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Early blight (EB) is one of the dreadful diseases of tomato caused by several species of Alternaria including Alternaria linariae (which includes A. solani and A. tomatophila), as well as A. alternata. In some instances, annual economic yield losses due to EB have been estimated at 79%. Alternaria are known only to reproduce asexually, but a highly-virulent isolate has the potential to overcome existing resistance genes. Currently, cultural practices and fungicide applications are employed for the management of EB due to the lack of strong resistant cultivars. Resistance sources have been identified in wild species of tomato; some breeding lines and cultivars with moderate resistance have been developed through conventional breeding methods. Polygenic inheritance of EB resistance, insufficient resistance in cultivated species and the association of EB resistance with undesirable horticultural traits have thwarted the effective breeding of EB resistance in tomato. Several quantitative trait loci (QTL) conferring EB resistance have been detected in the populations derived from different wild species including Solanum habrochaites, Solanum arcanum and S. pimpinellifolium, but none of them could be used in EB resistance breeding due to low individual QTL effects. Pyramiding of those QTLs would provide strong resistance. More research is needed to identify additional sources of useful resistance, to incorporate resistant QTLs into breeding lines through marker-assisted selection (MAS) and to develop resistant cultivars with desirable horticultural traits including high yielding potential and early maturity. This paper will review the current understanding of causal agents of EB of tomato, resistance genetics and breeding, problems associated with breeding and future prospects. [ABSTRACT FROM AUTHOR]

Nine parental lines and 18 hybrids derived by crossing them in Line × Tester fashion were screened against the early blight pathogen Alternaria solani along with a resistant, susceptible and a commercial check in the form of Arka Rakshak, IIHR2202 and Abhinava respectively. Parental lines and the resistant and susceptible checks were screened over two seasons and results obtained were almost similar with the line IIHR1816 exhibiting resistance with the disease severity of 25 % in both the trials, while the line IIHR977 was found to be resistant in the first season with PDI of 25 % and moderately resistant in the second season with the slightest increase in the disease severity up to 25.6 %. None of the hybrids were found to be resistant except, whereas about eight hybrids were found to be moderately resistant. IIHR2892 x IIHR2853 was found to be highly susceptible with severity of 68.75 %, which is on par with the susceptible check IIHR2202 (70.50 %). The results obtained from the detached leaf method of screening should be confirmed by the field or greenhouse screening methods before using them in further breeding programmes. [ABSTRACT FROM AUTHOR]

This study was carried out at the Experimental Farm, Faculty of Agriculture, Menoufia University, Shibin EI-Kom during three summer seasons. The cultivar Super Beef Steak and the line 81-15 were used as parents to produce the required populations, i.e., F1, F2 and Bcp1 and Bcp2. The six populations were evaluated for number of days to the first ripe fruit, average fruit weight, total soluble solids and ascorbic acid content, as well as, resistance to the root knot nematode, Meloidogyne incognita. A randomized complete blocks design was used. Data were recorded on an individual plant for each population. Regard to the resistance to root knot nematode, the experiment was carried out in pots. Data obtained suggested that the number of days to ripening showed over-dominance for the short period. Total soluble solids and ascorbic acid contents are controlled by additive gene with slight dominance for the low contents. Partial dominance for the small fruit was found. With regard to root knot nematode resistance, the character is controlled by single dominant gene for low number of galls and egg masses. Therefore, developing of tomato cultivars and F1 hybrids for resistance could be achieved by breeding programs. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the heterosis, inbreeding depression and genetics for yield, quality and resistance to early blight in tomato. Consequently, twenty inter-specific crosses of tomato were developed by crossing five susceptible cultivars and four wild resistant accessions and tested in field and glasshouse conditions for early blight (EB) resistance. Biochemical responses were also critically studied both in parents and hybrids. All the crosses showed moderately susceptible reaction except five crosses of EC-520061 ( Solanum habrochaites ). Biochemically the wild parents exhibited better results over susceptible parents but their hybrids showed moderate reaction for early blight resistance. High level of phenol was found both in resistant parents and hybrids. Among the 20 crosses, those made by EC-520061 and H-88-78-1 manifested resistance capacity, low heterosis and high inbreeding depression for EB disease. For yield associated traits most of the crosses expressed high heterosis and low inbreeding depression which indicated better yield capacity. The crosses made by EC-520061 ( S. habrochaites ) segregated in 3:1 (resistant:susceptible) Mendelian ratio and indicated monogenic dominant and additive gene effects. Remaining crosses showed 1:2:1 (resistant:intermediate:susceptible) genetic ratio and indicated heterozygous nature of crosses mediated by multiple genes or QTLs. This fact can be utilized in future tomato breeding program for developing resistant varieties against EB disease. [ABSTRACT FROM AUTHOR]

