Fresh Market Tomatoes Research Articles

Boron Improves Growth, Yield, Quality, and Nutrient Content of Tomato

Boron deficiency in fresh-market tomatoes (Lycopersicon esculentum Mill.) is a widespread problem that reduces yield and fruit quality but is often not recognized by growers. Tomatoes were grown in field and hydroponic culture to compare the effects of foliar and soil applied B on plant growth, fruit yield, fruit quality, and tissue nutrient levels. Regardless of application method, B was associated with increased tomato growth and the concentration of K, Ca, and B in plant tissue. Boron application was associated with increased N uptake by tomato in field culture, but not under hydroponic culture. In field culture, foliar and/or soil applied B similarly increased fresh-market tomato plant and root dry weight, uptake, and tissue concentrations of N, Ca, K, and B, and improved fruit set, total yields, marketable yields, fruit shelf life, and fruit firmness. The similar growth and yield responses of tomato to foliar and root B application suggests that B is translocated in the phloem in tomatoes. Fruit from plants receiving foliar or root applied B contained more B, and K than fruit from plants not receiving B, indicating that B was translocated from leaves to fruit and is an important factor in the management of K nutrition in tomato.

Processing tomato selection for corky root resistance in Italian environment

The study reports the results of a breeding program to transfer resistance to Pyrenochaeta lycopersici to new processing tomato lines. This program involved the Californian variety 'UC 82', as recurrent parent susceptibleto the fungal pathogen, and the fresh market tomato cultivars Victorio, Nikita and Rezano, as donors of partial resistance, repeatedly observed in these varieties under field conditions in southern Italy. The materials were selected with three self-fertilisation cycles following three backcrosses, on the basis of greenhouse fungal partial resistance in early growth stages and field evaluation of agronomic and quality features. The greenhouse selection examined i) taproot discoloration; ii) plant growth on infected soil as compared to control; iii) production of adventitious roots following taproot discoloration; iv) presence/absence of necrosis on adventitious roots. At the end of the breeding program, five selected lines had a significantly higher growth performance than 'UC 82' on standard and highly infected soil. The resistance of improved lines was due to several traits; high adventitious root production following taproot discoloration and improved root tissue resistance to discoloration were the most evident.

Responding to stakeholder's demands for climate information: from research to applications in Florida

Previous research shows that Florida's climate and agricultural production are influenced by the El Niño-Southern Oscillation, suggesting that farmers and ranchers might use new methods of climate forecasting to modify management, increase profits and reduce economic risks. The purposes of this paper are to describe the framework used by a Florida Consortium (FC) of researchers to assess the potential use of climate forecasts in agricultural decision-making and to summarize what was learned in the research process. The framework includes components for generation, communication and use of climate information as well as an implementation and evaluation component. Results showed that winter months are affected most by ENSO phase (higher rainfall and lower temperatures in El Niño years and the opposite during La Niña years). Yields of most crops were significantly associated with ENSO phase as were prices of some commodities. Through various mechanisms of interacting with farmers, ranchers, and extension faculty, we learned that interest in climate forecasts varied widely from highly optimistic to skeptical, and that these clients had good ideas of how to vary management if they have good forecasts. Case studies aimed at understanding potential value and risks associated with use of climate forecasts were conducted for winter fresh market tomato, cow-calf operations, and peanut production. Analytical results, confirmed by interactions with clients, showed significant value in using climate forecasts to alter specific decisions. Risks of using climate information varied among commodities, with considerable risk found in tomato due to the strong link between production and price. Perhaps the most important lesson learned was the importance of engaging trusted advisors in research and outreach efforts. A major output of the project was the close cooperation established between the FC and the Florida Cooperative Extension Service. Prospects for sustaining a climate information program in Florida are high due to joint research and extension initiatives.

