M. E. N. Fonseca

Sources of resistance to tomato spotted wilt virus (TSWV) in cultivated and wild species of Capsicum

SummaryA germplasm collection of 70 cultivars and wild species of Capsicum was evaluated for resistance to tomato spotted wilt virus (TSWV) under field (natural inoculum) conditions. Different levels of resistance to the disease caused by this virus were observed among the tested lines. High degree of field resistance was detected in two Capsicum baccatum var. pendulum, two C. chinense, and three C. annuum lines. Controlled greenhouse tests were also carried out to confirm the resistant reaction of these seven field selected lines. These lines were mechanically inoculated with two serologically distinct isolates of TSWV obtained from different geographic regions of Brazil. The two C. chinense lines (‘CNPH 275’ and ‘PI 159236’) were virtually immune against one specific (TSWV-BsB) isolate but were susceptible to another isolate (TSWV-SP) used in this assay. Sources of resistance for both isolates were not found. Our experimental results strongly indicate there exists a number of genetic mechanisms (probably including action of vertical and horizontal genes) to TSWV resistance in Capsicum spp.

Detection of avocado sunblotch viroid in chloroplasts of avocado leaves by in situ hybridization

SummaryIn situ hybridization experiments were carried out to detect avocado sunblotch viroid (ASBVd) in foliar tissue of avocado, using a digoxigeninlabelled RNA probe complementary to the ASBVd-RNA in sections of aldehyde-fixed, LRGold-embedded leaf samples. Detection of the probe was made through anti-digoxigenin antibody and protein-A colloidal gold (20 nm). Seventy to 80% of the signals came from chloroplast while the cytoplasm and vacuole were labelled with ca. 10% of the gold particles. This is in contrast with the subcellular localization of potato spindle tuber viroid and some other related viroids, which are mainly found in the nucleus.

Hortaliças como alimentos funcionais

Although a very old concept, the relationship between food and health has never been as close as it is today. Diets rich in fat, salt, and sugar and poor in complex carbohydrates, vitamins, and minerals in association with a more sedentary lifestyle, are responsible for an increase in diet-related diseases such as obesity, diabetes, cardiovascular problems, hypertension, osteoporosis, and cancer. It is believed that the ingestion of fruits and vegetables helps in the prevention of these diseases. Vegetables are an important component of the diet, usually in association with protein- and starch-rich foods. They are responsible not only for adding variety of color and texture to meals, but also for providing important nutrients. Vegetables are low fat and low calorie foods, with relatively small amounts of protein, but they are rich in carbohydrates and fibers and add significant amounts of micronutrients to the human diet. They are also a source of functional substances, which might benefit one or more physiological functions in the body, besides adequate nutritional effects. Functional elements might play a role in improving health and well-being, as well as reducing the risk of the onset of diet-related diseases. The development of vegetable cultivars with greater amounts of these substances is one of the main goals of modern breeding programs. Many of these programs, working on different vegetables, are currently underway in Brazil and other countries, aiming to improve the amount and variety of carotenoids present in the diet. In the present paper, the main aspects of vegetable crops as functional foods are discussed. The most important achievements of tomato and carrot breeding programs in Brazil aiming to improve the amount and types of functional compounds are also presented.

Pepper yellow mosaic virus, a new potyvirus in sweetpepper, Capsicum annuum

Summary. A potyvirus was found causing yellow mosaic and veinal banding in sweetpepper in Central and Southeast Brazil. The sequence analysis of the 3′ terminal region of the viral RNA revealed a coat protein of 278 amino acids, followed by 275 nucleotides in the 3′-untranslated region preceding a polyadenylated tail. The virus shared 77.4% coat protein amino acid identity with Pepper severe mosaic virus, the closest Potyvirus species. The 3′-untranslated region was highly divergent from other potyviruses. Based on these results, the virus found in sweetpepper plants could be considered as a new potyvirus. The name Pepper yellow mosaic virus (PepYMV) is suggested.

