Controlling tomato fruitworm

Tomato fruitworms (Helicoverpa zea), also called corn earworms and cotton bollworms, are insects that attack tomatoes and other plants. The fruitworm (in its larva form) attacks a tomato by tunnelling. It consumes the tomato’s interior and leaves a cavity filled with fluid and droppings. The tomato quickly decays and rots. Once tomatoes have been attacked by fruitworms, the fruit is no longer usable. Pick and discard them. The best way to deal with tomato fruitworms is to go on the offencive. Watch plants closely to keep an eye out for eggs and then larvae (worms).

Description of tomato fruitworm

A major agricultural pest, the tomato fruitworm can feed on many different plants. Hence, the species has been given many different common names including cotton bollworm and corn earworm. It has also been known to consume tobacco, legumes, grain sorghum, and other vegetables and fruits.

Adult moths have yellowish tanned bodies, a tan-coloured head and bright green eyes. A solitary dark dot in the middle of each forewing coupled with several dark markings help distinguish them. The hindwings are pale in colour and is enveloped by a dark brown border.

There are at least 15 other cultivated tomato fruitworm hosts in addition to the tomato, including corn, cotton, eggplant, okra, peppers, soybeans, and tobacco.

What does the tomato fruitworm look like?

Shape: caterpillar (in larvae stage)
Colour: cream, yellow, green, reddish, or brown
Markings: pale stripes and/or black spots; hairy
Size: about 1 ½ - 2 inches long

Tomato fruitworm adults are medium-sized moths with a wingspan of about 1 to 1.3 inch (25–35 mm). They are pale tan to medium brown coloured or sometimes have a slight greenish tinge. The front wings are variously marked and usually have an obscure dark spot in the centre and a lighter band inside a dark band around the tip. The hind wings are drab white and have a dark gray band around their tip. A diffuse light spot is in the centre of the dark band.

Life cycle

The eggs of this pest are each about ½ the diameter of a pinhead. They are spherical with a flattened base and white or cream in color, developing a reddish-brown band just prior to the young hatching. Depending on the temperature, the young hatch in 2-10 days.

The larvae measure 11/2-2 inches when fully grown and may be green, brown, pink, yellow, or even black. They have tan heads and alternating light and dark stripes run lengthwise on the bodies. The skin is coarse and has small, thorn-like projections called tubercles. The larval stage lasts 14-21 days.

When the larvae are finished feeding the worms drop to the ground and enter the soil near the base of the plant where they transform into shiny brown pupae. During summer adults emerge in 10-14 days and start the cycle over. In the fall, south of Interstate 70 the pupae survive winter 2-6 inches below the soil surface. The moths emerge from overwintering pupae during late April and May.

Adult moths are usually light yellow-olive in color with a single dark spot near the center of each forewing. Each forewing has 3 slanted dark bands. Their hind wings are white.

The cycle repeats itself with the moths laying eggs at dusk on host plants on warm days. The total generation time is 28-35 days.

The moths lay eggs on the foliage of the tomato plants. With corn the moths usually lay eggs on corn tassels and silks but the larvae will migrate down the silk to the ear tips within one hour of hatching where they will feed on the developing kernels protected by the husk. When larval development is complete the larvae chew through the husk and drop to the ground to begin the pupal stage.

Damage to the crop

When there is fruit present, the tomato fruitworm will complete its larval development inside fruit. Early stage larvae enter fruit at the stem end when it is between 0.75 to 2 inches in diameter. During development, caterpillars may emerge from one fruit and enter another. Their feeding results in a messy, watery, internal cavity filled with cast skins and feces. Damaged fruit will ripen prematurely. Late in the season, small larvae will also enter ripe fruit. Small larvae are difficult to detect and, thus, may be a problem in processing tomatoes for the canner. Tomato fruitworm is less of a problem for fresh market tomatoes because damaged fruit are easily culled at harvest.