Economic Evaluation of Alternative Production Systems for Fresh-Market Tomatoes in the Mid-Atlantic Region

ABSTRACT Growing competition in tomato production and marketing, in conjunction with environmental concerns, requires innovative systems for fresh-market tomato production that are profitable and environmentally sound. This study evaluated the performance of fresh-market tomato production in systems representing different levels of off-farm inputs from 1997 to 1999 at the Beltsville Agricultural Research Center in Maryland. These experimental systems included different cultivars (‘Sunbeam’, ‘Mountain Pride’), soil mulch practices (bare soil, black polyethylene, compost, hairy vetch cover crop), and fungicide application schedules (no fungicide, weekly application, and application determined by TOMCAST model predictions). Gross margins were computed based on experimental yields, production costs from enterprise budgets for staked and tied tomato crops, and weekly prices at the Baltimore fruit and vegetable wholesale market. The Roy's safety-first criterion was used to compare the preferred tomato systems for a risk-averse tomato grower. Gross margins from the hairy vetch system were higher than those from the other mulch systems in 1997, but tended to be lower in the other years. The black polyethylene system had the least overall economic risk, and the hairy vetch system had the highest risk. Gross margins among fungicide treatments were highest in the TOMCAST and weekly-based systems compared to the no fungicide system across all years. Economic risk also was similar in the weekly and TOMCAST systems. These results indicate that the TOMCAST system may be implemented to reduce fungicide applications with no additional economic risk, but that the environmental benefits of the hairy vetch system may require more economic risk to growers.

Marketable Yields of Fresh-market Tomatoes Grown in Plastic and Hairy Vetch Mulches

The use of mulches in vegetable production is undergoing a radical change away from high-input, nonrenewable resources, such as plastic, to the use of high-residue organic mulches from cover crops. The purpose of this study was to compare the marketable yield of various fresh-market tomato genotypes when grown under plastic and hairy vetch mulches. In 1996 and 1997, 12 fresh-market tomato genotypes were evaluated for yield on the North Farm of the Beltsville Agricultural Research Center (BARC), MD in a randomized split-plot design. Tomatoes were grown in conventional tillage plastic mulch (PM) and no-till hairy vetch mulch (HVM). Early blight, caused by Alternaria solani Sor., developed naturally in the plots both years and was recorded over time. All 12 genotypes were susceptible to early blight. Area under the disease progress curve (AUDPC) was calculated for each plot. AUDPC was similar both years. However, the year × mulch and year × mulch × genotype interactions were significant for AUDPC. Adjusting yields for AUDPC had a minimal effect on the data. Overall, yields were similar in PM and HVM both before and after adjusting for AUDPC. However, the mulch × genotype interaction was significant. The yield of eight of the genotypes was significantly higher in the HVM than in the PM system both years, ranging from 12% to 57% higher in 1996 and 10% to 48% higher in 1997. There was no yield difference for one genotype in HVM as compared to PM. The yield in the remaining three genotypes was either higher under HVM than PM or there was no difference. As yields from the HVM system are greater than or equal to yields in the PM system, soil compaction is reduced and nitrogen inputs are lower. The no-till HVM system is at least as good, and often better, than the conventional tillage PM system.

Foliar Disease in Fresh-Market Tomato Grown in Differing Bed Strategies and Fungicide Spray Programs.

A 3-year field study in central Maryland evaluated foliar disease in fresh-market tomato grown using combinations of four bed strategies and three fungicide programs. Bed strategies included uncovered beds with or without a composted dairy manure amendment or beds covered with black polyethylene or hairy vetch mulch. Fungicide programs included no fungicide, weekly fungicide, or fungicide applications scheduled according to the TOMCAST disease predictor. In plots with hairy vetch-covered beds, early blight caused by Alternaria solani, Septoria leaf spot caused by Septoria lycopersici, and defoliation were lower versus uncovered beds each year. Early blight and defoliation were lower in beds covered with vetch versus polyethylene mulch in 2 of 3 years. Disease severity, defoliation, and marketable yield were similar for the weekly and TOMCAST fungicide programs, with 40 to 50% fewer sprays using TOMCAST. Marketable yield was similar among bed strategies except for higher yields in covered versus uncovered and unamended beds in a relatively wet year and lower yields in vetch versus polyethylene beds in a dry year.

