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Majid Foolad Breeds Tomatoes with Blight Resistance, Plus Higher Lycopene

The Tomato Magazine
February 2007

By Dorothy Noble

Acres of deep, dark red experimental tomatoes bred by plant geneticist Majid Foolad will carpet Penn State’s Russell E. Larson Agricultural Research
Center at Rock Springs, Pa. this summer.

Some of these cherry, grape and plum prototypes possess both disease resistance and higher lycopene content. But even these breakthroughs are not the only attributes the Penn State professor strives for in his ambitious decade-long breeding program.

Breeding efforts by seed companies have typically developed cultivars for the major tomato growing areas of California and Florida. Consequently, growers in other areas plant commercial varieties that are not adapted to their conditions. The fungal diseases, early blight and late blight, are not prevalent in California and Florida. But in Pennsylvania and other areas of the Northeast, Mid-Atlantic, as well as some Southern and Central regions, these diseases afflict profits by increasing costs and limiting yields.

Blight Creates Losses
Annual yield reductions of 20-30 percent due to early blight can be assumed in areas with frequent rainfall, high humidity, or heavy dew. In the absence of early blight disease resistant cultivars, growers depend on chemical controls that can be costly. Foolad estimates that in Pennsylvania alone, growers spend about $1 million per year on their spray programs.

The most destructive early blight fungi, Alternaria solani and A. tomatophila, overwinter, demanding lengthy crop rotations and sanitation as well as preventive
fungicides. As tomato growers are aware, early blight both lessens the number of fruit produced and diminishes the quality. Foolad has noted that, while indeterminate cultivars can sometimes “outgrow” early blight, thus curtailing its damage, determinate processing and fresh market tomatoes suffer losses more easily.

Late blight, although occurring less frequently, is much more devastating in several regions. Foolad stepped up his late blight resistance efforts in 2004 when outbreaks hit. The disease was confi rmed in 40 percent of Pennsylvania’s counties. Since this fungus can totally destroy a crop in a mere ten days, some plantings in the eastern and south central parts of the state were wiped out. Growers, who normally sprayed eight times a season, applied fungicides as
often as twenty times to save their crops. Parts of New York and New Jersey had similar experiences.

Not only do production costs and environmental hazards merit consideration, but pesticide effectiveness is lost when frequent usage leads to the development of new fungal biotypes. In fact, new resistant strains of the late blight pathogen, Phytophthora infestans, have been detected in the Mid-Atlantic. These are particularly aggressive in tomato fields.

Lycopene Promises Better Health
A number of studies have linked lycopene in the diet to decreased incidence of several cancers. This antioxidant is also believed to protect against heart disease. And Foolad reports, “Lycopene has roughly twice the antioxidant capacity of beta carotene.”

Tomatoes and their products, such as catsup, spaghetti sauce, tomato juice and soup, contribute most of the lycopene in the U. S. diet because a great deal is consumed. Worldwide, only potatoes outrank tomatoes in consumption among vegetables. In the U. S., tomatoes are the third most economically important vegetables after potatoes and lettuce.

But compared to some wild tomatoes, current commercial cultivars have surprisingly low concentrations of lycopene. Foolad has developed tomatoes with two times or more the lycopene content of those now on the market. Since it is lycopene that imparts the red pigmentation, Foolad’s tomatoes are striking, with deep, dark red coloration.

Wild Tomatoes Provide the Genes
Because today’s cultivated tomatoes have such a narrow genetic base, Foolad says, “I knew the cultivated species would not have the genes I was seeking for disease resistance and high lycopene content.” So he turned to wild accessions. He began with the gene banks maintained at the C. M. Rick Tomato Genetics Resource Center at the University of California, Davis, and the U. S. Department of Agriculture’s Plant Genetic Resources Unit at Geneva, New York. More than 300 wild tomato accessions were evaluated during the first few years.

Conventional breeding requires timeconsuming and painstaking crossing, backcrossing, and re-crossing plus exacting record keeping. Tomato breeding is a complex process. With 30,000 to 35,000 genes in tomatoes, identifying the genes responsible for specific traits is daunting. Professor Foolad, however, also uses molecular markers and marker-assisted selection (MAS) techniques. This gene mapping speeds the process of locating the gene(s) controlling a trait of interest, and facilitates targeting the transfer of the desirable trait. Wild tomatoes have undesirable traits, notably low yields and huge plant size. Pinpointing a desirable trait while eliminating unwanted ones is a major challenge. Gene mapping and MAS techniques avoid a lot of trial and error.

Foolad believes he is probably the only tomato breeder in this country developing both fresh market and processing tomatoes. Although the two types demand different strategies, he has set out to obtain favorable characteristics in addition to improved disease resistance and lycopene content. Fruit size and shape, total solids content, color, firmness, ripening, nutritional quality and flavor are all essential factors for an ideal tomato. Fruit total solids content is particularly
important to the tomato processing industry.

Increasing fruit solids content has driven many breeding research programs. The total dry matter of tomato fruit comprises four to 7.5 percent of the fresh weight. Soluble solids account for about 75 percent, and insoluble solids account for 25 percent of this dry matter. The main components of the soluble solids are reducing sugars glucose, fructose, and a very small amount of sucrose. Organic acids, lipids, minerals, pigments, and volatiles make up the remaining soluble solids. The insoluble solids include proteins, cellulose, hemicellulose, pectins, and polysaccharides, which determine fruit viscosity. The quality of
tomato products is infl uenced by viscosity.

Both soluble and total solids are related to yield of concentrated tomato products, and yield and quality of certain processed products are determined by sugar content of the fruit. For tomato products that are sold on the basis of solids contents, the higher the solids of the raw products, the greater the value of crop yields. For example, an increase in solids of just one percent represents a 20 percent increase in yield of certain products. Estimates of the soluble solids contents of available commercial tomato cultivars range between 4.5 and 6.3 percent. However, the soluble solids of some accessions of tomato related wild species have been measured at concentrations between nine and 15 percent.

The ratio of sugars to acids is, of course, critical to flavor. However, lower pH reduces the risk of pathogen growth in tomato products.

In addition to the appearance and taste of tomatoes, health benefi ts are factoring more strongly in consumer perception. Thus, Foolad’s lycopene-boosted tomatoes promise favorable consumer acceptance.

Moreover, growers will experience healthier profits with disease resistant cultivars.

Foolad’s cherry, grape, and plum tomatoes are expected to be on the horizon soon. And seed companies, growers, and the tomato-loving public may not have to wait too long before Foolad perfects a large round fresh market disease-resistant, lycopene-enhanced dark red orb to grace.


© 2007 Columbia Publishing

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