Estimativa indireta de teores de licopeno em frutos de genótipos de tomateiro via análise colorimétrica

Indirect estimation of lycopene concentration in fruits of tomato genotypes via chromaticity values Lycopene (C 40 H 56 ) is a red carotenoid pigment, which naturally accumulates in flowers, fruits and roots of some vegetable and fruit crops. The unique properties of the lycopene molecule make this pigment one of the most powerful antioxidants available. Tomato (Lycopersicon esculentum Mill.) fruits and processed tomato products are the main sources of lycopene in the human diet. There is a growing amount of experimental data indicating that lycopene intake is associated with decreased risk of many types of degenerative and cardiovascular diseases as well as cancers in humans. In addition, lycopene concentration is associated with improved visual perception of tomato products. Therefore, there is a strong demand to increase the total amount of lycopene in tomato cultivars for either fresh market or processing. The development of cultivars for improved lycopene content is dependent upon the availability of simple yet accurate methodologies to quantify this carotene in tomato fruits and processed tomato products. The main objective of this work was to estimate the degree of correlation between the total lycopene content in tomato fruits measured spectrophotometrically and the chromaticity values (L*, a* and b*) obtained using a tristimulus colorimeter. Colorimetric readings were taken using three sampling strategies: (1) external fruit wall; (2) internal fruit wall and (3) the whole homogenized fruit pulp. For the achromatic component L* (relative darkness or lightness), the obtained R 2 range from 0.86 to 0.91), with these correlation values being consistently higher when the chromaticity readings were taken in whole homogenized fruit pulp. These results confirmed the feasibility of obtaining precise indirect estimation of lycopene content from chromaticity readings. The methodology described here could be useful for large scale selection of tomato lines with improved levels of lycopene without of high costs and of residue disposal problems associated with the employment of organic solvents in the standard spectrophotometric methods.

Resistance to potato virus Y (pathotype 1–2) in Capsicum annuum and Capsicum chinense is controlled by two independent major genes

SummaryThe genetic basis of the resistance to a pepper strain of potato virus Y (PVY pathotype 1–2) was investigated in two lines: Capsicum annuum ‘Criollo de Morellos 334’ and Capsicum chinense ‘PI 159236’. F1, backcrosses, and F2 populations were produced using C. annuum ‘Magda’ as the susceptible parent. Segregation ratios indicated that the resistance in C. annuum ‘Criollo de Morellos 334’ is governed by a nuclear, single dominant gene with a very high but incomplete penetrance. On the other hand, the resistant response of C. chinense ‘PI 159236’ is associated with the presence of a major recessive gene with an apparently complete penetrance. The failure in recovering or detecting PVY from/in the inoculated leaves of both resistant genotypes is strongly suggestive that both genes are acting by preventing the multiplication of the virus in the leaf tissue. Both mechanisms of resistance closely resemble either an operational immunity or a single-cell hypersensitive reaction to PVY pathotype 1–2. The name Ry 1–2 is suggested for the resistance gene from ‘Criollo de Morellos 334’. The gene for resistance to PVY pathotype 1–2 identified in C. chinense ‘PI 159236’ may be the same designated etc1, which is mentioned to be allelic to the etav locus. The phenotypic expression of the etav gene was characterized in C. annuum ‘Avelar’ as a tolerant but not immune or hypersensitive reaction against some potyviruses in Florida. These data suggest that a critical reexamination of the allelic relationships at the locus et should be performed.

Inheritance of resistance to the bipartite Tomato chlorotic mottle begomovirus derived from Lycopersicon esculentum cv. ‘Tyking’

Severe outbreaks of bipartite begomoviruses (family Geminiviridae) have been observed on tomatoes after the introduction of the whitefly Bemisia tabaci (biotype B) in Brazil. The Lycopersiconesculentum line ‘TX 468-RG’ was identified as one of the best sources of broad-spectrum resistance to species comprising the tomato-infecting Begomovirus complex in Brazil. The genetic basis of resistance to one Begomovirus isolate was investigated using populations from the cross between ‘TX 468-RG’ (P1) and the susceptible line ‘Ohio 8245’ (P2). Parental lines, F1, backcross (BC) to P1 and BC to P2 and F2 generations were inoculated at the two true-leaf stage using 20 viruliferous whiteflies per plant. Assessment was done two weeks after inoculation based upon visual analysis of symptom expression. The ratio of resistant to susceptible plants closely fit to a single recessive gene (locus) model. The sequence analysis indicated that the Begomovirus isolate used in this assay was closely related to the bipartite Tomato chlorotic mottle virus. Therefore, this gene/locus, was tentatively named tcm-1 (tomato chlorotic mottle virus resistance-1). This locus has been transferred to distinct tomato cultivars and levels of resistance similar to that of ‘TX 468-RG’ were observed in advanced (F8 and F9) generations. In addition, breeding lines carrying the tcm-1 locus were also resistant to other Brazilian bipartite tomato-infecting Begomovirus species.