Major insect pests and economics of fresh-market tomato in eastern Virginia

Major insect pests of fresh-market tomato, Lycopersicon esculentum Miller, in eastern Virginia were identified as those responsible for reducing marketable fruit yield from 1998 through 2000. Nineteen arthropod pest species infested spring- and fall-grown tomato crops, but only thrips, stink bugs, and Lepidopterans, particularly the corn earworm ( Helicoverpa zea [Boddie]), reduced yield. Fruit injury by thrips and stink bugs was greater in the spring crop than in the fall crop, whereas fruit injury by Lepidopterans was greater in the fall crop. Marketable fruit yield in untreated spring and fall crops averaged 34% (range=12–51%) and 33% lower (range=26–38%), respectively, than fruit yield in treated plots. Based on these reductions and typical prices for fresh-market tomato, the loss in return per hectare in an untreated tomato field was estimated to range from $US3015 to $US17,883 in the spring crop and $US2555 to $US11,074 in the fall crop. Development of an integrated pest management program for tomato in eastern Virginia should focus initially on thrips, stink bugs and Lepidopterans such as the corn earworm.

Pseudomonas corrugata Causing Pith Necrosis on Tomato Plants in Baja California Sur, México.

Fresh market tomato (Lycopersicon esculentum Mill.) cultivars are grown in field and greenhouse areas in Baja California Sur from October to June for international markets. During March and April 2001, field-grown tomato plants showing external necrotic stem lesions and hollowed necrotic pith were observed in a 50-ha field 30 km south of La Paz. The average disease incidence in the field was 3%. Most infected plants presented necrotic lesions in the main stem 20 to 30 cm above the soil line. A few plants also presented necrotic lesions in lateral branches. Transversally cut sections in the necrotic stem area showed rotting of the vascular system with hollow cavities, typical symptom of pith necrosis. To isolate the pathogen, 5-cm-long transverse portions of diseased stems were excised, washed with soap and brushed, and rinsed with tap water. The stem portions were soaked in 10% bleach for 2 min, blotted dry on sterile paper, and 1-cm2 sections were cut to include the margins of the necrotic pith. These sections were plated on nutrient agar and incubated at 28 to 30°C. Gram-negative, rod-shaped bacteria were consistently isolated from stems with pith necrosis. They were identified as Pseudomonas corrugata using Biolog analysis (carbon source utilization at 37°C), with a similarity index of 1.0. To confirm pathogenicity, experiments were conducted twice in a screenhouse on a total of 24 2-month-old tomato cv. Rutgers plants (50 to 60 cm tall). Bacteria were injected with a syringe into the stems above the point of lateral branching at two different sites, using 0.25 to 0.5 ml of a bacterial suspension (105 CFU/ml). Injection points were sealed after inoculation with a small amount of petroleum jelly. Necrotic lesions surrounding the point of injection were observed 10 days after inoculation. Four weeks after inoculation, plants showed necrotic pith symptoms similar to those observed on field-grown plants, and P. corrugata was recovered from the margins of areas with necrotic pith. Control plants, which were injected with water, remained healthy throughout the experiments. P. corrugata has been reported to cause pith necrosis in tomato plants in California (3), Florida (2), and the northern part of the Baja California peninsula (1). This report confirms the presence of P. corrugata in the Baja California peninsula, and to our knowledge, this is the first report of P. corrugata causing pith necrosis in tomato plants in the southern state of Baja California Sur, Mexico.

