Histological response of resistant tomato cultivars to infection of virulent Tunisian root-knot nematode (Meloidogyne incognita) populations

The response of a susceptible tomato cultivar (Solanum lycopersicum cv. Rio Grande) to infection by three populations of root-knot nematode (Meloidogyne incognita) was compared histologically with that of Lycopersicon esculentum cv. Monita, L. esculentum cv. VFN8 and Solanum lycopersicum cv. Nemador possessing the Mi-1 resistance gene and accession PI126443 of L. peruvianum possessing the Mi-3 gene. The resistant cultivars showed susceptibility to the Tunisian Meloidogyne populations. Feeding sites were characterised by the development of giant cells that contained granular cytoplasm and several hypertrophied nuclei. The cytoplasm of giant cells was aggregated along their thickened cell walls and consequently the vascular tissues within galls appeared disrupted and disorganised. Feeding site formed on resistant L. esculentum lines and susceptible cultivar Rio Grande are similar according to cell and nucleus number, and the nurse superficies. Resistant accession L. peruvianum PI126443, known to possess heat-stable nematode resistance, also showed susceptible reaction to Tunisian Meloidogyne incognita populations; however, nematode development was reduced in comparison with susceptible plants and less developed feeding cells were observed.     

Screening of tomato cultivars in the presence of the root-knot nematode,Meloidogyne javanica

In the present study, 12 varieties of tomato, viz., Arka Vikas, Damayanti, F-hybrid, Hybrid Padmarag, Hybrid Tripti, Marudam, Punjab chhoara, Pusa early dwarf, Punjab kesari, P.K.M.I, Roma and Pusa Ruby were screened for the presence of the root-knot nematode, M. javanica to obtain information on the varying degrees of resistances to tomato cultivars. All the cultivars of tomato tested were found to be infected with the root-knot nematode, M. javanica, however, to a varying extent. Consequently, there was a reduction in the growth parameters of cultivars leading to have an impact on the yield and quality of fruits. The cultivar, Marudam was found resistant while the cultivar the Pusa early dwarf was moderately resistant and rest of the 10 cultivars was highly susceptible.     

Relationship between root respiration and seedling age in tomato cultivars infested by Meloidogyne incognita

Measurements were made of respiration in the roots of tomato cultivars susceptible and resistant to Meloidogyne incognita. Nematode infestation of the susceptible cv. Roma VF caused an initial stimulation of the total respiration with an increase in the CN-sensitivity; the effect decreased and then disappeared as the seedlings aged. In the resistant cv. Rossol nematode infestation initially caused an inhibition of total respiration and a decrease in the CN-sensitivity; respiration and CN-sensitivity increased with seedling age. The activity of the alternative respiration pathway (m-chlorobenzhydroxamic acid-sensitive) was unchanged by nematode infestation in the resistant cultivar and increased markedly in the susceptible cultivar during the early stages of infestation.     

Role of alternative pathway respiration in tomato roots attacked by Meloidogyne incognita

The effect of nematode infestation on the alternative pathway respiration of mitochondria isolated from resistant and susceptible tomato roots greatly depended on the oxidisable substrate tested. The percentage of alternative respiration in NADH, malate and succinate oxidation was markedly different between the resistant (Rossol) and the susceptible (Roma VF) cultivars before infestation. Only the percentage of malate alternative oxidation in mitochondria from the resistant roots was influenced by nematode invasion. Conversely, attacked roots showed consistent variations in the content of mitochondria per unit fresh weight and in the phosphorylation efficiency (ADP/O) of the organelles. Expression of the alternative pathway (ρ' value) was found to be unchanged in intact roots and isolated mitochondria six days after nematode inoculation.     

Heat Stress and Spermidine: Effect on Chlorophyll Fluorescence in Tomato Plants

Two tomato (Lycopersicon esculentum L.) cultivars: Robin (tolerant) and Roma (sensitive to heat stress) were studied. Chlorophyll fluorescence induction parameters (F_v/F_p, A_max, and Rfd) at 25 °C showed that the PS2 activity was similar for both cultivars. The parameters, measured at 38 °C, decreased in both cultivars, but more in cv. Roma. Exogenous application of 4 mM spermidine improved the plant heat-resistance in both cultivars, and especially in cv. Roma. Analysis of chlorophyll fluorescence changes during linear increase in temperature showed that cv. Robin plants have higher ability to hardening and higher resistance to thermal damage of the pigment-protein complexes structure and the activity of PS2 than cv. Roma.     

