Foliar pubescence and resistance to potato moth, Phthorimaea operculella, in Lycopersicon hirsutum

Pubescence characteristics for six accessions of Lycopersicon hirsutum Dunal and five accessions of L. hirsutum f. glabratum CH Mull. were determined and compared with those of an accession of cultivated tomato (L. esculentum Mill.). Removal of trichome exudates from excised leaflets using ethanol solution resulted in a reduced mortality and increased survival of potato moth (Phthorimaea operculella (Zeller)) neonates for the accessions that were most lethal when not treated with ethanol solution. No such treatment effect was evident for L. esculentum or for the L. hirsutum accession with least effect on neonates when its trichomes were intact. In a glasshouse experiment with caged intact plants, mortality of neonate P. operculella placed on the abaxial surface was greater on seven accessions than for L. esculentum.Neonates were less severely affected on the adaxial surface. Eleven days after inoculation, no live larvae were found on LA 1927, PI 127827, PI 134418, and PI 134428, and numbers on other accessions were lower than for L. esculentum. Eventual emergence of adults followed a similar trend. Multiple regression of insect data against pubescence indicated a significant correlation between density of type IV and VI trichomes and neonate mortality, decreased larval development and decreased adult emergence. Non-glandular type V trichomes were positively correlated with high survival of insects to 11 days and to adult. Though factors other than glandular trichomes are likely to be important, increased density of type IV and VI, along with reduced type V, are shown to be important to select in breeding for P. operculella resistance.     

Replication of tomato yellow leaf curl virus (TYLCV) DNA in agroinoculated leaf discs from selected tomato genotypes

The leaf disc agroinoculation system was applied to study tomato yellow leaf curl virus (TYLCV) replication in explants from susceptible and resistant tomato genotypes. This system was also evaluated as a potential selection tool in breeding programmes for TYLCV resistance. Leaf discs were incubated with a head-to-tail dimer of the TYLCV genome cloned into the Ti plasmid ofAgrobacterium tumefaciens. In leaf discs from susceptible cultivars (Lycopersicon esculentum) TYLCV single-stranded genomic DNA and its double-stranded DNA forms appeared within 2–5 days after inoculation. Whiteflies (Bemisia tabaci) efficiently transmitted the TYLCV disease to tomato test plants following acquisition feeding on agroinoculated tomato leaf discs. This indicates that infective viral particles have been produced and have reached the phloem cells of the explant where they can be acquired by the insects. Plants regenerated from agroinfected leaf discs of sensitive tomato cultivars exhibited disease symptoms and contained TYLCV DNA concentrations similar to those present in field-infected tomato plants, indicating that TYLCV can move out from the leaf disc into the regenerating plant. Leaf discs from accessions of the wild tomato species immune to whitefly-mediated inoculation,L. chilense LA1969 andL. hirsutum LA1777, did not support TYLCV DNA replication. Leaf discs from plants tolerant to TYLCV issued from breeding programmes behaved like leaf discs from susceptible cultivars.The Hebrew University of Jerusalem, Faculty of Agriculture, Department of Field and Vegetable Crops     

Trichome‐based host plant resistance of Lycopersicon species and the biocontrol agent Mallada signata: are they compatible?

Trichome‐based host plant resistance of Lycopersicon (Solanaceae) species offers the potential to reduce pesticide use in tomato production, but its compatibility with biocontrol agents is largely unknown. The effect of trichome‐based host plant resistance on the lacewing biocontrol agent, Mallada signata, was assessed for five accessions of L. cheesmanii, four accessions of Lycopersicon hirsutum, two accessions of Lycopersicon pennellii, and one Lycopersicon esculentum cultivar. An intact leaf was isolated from the whole plant using Tangletrap to coat the petiole and 20 green peach aphids [Myzus persicae (Sulzer) (Homoptera: Aphididae)] were placed on the leaf surface. After 24 h, 10 lacewings were placed on the leaf. The numbers of dead, trapped by exudates, untrapped and predated lacewings and aphids, and the numbers that had left the leaf were recorded a further 24 h later. Differences in insect designations between accessions were analysed using ANOVA. A General Linear Model (GLM), consisting of the densities of each trichome type and leaf area, was fitted to the data to determine the role of trichomes on the observed effects on lacewings and aphids. Lacewing mortality was greater on one accession of L. pennellii and one accession of L. hirsutum than on L. esculentum. The GLM indicated that type IV trichomes decreased the numbers of aphids predated, and increased cannibalism and, along with type III trichomes, increased entrapment‐related predator mortality. Although there were no differences in the numbers of predated aphids, with the majority predated for all accessions, the compatibility of trichome‐based host plant resistance of Lycopersicon species and the biocontrol of aphids by lacewings is questionable.     