Factors Associated with Foliar Disease of Staked Fresh Market Tomatoes Grown Under Differing Bed Strategies

The use of mulch or compost to reduce foliar disease in fresh market tomato could reduce fungicide use. Between 1997 and 1999, foliar disease was monitored in tomatoes grown in beds with bare soil, black polyethylene, composted dairy manure, or hairy vetch. Early blight was reduced in plots with vetch compared with bare soil or compost in all years and compared with polyethylene cover in 1 year. Early blight was reduced in plots with polyethylene versus compost and bare soil in 1 and 2 years, respectively. Septoria leaf spot was reduced in plots with vetch versus other bed strategies in 1998 and bare soil or compost in 1999. This disease was reduced in plots with polyethylene versus bare soil or compost in 1998 and 1999. Soil coverage of tomato leaflets and soil particle dispersal were reduced in plots with polyethylene or vetch versus bare soil or compost in both years that these variables were assessed. Sensor wetness duration was reduced in plots with polyethylene or vetch versus bare soil or compost in one of two years. These findings suggest that foliar disease reduction in mulch was associated with reduced splash dispersal and, in one year, reduced leaf wetness.

Cucumbers Planted Immediately after the Termination of a Nematode-resistant Tomato Cultivar Produce Higher Yields

In the southern United States, the polyethylene-mulched and drip-irrigated beds remaining after the last harvest of fresh-market tomatoes (Lycopersicon esculentum) offer the potential for producing a cucumber (Cucumis sativus) crop to increase grower profit. A 2-year study of double-cropping cucumbers with `Celebrity' (nematode-resistant) and `Heatwave' (nematode-susceptible) tomato cultivars was conducted at the Red River Research Station in northwestern Louisiana to assess the benefits of this system and to determine how soon cucumbers should be planted following the termination of the tomato crop. Results indicated that cucumbers planted after `Celebrity' produced significantly greater premium and total yields per acre than did cucumbers planted after `Heatwave'. Plant fresh weight of cucumbers was greater and the percentage of galled roots was smaller when planted after `Celebrity' than when planted after `Heatwave'. Planting dates had significant effects on cucumber yield. Cucumbers planted in early July, immediately after the termination of the tomato crop produced the highest yield. Cucumbers planted in early August, 1 month after terminating the tomato crop produced an intermediate yield, and cucumbers planted in September, 2 months after the termination of the tomato crop, produced the lowest yield. A gradual decline of plant fresh weight and a gradual increase of galled-root percentage resulted from delaying cucumber planting beyond the July month. Year of planting had no significant effect on cucumber productivity, but it did influence plant fresh weight and the percentage of galled roots significantly. Average minimum temperature in September was lower than the minimum safe temperature for growing cucumbers. The combined effect of higher temperature and lower percentage of galled roots may have contributed to the increased yield of cucumbers planted in July.

Evaluation of breeding utility of a chromosomal segment from Lycopersicon chmielewskii that enhances cultivated tomato soluble solids

A chromosomal segment from the wild tomato species, Lycopersicon chmielewskii, when backcrossed into the tomato cultivar VF145B-7879, increases fruit soluble solids concentration. In the investigation reported here, the near-isoline (VF145B-7M) homozygous for the chmielewskii (chm) chromosomal segment was crossed to the cultivar to study allelic interactions and then hybridized to three commercial cultivars (UC204c, E6203, and ChicoIII) to investigate the effect of this segment when heterozygous in different genetic backgrounds. Parents, isogenic hybrids, and unmodified hybrid controls were evaluated in three consecutive years of field study. The chm segment, when either homozygous or heterozygous, significantly increased soluble solids concentration by 13% and 12%, respectively, over VF145B-7879 (esc/esc), suggesting dominant gene action. Averaged across the three isohybrids and one isoline, one dose of this segment significantly increased soluble solids concentration by 6.0% compared to the unmodified hybrids and VF145B-7879. Other than increasing fruit total and soluble solids in mature-green and ripe-red tomatoes, no consistent negative effects of the chmielewskii segment were observed in the various genetic backgrounds on plant yield, fruit weight, or fruit pH. These results favor the use of this segment in breeding programs to develop fresh market and processing tomato cultivars with enhanced quality and reduced processed product dehydration costs.

