|Author: ||J.W. Scott|
|Keywords: ||Lycopersicon esculentum, disease resistance|
About 55,000 ha of field-grown, fresh-market tomatoes with a crop value of around 1,150,000,000 dollars are grown annually in the United States.
Nearly 2/3 of this production is in the states of Florida and California.
Major issues facing the industry are competition from Canadian greenhouse and Mexican field and greenhouse tomatoes, the phasing out of the fumigant methyl bromide and urban encroachment on agricultural land and water use.
Over the last 30 years, there has been a sharp decline in the number of public tomato breeding programs with an increase in private sector breeding programs.
The only large-scale public fresh-market tomato breeding takes place at the University of Florida and North Carolina State University.
Some breeding does take place at a few other institutions such as Penn State and Cornell.
Large, round-fruited cultivars make up the major share of the market, but plum and grape tomatoes have increased their market share over the last several years.
With the exception of most cultivars of grape tomatoes, specific plants are mostly grown staked with light pruning.
Prices are generally higher for large fruit (>7 cm diameter) and thus breeding emphasis is on developing large, firm, smooth, uniform green shoulder, defect-free fruit.
A small percentage of current cultivars grown in the USA use the rin gene, unlike Mexico where heterozygous rin cultivars are widely grown.
A majority of the production is harvested at the mature-green stage with a trend for more vine-ripe harvesting over the last several years.
Heat-tolerance breeding is being emphasized for the potentially more reliable fruit setting in a range of environments, but few heat-tolerant cultivars are presently grown.
Some work is being done on developing high lycopene and good color based primarily on the crimson gene (ogc). Research is ongoing to develop tomatoes which can be grown without staking.
These are called compact growth habit tomatoes, and they have the brachytic (br) and prostrate growth habit genes.
Standard disease resistances of most commercial cultivars are to Fusarium oxysporum f. sp. lycopersici races 1 and 2 (I, I-2), Verticillium dahliae race 1 (Ve), Stemphylium spp. (Sm) and sometimes Meloidogyne incognita (Mi). A few field cultivars also have Tomato mosaic virus resistance (Tm-2 or Tm-22). Some recent cultivars have resistances to F. oxysporum f. sp. lycopersici race 3 (I-3), Tomato spotted wilt virus (Sw-5) or Fusarium oxysporum f. sp. radicis-lycopersici (Frl). Major disease resistances being developed in Florida are to bacterial spot and Tomato yellow leaf curl virus (TYLCV). In other eastern states breeding emphasis is on early blight and late blight.
Spotted wilt is also a problem in the southeast.
Some bacterial speck resistance (Pto) breeding is being done in California.
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