Effect of plant variety, plant age and photoperiod on glandular pubescence and host-plant resistance to potato moth (Phthorimaea operculella) in Lycopersicon spp.

The effect of plant age and daylength on glandular pubescence was determined for two lines of tomato derived from Lycopersicon hirsutum (BTN 979 and LA 1777A) and a variety of L. esculentum (N 91‐1‐1‐1‐1). Densities of type I, IV, VI and VII glandular trichomes were lowest in N 91‐1‐1‐1‐1 and, over all varieties, were more dense on plants aged greater than 6 wk. Daylength interacted with variety to significantly affect densities of type VII trichomes only. Host‐plant resistance to Phthorimaea operculella was determined in preliminary tests using insects cultured from founders from a potato crop and in confirmatory tests using (less readily available) insects recovered from foliage of a tomato crop. Mortality of ex‐potato neonates on LA 1777 A and BTN 979 foliage was higher 18 h after placement than for N 91‐1‐1‐1‐1, with no effect of day length or plant age. Mortality for ex‐tomato neonates followed a similar trend. Ten days later, two‐thirds of ex‐tomato larvae had established mines on N 91‐1‐1‐1‐1 but fewer (16.7%) were live on other varieties. Stepwise multiple regression using variety as the sole factor was significant (P<0.001) in accounting for 61.4% of the variation in ex‐tomato larval survival but addition of other factors to the regression model was not significant. BTN 979 supported fewer, smaller adults to develop than did N 91‐1‐1‐1‐1, whilst no adults developed on LA 1777 A. In a non‐choice test using ex‐potato adults, significantly more eggs were laid on N 91‐1‐1‐1‐1 than on L. hirsutum varieties and 9‐wk‐old plants were preferred over plants three weeks older or younger. The same variety and plant age trends were evident in a free‐choice test using ex‐tomato adults.     

Analysis of Low-temperature Tolerance of a Tomato (Lycopersicon esculentum) Cybrid with Chloroplasts from a more Chilling-tolerant L. hirsutum Accession

Growth and photosynthesis of an alloplasmic tomato (cybrid),i.e. line AH47, containing the nuclear genome of the chilling-sensitivecytoplasmic albino mutant of L. esculentum Mill. ‘LargeRed Cherry’ (LRC) and the plastome of a more chilling-toleranthigh-altitude accession of the related wild species L. hirsutumHumb. & Bonpl. LA 1777, were investigated at an optimal(25/20°C) and suboptimal (16/14°C) day/night temperatureregime and their performance compared with that of both euplasmicparents. The cybrid shoot had a similar biomass and developmentrate to the nuclear tomato (L. esculentum) parent at both temperatureregimes. Compared with the biomass production of shoots grownat optimal temperature, the reduction in shoot biomass at suboptimaltemperature was smaller for L. hirsutum than for L. esculentumand the cybrid. This difference was related to a stronger inhibitionof leaf area expansion in L. esculentum and the cybrid in thesuboptimal temperature regime than in L. hirsutum. Irrespectiveof the temperature regime under which the plants were grown,photosynthetic performance and leaf pigment, carbohydrate andsoluble-protein contents of the cybrid resembled those of thenuclear parent. No advantages of the alien L. hirsutum chloroplastwith respect to growth and photosynthesis-related characteristicswere observed in the cybrid in the suboptimal temperature regime,indicating that the temperature sensitivity of the photosyntheticapparatus is regulated by nuclear genes. An adverse consequenceof interspecific chloroplast transfer was the increased susceptibilityto chill-induced photoinhibition of the cybrid. It is concludedthat cybridization is not a useful tool for improving low-temperaturetolerance of tomato. Copyright 2000 Annals of Botany Company Alloplasmic tomato, chloroplast, cybrid(ization), growth, low-temperature tolerance, Lycopersicon esculentum, L. hirsutum, photosynthesis, plastome, tomato     