Introduction of the Exotic Tomato yellow leaf curl virus-Israel in Tomato to Puerto Rico.

Thirty-five-day-old tomato plants (cultivar Florasette) exhibited yellow leaf curling, stunting, and extremely reduced fruit set in spring 2001, in Guanica, Puerto Rico (PR). Twenty percent disease incidence was observed in this field and, 8 weeks later, 75% of the plants showed symptoms. These symptoms were distinct from those caused by other tomato-infecting begomoviruses reported previously from PR, namely Merremia mosaic virus, Tomato mottle virus (ToMoV), and Potato yellow mosaic virus (1). A colony of the B biotype of Bemisia tabaci (Genn.) was used to transmit the suspect virus from symptomatic plants collected in the field and established in the greenhouse in Rio Piedras, PR. The suspect virus was transmitted readily to tomato cultivar Roma (10 of 10 plants), and symptoms were like those observed in the field. Symptoms also were reminiscent of those described for several Old World begomoviruses, referred to as Tomato yellow leaf curl virus (TYLCV). Total nucleic acids were isolated from three symptomatic field samples and three greenhouse-inoculated tomato plants showing typical disease symptoms. Extracts were analyzed by polymerase chain reaction (PCR) with primers AV2466 and AC1145 to amplify a begomoviral fragment (approximately 1.1 bp) that contains a portion of the intergenic region and the viral coat protein gene (CP) (2). Amplicons were cloned, and their nucleotide sequences were determined. A comparison of CP with other well-studied begomoviral nucleotide sequences revealed that the CP sequences for field isolates 1 to 6 shared 99.7 to 100% identity with each other and 99.9 to 100% identity with TYLCV from Israel (TYLCV-IL; accession no. X76319) as well as TYLCV-IL isolates discovered in the Dominican Republic (DO; accession no. AF024715) and, subsequently, in Florida. TYLCV-specific PCR primers (forward) 5'-GAATTCCGCCTTTAA-TTTG-3' and (reverse) 5'-GAATTCCCACTATCTTTCTC-3' were used to amplify the complete viral genome form a PR field isolate. An expected-sized amplicon of approximately 2.8 kb was obtained, and the nucleotide sequence of two cloned amplicons was determined. Genome organization revealed a predicted precoat open reading frame of 351 bp, which is characteristic of other Old World begomoviruses, including TYLCV-IL. Nucleotide comparisons indicated that the PR isolate shared 99% nucleotide sequence identity with TYLCV-IL (first reported from Israel) and introduced TYLCV-IL isolates in DO and Florida, thereby confirming the introduction of TYLCV-IL into PR. TYLCV-IL was first identified several years ago in the Western Hemisphere, and the virus has been reported in five offshore locations and three continental U.S. states since its initial introduction into the DO in the early 1990s. Considering the extreme virulence of TYLCV-IL compared with most New World tomato-infecting begomoviruses, this introduction, which likely occurred from a nearby Caribbean country or Florida, has the potential to destroy the fresh-market tomato industry in PR, which supplies tomatoes to the continental United States during the winter months. There is compelling evidence for the routine movement of tomato seedlings from the continental United States to this location in PR throughout the last 10 years, including the previous introduction of ToMoV (1). These incidences and others indicate the need for those in infected areas to take precautions to avoid further spread of this highly damaging virus in and adjacent to the Caribbean region.

First Report of Fusarium oxysporum f. sp. lycopersici Race 3 on Tomato in Tennessee.

