fluctuating soil moisture, which can temporarily reduce calcium concentrations in expanding fruit. Calcium is carried through the plant in the water transport system (xylem). Those plant parts that are rapidly transpiring will have more than adequate levels of calcium, while fruit often receives just adequate levels of calcium. Any moisture stress will reduce calcium uptake. 2. Nitrogen in the form of ammonium can cause a reduction in calcium absorption and concentration in the tomato plant and 3. Damage to the root system from disease, nematodes or heavy pruning can reduce the uptake of calcium from the soil. Foliar applications of calcium do not reduce blossom end rot, because the calcium taken up by the leaves is not translocated to the fruit. This fruit problem can be prevented with good water management and proper fertilization.

Catfacing is the term used to describe fruit with deep indentations in the blossom end or fruit with significant distortions (Fig.2). The specific cause is not known, but it appears to be related to problems during the formation of the flower. Temperatures below 50°F at flowering or fruit set, resulting in poor pollination, can increase the amount of catfacing. Heavy pruning in indeterminate varieties may increase catfacing because of auxin reduction in the plant. Jointless tomato varieties seem to be more prone to catfacing than jointed varieties. Unfortunately there is little that can be done for control of catfacing, except selecting varieties that are not prone to the problem. Older cultivars and large fruited varieties are more susceptible.

Growth Cracking in tomato fruit can occur as radial cracking that originates from the stem end down toward the blossom end, and as concentric cracking, which occurs as rings around the stem scar (Fig. 3). Cracking occurs when internal expansion is faster than the expansion of the epidermis, causing the outer skin to split. Varieties differ greatly in their susceptibility to cracking. Cracking can occur at all stages of fruit growth but as fruit mature they become more susceptible, especially as color develops. Those varieties that are very susceptible to cracking may crack when fruit is still green while varieties that are tolerant may start to crack at the breaker stage. Management is accomplished by reducing, to the extent possible, large fluctuations in growth rates by selecting tolerant varieties, reducing fluctuations in soil moisture, and maintaining good foliage cover, since exposed fruit are more susceptible.

Dimpling is characterized by small depressions (dimples) in the fruit (Fig. 4a). The injury is caused most often by female thrips inserting an egg into the fruit just below the cuticle when the fruit is very small. Sometimes dimples are caused by small Lepidopteran larvae that feed briefly (one or two “bites”) on very small fruit. In either case dimpling occurs very early during fruit formation, usually while the flower is still attached. A few dimples usually do not result in grade reduction, however, numerous dimples can reduce grade. Western flower thrips, Frankliniella occidentalis, at times causes a different, but noticeable ovipositioning injury on tomato fruit. The damage appears as a round white halo around the center oviposition mark (Fig. 4b). Unlike damage by stink bug feeding (see below) the cells under this white halo are firm rather than soft and spongy. The dimpling caused by thrips ovipositioning occurs sporadically and thrips usually do not need treatment. However at times thrips populations can build and cause significant damage. Tomato flowers should be checked by peeling the petals open and observing any movement of thrips within the flower. A 10x handlens is useful for observing thrips. A threshold used in the South is 5 thrips/flower before treatment is justified. If the thrips population in the field consists mostly of western flower thrips than the threshold is reduced to 1-2 thrips/flower. You cannot determine thrips species in the field, but you can send them to me for identification if you wish. Adult tarnished plant bugs, which are about ¼-inch long and are brown, tan or greenish with dark markings on their wings and back (Fig.5), prefer to feed on newly formed fruits. They secrete a toxic substance from their salivary glands which kills the cells surrounding the feeding sites. As the fruit enlarges, healthy tissue will expand while the dead tissue does not, which results in distorted (dimples) or malformed (catfacing) fruit.

Gold Fleck, or fleck develops as small irregular green spots found randomly on the surface of green fruit which become yellow (gold) as the fruit ripens (Fig. 6). Some tomato researchers believe fleck is caused by thrips or other sucking insects, while others believe its cause is genetic or environmental. There is evidence from NC that insecticide use can greatly reduce flecking, however other work has shown fleck appearing when no thrips or sucking insects were present. Certain varieties show a predisposition to developing fleck, whatever its cause. In my experience with Florida tomato production, fleck has not been associated with thrips feeding even though thrips are present in the field 8 or 9 months of the year. The most common thrips species in Florida tomato fields is Frankliniella bispinosa, Florida flower thrips. In the North F. tritici may be the most common species, found in vegetable fields. The inconsistency in associating fleck with thrips could be due to the difference in the species of thrips most commonly found in the field. One of my goals next year is to take a survey of the thrips species found in and around different vegetable fields throughout Maryland to see what thrips species are present, where they are located and what damage is associated with their presence.

Pox appears as small brown crusty disruptions found randomly on the fruit surface (Fig. 6). The cause is not well understood, but it seems to be genetic in nature. Pox usually shows up on the same fruit as gold fleck but its association with thrips or sucking bug feeding has yet to be determined. Pox is difficult to work with because it appears sporadically, possibly due to certain environmental conditions. Not surprisingly there are differences in varieties as to the frequency of pox development.

Cloudy spot is characterized as pale, yellow, or white spots on the fruit surface with shallow, white spongy areas in the flesh (Fig. 7a). When the spots are cut open they do not penetrate into the flesh of the tomato to any great extent (Fig. 7b). Cloudy spot is caused by stink bug feeding. Stink bugs insert their syringe-like mouth parts into green fruit and withdraw cell contents. This results in empty cells filled with air, spongy and white. Stink bug feeding rarely results in deformed growth of the fruit.