High temperature effects on RuBP carboxylase and carbonic anhydrase activity in two tomato cultivars

The effects of temperature on ribulose bisphosphate carboxylase activity were studied in two tomato ( Lycopersicon esculentum Mill.) cultivars which differed in sensitivity to high temperatures. The heat tolerant cultivar, Saladette, had a smaller reduction in photosynthesis and a smaller increase in mesophyll resistance then the sensitive cultivar Roma VF, after 24 h at 35 to 40°C. One hour in vitro treatments at 50°C decreased the activity of ribulose bisphosphate carboxylase extracted from Roma VF by 75%, while Saladette was not affected. Heat stress to the entire plant caused greater inhibition of ribulose bisphosphate carboxylase in the heat sensitive cultivar. Ribulose bisphosphate carboxylase activity in both cultivars decreased with heat treatment but recovered under normal temperatures. Ribulose bisphosphate oxygenase activity decreased similarly in both cultivars under 37/18°C day/night temperatures, which resulted in an apparent change in the relative carboxylase/oxygenase activity of the two cultivars. Carbonic anhydrase activity was slightly greater in Saladette than in Roma VF but no significant decrease in activity was observed in plants exposed to high temperatures.     

Involvement of salicylic acid in induction of nematode resistance in plants

The role of salicylic acid (SA) as a possible signaling component in the case of the infection of plants with nematodes has been studied using a model system consisting of the tomato (Lycopersicon esculentum (Mill.) and race 1 of the gall eelworm Meloidogyne incognita (Kofoid and White, 1919; Chitwood, 1949). The preplanting SA treatment of tomato seeds results in an increased nematode resistance of susceptible tomato cultivars; the protective effect is higher in the case of SA combined with chitosan, a biogenic elicitor of plant resistance. The studied preparations stimulate the growth and development of the plants. The increase in the resistance of tomato plants is related to the increased activity of phenylalanine ammonia-lyase and an increased SA content in plant tissues infected with nematodes; both these factors significantly influence nematode development.     

Induction of Isoperoxidases in Resistant and Susceptible Tomato Cultivars by Meloidogyne incognita

Isoperoxidases were detected in resistant Rossol and susceptible Roma VF tomato roots uninfected and infected by Meloidogyne incognita. Syringaldazine, guaiacol, p-phenylenediamine-pyrocatechol (PPD-PC), and indoleacetic acid (IAA) were used as substrates, and the corresponding peroxidative activities were detected either in cytoplasmic or in cell wall fractions, except for IAA oxidase, which was measured in soluble and microsomal fractions. Isoperoxidase activities and cellular locations were induced differently in resistant and susceptible cultivars by nematodes. Nematode infestation markedly enhanced syringaldazine oxidase activity in cell walls of the resistant cultivar. This isoperoxidase is involved in the last step of lignin deposition in plants. Conversely, the susceptible cultivar reacted to M. incognita infection with an increase in cytoplasmic PPD-PC oxidase activity, which presumedly is involved in ethylene production; no changes in cell wall isoperoxidases were observed. IAA oxidase was inhibited in susceptible plants after nematode inoculation, whereas in resistant plants this activity increased in the soluble fraction and decreased in the microsomal fraction.     

Improvement of the production of 5-methoxypodophyllotoxin using a new selected root culture of Linum flavum L.

Differences in transformation of the tomato cultivar (Ohio 7870, Roma, UCD82b) by wild-type Agrobacterium strains (A6, A66, A281) were identified in a leaf disk assay system. Transformation was expressed as the percentage of explants producing callus on hormone-free medium and was confirmed by opine production. Ohio 7870 and Roma were more readily transformed than UCD82b by all three strains of A. tumefaciens. Cotyledons and older true leaves of all three cultivars were more readily transformed than younger leaves. Transformation was biphasic over the bacterial concentrations tested (2×10³–7×10⁹ colony forming units ml^-1; cfu ml^-1) for all cultivars and leaf ages, and was greatest at 5×10⁸ cfu ml^-1. Transformation decreased significantly at levels less than 2×10⁷ cfu ml^-1 and slightly at concentrations higher than 5×10⁸ cfu ml^-1. UCD82b tissue was more necrotic than Ohio 7870 or Roma after incubation with bacteria, which may account for reduced transformation of this cultivar.     