In the summer of 2000, tomato (Lycopersicon esculentum Mill.) plants in several commercial fields in southeastern and eastern Tennessee exhibited symptoms of Fusarium wilt. All cultivars on which symptoms were observed are classified as resistant to races 1 and 2 of the causal fungus, Fusarium oxysporum Schlechtend.:Fr. f. sp. lycopersici (Sacc.) W.C. Snyder and H.N. Hansen. Race 3 has been reported from several areas (1), but not from Tennessee, a major producer of fresh market tomatoes. F. oxysporum was consistently isolated from discolored vascular tissue on potato dextrose agar (PDA). Pathogenicity and race determination tests for six isolates representing three counties were conducted by inoculating cultivars susceptible to races 1, 2, and 3 (Rutgers); resistant to race 1 (Bradley, Roma VF); resistant to races 1 and 2 (Conquest, Florida 47); or resistant to races 1, 2, and 3 (Floralina). Inoculum suspensions were obtained from 1-week-old cultures grown on PDA. Seedlings were grown in commercial potting mix for 3 weeks. The roots were rinsed and submerged for 30 s in inoculum suspensions (1 × 107 conidia per ml). Seedlings were then transplanted into potting mix in metal flats and placed in a greenhouse. Natural light conditions provided a 12-h photoperiod, and day and night temperatures averaged 29 and 17°C, respectively. Within 4 weeks after inoculation, all isolates caused symptoms of Fusarium wilt in all cultivars except Floralina, indicating that the isolates were race 3. The pathogen was reisolated from the discolored vascular tissue of diseased plants. Among the cultivars most severely affected by all six isolates was Conquest, which is resistant to F. oxysporum f. sp. radicis-lycopersici, the cause of Fusarium crown and root rot. Reference: (1) M. L. Marlatt et al. Plant Dis. 80:1336, 1996.

Pest damage and arthropod community structure in organic vs. conventional tomato production in California

Summary 1. To test common assumptions that the reduction in agrochemicals on organic farms allows (i) the conservation of biodiversity but (ii) has some cost in terms of increased pest damage, we compared arthropod communities and pest damage levels to fresh market tomato Lycopersicon esculentum on 18 commercial farms. These farms represented a range of management practices, with half of them operating as certified organic production systems and half as conventional operations. 2. Purported drawbacks to the adoption of organic farming include an increased incid ence of pest damage and higher risk of pest outbreaks. Although insect pest damage levels varied across the spectrum of farm management practices, they were not asso ciated with whether the farming operation was organic or conventional; organic and conventional farms did not differ significantly for any type of damage to tomato foliage or fruit. 3. Although conventional and organic farms shared a similar range of arthropod damage levels to tomato, we detected a significant difference between the actual community structures of arthropods associated with the crop. Using canonical discriminant analysis, we found that whereas herbivore abundance did not differ, higher natural enemy abundance and greater species richness of all functional groups of arthropods (herbivores, predators, parasitoids and other) distinguished organic from conventional tomato. Thus, any particular pest species would have been associated with a greater variety of herbivore species (diluted) and subject, on average, to a wider variety and greater abundance of potential parasitoids and predators, if it occurred in organically grown tomato. 4. Trophically based community parameters, specifically species richness and relative abundance of functional guilds, were clearly associated with farm management category (organic vs. conventional). However, the abundance patterns of prominent pests and natural enemies were associated with specific on-farm practices or landscape features. Fallow management, surrounding habitat and transplant date of the crop field were strongly associated with arthropod species that explained the major variability among farms. Insecticide intensity was a weaker factor. Other factors, such as distance to riparian habitats and tissue nitrogen levels, did not emerge as indicators of pest or natural enemy abundance. 5. This comparative study of active commercial farms does not support predictions of increased crop loss in California tomato when synthetic insecticides are withdrawn. It highlights the importance of large-scale on-farm comparisons for testing hypotheses about the sustainability of agro-ecosystem management schemes and their effects on crop productivity and associated biodiversity.