Damage is caused only by the larvae. Although larvae can feed and develop on leaf tissue, the preferred feeding sites in most crops are the reproductive sites, such as tomato fruit and corn ears. On corn, the larvae feed on fresh silk before moving down the ears eating kernels and leaving trails of excrement. In tomatoes, evidence of damage is usually a visible black hole at the base of the fruit stem. They will also eat the flower buds and chew holes in the leaves. It is much the same, though less common, on the other types of plants.

Other damage includes:

• Tomato fruitworms feed on leaves, stems, and fruit.
• Worms (larvae) enter fruit, usually at the stem end, and can work their way through the entire tomato. The entry hole can be up to the size of a pea.
• Worms prefer green fruit.
• Worms leave an interior hollow space filled with water, frass, decay, and rot. Fruit is inedible after a fruitworm infestation.

Prevention of tomato fruitworm

• Avoid planting corn near tomatoes because corn is one of the most significant fruitworm hosts.
• Monitor plants for eggs and hand pick leaves where eggs are laid. Adults lay eggs on both sides of tomato leaves, beginning closest to blossoms. Eliminating eggs reduces population dramatically.
• Prevent larvae from entering fruit by covering plants with fine netting.
• Encourage natural predators. Plant dill, parsley, and asters to attract parasitic Trichogramma wasps. Parasitic wasps can also be purchased and released into the garden. Big-eyed bugs, minute pirate bugs, lacewing, and damsel bugs also feed on tomato fruitworms. Plant goldenrod, daisies, alfalfa and stinging nettle to attract them.
• Remove and destroy affected plants at the end of the season.
• Till soil after harvest, in late winter, and in early spring to destroy pupae.

Management and control

Management of tomato fruitworm requires careful monitoring for eggs and small larvae. When control is needed, it is essential to treat before large numbers of larvae enter fruit, where they are protected from sprays. Trichogramma parasites and other natural enemies often destroy significant numbers of eggs, so it is important to check for parasites before making treatment decisions. Except in the desert valleys, early-season processing tomatoes rarely need treatment. Late-season fields may be more seriously affected.

Biological control

Naturally occurring beneficial insects are very important in the biological control of tomato fruitworm, especially in the Delta areas. These include Trichogramma spp. egg parasites, the larval parasite Hyposoter exiguae, and predators such as bigeyed bug and minute pirate bug. Conserve these parasites whenever possible and monitor their presence.

A tomato fruitworm egg parasite, Trichogramma pretiosum, is available from many commercial insectaries. Inundative releases of 100,000 parasites/acre during the period of fruitworm oviposition and when fruit are susceptible to fruitworm feeding can reduce damage to acceptable levels. Monitor releases using the egg sampling technique to determine the success of the release (indicated by black, parasitized eggs) and use the table below to determine if pesticide treatments are needed. Be sure to monitor the releases to make certain that parasitism is occurring.

Controlling tomato fruitworms origanically

You can avoid the use of harsh chemicals and employ organic methods to rid your tomato crop of fruitworms. Instructions:

1. Release fruitworm predators in your garden. Predators include minute pirate bugs, bigeyed bugs, the parasite trichogramma and Hyposoter exiguae wasps.
2. Till the soil around the tomato plants in the fall. This exposes fruitworms to predators. Exposure to cold weather also kills fruitworm pupae.
3. Look for signs of fruitworm infestation regularly. Fruitworm moths lay eggs on tomato plant leaves. The eggs appear white when first laid, then turn brown before the larvae hatch.
4. Handpick and destroy fruitworm eggs and larvae as you find them.
5. Spray tomato plants with Bacillus thuringiensis at the first sign of eggs or infestation. To prepare the spray, combine 1 to 2 tablespoons of the bacteria with 1 gallon of water. Apply the spray to the tops and bottoms of leaves.

Trim tomato plants so that there are no leaves or stems any lower than 12 inches from the ground. This allows ample airflow from ground up and helps keep away many insects from dwelling in your plants and feasting on your precious tomatoes.

Look for signs of fruitworm infestations regularly. Adults lay eggs on both sides of leaves, usually close to blossoms. Ridding of eggs can reduce fruitworm populations drastically. Handpick and destroy fruitworm eggs and larvae as you find them.