Variation in tomato host response to Bemisia tabaci (Hemiptera: Aleyrodidae) in relation to acyl sugar content and presence of the nematode and potato aphid resistance gene Mi

Two commercial cultivars of tomato, Alta and Peto 95, the accession line number LA716 of Lycopersicon pennellii and lines 94GH-006 and 94GH-033 (backcrosses between Peto 95 and LA716), with different leaf acyl sugar contents were screened for resistance to Bemisia argentifolii Bellows & Perring (corresponding to the Spanish B-biotype of Bemisia tabaci (Gennadius)), in greenhouse- and field-no-choice experiments. There was no oviposition on LA716 (with the highest acyl sugar content) while the greatest fecundity and fertility values were observed on the cultivar Alta (no acyl sugar content). However, no clear relationship was found between the low acyl sugar content in the other tomato cultivars tested and whitefly reproduction. Thus, resistance to B. tabaci did not appear to correlate with acyl sugar content below a threshold level of 37.8 microg cm-2 leaf. In a greenhouse choice-assay, B. tabaci exhibited reduced host preference and reproduction on the commercial tomato cultivars Motelle, VFN8 and Ronita all of which carry the Mi gene resistance to Meloidogyne nematodes and the aphid Macrosiphum euphorbiae (Thomas), than on the Mi-lacking cultivars Moneymaker, Rio Fuego and Roma. When data of Mi-bearing plants were pooled, the mean values for daily infestation and pupal production of B. tabaci were significantly lower than those of Mi-lacking plants. This reflected a level of antixenosis- and antibiosis-based resistance in commercial tomato and indicated that Mi, or another closely linked gene, might be implicated in a partial resistance which was not associated either with the presence of glandular trichomes or their exudates. These findings support the general hypothesis for the existence of similarities among the resistance mechanisms to whiteflies, aphids and nematodes in commercial tomato plants.     

Pathogenicity of Race-1 and Race-2 Tomato Wilt Isolates of Verticillium dahliae from Different Geographical Origins

Fourteen race-1 and race-2 isolates of Verticillium dahliae from North America, Europe and Australia were screened against the near isogenic pair of tomato cultivars Roma and Roma VF. The foliar symptoms, extent of stunting and vascular colonization were assessed. Race-1 isolates were significantly more pathogenic on Roma which lacks the Ve resistance gene. Race-2 isolates from N. America were more pathogenic than those from Australia. All isolates tested colonized both cultivars to some extent although the level of colonization by race-1 isolates was significantly higher in Roma than in Roma VF. All race-1, and the majority of race-2, isolates caused stunting of Roma. No isolates stunted Roma VF.     

Influence of fruit traits on oviposition preference and offspring performance of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) on three tomato (Lycopersicon lycopersicum) cultivars

Abstract  In Queensland, three tomato ( Lycopersicon lycopersicum ) cultivars, Grosse Lisse, Roma and Cherry, are infested by Queensland fruit fly, Bactrocera tryoni (Froggatt). In this study, we examined if there was a correlation between oviposition preference and offspring performance of B. tryoni among the three tomato cultivars. We also investigated host plant traits that may explain any variation in preference and performance. Choice and no-choice experiments were carried out under laboratory conditions. A positive correlation between oviposition preference and offspring performance of B. tryoni was observed in the three tomato cultivars. Grosse Lisse and Roma cultivars were highly preferred by B. tryoni over Cherry cultivar. Performance (measured as proportion of eggs developing to the pupal stage) was significantly higher in Grosse Lisse and Roma cultivars than in Cherry cultivar. The pericarp toughness of Cherry cultivar appears responsible for its low rate of infestation, while the presence of 2-butanol and 1,4-butanediamine in Roma and Grosse Lisse, respectively, may partly be responsible for the high oviposition preference shown by B. tryoni towards these cultivars.     

Characterization of Anionic Peroxidases in Tomato Isolines Infected by Meloidogyne incognita

Changes in peroxidase activity during nematode infection were studied using root extracts of tomato near-isogenic lines differing in resistance to Meloidogyne incognita. Total peroxidase activity increased slightly in crude extracts of four susceptible isolines but doubled in two resistant lines, Monita and Motaci. Nematode infection enhanced levels of both p-phenylenediamine-pyrocatechol oxidase and syringaldazine oxidase 7 days after inoculation, especially in resistant lines. This elevated peroxidase activity in resistant isolines was caused by an increase in anionic peroxidase activity. These enzymes, which likely are involved in lignification, were isolated and purified from tomato isolines by ammonium sulfate precipitation, high performance ion-exchange chromatography, and gel electrophoresis. The purified anionic peroxidase extracts contained an electrophoretic band with Rf 0.51 that was present in extracts of infected but not uninfected roots.     