Late blight (LB), caused by Phytophthora infestans, is one of the most devastating diseases of tomato ( Solanum lycopersicum) worldwide. Due to the emergence of new and aggressive P. infestans isolates, identifying new genetic resistance to LB is a priority in tomato breeding. Recently, we reported the identification of several Solanum pimpinellifolium accessions with strong LB resistance. In this study, we investigated the utility of resistant accession PI 163245 for tomato breeding by examining heritability ( h2) of resistance and the response to selection for resistance. Estimates of h2 based on F2 : F3 and F3 : F4 parent : offspring correlation analyses averaged 0.79 and 0.94, respectively, suggesting the heritable nature of LB resistance in PI 163245. Analysis of response to selection for resistance from F2 to F4 generations indicated a realized h2 of 0.63, confirming the utility of this resistance in tomato breeding. Two methods of estimating the minimum number of loci involved indicated the presence of one major resistance locus. Currently, genetic mapping and breeding efforts are underway to further confirm the viability of this accession for improving tomato LB resistance. [ABSTRACT FROM AUTHOR]

Advances in tomato breeding for pest resistance have been achieved via gene introgression from wild Solanum (section Lycopersicon) species ( Solanaceae). Ninety-nine F3 families derived from an interspecific cross using as parental lines Solanum lycopersicum L. ' LAM-148' (susceptible standard) and Solanum pimpinellifolium L. ' TO-937-15' (multiple pest resistance accession with type IV glandular trichomes and acylsugar accumulation) were evaluated for their resistance against the whitefly Bemisia tabaci ( Gennadius) ( Hemiptera: Aleyrodidae) biotype B in free-choice and no-choice tests for oviposition and adult colonization. The parental lines and eight F3 families with contrasting levels of resistance against the whitefly were selected and investigated in additional assays, which included the estimation of trichome densities and foliar acylsugar levels. The F3 families BTR-302 and BTR-331 exhibited low amounts of eggs of whitefly and transgressive segregation for type IV glandular trichome density with values greater than that of TO-937-15 plants. However, the tested families did not surpass the total foliar acylsugar content found in TO-937-15. BTR-331 exhibited low colonization in the free-choice test and it was the least preferred F3 family in the no-choice test. The higher resistance levels of BTR-331 were associated with a positive combination of higher type IV trichome density and higher acylsugar levels. Some F3 families displayed reduced fruit set due to the presence of flowers with style exertion of the antheridial-cone. Fruit weight at harvest stage of the selected families (from 4.9 to 14.5 g) was lower than that of LAM-148 (139.5 g) but higher than that of TO-937-15 plants (1.3 g). Therefore, although difficult to reach due to the simultaneous segregation of many polygenic traits, the combination of high B. tabaci resistance levels with superior horticultural traits is feasible. These results confirm TO-937-15 as a source of biotype B resistance. From the breeding standpoint, the genetic similarity between S. lycopersicum and S. pimpinellifolium would allow a more efficient resistance introgression by facilitating recombination and minimizing the potentially undesirable linkage drag associated with this trait. [ABSTRACT FROM AUTHOR]

Root-knot nematodes ( Meloidogyne spp.) can cause severe problems in tomato production in warm climates. To date, Mi-1 is the only gene that has been used widely to develop cultivars for controlling disease caused by nematodes around the world. However, Mi-1 does not provide resistance to the pest when the soil temperature is above 28 °C. Tomato breeding line ZN17 has been reported to possess resistance to Meloidogyne incognita at high temperatures (32 °C). To identify markers linked tightly to resistance, an F population was developed by crossing the resistance line ZN17 to susceptible line 09C84. Analysis of F individuals by inoculating M. incognita suggested that resistance in ZN17 is conditioned by a single dominant gene temporarily designated as Mi-HT. Linkage analysis suggested that Mi-HT is located on the short arm of chromosome 6. One marker, W737, co-segregated with Mi-HT. Comparisons of map positions of Mi-HT, Mi-1, and Mi-9, as well as marker genotypes in LA2157, Motelle, and ZN17 suggested that Mi-HT might be a homologue of Mi-1 and Mi-9 or a new gene. The results obtained in this study will facilitate fine-mapping and cloning of the gene as well as marker-assisted breeding for heat-stable resistance to southern root-knot nematodes in tomato. [ABSTRACT FROM AUTHOR]

