Susceptible Tomato Varieties Research Articles

Characterization and function of Tomato yellow leaf curl virus-derived small RNAs generated in tolerant and susceptible tomato varieties

Virus-tolerant plant, which allows the accumulation of virus and then generates virus-derived small RNAs (vsRNAs), is a valuable material to reveal the antiviral efficiency of vsRNAs. Here, a comparison of vsRNAs in Tomato yellow leaf curl virus tolerant and in susceptible tomato varieties showed the consistent trend of vsRNAs' distribution on virus genome, which is presented as an obvious characteristic. However, the expression level of vsRNA in tolerant variety is less than that in susceptible variety. Slicing targets of vsRNA-mediated viral transcripts were investigated using parallel analysis of RNA ends, and geminivirus DNA methylation was determined by bisulfite sequencing, which uncovered that not all vsRNAs participated in viral mRNA degradation and DNA methylation. Additionally, by comparing with the expression pattern of vsRNAs, viral DNA and mRNA, we proposed the quantity of vsRNAs is corresponding to the expression level of viral mRNA, while the virus-suppression of vsRNAs is not high-efficient.

Molecular phylogeny, pathogenicity and toxigenicity of Fusarium oxysporum f. sp. lycopersici.

The present study aimed at the molecular characterization of pathogenic and non pathogenic F. oxysporum f. sp. lycopersici strains isolated from tomato. The causal agent isolated from symptomatic plants and soil samples was identified based on morphological and molecular analyses. Pathogenicity testing of 69 strains on five susceptible tomato varieties showed 45% of the strains were highly virulent and 30% were moderately virulent. Molecular analysis based on the fingerprints obtained through ISSR indicated the presence of wide genetic diversity among the strains. Phylogenetic analysis based on ITS sequences showed the presence of at least four evolutionary lineages of the pathogen. The clustering of F. oxysporum with non pathogenic isolates and with the members of other formae speciales indicated polyphyletic origin of F. oxysporum f. sp. lycopersici. Further analysis revealed intraspecies variability and nucleotide insertions or deletions in the ITS region among the strains in the study and the observed variations were found to be clade specific. The high genetic diversity in the pathogen population demands for development of effective resistance breeding programs in tomato. Among the pathogenic strains tested, toxigenic strains harbored the Fum1 gene clearly indicating that the strains infecting tomato crops have the potential to produce Fumonisin.

Grafting on a Non-Transgenic Tolerant Tomato Variety Confers Resistance to the Infection of a Sw5-Breaking Strain of Tomato spotted wilt virus via RNA Silencing.

RNA silencing controls endogenous gene expression and drives defensive reactions against invasive nucleic acids like viruses. In plants, it has been demonstrated that RNA silencing can be transmitted through grafting between scions and silenced rootstocks to attenuate virus and viroid accumulation in the scions. This has been obtained mostly using transgenic plants, which may be a drawback in current agriculture. In the present study, we examined the dynamics of infection of a resistance-breaking strain of Tomato spotted wilt virus (RB-TSWV) through the graft between an old Apulian (southern Italy) tomato variety, denoted Sl-Ma, used as a rootstock and commercial tomato varieties used as scions. In tests with non-grafted plants, Sl-Ma showed resistance to the RB-TSWV infection as viral RNA accumulated at low levels and plants recovered from disease symptoms by 21 days post inoculation. The resistance trait was transmitted to the otherwise highly susceptible tomato genotypes grafted onto Sl-Ma. The results from the analysis of small RNAs hallmark genes involved in RNA silencing and virus-induced gene silencing suggest that RNA silencing is involved in the resistance showed by Sl-Ma against RB-TSWV and in scions grafted on this rootstock. The results from self-grafted susceptible tomato varieties suggest also that RNA silencing is enhanced by the graft itself. We can foresee interesting practical implications of the approach described in this paper.

Differential responses of resistant and susceptible tomato varieties to inoculation with Alternaria solani

In spite of numerous studies on host pathogen interaction, very few address the differences in response in a resistance and a susceptible host. This study investigates the defense responses of resistant versus susceptible variety of tomato against the necrotrophic pathogen Alternaria solani. Various histochemical, biochemical and molecular methods were employed to compare the production and localization of phenolics, hydrogen peroxide, superoxide dismutase, polyphenol oxidases and protein cross-linking. Comet assays showed different rates of apoptosis in the hosts. A. solani transformed with green fluorescent protein gene under a constitutive promoter was used to compare progress of infection in the two varieties. The differential expression profiles of TPK1b gene were obtained over time in the two hosts. The implication of the findings, in the context of mechanism of resistance in plants, is discussed.