Prevent fruitworms from boring into fruit by covering fruit with fine netting. Better yet, cover plants with floating row-covers to prevent adults from laying eggs on host plants.

Avoid growing tomato near corn or any other aforementioned crop, unless your intention is to use them as a trap crop. If one plant gets infested, you could have your garden teeming with fruitworms!

Encourage natural predators of the tomato fruitworm. Big-eyed bugs, minute pirate bugs, lacewing and damsel bugs feed on tomato fruitworms. Attract them by planting goldenrod, daisies, alfalfa and stinging nettle.Trichogramma wasps and Hyposoter exiguae wasps parasitize the eggs and larvae respectively. Planting dill, parsley and asters attracts the parasiticTrichogramma wasps. These wasps are available commercially and can be ordered.

Bacillus thuringiensis (Bt), a microbial biological control, is effective against tomato fruitworms among several other pests. Use Bt at the first sign of fruitworm eggs. Apply as directed by the product label. Bt works by paralyzing the digestive system and infected fruitworms stop feeding within hours.

Neem oil and biodegradable insecticidal soaps have been found to deter fruitworm infestations. Spinosad, a natural, broad-spectrum biological insecticide made from soil microbes works on tomato fruitworms too.

Cultural control: Remove and destroy infected plants. Roto-till the soil at the beginning and end of the season to expose and destroy overwintering fruitworm pupae. Rotate crops by planting tomatoes in a different area of your garden each year. Companion planting with garlic has been said to repel many pests.

Dusting plants with diatomaceous earth or Rotenone can help deter fruitworms from moving about the plant.

Monitoring and treatment decisions

Damaging populations of tomato fruitworm rarely occur before August. Monitor adult activity in July using a Heliothis trap baited with a pheromone lure to determine when to sample for eggs, which are laid during the flight periods. When moths are being caught in the traps, begin sampling leaves for eggs. If eggs are detected in samples taken during July, start accumulating degree-days using a lower threshold of 55°F and an upper threshold of 92°F to predict egg laying of the generation in August that attacks the fruit. It takes an average of 968 degree-days for tomato fruitworm to complete a generation.

Prevention is the most effective way to control worms (see above). Once larvae enter fruit, they cannot be treated directly, since they’re protected by the tomato’s exterior. But before that happens, you can take these precautions.

• Apply Bt: Bacillus thuringiensis (Bt), a microbial biological control, is considered to be very effective on fruitworms. Bt doesn't harm a majority of beneficial insects. It’s available in liquid, powder, and granules. Follow manufacturer’s directions for application. Treat plants with Bt in the afternoon or evening, since it breaks down in UV light. Apply Bt at the first sign of worm eggs. Once the pests hatch and ingest the chemical, they are paralyzed, unable to eat, and die.
• Apply oils. Use neem oil or insecticidal soap once a week and after rain.
• Apply other controls. Treat plants with Spinosad, a natural, broad-spectrum insecticide made from soil microbes. Or treat plants with the insecticide Sevin every 5-7 days when fruit begins to set (worms are untouchable once they get inside tomatoes).

Molybdenum deficiency in tomato plants

These leaves show some mottled spotting along with some interveinal chlorosis. An early symptom for molybdenum deficiency is a general overall chlorosis, similar to the symptom for nitrogen deficiency but generally without the reddish coloration on the undersides of the leaves. This results from the requirement for molybdenum in the reduction of nitrate, which needs to be reduced prior to its assimilation by the plant. Thus, the initial symptoms of molybdenum deficiency are in fact those of nitrogen deficiency. However, molybdenum has also other metabolic functions within the plant, and hence there are deficiency symptoms even when reduced nitrogen is available. At high concentrations, molybdenum has a very distinctive toxicity symptom in that the leaves turn a very brilliant orange.