Serological studies on the accumulation and localisation of three tomato leaf curl geminiviruses in resistant and susceptible Lycopersicon species and tomato cultivars

Accessions of wild Lycopersicon spp. and selected Fl hybrid tomato cultivars were compared for their resistance to three whitefly-transmissible geminiviruses: Indian tomato leaf curl virus (ITmLCV) and tomato yellow leaf curl viruses from Sardinia (TYLCV-Sar) and Senegal (TYLCV-Sen). The resistance of different plant lines was expressed in different ways but in most instances a given line reacted similarly to graft inoculation with the three viruses. L. pimpinellifolium LA1478 produced as much virus antigen, assessed by triple antibody sandwich-ELISA, as the susceptible cv. Moneymaker but developed only very mild symptoms and is therefore tolerant of infection. In L. hirsutum LA1777 and L. peruvianum CMV-INRA, very mild or no symptoms developed but antigen concentrations were substantially less than in Moneymaker. L. chilense LA1969 remained symptomless and its antigen concentration was < 1% of that in Moneymaker. Symptoms were mild or barely evident in the Fl hybrid cultivars. Cultivars Tyking and Fiona had antigen concentrations about 5–10% of those of Moneymaker, whereas TY20, Top 21 and Tyger had intermediate antigen concentrations. In a few instances, the extent to which virus accumulation was restricted depended on the challenge virus. Accumulation of TYLCV-Sen in TY20, Top 21 and Tyger was less affected than that of the other two viruses, and accumulation of TYLCV-Sar in accessions LA1777 and CMV-INRA was less affected than that of TYLCV-Sen or ITmLCV. Tissue-printing tests showed that ITmLCV and TYLCV-Sen antigens were confined to phloem tissue. In Tyking, the number of virus antigen-containing phloem traces and the antigen content of individual traces were less than in Moneymaker but the partitioning of antigen between internal and external phloem was unaffected.     

Effect of cropping season and possible compounds involved in the resistance of Lycopersicon hirsutum f. typicum to Tuta absoluta (Meyrick) (Lep., Gelechiidae)

The effect of cropping season on the resistance of the accession LA 1777 of Lycopersicon hirsutum f. typicum to the tomato leafminer Tuta absoluta (Meyrick) and the preliminary identification of the possible compounds involved in this trait were the objectives of this study. Two experiments were carried out with the accession LA1777 and the commercial cultivar Santa Clara of Lycopersicon esculentum . The first experiment was carried out during the summer season (January to April 1997) and the second was carried out during the autumn–winter season (May to September 1997). The accession LA 1777 was significantly more resistant to T. absoluta than the commercial cultivar, especially during the autumn–winter cropping season. Either antibiosis or antixenosis was probably responsible for the higher larvae mortality (54.2 and 91.2% for the summer and autumn–winter seasons, respectively) and longer larval development of T. absoluta (14.2 and 25.9 days for summer and autumn–winter seasons, respectively) on L. hirsutum f. typicum as compared with L. esculentum (11.0 and 19.6 days for summer and autumn–winter seasons, respectively). Insect fecundity parameters such as oviposition period, number of eggs/female, and rate of larvae eclosion were also negatively affected by L. hirsutum f. typicum . Fourteen main peaks were observed in total ion chromatograms of both tomato species. Eleven of these were present only in chromatograms of the accession, one was only present in chromatograms of the commercial cultivar, and two peaks were present in chromatograms from both when hexane extracts of leaves were subjected to a gas chromatographic–mass spectrometric analysis (GC–MS). However, the matches obtained between the peak spectra and the MS database were too low to justify even preliminary identification of the compounds.     