Sunscald appears as yellow, sunken, and wrinkled, areas usually on the shoulder of the fruit (Fig. 8). It occurs when tissue temperature rises above 85° F. The high temperature causes yellow pigments to develop, but inhibits red pigment development. In severe sunscald cases (tissue temperatures above 103° F) the tissue turns white and dies. Damage takes place when leaves are moved about or when there is foliage loss suddenly exposing the fruit to sunlight for a period of time. This can occur during harvesting, excessive pruning, a storm or foliar disease. Some growers use a sun screen material such as Surround to help reduce sunscald, but problems with removing the sunscreen material from the fruit at harvest usually make this method uneconomical on large acreages.

Puffiness causes fruit to appear somewhat bloated and flat-sided or angular (Fig. 9). When fruit are cut, cavities may be present that lack the normal seed gel. Fruit is less dense and feels very light in relation to its size. Puffiness is caused by incomplete pollination and seed development. Poor pollination can occur at temperatures that are too low or too high during fruit set. Other factors such as low light or rainy conditions can also cause seed set problems.

Rain check appears on tomato fruit as numerous tiny concentric cracks that develop on the shoulder of the fruit (Fig. 10). In severe cases, the cracks can extend 1/4 to 1/3 of the way down the side of a fruit. Cracks feel rough to the touch and affected areas can take on a leathery appearance. Green fruits are most susceptible. Damage occurs on exposed fruit when a heavy rain occurs after a long dry period. There are varietal differences in susceptibility to rain check.

Zippering fruit have lines along the side of the fruit usually from the stem end to the blossom end due to abnormalities in early flower development (Fig. 11). Although sometimes attributed to high humidity or an anther that is attached to the newly forming fruit the cause of the zipper scar is unknown. The only control is to select varieties that are not prone to zippering.

Blotchy ripening/yellow shoulders of tomatoes is characterized by areas of the fruit that fail to ripen or do so after the rest of the fruit is ripe (Fig. 12). White or yellow blotches can also appear on the surface of ripening fruit while the tissue inside remains hard. The affected area is usually on the upper portion of the fruit. This problem is more prevalent in cool, wet, often cloudy conditions. Soils high in nitrogen and/or low in potassium will increase its severity. Blotchy ripening appears more frequently on older cultivars. Studies at UC-Davis demonstrate that for uniform color development more available potassium than is necessary for yield alone is needed. Their studies show the incidence of yellow shoulder was lower in fields with a high potassium status of both soil and plant. Foliar applications of potassium, however, were not effective in relieving this disorder. Work in the Great Lakes region has suggested the importance of soil organic matter and pH. Tomatoes grown on soils containing greater than 3.5% organic matter produced fruit with a low incidence of blotchy ripening/yellow shoulder while tomatoes grown on soils with organic matter below 2.5% produced fruit with a high incidence of the disorder. Tomatoes produced on soils at a pH of 6.4 had a low incidence of yellow shoulder while tomatoes grown on soils in excess of 6.7 had a high incidence.

Internal white tissue is a disorder where the affected fruit rarely shows any external symptoms. However, when ripe fruits are cut, white hard areas are present in the outer walls (Fig. 13). High temperatures during the ripening period seem to trigger the symptoms. Maintaining sufficient potassium fertilization (a soil exchangeable K+ level of 130 ppm in sandy loams) can reduce symptoms but may not eliminate them. As is common with many of these fruit problems some varieties are more prone to the disorder than others.

Graywall appears as grayish often slightly sunken areas of the fruit. It is caused by a partial collapse of the vascular wall tissue causing dark necrotic areas in the outer walls (Fig.14). The collapsed tissue is sometimes present in the cross-walls of the fruit. This problem usually does not affect tomato crops in our area as graywall is more of a problem during cool, short days, which may be possible to find in a very late or early season tomato crop in the north (high tunnels).

References

Fig. 10 found at: http://www.umassvegetable.org/index.html

Fig. 8 K-State Research and Extension Newsletter Horticulture '98, No. 26, July 1, 1998.

Figs. 1 and 4a Bartolo, M.E. at: http://www.ppdl.purdue.edu/ppdl/weeklypics/
Weekly_Picture8-6-01-1.html

Fig. 11 Hodges, L. Extension Horticulture Specialist Nebraska Cooperative Extension NF97-35.

Fig. 2 Lapaire, C. at: http://www.ppdl.purdue.edu/ppdl/weeklypics/
Weekly_Picture8-6-01-1.htm

Fig. 5 LeBoeuf, J. - Vegetable Crop Specialist/OMAF
http://www.omafra.gov.on.ca/english/index.html

Figs. 4b, 6, 9, 13 and 14. Olson, S. Department of Horticultural Sciences, North Florida Research and Education Center, Quincy. Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611HS-954, Publication date: February 2004.

Fig. 3 at: http://www.colostate.edu/Depts/CoopExt/4DMG/
Pests/Diseases/tomaprob.htm
Sedbrook, J. Colorado Master Gardener SM, Colorado State University Cooperative Extension, Denver County.

Fig. 12 at: http://www.luminet.net/~wenonah/min-def/
index.html
Wallace, T. University of Bristol Agricultural and Horticulture Research Station, Long Ashton, Bristol. found at: The Diagnosis of Mineral Deficiencies in Plants by Visual Symptoms.

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For more information, contact: Gerald E. Brust