Biochemical and molecular studies of early blight disease in tomato

Tomato early blight occurs worldwide and it is prevalent wherever tomatoes are grown. Alternaria solani Sorauer, the causal agent, has been recognized as a serious foliar pathogen of tomato and there are very few cultivars which possess resistance against early blight. Alternaric acid is the major toxin of A. solani. In this study, alternaric acid and fungal culture filtrate were used as an elicitor in NDT-96 (tolerant) and GP-5 (susceptible) tomato varieties in order to study and compare their abilities to induce defense-related enzymes, viz., catalase, peroxidase, β-1,3 glucanase, phenylalanine-ammonia-lyase (PAL), chitinase and polyphenol-oxidase (PPO) along with total phenols, and total soluble proteins. NDT-96 showed a rapid induction of all these pathogenesis-related enzymes except catalase along with total phenols as compared to GP-5 with both the treatments. Differential expression of total soluble proteins revealed higher protein content in NDT-96 as compared with GP-5. A 49.48 kDa protein was observed to be absent in GP-5. In addition, 25 microsatellite markers (SSR) were screened for polymorphisms among the above mentioned two tomato varieties. Of these, SSR 286 revealed a significant polymorphic band of 108 bp in NDT-96.

Using small RNA sequences to diagnose, sequence, and investigate the infectivity characteristics of vegetable-infecting viruses

In a virus-infected plant, small interfering RNAs (siRNAs) corresponding to the viral genome form a large proportion of the small RNA population. It is possible to reassemble significant portions of the virus sequence from overlapping siRNA sequences and use these to identify the virus. We tested this technique with a resistance-breaking and a non-resistance-breaking strain of tomato spotted wilt virus (TSWV). We were able to assemble contigs covering 99% of the genomes of both viruses. The abundance of TSWV siRNAs allowed us to detect TSWV at early time points before the onset of symptoms, at levels too low for conventional detection. Combining traditional and bioinformatic detection methods, we also measured how replication of the resistance-breaking strain differed from the non-resistance-breaking strain in susceptible and resistant tomato varieties. We repeated this technique in identification of a squash-infecting geminivirus and also used it to identify an unspecified tospovirus.

Occurrence of virulent root-knot nematode populations on tomatoes bearing the Mi gene in protected vegetable-growing areas of Turkey

Root-knot nematodes (Meloidogyne spp.; RKN) are one of the most important pathogens of vegetables in Turkey. Assessing the existing virulent RKN populations is of importance for pathogen mapping in the west Mediterranean region of Turkey. Therefore, 95 populations of RKN were collected from different protected vegetable-growing locations in the region. Pure cultures were obtained and identified by means of species-specific primers. Virulence of the populations against the Mi-1 gene conferring resistance to Meloidogyne incognita, M. javanica and M. arenaria was determined according to their egg masses and gall rating on resistant and susceptible tomato varieties. Results showed that seven populations of M. incognita and six populations of M. javanica were able to overcome the resistance controlled by the Mi-1 gene. The frequency of virulent populations of M. incognita and M. javanica collected from different protected-grown vegetables was 11.7% and 21.4%, respectively. To our knowledge, this is the first report of populations of RKN virulent to the Mi-1 gene in Turkey.

Effect of plant age at inoculation on expression of genetic resistance to tomato yellow leaf curl virus