Role of molybdenum in tomato plants

Molybdenum is needed by plants for chemical changes associated with nitrogen nutrition. In non-legumes(such as cauliflowers, tomatoes, lettuce, sunflowers and maize), molybdenum enables the plant to use the nitrates taken up from the soil. Where the plant has insufficient molybdenum the nitrates accumulate in the leaves and the plant cannot use them to make proteins. The result is that the plant becomes stunted, with symptoms similar to those of nitrogen deficiency. At the same time, the edges of the leaves may become scorched by the accumulation of unused nitrates.

Symptoms

The main symptoms of molybdenum deficiency in non-legumes are stunting and failure of leaves to develop a healthy dark green colour. The leaves of affected plants show a pale green or yellowish green colour between the veins and along the edges. In advanced stages, the leaf tissue at the margins of the leaves dies. The older leaves are the more severely affected. In cauliflowers, the yellowing of the tissue on the outer leaves is followed by the death of the edges of the small heart leaves. When these develop, the absence of leaf tissue on their edges results in the formation of narrow, distorted leaves to which the name ‘whiptail’ has been applied. Affected leaves are usually slightly thickened and the leaf edges tend to curl upwards, especially in tomatoes

Control

In most soils, molybdenum present in an unavailable form will be released by applying lime or dolomite.The effect of liming on molybdenum availability is slow and it may take several months to correct the deficiency. The amounts of lime or dolomite needed may range from 2 to 8 tonnes per hectare, depending on initial pH of the soil and whether it is sandy or heavy textured. Unless lime is likely to be beneficial for other reasons, it is quicker and cheaper to apply a molybdenum compound to the soil or to the crop. Where one of the molybdenum compounds is used, the quantities recommended vary from 75 g to 1 kg/ha depending on the crop and the molybdenum material.

Molybdenum can be applied in the following ways:
• mixed with fertiliser; or
• in solution, to
— seedlings in the seedbed before transplanting;
— the leaves of plants in the field; or
— the soil at the base of plants in the field.

Genetic Control of Fruit Color in Tomatoes

There are multiple genes that can affect fruit color in tomatoes.  Although the major genes have individual effects, it is often the interaction between these major genes that produces the fruit color phenotype.  What we see as fruit color is a combination of pigmentation in three separate tissue types; the epidermis, a sub-epidermal layer, and the fruit pericarp (flesh).  The genes listed below describe most of the known major genes controlling fruit color, and the various alleles of those genes with their associated phenotypes.  A few uncommonly found genes/alleles are omitted to try and simplify an already complicated matrix of gene interactions determining the fruit color phenotype.  Most of this information is from a thorough literature review on this topic, and combined with some personal experience and observation when appropriate.

In this document the wild type allele (responsible for the typical phenotype in cultivated tomatoes) is noted as + and mutant alleles at a locus are noted by the allele abbreviation (see TGRC list of accepted allele abbreviations), either in lower case (if the allele is recessive to the wild type), or upper case (if the allele is dominant to the wild type).  Thus +/+ denotes that the plant is homozygous for the wild type allele at a particular locus (gene) and exhibits the wild type phenotype; t/t notes the plant is homozygous for the recessive  “t” allele at the tangerine locus and has the tangerine phenotype; and Del/+ notes the plant is heterozygous for the dominant Del allele at the delta-carotene locus and has the Del phenotype. The “-“ character denotes that all alleles have an equal effect on phenotype, for example at the tangerine locus +/- means either +/+ or +/t, since either will result in the wild type phenotype.

Major genes responsible for fruit color in tomatoes

Pigmentation in the Epidermis and Sub-epidermis

In tomato fruit the epidermis is a single layer of cells designed to protect the fruit from desiccation and mechanical injury.  In the wild type tomato the epidermis is yellow (Y allele).  This coloration is due to the flavonoid pigment naringenin chalcone which is embedded in the cuticle.  It is thought that this pigmentation protects against UV radiation and may provide some protection against pathogens.  The biosynthetic pathway for naringenin chalcone is controlled by a myb12 transcription factor.  The recessive y allele is due to a loss of function mutation in this myb12 gene, resulting in a clear cuticle without significant naringenin chalcone pigmentation.  The myb12 loss of function associated with the y allele also results in a cuticle that is thinner, lower in cutin content, and with less elasticity (see photo and graphs below).  Myb12 also has broad effects on flavonoid and carotenoid pathways beyond the cuticle and the y allele is associated with generally lower levels of these compounds in the fruit (reference).  



