Interspecific interference competition between Encarsia formosa and Encarsia sophia (Hymenoptera: Aphelinidae) in parasitizing Bemisia tabaci (Hemiptera: Aleyrodidae) on five tomato varieties

Abstract Interspecific competition between Encarsia formosa and Encarsia sophia, two major parasitoids of Bemisia tabaci, and the influence of five tomato varieties on competition outcome were investigated under laboratory conditions. E. formosa parasitized more B. tabaci than E. sophia when in single wasp assays on any of the tomato varieties investigated. When B. tabaci nymphs were exposed to both wasp species (either simultaneously or sequentially), the number of B. tabaci nymphs parasitized by either wasp species was significantly decreased compared to the sole access condition. Total mortality of B. tabaci was increased when B. tabaci nymphs were exposed to both wasp species compared to only one wasp species. Thus competition between E. formosa and E. sophia apparently reduced parasitoid offspring numbers, but not the efficiency of biological control. In fact, control efficiency was enhanced in some cases, particularly on tomato variety Huangtuoyuan (HTY). When wasps were allowed sequential access to hosts, interference occurred through host feeding by the second wasp, especially if it was E. sophia. The effect of different tomato varieties was not significant.     

Salt stress increases ferredoxin-dependent glutamate synthase activity and protein level in the leaves of tomato

Ferredoxin-dependent glutamate synthase (EC 1.4.7.1) catalyzes an essential step in the pathway of glutamate biosynthesis. Exposing detached tomato ( Lycopersicon esculentum ) leaves for 6 h to 12 g l⁻¹ NaCl resulted in a significant two-fold increase in the activity of ferredoxin-dependent glutamate synthase extracted from the leaves. Western blot studies demonstrated that salt treatment also increased the ferredoxin-dependent glutamate synthase content of the leaves. A similar effect of salt on the concentration of this enzyme was found in the leaves of hydroponically-grown tomato plants. The induction of ferredoxin-dependent glutamate synthase under salt stress may provide the glutamate required for the proline synthesis which is a common response to salt stress.     

Bemisia tabaci (Gennadius) population density and pupal size are dependent on rootstock and nitrogen in hydroponic tomato crop

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Isolation and characterization of microsatellite loci in Bemisia tabaci

Bemisia tabaci (Hemiptera: Aleyrodidae) is a haplo‐diploid species with a global distribution demonstrating strong geographical structure with eight recognizable genetic groups. Fifteen microsatellite loci (335 alleles, 6–44 alleles per locus) were derived from four of the eight groups and were then screened across 33 populations. These loci clearly differentiate the populations. The microsatellites amplified best in individuals from genetic groups rep‐resenting the Mediterranean, Middle East, Asia (three groups) and Australasia/Oceania and amplified less well with populations from sub‐Saharan Africa and the New World. This differential amplification pattern is a direct result of the relatedness to the microsatellite source material.     

Binomial sampling plans for estimatingBemisia tabaci populations in cantaloupes

Early season infestations of the sweet potato whitefly, Bemisia tabaci (Gennadius), on cantaloupes, Cucumis melo L., were determined by counts of the number of adults per leaf in fields near Yuma, Arizona. We used these data to develop binomial sampling plans based on the relationship between mean densities of whiteflies per leaf, m, and proportion of leaves infested with more than I whiteflies, P_I, according to the empirical model ln m=a′+b′ ln[−ln(1−P_I)]. The models were developed for the presence-absence approach (I=0) and for a cutoff value of three whiteflies per leaf (I=3). Four independent data sets were used to evaluate the models. Both methods yielded reliable predictions at low infestation levels, but some of the higher m values were overestimated. As the tentative economic threshold for B. tabaci is three adults per leaf, which corresponds to low P_I values, results of the binomial sampling were satisfactory for pest management purposes.     

Distribution and phytotoxicity of cadmium in tomato seedlings

Thirty-day-old seedlings of tomato (Lycopersicon esculentum cv. Kwangsoo) were treated with various cadmium (Cd) concentrations (0, 10, 50, 100, and 500 μM) for up to 20 days, and the detailed distribution of absorbed Cd and its phytotoxicity in different plant parts (root, stem, and leaves) were investigated. The accumulation of Cd in plants increased with external Cd concentrations and Cd was strongly retained by roots, with less than 30% of the absorbed Cd being transported to shoots. Among the leaves, the lower positioned older leaves accumulated more Cd than the younger leaves. Furthermore, Cd-exposure not only reduced the dry weight and length of both shoot and root, chlorophyll levels in leaves, and levels of photosynthesis, but also enhanced the concentration of malondialdehyde (a lipid peroxidation product) in all plant parts. Our results indicate that the physiological impairment of tomato seedlings exposed to toxic levels of Cd may be related to the internal distribution of absorbed Cd, prolonged exposure, and oxidative stress in different plant parts.     