To determine the effects of plant age on the expression of genetic resistance to tomato yellow leaf curl virus (TYLCV), six TYLCV-resistant and two susceptible tomato varieties were inoculated at 14, 28 or 45 days after sowing (DAS). Inoculation at 14 and 28 DAS was performed in the greenhouse, and the plants were transplanted to the field at 30 DAS. Inoculation at 45 DAS was performed in the field, by covering the target plants with polypropylene ("Agril") sheets and releasing viruliferous whiteflies under them. Resistance was assayed mainly by comparing yield components of inoculated plants to those of control, non-inoculated plants of the same variety. Symptom severity and plant height were also followed. Plant age at inoculation had no effect on disease-severity scores of the susceptible varieties, and little or no effect on those of the resistant varieties. In contrast, plant age at inoculation had a significant effect on the yield of all varieties tested. All varieties suffered a significant yield reduction due to inoculation with TYLCV; the lowest yield was produced by plants inoculated at 14 DAS. A smaller TYLCV-induced yield reduction (yield increase of 50 to 100%, depending on the variety's resistance level), was achieved following inoculation at 28 DAS. A further reduction in yield loss (yield increase of 30 to 40%) was achieved following inoculation at 45 DAS. Our results clearly demonstrate the occurrence of age-related (or mature-plant) resistance in tomato plants to TYLCV.

RAPD genetic homogeneity and high levels of bacterial wilt tolerance in Solanum torvum Sw. (Solanaceae) accessions from Reunion Island

Solanum torvum Sw. is a wild species closely related to eggplant ( S. melongena L.), native to India. Although invasive in some areas of introduction, this species is of particular interest as it has been identified as a potential source of resistance to bacterial wilt disease for cultivated susceptible Solanaceae species. Little is known about the levels of resistance and genetic diversity in this species, particularly in areas of introduction such as Reunion Island, where it is used as rootstock for grafting of susceptible tomato and eggplant varieties. Eight accessions were collected in diverse geographical locations on Reunion Island for further characterisation. Regardless of the accession, no wilted plants were detected four weeks after inoculation with three different Ralstonia solanacearum strains (phylotypes) from Reunion Island. Latent bacterial colonisation in symptomless plants was however demonstrated, mainly in roots and/or lower stem, showing that S. torvum can be considered as resistant to the race 1 biovar 1 strain, and tolerant to the race 1 biovar 3 and race 3 biovar 2 strains. The homogeneity between accessions regarding high bacterial wilt tolerance was confirmed by the genetic homogeneity (0% polymorphism) revealed using 168 RAPD markers. Similarly, only 1.2% polymorphism was revealed by the genetic study of seven accessions of S. torvum from Java used as reference. All the Java accessions, but one, were identical to Reunion accessions. The level of polymorphism between S. torvum accessions is assumed to be similar to the level of genetic differences existing between vegetatively propagated clones, therefore reduced to minimal mutational events. This reduced genetic variation is typical of what is expected for an autogamous species introduced on an island. Some differences in latent bacterial colonisation scores for some of the Reunion accessions were however noticed. These results are essential for further genetic and epigenetic studies on bacterial wilt resistance in S. torvum.

Trichome Exudates and Resistance to Beet Armyworm (Lepidoptera: Noctuidae) in Lycopersicon hirsutum f. typicum Accessions

Three accessions of Lycopersicon hirsutum f. typicum Humb. and Bonpl. were highly resistant to beet armyworm, Spodoptera exigua (Hubner), as indicated by reduced survival and growth on excised leaflets, compared with leaflets of a susceptible tomato variety. Removal of trichome exudates from LA 1777 and LA 2329 eliminated resistance affecting early instars ; but this treatment had no effect on the resistance of PI 126445. Primarily, lamellar factors must condition resistance in PI 126445 and contribute to resistance to later instars in LA 1777 and LA 2329. Type-VI trichome exudates of all 3 accessions were topically toxic to 1st-instar S. exigua, and this toxicity differed among the accessions (LA 1777 > LA 2329 > PI 126445). The lower toxicity of trichome exudates on PI 126445 apparently accounts for their minimal role in resistance in this accession. During feeding, 1st instars ruptured sufficient numbers of type-VI trichome glands to account for the observed mortality on both LA 1777 and LA 2329. Toxicities of trichome exudates from the accessions were not correlated with their sesquiterpene and total phenolic contents ; the most toxic trichomes (LA 1777) had the lowest concentrations of volatiles detectable by gas chromatography, and total phenolic compounds. The important toxins remain unidentified. Identification of the lamellar factors from the accessions, and the toxins in the trichome exudates of LA 1777 and LA 2329, will facilitate the use of these accessions in breeding programs for resistance to S. exigua and possibly other pests of tomatoes.