Bacterial canker of tomato, caused by Clavibacter michiganensis subsp. michiganensis (Cmm), is considered the most serious bacterial threat, resulting in high damages in production areas. Worldwide, Cmm is subjected to quarantine regulations.There is no cultivar in market containing Cmm resistance genes. This project aimed to screen tomatoes or wild relatives of tomato for resistance to Cmm, to be used for starting breeding programs. We have screened 24 different wild accessions of tomato and found several new tolerant sources: Solanum pimpinellifolium GI.1554, S. parviflorum LA735 and S. parviflorum LA2072. We also confirmed the tolerance which was reported previously in S. peruvianum LA2157, S. peruvianum PI127829, S. peruvianum LA385, S. habrochaites LA407 and S. lycopersicum cv. IRAT L3. No immunity was found. Also accessions showing a low disease score still contained high titers of bacteria as determined by a dilution plating method, using tow selective media. These results were confirmed with a TaqMan real time PCR assay, which was developed to determine and quantify Cmm in planta. [ABSTRACT FROM AUTHOR]

The tomato yellow leaf curl virus (TYLCV), transmitted by whitefly, causes major disease losses to tomato crops in tropical and subtropical regions of the world. Several genes conferring resistance to TYLCV, mainly Ty- 1 and Ty- 3 genes, have been introgressed to cultivated tomato ( Solanum lycopersicum) from the wild relative species Solanum chilense. By combining bulked segregant analysis and amplified fragment length polymorphisms (AFLP), several AFLP markers closely linked to Ty- 1 and Ty- 3 genes were identified from the resistant breeding line TZ841-4. Cloning and sequencing of the selected AFLP fragments allowed us to develop codominant cleaved amplified polymorphic sequence and dominant sequence characterized amplified region markers closely linked to Ty- 1. In addition, Ty- 3-linked allelic-specific markers have been discriminated by a quantitative real-time PCR protocol. Taken together, these markers constitute useful tools for marker-assisted selection breeding programs to improve genetic resistance to TYLCV, and also to initiate map-based cloning approaches to isolate the resistance genes. [ABSTRACT FROM AUTHOR]

Late blight caused by Phytophthora infestans (Mont.) De Bary is among the most economically important diseases of tomato. The use of host-plant resistance offers a potentially cost-effective and environmentally sound complementary disease management strategy for incorporation into tomato late blight integrated pest management (IPM). Late blight resistance in tomato (Solanum lycopersicum L.) was derived from S. pimpinellifolium and introgressed into highland-adapted tomato already resistant to Fusarium wilt, root-knot nematodes, tomato mosaic virus (ToMV) and tomato yellow leaf curl virus (TYLCV). Evaluation and selection for durability of late blight resistance, yield, and other horticultural traits was done in a controlled environment at AVRDC, The World Vegetable Center headquarters in Shanhua, Taiwan, and under field conditions at the Regional Center for Africa in Arusha, Tanzania. Four lines were subjected to multilocational trials with a local check at 5 sites representing 4 agroecological zones. Two of the best performing lines with enduring resistance to late blight, LBR19-2 and LBR44-2, were released as new varieties in Tanzania under trade names 'Meru' and 'Kiboko' in 2007 and 2008, respectively. [ABSTRACT FROM AUTHOR]

The article presents the study that investigates the breeding lines of tomatoes which are resistant to spotted wilt virus and mosaic virus in Spain. The topics discussed include the susceptibility of the de la pera tomato variety to different diseases and viruses, ways on how farmers can benefit from knowing the breeding lines of tomatoes, and the traits and characteristics of tomatoes.

Tomato ( Solanum lycopersicum) production in tropical and subtropical regions of the world is limited by the endemic presence of Tomato yellow leaf curl virus (TYLCV). Breeding programmes aimed at producing TYLCV-resistant tomato cultivars have utilized resistance sources derived from wild tomato species. So far, all reported breeding programmes have introgressed TYLCV resistance from a single wild tomato source. Here, we tested the hypothesis that pyramiding resistances from different wild tomato species might improve the degree of resistance of the domesticated tomato to TYLCV. We have crossed TYLCV-resistant lines that originated from different wild tomato progenitors, Solanum chilense, Solanum peruvianum, Solanum pimpinellifolium, and Solanum habrochaites. The various parental resistant lines and the F1 hybrids were inoculated in the greenhouse using viruliferous whiteflies. Control, non-inoculated plants of the same lines and hybrids were exposed to non-viruliferous whiteflies. Following inoculation, the plants were scored for disease symptom severity, and transplanted to the field. Resistance was assayed by comparing yield of inoculated plants to those of the control non-inoculated plants of the same variety. Results showed that the F1 hybrids between the resistant lines and the susceptible line suffered major yield reduction because of infection, but all hybrids were more resistant than the susceptible parent. All F1 hybrids resulting from a cross between two resistant parents, showed a relatively high level of resistance, which in most cases was similar to that displayed by the more resistant parent. In some cases, the hybrids displayed better levels of resistance than both parents, but the differences were not statistically significant. The F1 hybrid between a line with resistance from S. habrochaites and a line with resistance from S. peruvianum (HAB and 72-PER), exhibited the lowest yield loss and the mildest level of symptoms. Although the resistance level of this F1 hybrid was not statistically different from the level of resistance displayed by the 72-PER parent itself, it was statistically better than the level of resistance displayed by the F1 hybrids between 72-PER and any other resistant or susceptible line. [ABSTRACT FROM AUTHOR]