Shoot regeneration and protein synthesis in tomato tissue cultures

Shoot regenerations from hypocotyls and cotyledons of tomato(Lycopersicon esculentum Mill.) was inhibited by NaCl (100 and 150 mM).Shoot fresh and dry masses were also reduced. Addition of proline (100 mgdm-3) counteracted the inhibitory effect of NaCl. SDS-PAGE analyses of extracted proteins, revealed that in cultures grown in medium with 25 mM NaCl plus proline, extra polypeptides of Mr 190, 58, 45 and 26 kDa accumulated. As NaCl was increased in the medium a new protein of Mr 67 kDa also accumulated. This revised version was published online in July 2006 with corrections to the Cover Date.     

烟盲蝽对不同虫态烟粉虱的捕食作用及捕食偏好性

杂食性昆虫烟盲蝽Nesidiocoris tenuis是烟粉虱Bemisia tabaci的重要天敌之一。为探索烟盲蝽对不同虫态烟粉虱的捕食作用及捕食偏好性,在室内进行了非选择性和选择性试验。结果表明,在非选择性试验中,烟盲蝽雌成虫、雄成虫以及5龄若虫可以捕食烟粉虱成虫和各龄若虫,但极少捕食卵。其中,烟盲蝽雌成虫、雄成虫及5龄若虫对烟粉虱1龄若虫的捕食量最大,分别为134.2头、101.3头和88.1头,其次是2~3龄若虫,捕食量分别为94.1头、64.2头和53.4头。而在选择性试验中烟盲蝽雄虫更偏好捕食烟粉虱的2~3龄若虫,其次是1龄若虫、4龄若虫和成虫。该结果对了解烟盲蝽控制烟粉虱的作用以及如何对烟盲蝽和其他天敌组合应用提供了参考信息。     

Heat treatment to decrease chilling injury in tomato fruit. Effects on lipids, pericarp lesions and fungal growth

Tomato fruits are sensitive to low temperature and develop chilling injury, while at nonchilling temperatures they ripen rapidly. Previously, a hot-air treatment was found to reduce the sensitivity of the fruit to low temperatures. In the present study hot air was compared to hot water and their effects on reducing chilling injury and fungal decay were investigated. Tomatoes ( Lycopersicon esculentum cv. Daniella) at the breaker stage were subjected to hot air, 48 h at 38°C, or various hot water dips, 30 min at 40°C or 2 min at 46, 48 or 50°C, before holding at 2°C. The unheated tomatoes developed chilling injury and fungal infections at 2°C, but not at 12°C. All the heat treatments reduced chilling injury and decay in tomatoes held for 3 weeks at 2°C. The outer pericarp tissue of heated tomatoes had higher phospholipid and lower sterol contents than unheated tomatoes. Heated tomatoes also had less saturated fatty acids than unheated tomatoes held at 2°C, but not at 12°C. Scanning electron micrograph observations showed that all the fruits had microcracks in their surface, but the unheated chilled tomatoes had also fungal growth in the cracks, while those of the heated tomato fruit did not. In the areas of chilling injury collapsed cells were present under the peel and could also support pathogen development. It is suggested that the heat treatment institutes a response to high temperature stress in the fruit tissue that leads to strengthened membranes. This prevents the loss of function and cell collapse which was found in the chilling-injured areas of affected fruit.     

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.     

Bemisia tabaci in Iraq: Population structure,endosymbiont diversity and putative species

Whiteflies (Hemiptera: Aleyrodidae) are major pests of many crops worldwide. Bemisia tabaci is a cryptic species complex composed of more than 39 putative species. Understanding which putative species of B. tabaci are predominant in an area is vital for effective pest management since they may vary considerably with respect to insecticide resistance, host plant range and virus transmission. Here, for the first time, the genetic diversity, the symbiont diversity and population structure of B. tabaci in Iraq were studied. Fourteen populations were analysed using mitochondrial cytochrome C oxidase subunit 1 (mtCO1) sequencing and microsatellite genotyping. Symbiotic bacteria were identified using 16S rRNA and 23S rRNA sequencing. MtCO1 sequencing detected two putative species of B. tabaci. The predominant putative species in Iraq was Middle East-Asia Minor (MEAM) 1 subcladeB2. In addition, one individual was MEAM1-subcladeB. The second putative species was a single individual of MEAM2. The microsatellite data indicated low genetic diversity, with no biologically informative clustering. All MEAM1 individuals harboured one primary symbiont, Portiera aleyrodidarum, and most (96%) have two secondary symbionts: Hamiltonella sp. and Rickettsia sp. This study has identified the genetic diversity and population structure of B. tabaci in Iraq. Further investigation is needed to update the pest status of B. tabaci in this region. The current data, combined with investigations into the capacity of the various putative species to transmit plant viruses, especially tomato yellow leaf curl virus, will aid pest management and horticultural production.     