AAL‐toxin, a potent natural herbicide which disrupts sphingolipid metabolism of plants

AbstractAAL‐toxin, a product of Alternaria alternata (Fr.) Keissl., is effective as a herbicide at low concentrations against a range of broadleaf plants (e.g. jimsonweed, prickly sida and black nightshade). However, monocotyledonous crops such as maize and wheat, as well as some varieties of tomato, are tolerant to it. The IC50 values for cellular electrolyte leakage and chlorophyll loss in duckweed (Lemna pausicostata L.) after 72 h treatment were 20–40 nM. Similar results were obtained with a susceptible tomato variety. AAL‐toxin caused rapid cellular leakage of electrolytes, followed by cellular collapse; the first symptom at the ultrastructural level is disruption of the plasma membrane. The effects of the toxin are not light‐dependent and appear to be associated with dysfunction of the plasma membrane. Fumonisins and sphingoid bases such as phytosphingosine cause similar effects, although these compounds are less potent (fumonisins, about 10‐fold; sphingoid bases, about 100‐fold). Recent studies suggest that in duckweed and in susceptible tomato varieties, AAL‐toxin‐ and fumonisin B1‐induced disruption of sphingolipid metabolism is an early event in the cascade of events leading to phytotoxic injury and cell death.

Reproduction of Meloidogyne Javanica On Legume Crops and Some Weed Species Associated With Their Cultivation in Malawi

Seven legume crops and 18 associated weed species in maize-based, mixed crop small-holdings in Malawi were evaluated as hosts for Meloidogyne javanica in pot experiments. Plants were inoculated with the nematode by applying a water suspension of 2000 (for crops) or 3000 (for weeds) juveniles around the seedling roots. Host suitability was assessed, relative to a susceptible tomato variety, on the basis of severity of galling, number of mature females per g of root and number of eggs per egg sac. With the exception of groundnut (Arachis hypogaea), all the legume crops tested were able to support nematode reproduction to some extent. Bambara (Voandzeia subterranea) was the most susceptible host. French bean (Phaseolus vulgaris) was also susceptible, while chickpea (Cicer arietinum), cowpea (Vigna unguiculata) and soya (Glycine max) were moderately good. Pigeonpea (Cajanus cajan) was a poor host. Several of the weed species were able to support the nematode and two of these, Ageratum conyzoides and Nicandra physaloides, could be considered to be good hosts.

Field performance of tomato varieties resistant to root-knot nematodes

The performance of 15 potentially useful nematode-resistant tomato varieties (Ace Hy, Better Boy, Bigset, Bonus, Calmart, Magnifico, Monte Carlo, Patriot, Red Supreme, Rich Reward, Surprise, Terrific, VFN Bush, VFN 8 and Vine Ripe) was assessed in field trials at Loveday and Loxton, South Australia. All varieties showed some nematode resistance when grown in sites heavily infested with root-knot nematodes (Meloidogyne javanica) and most produced yields which were not significantly less than the commonly used susceptible varieties (Burnley Gem, Floradade, Grosse Lisse and Q3) grown in soil treated with nematicides. However, the nematode-resistant varieties were of limited value commercially because the fruit was either susceptible to cracking or too soft to be transported long distances. In glasshouse tests, biotypes of root-knot nematode capable of attacking resistant varieties were not observed. All resistant varieties exhibited resistance against populations of M. javanica from grape, peach, sweet corn, tomato (variety Floradade), tomato (variety VFN Bush), and against field populations of Meloidogyne from both resistant and susceptible tomato varieties. These results suggest that agronomically acceptable nematode-resistant varieties would be useful in management programs to control root-knot nematodes in the Murray Valley.

Influence of temperature on penetration and development of 2 species of root-knot nematodes to and in susceptible and resistant tomato varieties

Influence of temperature on penetration and development of 2 species of root-knot nematodes to and in susceptible and resistant tomato varieties