Screening additional wild tomatoes for resistance to the whitefly-borne tomato yellow leaf curl virus

Plants of 25 wild Lycopersicon accessions were screened in the greenhouse for resistance to the whitefly-borne tomato yellow leaf curl virus (TYLCV). High levels of resistance were detected in 7 of 9 accessions of L. peruvianum and in all 5 accessions of L. chilense tested. In contrast, plants of 7 accessions of L. hirsutum and 3 of 4 accessions of L. pimpinellifolium were highly susceptible. Plants of accession CIAS 27 (L. pimpinellifolium) showed moderate resistance to TYLCV.     

Trichome-borne and artificially applied acylsugars of wild tomato deter feeding and oviposition of the leafminer Liriomyza trifolii

Oviposition and adult feeding of the leafminer Liriomyza trifollii (Burgess) (Diptera, Agromyzidae) on Lycopersicon pennellii (Corr.) D'Arcy and its F₁ hybrid with Lycopersicon esculentum (Mill.) was significantly less than that on the cultivated tomato, L. esculentum. The resistance of L. pennellii and the F₁ was reduced following rinsing of foliage with ethanol. Resistant attributes of L. pennellii were transferred to L. esculentum through appression of L. pennellii foliage to L. esculentum leaflets. Application of purified 2,3,4-tri-O-acylglucoses (the principal component of type IV glandular trichome exudate of L. pennellii) to L. esculentum significantly decreased feeding and oviposition on L. esculentum leaflets by 61–99%. Therefore the principal mechanism of resistance to this leafminer by L. pennellii is the secretion of these acylglucoses. Dose response analysis of acylglucoses applied to L. esculentum shows that dosages as low as 10% those found on L. pennellii provide large reductions (91%) in leaf punctures and mines.     

Influence of Root and Content on the Temperature Response of Net and Uptake in Chilling Sensitive and Chilling Resistant Lycopersicon Taxa

We studied the influence of internal ammonium and nitrate contenton the temperature response of ammonium and nitrate uptake inboth chilling sensitive and chilling resistant tomatoes. Threetaxa were examined: Lycopersicon esculentum Mill. cv. T-5, achilling sensitive cultivar, Lycopersicon hirsutum Humb. andBompl. LA 1264, a wild, chilling sensitive accession from thelowlands of Ecuador, and Lycopersicon hirsutum LA1778, a chillingresistant accession from the highlands of Peru. Short exposures(4 h) of L. esculentum cv. T-5 to chilling temperatures irreversiblyinhibited ammonium absorption for at least 6 h. Nitrate absorptionin this taxon and ammonium and nitrate absorption in the L.hirsutum accessions recovered fully and immediately from suchexposures. The chilling resistant accession, L. hirsutum LA1778,showed a lower Q₁₀ for ammonium absorption (1?54?0?10, mean?s.e.)than its chilling sensitive relatives, L. hirsutum LA1264 (2?37?0?35)and L. esculentum cv. T-5 (1?92?0?11). The temperature responseof nitrate absorption depended on internal nitrate status; plantsgrown at high levels of ammonium and nitrate (200 mmol m^–3)showed higher Q₁₀'s for nitrate uptake (2?29?0?10) than thosedepleted of internal (1?86?0?12). Key words: Lycopersicon, ammonium, nitrate, temperature response, chilling     

A gene silencing of V‐ATPase subunit A interferes with survival and development of the tomato leafminer,Tuta absoluta

RNA interference (RNAi) technology is not only considered as a tool to analyze gene function, but it is also potentially considered as a strategy to develop novel biopesticide. In the current study, a double‐stranded RNA specific to v‐ATPase subunit A of the tomato leafminer, Tuta absoluta (Meyrick; Lepidoptera: Gelechiidae), was orally administered. A gradual decrease in the expression of the gene was observed from Day 1 to 3 and resulted in significant larval mortality. These results suggest that v‐ATPases A can be considered as a promising target gene by RNAi technology to be used in the management of the tomato leafminer.     