Adato, et.al (2009)

Pink (y/y) and Red (+/-) segregates in the F2

In the presence of the genes Aft and atv, anthocyanin pigment is accumulated in a few layers of cells in the fruit epidermis and sub-epidermis (see Breeding the Blue Tomato).  Both genes were introgressed from wild relatives and are up-regulated by direct exposure to UV light.  There is considerable variation in intensity of pigmentation among Aft/Aft atv/atv plants, strongly suggesting an epistatic effect from one or more unknown modifier genes.

Yellow fruit with indigo

Epidermal peal of yellow/indigo

We have found there can also be sub-epidermal accumulation of carotenoid pigments.  As a result, the color of the “skin” may be very different than the color of the flesh.  We have developed several lines with red or reddish orange pigmentation of the sub-epidermis with yellow or green flesh (see photos).  There is no previous report of this phenomenon in the literature.  This trait is heritable and appears to be controlled by a single recessive gene.  Last year we identified plants with a green sub-epidermis and red flesh.  Although there appears to be considerable potential to modify “skin color” independent of flesh color in tomatoes, there is much to be learned.

2013 taste test winner - green on red

The green stripe trait, which is governed by the recessive gs allele, causes chlorophyll accumulation in irregular stripes in the fruit epidermis/sub-epidermis of unripe fruit, changing to stripes of various colors in mature fruit (see Genetic Control of Fruit Stripes in Tomato).  The pattern of the stripes can vary widely, though the genetic basis for this variation is not understood.  The color of the stripes in mature fruit is determined in part by flesh color, but also subject to other factors, yet unknown.  In particular some striped tomatoes have metallic silver, bronze, green of gold stripes – the nature of which is currently a mystery (see photo)

Painted with metallic green

Orange w/ broad gold stripes

Very dark blood red flesh w/ metallic stripes

GWR flesh with gs/gs; Aft/Aft and atv/atv

Fruit stripes are dark longitudinal stripes that develop on ripening tomato fruit in the sub-epidermis.  In the literature this trait is described as being controlled by a dominant “Fs” allele.  Our experience is that the trait is very sensitive to environment, not consistently expressed, and that dominance appears to be incomplete.  Fs/Fs in combination with gs/gs can give some very interesting striping patterns (e.g. Beauty Queen), and Fs/Fs in a Aft/Aft – atv/atvbackground has shown a very striking tiger-like striping (see Siberian/Bengal Tiger blog).

Bengal Tiger

Freckles are another possible feature of the epidermis that can significantly alter fruit phenotype.  A detailed discussion on what is known about the genetic control of freckles can be found here, but there is little reported in the literature and still a lot is not well understood.  One interesting manifestation of this trait is in combination with the anthocyanin fruit phenotype, with gold/yellow flecks on a indigo background (see photo below).

Freckled Indigo

Pericarp pigmentation

Coloration of the tomato pericarp (flesh) is a result of accumulation of various carotenoid pigments.  The pathway for biosynthesis of these various carotenoid compounds is illustrated below.  In the next few paragraphs the common mutations that lead to variations from the wild type phenotype are described, discussed and illustrated (our photos unless noted otherwise).

"Wild type"

In the wild type, tomato pericarp pigmentation is red (R allele).  The recessive r allele is the result of a loss of function mutation in the gene coding for the enzyme PSY1, which is involved in an early and critical step in the lycopene/carotenoid biosynthetic pathway.  This mutation greatly reduces pigment synthesis generally during fruit maturation.  The yellow flesh phenotype of r/r plants is due to low levels of beta-carotene (77% reduction vs wild type) and an almost complete lack of lycopene.  At this same locus, a third allele " r^y ” is a modifier of r, and results in yellow fruit with various intensity and patterns of red streaks/blotches (e.g. bicolor). 