Auxin and Ethylene Regulation of Petiole Epinasty in Two Developmental Mutants of Tomato, diageotropica and Epinastic

The epinastic growth responses of petioles to auxin and ethylene were quantified in two developmental mutants of tomato (Lycopersicon esculentum Mill.). In the wild type parent line, cultivar VFN8, the epinastic response of excised petiole sections was approximately log-linear between 0.1 and 100 micromolar indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations, with a greater response to 2,4-D at any concentration. When ethylene synthesis was inhibited by aminoethoxyvinylglycine (AVG), epinasty was no longer induced by auxin, but could be restored by the addition of ethylene gas. In the auxin-insensitive mutant, diageotropica (dgt), no epinastic response to IAA was observed at IAA concentrations that effectively induced epinasty in VFN8. In the absence of added IAA, epinastic growth of dgt petioles in 1.3 microliters per liter exogenous ethylene gas was more than double that of VFN8 petioles. IAA had little additional effect in dgt, but promoted epinasty in VFN8. These results confirm that tomato petiole cells respond directly to ethylene and make it unlikely that the differential growth responsible for epinasty results from lateral auxin redistribution. The second mutant, Epinastic (Epi), exhibits constitutively epinasty, cortical swelling, and root branching symptomatic of possible alternation in auxin or ethylene regulation of growth. Only minor quantitative differences were observed between the epinastic responses to auxin and ethylene of VFN8 and Epi. However, in contrast to VFN8, when ethylene synthesis or action was inhibited in Epi, auxin still induced 40 to 50% of the epinastic response observed in the absence of inhibitors. This indicates that the target cells for epinastic growth in Epi are qualitatively different from those of VFN8, having gained the ability to grow differentially in response to auxin alone. The dgt and Epi mutants provide useful systems in which to study the genetic determination of target cell specificity for hormone action.     

Comparative proteomic analysis of bacterial wilt susceptible and resistant tomato cultivars

To investigate the molecular mechanisms of bacterial resistance in susceptible and resistant cultivars of tomato, a proteomic approach was adopted. Four cultivars of tomato were selected on the basis of their response to bacterial (Pseudomonas solanacearum) inoculation wherein cultivar Roma and Riogarande, and cultivar Pusa Ruby and Pant Bahr were considered as resistant and susceptible cultivars, respectively. Proteins were extracted from leaves of 3-week-old seedlings of the four cultivars and separated by 2-DE. A total of nine proteins were found to be differentially expressed between the susceptible and resistant cultivars. Amino acid sequences of these proteins were determined with a protein sequencer. The identified proteins belongs to the categories of energy, protein destination and storage, and defense. Of these proteins, a 60 kDa chaperonin and an apical membrane antigen were significantly upregulated in resistant cultivars compared with susceptible cultivars. Application of jasmonic acid and salicylic acid resulted in significant changes in levels of apical membrane antigen and protein disulfide-isomerase. Taken together, these results suggest that apical membrane antigen might be involved in bacterial resistance process through salicylic acid induced defense mechanism signaling in tomato plants.     

Interaction of vesicular-arbuscular mycorrhizal fungi and root knot nematode on cultivars of tomato and white clover susceptible to Meloidogyne hapla

The interactive effects of vesicular-arbuscular mycorrhizal (VAM) fungi and root-knot nematode (Meloidogyne hapla) were studied on nematode-susceptible cultivars of tomato (cv. Scoresby) and white clover (cv. Huia) at four levels of applied phosphate. The relative merits of simultaneous inoculation with mycorrhizal fungi and nematodes and of inoculation with mycorrhizal fungi prior to nematode inoculation were evaluated. Mycorrhizal plants were more resistant than non-mycorrhizal plants to root-knot nematode at all phosphate levels and growth benefits were generally greater in plants preinfected with mycorrhizal fungi. Nematode numbers increased with increasing levels of applied phosphate. In mycorrhizal root systems, nematode numbers increased in the lower phosphate soils; at higher phosphate levels nematode numbers were either unaffected or reduced. The numbers of juveniles and adults per gram of root were always lower in mycorrhizal treatments. Mycorrhizal root length remained unaffected by nematode inoculation. Mycorrhizal inoculation thus increased the plants' resistance to infection by M. hapla. This was probably due to some alteration in the physiology of the root system but was not entirely a result of better host nutrition and improved phosphorus uptake by mycorrhizal plants.     