The objective was to obtain and identify native isolates of Trichoderma spp. from soils cultivated with tomato in Tlayacapan, Morelos, México with incidence of Alternaria solani and Phytophthora infestans; also, to determine their in vitro antagonistic capacity. Trichoderma was isolated directly from the soil by the dilution method in Petri dish with potato-dextrose-agar (PDA) medium culture. The antagonistic capacity was evaluated throughout the cellophane technique and antagonism class with the dual cultures technique. Analyses of variance were used and mean separation was achieved using the Tukey test. 20 isolates of Trichoderma were obtained. The percentage of inhibition of the growth mycelium of plant pathogen for the isolates varied from 38.8 to 81.3% in A. solani and from 16.3 to 85.5% in P. infestans. Ten isolates that inhibited at least 65% of the growth were selected: T. harzianum (Thz), T. longibrachiatum (Tl) and T. koningii (Tk). The isolates Tl-17, Tl-19, Tl-20, Tl-21, Thz-16 and Tk-4, selected against A. solani, presented antagonism class 1 by over-growing the plant pathogen and sporulating on it. The isolates Thz-17, Thz-18, Tl-17, Tl-18 and Tl-19 selected against P. infestans, present antagonism class 2 and Thz19 antagonism class 3. For its antagonistic action in vitro on P. infestans and A. solani, Trichoderma can be considered as a promissory agent in the biological control of the diseases caused by these plant pathogens. [ABSTRACT FROM AUTHOR]

Abstract??The prevailing reaction of plants to pest attack is the activation of various defense mechanisms. In tomato, several studies indicate that an 18 amino acid (aa) peptide, called systemin, is a primary signal for the systemic induction of direct resistance against plant-chewing pests, and that the transgenic expression of theprosystemingene (encoding the 200 aa systemin precursor) activates genes involved in the plant response to herbivores. By using a combination of behavioral, chemical, and gene expression analyses, we report that systemin enhances the production of bioactive volatile compounds, increases plant attractivity towards parasitiod wasps, and activates genes involved in volatile production. Our data imply that systemin is involved in the systemic activation of indirect defense in tomato, and we conclude that a single gene controls the systemic activation of coordinated and associated responses against pests. [ABSTRACT FROM AUTHOR]

The tomato yellow leaf curl virus (TYLCV) constitutes one of the biggest restrictive factors for tomato crop in Cuba. Obtaining resistant genotypes is one of the most attractive solutions for production, as a result of the threat of this virus to crop yield. In the National Institute of Agricultural Sciences (INCA), a breeding program began using commercial varieties with the resistant gene (Ty-1) to TYLCV starting from the resistant variety Vyta. Crosses between the resistant variety Vyta and the susceptible varieties Amalia, Mariela, Mara, Inifat-28 and Inca-33 were carried out, and their hybrid offspring, F1, was subjected to a virus diagnosis (molecular and not molecular); also the agronomic evaluation to them, to the parental genotypes, to the hybrid HA-3019 and the variety Campbell-28 was performed, these ones used as resistant and susceptible control respectively. Results of the diagnosis proved the resistant character of Vyta to the disease, the good behavior of hybrids derived from this and HA-3019 hybrid, the susceptibility of commercial varieties and Campbell-28. Results from the diagnosis along with the agronomic evaluations allowed to select Mara x Vyta and Mariela x Vyta as promising hybrids to continue the plant breeding program to TYLCV that is being developed at INCA. [ABSTRACT FROM AUTHOR]