 

 r^y/ r^y in a gf/gf background

At an independent locus, the tangerine gene “t” is responsible for the vast majority of tomatoes with orange flesh.  The recessive t allele is the result of a loss of function mutation in the gene coding for the enzyme CRTISO which causes an accumulation of prolycopene (orange pigment) rather than lycopene (red pigment).  A plant homozygous for this mutation (t/t) will be dark orange in combination with R/- and lighter orange in combination with r/r.  The double recessive r/r - t/t has a 90% reduction to total carotenoid pigments compared to t/t in a R/- background (reference and photo).   It has been recently shown that prolycopene, a cis isomer of lycopene, is 5x more efficiently utilized by humans than its red wild type trans-lycopene cousin (reference).

F3 segregating for the t allele (red/tangerine)

At another independent locus, the “Del” allele of the delta-carotene gene is a much less common determinate of orange flesh in cultivated tomatoes.  This gene was found in various wild relatives and has been introgressed into tomatoes.  Crtl-e is an enzyme that converts lycopene to delta-carotene.  In the wild type the gene controlling this enzyme is only very weakly expressed during fruit maturation.  The Del allele of this gene is expressed 30x higher than the wild type leading to an increase in delta-carotene concentration and a corresponding decrease in lycopene content.  Del has functional incomplete dominance and Del/+ plants have red/orange flesh with <50% of total pigment being delta-carotene and Del/Del plants having orange/red flesh with >50% of the total pigment being delta-carotene.  Like tangerine gene, the phenotypic expression of the Del phenotype is partially dependent on the genotype at the R locus.

Del (photo by Keith Mueller)

Del + high pigment (hp1/hp1) - Mueller photo

UC Davis TGRC photo

In wild type tomatoes the gene coding for the Lcy-B enzyme, that converts lycopene to beta-carotene, is expressed at a low level in ripening fruit - lycopene content is normally >50x the content of beta-carotene.  There are two important variants of the Lcy-B gene, alleles which can significantly alter the red fleshed wild type phenotype.  The “B” allele was introduced from tomato wild relatives and greatly increases expression of Lcy-B, resulting in increased beta-carotene content at the expense of lycopene – resulting in orange fruit.  "B" is inherited as a dominant allele.  The second variant “ b^og”  (AKA old gold crimson) is a loss of function mutant for the gene coding for Lcy-B and reduces the normally low levels of beta-carotene to near zero, with a corresponding increase in lycopene content.  Crimson type tomatoes, with elevated lycopene content are b^og/b^og in a red fleshed background (see photo).

Crimson striped mini-heart

Crimson and bicolor saladettes

at/at - photo by Keith Mueller

A novel tomato fruit color, apricot, was discovered in tomatoes purchased in a Mexican market.  Flesh color is yellow/orange, often with a red blush near the fruit center. Both at/at and r/r plants have very low lycopene content.  Fruit from at/at plants have beta-carotene levels similar to wild type, significantly higher levels than from yellow fleshed fruit of y/y plants.  The biochemical mechanism for this trait is not well understood, but is thought to be related to a mutation in a transcription factor associated with fruit ripening.  Although there are no commercial tomato varieties with this trait, Keith Mueller has been working with an at/at breeding line – and finding very interesting coloration (reference).

Recently scientists have identified several QTL markers, associated with independent genes of unknown function, that enhance lycopene concentration in tomato fruit (reference).  These are independent of, and perhaps additive to, b^og/b^og (i.e. crimson trait).

The Green ripe trait is one of several that affect normal fruit maturation.  The mutant Gr allele (allelic to Nr – never ripe) is a deletion in a wild type gene that has the effect of  making the fruit less sensitive to the plant hormone ethylene.  Ethylene governs many key steps in fruit maturation and plants containing the Gr allele (Gr/-) make fruit that never fully ripen.  The color of ripe fruit is green with a yellowing blush, often with a red/pink center.  The fruit remains very firm and does not significantly accumulate sugars, acids or other flavor compounds.  The delayed ripening genes “rin” and “nor” when homozygous, give a similar fruit phenotype.  Plants that are rin/+ or nor/+ have normal fruit coloration and delayed fruit senescence (see Fountain of Youth blog).