Efficacy of entomopathogenic nematodes against the tomato leafminer <Emphasis Type="Italic">Tuta absoluta</Emphasis> in laboratory and greenhouse conditions

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an important pest of tomato crops in South America and it has recently arrived in Europe affecting tomato plantations. The susceptibility of T. absoluta larvae and pupae to three species of entomopathogenic nematodes (Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora) was examined under laboratory conditions. Leaf bioassays were conducted to evaluate the nematode’s capability to reach the larvae and kill them within the galleries. The efficacy of the three nematode species after foliar application to potted tomato plants was evaluated under greenhouse conditions. High larval mortality (78.6–100%) and low pupae mortality (<10%) was determined in laboratory experiments. In the leaf bioassay a high level of larval parasitation (77.1–91.7%) was recorded revealing the nematode’s capacity to kill the larvae inside the galleries. In the pot experiments nematode treatment reduced insect infection of tomato plants by 87–95%. The results demonstrate the suitability of entomopathogenic nematodes for controlling T. absoluta.     

Resistance of wild Lycopersicon species to the potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

Abstract  Trichome-based host plant resistance of Lycopersicon species to potato moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), was examined in a laboratory bioassay. Neonate P. operculella were placed on the foliage of accessions of L. hirsutum , L. hirsutum f. glabratum , L. pennellii , L. cheesmanii f. minor and L. esculentum for 48 h . At the end of this period, larval mortality, the numbers of larvae emigrating from, and mining into, the leaf surface were recorded as were leaf area and the densities of trichomes. Analysis by categorical logistic regression found accessions differed in levels of resistance to P. operculella ( P  < 0.001). Further analysis using generalised linear models showed mortality was associated with high densities of type VI and low densities of type V trichomes; emigration from the leaf was associated with high densities of type I and type VII trichomes; and the numbers of mines associated with low densities of type I and type VI trichomes and increased leaf area. Although results indicate that certain accessions of L. hirsutum and L. hirsutum f. glabratum may be most appropriate for inclusion in a breeding program aimed at introducing trichome-based host plant resistance of wild Lycopersicon species into the tomato, further research is necessary to fully understand the mechanisms.     

Efficacy of some biorational insecticides against Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) under laboratory and greenhouse conditions in Kuwait

The tomato leafminer, Tuta absoluta, is one of the most destructive pests of tomato worldwide. Management of the pest is mainly based on chemical insecticides. Reliance on insecticides is difficult to sustain because of unintended long‐term adverse effects on the environment and human health. Consequently, there is a need to develop pest management strategies that ensure the production of high‐quality products, while at the same time ensuring environmental sustainability and maximum consumer protection. We evaluated the efficacy the biopesticides: Azadirachtin, Bacillus thuringiensis, Steinernema feltiae and Beauveria bassiana individually and in combination against T. absoluta under laboratory and greenhouse conditions. When second instar larvae were exposed to tomato leaf discs treated with Azadirachtin (3 g / L), B. thuringiensis (0.5 g/L) or B. bassiana (1.5 g/L), 70%–86%, 55%–65%, and 45.5%–58.5% mortality was observed, respectively. Steinernema feltiae (1,000 IJs/ml) was the least effective biopesticide, with 26%–42% mortality. In the greenhouse trials on tomato, pest infestation (mines/10 leaves/plant) and fruits damaged were significantly lower on plants treated with Azadirachtin  +  B. thuringiensis or Azadirachtin  +  B. bassiana compared to plants treated with Azadirachtin, B. thuringiensi, B. bassiana or S. feltiae alone. Azadirachtin  +  B. thuringiensis and Azadirachtin  +  B. bassiana resulted in 90% and 81% reduction in fruits damaged in the summer experiments, respectively, and 96% and 91% in winter. The most severe pest infestation was observed on plants treated with S. feltia. The results indicate that the biopesticides, except S. feltia, can contribute to T. absoluta control in greenhouse tomato crops. In particular, the combined use of Azadirachtin with B. thuringiensis or B. bassiana provided the highest level of control of the pest. The potential for including these biopesticides in an overall sustainable integrated pest management programme for T. absoluta is discussed.     