Most commercial cultivars of tomato, Lycopersicon esculentum Mill., are susceptible to early blight (EB), a devastating fungal (Alternaria solani Sorauer) disease of tomato in the northern and eastern parts of the U.S. and elsewhere in the world. The disease causes plant defoliation, which reduces yield and fruit quality, and contributes to significant crop loss. Sources of resistance have been identified within related wild species of tomato. The purpose of this study was to identify and validate quantitative trait loci (QTLs) for EB resistance in backcross populations of a cross between a susceptible tomato breeding line (NC84173; maternal and recurrent parent) and a resistant Lycopersicon hirsutum Humb. and Bonpl. accession (PI126445). Sixteen hundred BC1 plants were grown to maturity in a field in 1998. Plants that were self-incompatible, indeterminant in growth habit, and/or extremely late in maturity, were discarded in order to eliminate confounding effects of these factors on disease evaluation, QTL mapping, and future breeding research. The remaining 145 plants (referred to as the BC1 population) were genotyped for 141 restriction fragment length polymorphism (RFLP) markers and 23 resistance gene analogs (RGAs), and a genetic linkage map was constructed. BC1 plants were evaluated for disease symptoms throughout the season, and the area under the disease progress curve (AUDPC) and the final percent defoliation (disease severity) were determined for each plant. BC1 plants were self-pollinated and produced BC1S1 seed. The BC1S1 population, consisting of 145 BC1S1 families, was grown and evaluated for disease symptoms in replicated field trials in two subsequent years (1999 and 2000) and AUDPC and/or final percent defoliation were determined for each family in each year. Two QTL mapping approaches, simple interval mapping (SIM) and composite interval mapping (CIM), were used to identify QTLs for EB resistance in the BC1 and BC1S1 populations. QTL results were highly consistent across generations, years and mapping approaches. Approximately ten significant QTLs (LOD ≥ 2.4, P ≤ 0.001) were identified (and validated) for EB resistance, with individual effects ranging from 8.4% to 25.9% and with combined effects of >57% of the total phenotypic variation. All QTLs had the positive alleles from the disease-resistant parent. The good agreement between results of the BC1 and 2 years of the BC1S1 generations indicated the stability of the identified QTLs and their potential usefulness for improving tomato EB resistance using marker-assisted selection (MAS). Further inspections using SIM and CIM indicated that six of the ten QTLs had independent additive effects and together could account for up to 56.4% of the total phenotypic variation. These complementary QTLs, which were identified in two generations and 3 years, should be the most useful QTLs for MAS and improvement of tomato EB resistance using PI126445 as a gene resource. Furthermore, the chromosomal locations of 10 of the 23 RGAs coincided with the locations of three QTLs, suggesting possible involvement of these RGAs with EB resistance and a potential for identifying and cloning genes which confer EB resistance in tomato. [ABSTRACT FROM AUTHOR]

Reports on the tomato breeding line TY172 that exhibits high levels of resistance to the tomato yellow leaf curl begomovirus (TYLCV). Symptomless carrier of TYLCV; Effect of growth conditions on crop loss due TYLCV; Inheritance of resistance trait.

The article discusses breeding lines UMH 916, UMH 972, UMH 1127, and UMH 1139, that are resistant to viruses within the Muchamiel tomato. It mentions that the breeding lines were obtained by crossing a Muchamiel cultivar with the commercial cultivar Anastasia. It adds that UMH 916 and UMH 972 are genetically resistant to tomato mosaic virus (ToMV), whereas UMH 1127 and UMH 1139 have genetic resistance to ToMV and Tomato spotted wilt virus (TSWV).

To facilitate testing large numbers of tomato somaclones for resistance to bacterial canker, a fast screening procedure was developed. Two inoculation methods were investigated, i.e. excision with an infected scalpel of I) one cotyledon of 2-week-old seedlings, and II) the first true leaf of 3-week-old seedlings, followed by applying a drop of inoculum on the wound. Inoculation by method II discriminated well between populations of partially resistant and susceptible tomato genotypes. A criterion for the selection of single, putatively resistant plants, based on rating scores of the severity of wilting symptoms, was proposed and tested with plants of a Lycopersicon peruvianum accession with a relatively high level of resistance to bacterial canker. Progenies of 279 somaclones, derived from tissue explants of the susceptible tomato cultivar 'Moneymaker', were evaluated for resistance. The presence of somaclonal variation for morphological characters in these populations was previously shown. However, no differences were detected between the somaclone population and controls in either mean susceptibility or distribution of plants over disease severity categories. Moreover, plants with major increases in resistance were not detected. These results suggest that the potential of somaclonal variation as a source of resistance to bacterial canker may be limited. [ABSTRACT FROM AUTHOR]