PETIOLE SAP NITRATE SUFFICIENCY VALUES FOR FRESH MARKET TOMATO PRODUCTION1*

Two tomato (Lycopersicon esculentum Mill.) cultivars, Mtn. Spring and Jet Star, were grown on black polyethylene-mulched beds of a loam soil with an organic matter content of 2.4% for two seasons, 1996 and 1997, to evaluate preplant N rate effects on fruit yield and leaf blade total nitrogen (N) and petiole sap NO3-N concentration. Four rates of N fertilizer (0 to 136 kg ha−1), as urea, were rotovated into the bed prior to laying the plastic mulch. Samples of the most recently matured leaves were taken every two weeks for N and NO3-N content. Fruit yield and quality were associated with early season, 4 and 6 week, petiole sap NO3-N concentration. Mtn. Spring required 1050 ppm sap NO3-N compared with 900 ppm for the Jet Star cultivar. In 1996, Mtn. Spring achieved maximum yield at 31 kg N ha−1 whereas Jet Star required 67 kg N ha−1. Maximum yield occurred at 67 kg N ha−1 for both cultivars in 1997. Nitrogen rates above the optimum decreased early yields in 1996, but not in 1997. Soil N mineralization data showed > 112 kg N ha−1 by mid-July in the top 30 cm of the soil profile. On the prairie soils of the upper Midwest soil N management should be similar for both determinate and indeterminate fresh market tomatoes. *Journal Paper No. J-19063 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA. Project no. 3706, and supported by Hatch Act and State of Iowa funds.

Cultivar e adubação NPK na produção de tomate salada

O objetivo deste trabalho foi estudar o efeito de cultivar, da adubação NPK e da interação desses fatores na produção de tomate salada tutorado. O experimento foi conduzido em Pelotas (RS) no ano agrícola 1995/96. Foram utilizadas cinco cultivares (Flora-Dade, Max, Empire, Pacific e Diva) e três níveis (2,0, 3,5 e 5,0 t/ha) de adubação NPK (3,6-7,2-10). Os tratamentos foram dispostos sob esquema fatorial em delineamento de blocos casualizados, com três repetições. As cultivares Empire e Pacific apresentaram frutos com maior peso médio do que Flora-Dade, Max e Diva. O número de frutos por planta aumentou com a elevação do nível de adubação de 2,0 para 3,5 t/ha, enquanto que o peso médio de frutos diminuiu, sem alterar a produção. As cultivares apresentaram respostas diferenciais aos níveis de adubação, em relação ao peso médio de frutos.

Genetic analysis of organoleptic quality in fresh market tomato. 1. Mapping QTLs for physical and chemical traits

Improving organoleptic quality is an important but complex goal for fresh market tomato breeders. A total of 26 traits involved in organoleptic quality variation were evaluated, in order to understand the genetic control of this characteristic. A recombinant inbred line (RIL) population was developed from an intraspecific cross between a cherry tomato line with a good overall aroma intensity and an inbred line with a common taste but with bigger fruits. Physical traits included fruit weight, diameter, color (L,a,b), firmness and elasticity. Chemical traits were dry matter weight, titratable acidity, pH, and the contents of soluble solids, sugars, lycopene, carotene and 12 aroma volatiles. RILs showed a large range of variation for most of the traits and many of them were transgressive. Some correlations between aroma volatiles were in accordance with the metabolic pathway they originated from. A total of 81 significant QTLs were detected for the 26 traits by simple and composite interval mapping. They were mainly distributed in a few regions on chromosomes 2, 3, 4, 8, 9, 11 and 12. Major QTLs (R2>30%) were detected for fruit weight, diameter, and color, and for six aroma volatiles. Co-localization of QTLs controlling correlated traits was mainly found on chromosome 2. QTLs for fruit weight and sugar content or dry matter weight were often co-localized. However, a QTL for soluble-solids content and dry matter weight have been detected on chromosome 9 in a region without fruit weight QTLs. QTLs for seven aroma volatiles, lycopene content and fruit color were also co-localized. The QTL localizations were compared with those detected in crosses between Lycopersicon esculentum and wild tomato species.