Development of a locus-specific, co-dominant SCAR marker for assisted-selection of the Sw-5 (Tospovirus resistance) gene cluster in a wide range of tomato accessions

The best levels of broad-spectrum Tospovirus resistance reported in tomatoes thus far are conferred by the Sw-5 locus. This locus contains at least five paralogues (denoted Sw-5a through Sw-5e), of which Sw-5b represents the actual resistance gene. Here we evaluated a panel of seven PCR primer pairs matching different sequences within a genomic region spanning the Sw-5a and Sw-5b gene cluster. Primer efficiency evaluation was done employing tomato isolines with and without the Sw-5 locus. One primer pair produced a single and co-dominant polymorphism between susceptible and resistant isolines. Sequence analysis of these amplicons indicated that they were specific for the Sw-5 locus and their differences were due to insertions/deletions. The polymorphic SCAR amplicon encompass a conserved sequence of the promoter region of the functional Sw-5b gene, being located in the position −31 from its open reading frame. This primer pair was also evaluated in field assays and with a collection of accessions known to be either susceptible or resistant to tospoviruses. An almost complete correlation was found between resistance under greenhouse/field conditions and the presence of the marker. Therefore, this primer pair is a very useful tool in marker-assisted selection systems in a large range of tomato accessions.

Efeito da infecção precoce por Begomovirus com genoma bipartido em características de frutos de tomate industrial

oBrix) utilizando uma cultivar de tomateiro para processamento industrial suscetivel a Begomovirus. A inoculacao controlada das mudas (18 dias apos semeadura) foi realizada inicialmente em casa de vegetacao usando moscas-brancas (Bemisia tabaci biotipo B) viruliferas, sendo as mudas expostas aos insetos por quatro dias. Um grupo de mudas nao inoculadas (controles) foi mantido isolado em uma casa de vegetacao livre do inseto vetor. Plantas inoculadas e nao inoculadas foram simultaneamente transplantadas em campo e dispostas em um delineamento de blocos ao acaso com quatro repeticoes com dez plantas por parcela. A analise de sequencia de nucleotideos de parte do genoma do DNA-A do virus utilizado na inoculacao indicou ser um isolado distinto, mas geneticamente relacionado com Tomato chlorotic mottle virus (uma das especies do complexo de Begomovirus infectando tomateiro no Brasil). Foi observada diferenca significativa para producao total, sendo 109,0 t/ha nas plantas controle e 48,2 t/ha nas mudas submetidas a inoculacao precoce; tendo-se reducao de aproximadamente 60% na produtividade. A diferenca mais acentuada foi observada para o parâmetro numero de frutos por planta. As plantas nao infectadas apresentaram uma media de 66 frutos, enquanto que nas plantas infectadas esta media foi de 38 frutos. O peso medio e o teor de solidos soluveis dos frutos nao foram significativamente influenciados pela infecao precoce. Desta forma, existe a possibilidade de reduzir perdas de produtividade devido a infecao de Begomovirus por meio do manejo adequado do sistema de producao, incluindo isolamento de viveiros e sementeiras e datas de transplantio. Com estes resultados salienta-se a importância epidemiologica de, quando possivel, retardar ao maximo o processo de infecao precoce por Begomovirus em mudas de tomateiro.

Search in Solanum (section Lycopersicon) germplasm for sources of broad-spectrum resistance to four Tospovirus species

The genus Tospovirus was considered as monotypic with Tomato spotted wilt virus (TSWV) being the only assigned species. However, extensive studies with worldwide isolates revealed that this genus comprises a number of species with distinct virulence profiles. The Neotropical South America is one center of Tospovirus diversity with many endemic species. Groundnut ringspot virus (GRSV), TSWV, Tomato chlorotic spot virus (TCSV), and Chrysanthemum stem necrosis virus (CSNV) are the predominant tomato-infecting species in Brazil. Sources of resistance were found in Solanum (section Lycopersicon) mainly against TSWV isolates from distinct continents, but there is an overall lack of information about resistance to other viral species. One-hundred and five Solanum (section Lycopersicon: Solanaceae) accessions were initially evaluated for their reaction against a GRSV isolate by analysis of symptom expression and systemic virus accumulation using DAS-ELISA. A subgroup comprising the most resistant accessions was re-evaluated in a second assay with TSWV, TCSV, and GRSV isolates and in a third assay with a CSNV isolate. Seven S. peruvianum accessions displayed a broad-spectrum resistance to all viral species with all plants being free of symptoms and systemic infection. Sources of resistance were also found in tomato cultivars with the Sw-5 gene and also in accessions of S. pimpinellifolium, S. chilense, S. arcanum, S. habrochaites, S. corneliomuelleri, and S. lycopersicum. The introgression/incorporation of these genetic factors into cultivated tomato varieties might allow the development of genetic materials with broad-spectrum resistance, as well as with improved levels of phenotypic expression.