A differential interaction study of Bemisia tabaci Q-biotype on commercial tomato varieties with or without the Mi resistance gene, and comparative host responses with the B-biotype

Three tomato varieties (Motelle, Ronita, and VFN8) bearing the Mi-1.2 gene providing resistance to nematodes Meloidogyne spp. and to the potato aphid Macrosiphum euphorbiae Thomas, and three varieties not bearing this gene (Moneymaker, Roma, and Río Fuego), were compared by choice assay for host preference using the Q-biotype of Bemisia tabaci (Gennadius). The most preferred hosts, determined by infestation levels and numbers of feeding adults were Moneymaker, Río Fuego and Roma, all of which were not carrying the Mi gene. Ronita and Motelle, both of which bore the Mi gene, were the least preferred hosts. In a no-choice assay, B. tabaci females laid a significantly lower number of eggs on the varieties that carried the Mi gene than on those lacking the gene. Differences were more dramatic when plants carrying the Mi gene were pooled together and compared with pooled plants without this gene. Significantly greater values were obtained for the Mi-lacking group for all parameters tested. Comparing these results with those from a previous study on the B-biotype of B. tabaci, Q-biotypes were found to produce higher daily infestation rates on most of the tomato varieties. When results from plants carrying Mi were pooled, they showed lower infestation levels of Q-biotypes than B-biotypes. The Q-biotype infested less Mi-plants and more non-Mi plants than B-biotype. Q-biotype females produced significantly less pupae than the B-biotype females on both groups of plants. These results suggest the existence of an antixenosis and antibiosis-based resistance to the Q-biotype of B. tabaci in Mi-bearing commercial tomato varieties, which is greater than that previously reported for the B-biotype.     

Mykoplasmaähnliche Organismen in Früchten proliferationskranker Apfelbäume Kurze Mitteilung

The potential of an in vitro technique to study root‐knot nematode infection on banana roots was investigated. Regenerated banana plants were placed horizontally on Gamborg B5 (GB5)‐medium and incubated under a light‐dark regime of 16h‐8h. Temperature fluctuated between 24 and 33 °C. Banana roots were inoculated with Meloidogyne incognita race 1 coming from roots of a transgenic tomato (Lycopersicon esculentum cv. Moneymaker) grown on GB5‐medium at 28 °C in complete darkness. Root‐knots appeared on primary and secondary banana roots two to seven days after nematode inoculation. After 28 days, egg masses protruded through the cortex and two days later juveniles hatched and reinfected banana roots. This method holds promise for dynamic studies of banana root infection with root‐knot nematodes.     

Zoosporangial root infection of tomato by Spongospora subterranea in hydroponic and glasshouse culture results in diminished plant growth

Tomato plants are highly susceptible to root infection by Spongospora subterranea and are commonly used as bioassay hosts. The impacts of root infection with S. subterranea on plant productivity and yield have been debated. Recent experiments with potato, the major economic host of S. subterranea, have indicated significantly reduced plant growth and potato yield following heavy infection. However, there have been very few similar studies that have examined the possible impacts of S. subterranea infection on tomato plant growth. Three tomato cultivars, “Grape,” “Roma” and “Truss,” were challenged with S. subterranea inoculum in hydroponic culture. Moderate to severe zoosporangial infections were observed with minor but statistically significant differences in susceptibility among the three tomato cultivars. Zoosporangial root infection in the absence of root gall formation resulted in significantly diminished shoot lengths and plant fresh weights in pathogen challenge tests conducted both in hydroponic culture and glasshouse‐grown plants in potting mix. Root lengths were reduced, but the differences were statistically significant in a single trial only. The findings from this study demonstrate that, as with potato, root infection by S. subterranea can result in reduced tomato plant growth and that root gall production associated with root infection was not necessary for this retardation of growth response. This further suggests that possible yield impacts in other crop species that are hosts for S. subterranea root infection are worthy of examination.