Functional response and egg distribution among hosts by Pseudapanteles dignus,a larval endoparasitoid of Tuta absoluta

The functional response of a biocontrol agent has been classically pointed out as a quantitative evaluation criterion to understand its killing capacity to an arthropod pest. In this paper, we revisited the functional response of the internal larval parasitoid Pseudapanteles dignus (Muesebeck) (Hymenoptera: Braconidae), a candidate for biocontrol of the South American tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), measured as the daily egg oviposition of single parasitoid females at increasing densities of T. absoluta larvae through dissection of hosts. The functional response curve of the number of parasitized hosts was fitted out taking into account the number of eggs laid and their distribution among hosts at each T. absoluta larval density. The data also allowed us to discuss the self-superparasitism strategy of this parasitoid as an adaptive trait. Pseudapanteles dignus showed a sigmoid shape functional response and a contagious distribution of eggs among hosts, favouring self-superparasitism and laying a similar number of eggs in each superparasitized host at each T. absoluta density. This research is firstly intended to ascertain about the oviposition behaviour of P. dignus and additionally to provide information on its reproduction to be applied in mass rearing procedures and augmentative releases against T. absoluta.     

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.     

First record of an entomopathogenic fungus of tomato leafminer,Tuta absoluta (Meyrick) in Tanzania

Tuta absoluta (Meyrick) is a destructive pest causing adverse environmental and economic effects globally. Management of T. absoluta by synthetic chemicals is of diminutive achievement due to resistance trick of the pest. Harnessing of biocontrols is currently fascinating and efficient for management of the tremendous pests. This study isolated an entomopathogenic fungus from dead larvae of T. absoluta on tomato leaves from farmer’s field Tanzania. Two Aspergillus fungal isolates were isolated and tested against larvae and adults of T. absoluta under conditions of 19.5°C and 50%RH, 30.4°C and 70% RH, respectively, in the laboratory. Sequence analysis of Aspergillus isolates that we referred as A-Tz1 and A-Tz2 were analysed with the BLAST program available at the National Center for Biological Information (NCBI). The two isolates (A-Tz1 and A-Tz2) showed 100% similarity with Aspergillus oryzae of GeneBank accession numbers EF121337.1 and MG519722.1. Such similarity implied that both A-Tz1 and A-Tz2 isolates were A. oryzae. To confirm pathogenicity, bioassays were conducted against the larvae, pupa and adults of T. absoluta. Results showed that at 1.0?×?10⁸?conidia/mL, fungal isolates caused up to 70% larval mortality 3 days post inoculation and consequently inhibited pupation by 84.5% and adult emergence by 74.4%. The identified A. oryzae reduced the life span of adult T. absoluta up to 5 days post inoculation at 1.0?×?10⁸?conidia/mL whereas in control T. absoluta survived up to 25 days. This study found that isolates of Aspegillus species have the potential to be used as active ingrediennt for the formulation of a new bioinjections for application by farmers to control the pest in fields.     

Mortality of second-instar larvae of Tuta absoluta produced by the hexane extract of Lycopersicon hirsutum f. glabratum (PI 134417) leaves

1 The mortality resulting from exposure of second‐instar larvae of Tuta absoluta to a hexane extract of Lycopersicon hirsutum f. glabratum (PI 134417) leaves was evaluated in the laboratory. 2 A crude hexane extract was fractionated on a silica gel column to produce 17 fractions. The toxicity of the fractions was evaluated on T. absoluta larvae at 2 and/or 6 mg/10 larvae/Petri dish along with a control. 3 Only two fractions, 4.50 and 10.18% of the total hexane extract, were found to result in very high mortality of second‐instar T. absoluta. 4 All the 17 fractions were analysed by capillary gas chromatography/mass spectrometry (GC/MS). The two most toxic fractions were virtually identical and contained mainly undeca‐2‐one (2‐UD) and trideca‐2‐one (2‐TD). 5 A third major sub‐fraction 13 (50.73% of the total hexane extract) was further fractionated on a silica gel column to obtain five additional sub‐fractions. The toxicity of all the five sub‐fractions was evaluated using second‐instar T. absoluta at 2 mg/10 larvae/Petri dish and also analysed by GC/MS. The most toxic sub‐fractions contained mostly 2‐UD and 2‐TD. 6 The results suggest that 2‐UD and 2‐TD could be related to resistance of L. hirsutum to T. absoluta.     