Genetic analysis of organoleptic quality in fresh market tomato. 2. Mapping QTLs for sensory attributes

The organoleptic quality of fresh market tomato can be described by a set of attributes, including fruit appearance, taste, aroma and texture. Sensory analysis is the most-valid method to study organoleptic characteristics, particularly aroma and texture. A range of 144 recombinant inbred lines of tomato derived from a cross between a cherry tomato line and a large-fruited line was evaluated by descriptive sensory profiling. Taste was analyzed through sweetness and sourness, and aroma was analyzed through the overall aroma intensity, together with candy, lemon, citrus-fruit and pharmaceutical aroma. Texture was characterized by firmness, meltiness, mealiness, juiciness and difficulty to swallow the skin. A wide range of overall variation was shown for all the attributes and significant differences among genotypes were detected. The overall aroma intensity was positively correlated with sweetness and sourness, as well as with lemon, candy and citrus fruit aromas. It was negatively correlated with mealiness. Sweetness and sourness were negatively correlated together. Molecular markers were used to map quantitative trait loci (QTLs) for each sensory attribute. One to five QTLs were detected, by simple and composite interval mapping, per attribute. The percentage of phenotypic variation explained ranged from 9% to 45% per QTL. Clusters of QTLs were observed on chromosomes 2 and 9, involving QTLs for aroma, taste and texture attributes. Most of the favorable alleles came from the cherry tomato parent, showing the potential usefulness of this line for tomato organoleptic quality improvement.

MARKER-ASSISTED SELECTION FOR THE TRANSFER OF QTLS CONTROLLING FRUIT QUALITY TRAITS INTO TOMATO ELITE LINES

Marker assisted selection (MAS) should increase the efficiency of plant breeding both for the introgression of major genes and for the simultaneous transfer of favorable alleles of many QTLs. After a review of the various MAS strategies, a MAS scheme for the improvement of tomato fruit quality is presented. Improving organoleptic quality of fresh market tomato fruit has become an important objective for tomato breeders. Several QTLs controlling the variation of tomato quality traits have been detected using a recombinant inbred line population derived from a cross between a cherry tomato chosen for its good flavor and a line with bigger fruits but poor taste. A MAS scheme was then set in order to transfer the five most important QTLs involved in fruit quality into three recurrent lines. The backcross optimisation (population size, number and position of markers) is presented, taking into account both theoretical and practical aspects.

A Case Study of Salmonellosis Associated with Consumption of Fresh-market Tomatoes and the Development of a Hazard Analysis Critical Control Points (HACCP) Program

In most developed countries, Salmonella is the main pathogen associated with documented illnesses caused by foodborne microbes (Bean and Griffin, 1990; Buzby et al., 1996). The annual cost of salmonellosis outbreaks in medical fees and time lost from work in the United States was estimated at ≈$1 billion in 1989 (Roberts and van Ravenswaay, 1989). By 1996, this estimate had soared to $3.5 billion, but the data are subject to interpretation because of: a) the difficulty in estimating medical costs for ill persons; b) the impossible task of determining lost work productivity in unreported cases of illness; and c) the tenuous nature of placing a value on the loss of life (Buzby et al., 1996). There are no reliable estimates of annual losses to businesses. Salmonellosis was traditionally linked to the consumption of meat and meat products, but in recent years the consumption of raw fruits and vegetables has been implicated in several outbreaks (Beuchat and Ryu, 1997; Brackett, 1998; Buzby, 1995; Hedburg et al., 1994). While the percentage of cases linked to produce is low compared with other foods, there are sufficient incidents to warrant concern. Not only have the food groups changed, but the typical scenario of an outbreak has changed as well. The classic “potato salad at the picnic,” where a few people become ill from a poorly handled dish at a single gathering, has given way to a scenario involving low-level contamination of massproduced, widely distributed products that tend to produce sporadic illness across state and national borders (Stephenson, 1997). The case study presented here for tomatoes (Lycopersicon esculentum Mill.) could be typical of virtually any fresh produce item.