As fruit of wild type tomato plants mature, concentration of the green photosynthetic pigment chlorophyll decreases and carotenoid pigments increase – chloroplasts become chromoplasts, and the fruit begin to turn their predestined color: red, orange or yellow.  The green flesh allele “gf” is a loss of function mutant in SGR1, a gene responsible for producing a protein required for chlorophyll breakdown in maturing tomato fruit.  It was recently reported that there are at least five independent loss of function mutations in this gene, giving rise to several alleles of gf, all with the same gf phenotype.  Tomato plants homozygous for this recessive mutation (gf/gf) retain chlorophyll in mature fruit, but also accumulate their normal carotenoid pigments as determined by the major genes described above.  In the presence of retained chlorophyll, fruit predestined to have red flesh become muddy brown (AKA “black”), pink becomes purple, orange becomes orangish/green and yellow becomes green when ripe (GWR).

gf/gf F2 segregate (Michael Pollan x Cowlicks Brandywine)

gf/gf F3 segregate in a cross with Berkeley Tie Dye

In tomatoes the term bicolor generally refers to fruit that has some combination of two (or three) flesh colors, in a vast array of potential patterns.  As discussed earlier, the r^y  allele at the R locus confers red steaks in yellow flesh (e.g. Big Rainbow and many others) with blotchy red pigmentation often evident even on the fruit surface.  In a gf/gf background r^y/r^y probably leads to red streaks in green flesh, as in the variety Berkeley Tie Dye and others.  However, there are much more complex combination of bi/tri-color flesh pigmentation (see photos) not easily explained by these or any other combinations of the genes discussed above. 

             Typical genotypes for common fruit colors in tomato

Fruit Phenotype	Y locus	R locus	T locus	B locus	Gf locus	example
Red fruit	+/-	+/-	+/-	+/+	+/-	Big Boy
Pink fruit	y/y	+/-	+/-	+/+	+/-	Brandywine
Brown (black) fruit	+/-	+/-	+/-	+/+	gf/gf	Black from Tula
Purple fruit	y/y	+/-	+/-	+/+	gf/gf	Cherokee Purple
Yellow fruit	+/-	r/r	+/-	+/+	+/-	Yellow Pear
“White” fruit	y/y	r/r	+/-	+/+	+/-	Blonde Boar
Orange (tangerine)	-/-	-/-	t/t	+/+	-/-	Woodle Orange
Orange (b-carotene)	-/-	-/-	+/-	B/-	-/-	Caro-red
Crimson fruit	-/-	+/-	+/-	bog/bog	+/-	Tasti-Lee
GWR fruit	y/y	r/r	+/-	+/+	gf/gf	Green Zebra
Yellow/red bicolor	+/-	ry/ ry	+/-	+/+	+/-	Big Rainbow
Green/red bicolor	+/-	ry/ ry	+/-	+/+	gf/gf	Captain Lucky

Not just for color

The degradation of carotenoid pigments leads to the formation of numerous aromatic/volatile compounds that affect tomato flavor.  This is particularly true for the +/- red wild type, crimson, tangerine and delta-carotene type tomatoes, and much less so for the r/r, B/- and at/at low lycopene types (reference).  As we hopefully learn more about particular volatile compounds and their effect on flavor – a breeding strategy for manipulating pigment types/concentrations may one path for better tasting tomatoes.

The carotenoid and flavonoid compounds found in tomato also have direct benefits in human nutrition.  These compounds generally are very effective anti-oxidants, and have demonstrated significant anti-cancer activity.  Beta-carotene is also a direct precursor for vitamin A.

Summary

Our primary interest in better understanding the genetics and inheritance of fruit color in tomatoes is to better predict the phenotype of crosses between various types, and to best design selection strategies for achieving complex combinations of colors, stripes, etc.  The fact that we continue to get unexpected results from crosses and find a few very novel phenotypes not described in the literature – suggests to us there are still a lot of unknown genetic factors at work, probably mostly modifier genes with an epistatic effect on one or more of the major genes described above.