Teaching Principles of Linkage and Gene Mapping with the Tomato

G iENETIC LINKAGE AND CROSSING-OVER are two key biological phenomena because they are involved in the transmission and rearrangement of the hereditary material. Analysis of crossing-over events also provides geneticists with a way to construct linkage maps depicting both gene order and distance. Mertens (1972) suggested student linkage experiments based on the analysis of testcross data in Drosophila melanogaster, but higher plants could provide an alternative system to stimulate the interests of plantoriented students in genetics. Plants also free teachers from time-consuming maintenance requirements because seeds are easy to store. Linkage in plants is also of much practical importance as illustrated by the close linkage on chromosome 9 of the tomato of a gene affecting hypocotyl color (ah) and one conferring tobacco mosaic virus resistance (Tm-2) [Knush and Rick 1964]. This linkage facilitates transfer of disease resistance to susceptible tomato varieties because seedlings can be pre-screened for disease resistance by examination of the hypocotyl color. Ears of corn demonstrating two-point linkage are commercially available, but our experience indicates that student interest is increased by studying seedling populations. We describe here a three-point linkage system in the tomato that encompasses the basic principles of linkage and gene mapping and certain principles of probability and statistics. Students using this system gain the experience of classifying segregating progenies, analyzing data, and experiencing the reasoning used by geneticists to determine the behavior, order and location of genes through the statistical analysis of F2 and testcross data.

The occurrence of acid hydrolyzable phenolics in relation toFusarium wilt disease in tomato plants

Infection of a susceptible tomato variety led to an accumulation of acid hydrolyzable phenolic acids. This accumulation doesn't support the view in which the phenolic acids are hold to be responsible for the resistance against the wilting disease.

Título en español.

Varias especies de nemátodos parasíticos de plantas, particularmente el Meloidogyne incognita que produce agallas en las raíces y el Rotylenchulus reniformis que tiene forma de riñón, atacan muy severamente las siembras de tomate en Puerto Rico. Se hicieron distintos experimentos con el objeto de determinar la eficacia de varios nematocidas para controlar estos nemátodos. Aquí se discute el último experimento que incluyó ocho nematocidas distintos y con los cuales se trató el terreno donde se sembraron plantas del tomate variedad Rutgers, una de las más susceptibles al ataque de los nemátodos. Se presentan cuadros y gráficas para demostrar que, por lo menos, cuatro de los fumigantes aplicados (D-D, Dorlone, EDB y Nemagon), a razón de 2 cm. cúbicos por cada pie cuadrado de terreno, son eficaces para combatir las dos especies de nemátodos arriba mencionados. Se probaron, además, otros dos compuestos químicos (Telone y Fumazone), pero sus efectos no fueron completamente eficaces para controlar el nemátodo de agalla, aunque sí para el reniforme. Las aplicaciones de Dorlone mejoraron el crecimiento de las plantas, el peso de los tallos y los rendimientos y también mejoraron la apariencia general de las plantas en mayor grado que los otros agentes químicos usados. El Dorlone también fue eficaz para controlar tanto los nemátodos que forman agallas en la raíz como los reniformes. La diferencia en tamaño de las plantas sobre el testigo fue estadísticamente significativa al nivel del 5 por ciento con EDB y al nivel del 1 por ciento con Dorlone y Nemagon. No hubo diferencia estadística significativa entre los resultados obtenidos de los otros agentes químicos, ni entre el resto de estos últimos y los del testigo. La incidencia de agallas y nudos en la raíz varió desde el grado 0, o sea, completa ausencia de infestación, hasta el grado 5, que se considera como el más alto grado de infestación posible. Las plantas del tratamiento testigo demostraron una infestación promedio muy alta del grado 5. Al tiempo de cosecharse, las plantas tenían un tamaño menor que en los demás tratamientos, aunque mostraban muy pocos síntomas de clorosis y amarillez. Se observó en experimentos anteriores que los síntomas se manifestaron plenamente después de la florecida y después de cosecharse las primeras frutas. En esta prueba la florecida se retardó, de ahí que hubiera poca cantidad de frutas de poco peso. También se observó que estas plantas tenían grandes protuberancias en sus raíces y que las raíces secundarias se desarrollaron en número excesivo.

Distribution of physiological races ofPhytophthora infestans (Mont.) de Bary in Canada

A gene conferring resistance to Race 0 ofPhytophthora infestans was found in a strain ofL. esculentum var.cerasiforme. In crosses with the susceptible tomato variety Stokesdale, this gene was found to behave as a simple dominant. The resistant tomato, Geneva T-5, was therefore assigned the genotype R1 t and included in the series of hosts used to differentiate physiological races ofP. infestans. Stokesdale was included under the genotype rt.