Tomato pollen development: stages sensitive to chilling and a natural environment for the selection of resistant genotypes

Abstract The time during which pollen development is most sensitive to chilling was investigated. Five cultivars of tomato (Lycopersicon esculentum Mill.) bearing flower buds at different stages of development were kept at 7°C for 1 week under 12-h light periods, during which time growth stopped. After returning the plants to minimum temperatures of 18°C, the presence of chromatin in the pollen was assessed daily as the flowers reached anthesis. The results suggested that there are two stages of acute sensitivity to cold during pollen development, each of which results in cold-stressed plants having pollen empty of chromatin. The first and most sensitive stage is about 11.2 d (SE = 0.3 d) before anthesis, and this is followed by a second stage of sensitivity about 5.6±0.2 d before anthesis. Flowers that had wholly developed under simulated natural temperatures that decreased diurnally from a maximum of 18°C to a minimum of 7°C also had defective pollen, but pollen of normal appearance was regained within 14°d on return to higher temperatures. Plants of L. esculentum, and a form (LA 1363) of the wild species L. hirsutum from high altitudes in the Andes, as well as F1 and F3 generations of their hybrid, were grown to the flowering stage at an altitude of 600 m in Hawaii and then grown for a further 30°d at 2000 m, where night temperature was below 10°C. The high altitude environment severely affected the quality of pollen produced and its release from the stamen in L. esculentum, but not in L. hirsutum LA 1363. The results with the hybrids suggested that such tropical mountain environments can be used as a natural phytotron in the selection of chilling resistance that is only expressed in the mature plant.     

Resistance to the potato cyst-nematode, Heterodera rostochiensis, in the plant genus Lycopersicon

Forty-eight lines of Lycopersicon and four lines of Solanum were screened for resistance to twelve Heterodera rostochiensis populations of known patho-type(s). Plant lines were assessed for resistance first by examining the outside of the root ball for cysts and later by washing the root ball to extract all cysts. Possible resistant plant selections were re-tested against three eelworm populations, including the one to which they were first shown resistant. Resistance was discovered in two lines of Lycopersicon pimpinelli-folium, two L. esculentum L. pimpinellifolium crosses, L. esculentum var. cerasiforme, six lines of L. peruvianum, in L. peruvianum var. humifusum, L. hirsutum var. glabratum, and in Solanum indicum. Because resistance was found most commonly in L. peruvianum and because it has already been used as a resistant parent in breeding programmes to incorporate resistance to root-knot nematode (Meloidogyne spp.) in tomato, L. peruvianum seems to be the best source of resistance among plants tested so far. The host-parasite relationships of resistant L. hirsutum var. glabratum (B 6013) were compared with those of a commercial, susceptible tomato, L. esculentum‘Ailsa Craig’. Plants were inoculated with three eelworm isolates; the extent of eelworm invasion, plant reaction and eelworm development were studied. Larvae invaded and penetrated roots of the resistant plant as freely and in as large numbers as they penetrated roots of the susceptible tomato. In the latter, numerous larvae matured while, in contrast, few larvae matured in the roots of L. hirsutum var. glabratum. L. hirsutum var. glabratum was shown to possess a root diffusate as active in hatching larvae of Heterodera rostochiensis as that of L. esculentum‘Ailsa Craig’. The existence of pathotypes of H. rostochiensis, identifiable by their differing abilities to increase on resistant tomato lines, was not clearly revealed in the experiments.