Quantitative resistance against Bemisia tabaci in Solanum pennellii: Genetics and metabolomics

The whitefly Bemisia tabaci is a serious threat in tomato cultivation worldwide as all varieties grown today are highly susceptible to this devastating herbivorous insect.Many accessions of the tomato wild relative Solanum pennellii show a high resistance towards B. tabaci. A mapping approach was used to elucidate the genetic background of whiteflyresistance related traits and associated biochemical traits in this species. Minor quantitative trait loci(QTLs) for whitefly adult survival(AS) and oviposition rate(OR) were identified and some were confirmed in an F2BC1 population, where they showed increased percentages of explained variance(more than 30%). Bulked segregant analyses on pools of whiteflyresistant and-susceptible F2 plants enabled the identification of metabolites that correlate either with resistance or susceptibility. Genetic mapping of these metabolites showed that a large number of them co-localize with whiteflyresistance QTLs. Some of these whitefly-resistance QTLs are hotspots for metabolite QTLs. Although a large number of metabolite QTLs correlated to whitefly resistance or susceptibility, most of them are yet unknown compounds and further studies are needed to identify the metabolic pathways and genes involved. The results indicate a direct genetic correlation between biochemical-based resistance characteristics and reduced whitefly incidence in S. pennellii.     

Potassium utilization and fluxes in wild salt-tolerant relatives of the cultivated tomato

The growth of the wild tomato species Lycopersicon peruvianum (L.) Mill, and L. pennellii (Correll) D'Arcy, was compared with that of the cultivated tomato, L. esculentum Mill. cv. VE 234, under conditions of reduced K⁺ supply. Growth was impaired less in the wild than in the cultivated species. The higher efficiency of K⁺ utilization in the wild species was not associated with more efficient JC uptake from the medium. The rate of K⁺ uptake by whole plants was similar in the three species, but the rate of uptake by detached root tips was lower in the wild species. The permeability of the plasma membrane to K+ was apparently similar in root tips of the three species, but the tonoplast permeability was much lower in the wild than in the cultivated species.     

Changes in free polyamine levels induced by salt stress in leaves of cultivated and wild tomato species

The effects of N_aCl on endogenous free levels of the poluamines putrescine, spermi dine and spermine, and the relationships between polyamines, K⁺ levels and Na⁺ accumulation were determined in leaves of the cultivated tomato ( Lycopersicon esculentum Mill.) and its wild, salt-tolerant relative L. pennellii (Correll) D' Arcy at different exposure times during a 32-day period. Both stress treatments (100 and 200 m M NaCl) decreased the levels of putrescine and spermidine, although to a different degree for the cultivated and wild tomato species. The spermine levels did not decrease with salinity in L. pennellii over the salinization period, whereas they decreased in L. esculentum , except at the first application of the 100m M NaCl treatment. In both species, the changes induced by salinity in total polyamines and K⁺ were very similar, with the accumulation of Na⁺ in the leaf being concomitant with a decrease in both total polyamines and K⁺. This suggests that the main role of the polyamines in the leaf tissues. In this sense, a direct relationship between total polyamines and K⁺, and inverse relationship between polyamines and Na⁺ and between K⁺ and Na⁺ were found for both species. In the short term (up to 4 days) a peculiar physiological behavior was found in L. pennellii , as the total polyamine and K⁺ levels decreased at 100 m M but not at 200 m M NaCl, while after this time the latter plants had values lower than those of the 100 m M NaCl-treated plants at day 11.     

Graft union formation in tomato plants: peroxidase and catalase involvement

BACKGROUND AND AIMS: The use of grafted plants in vegetable crop production is now being expanded greatly. However, few data are available on the formation of graft unions in vegetables. In this work, the structural development of the graft union formation in tomato plants is studied, together with the possible relationship with activities of peroxidases and catalases. METHODS: Tomato (Lycopersicon esculentum Mill.) seedlings of cultivar Fanny were grafted on the rootstock of cultivar AR-9704 using the 'tongue approach grafting' method, and were grown in a crop chamber. A study of the structural development of the graft union and the involvement of peroxidases and catalases in the process of graft formation was carried out during the first stages of the graft union (4, 8 and 15 d after grafting). KEY RESULTS: Observation of the structure of the graft union showed formation of xylem and phloem vessels through the graft union 8 d after grafting. In addition, root hydraulic conductance, L0, indicate that the graft union is fully functional 8 d after grafting, which coincided with an increase of peroxidase and catalase activities. CONCLUSIONS: These results suggest that increased peroxidase and catalase activities might be implicated in graft development in tomato plants.     

Isolation and characterization of nitrate reductase-deficient mutants in tomato (Lycopersicon esculentum Mill.).

Summary Five nitrate reductase-deficient mutants of tomato were isolated from an M2 population after ethyl-methanesulphonate (EMS) seed treatment by means of selection for chlorate resistance. All mutations were monogenic and recessive and complementation analysis revealed that they were non-allelic. Biochemical and molecular characterization of these mutants showed that four of them are cofactor mutants while one is an apoenzyme mutant.     

Differential responses between a vector species Bemisia tabaci and a nonvector species Trialeurodes vaporariorum following ingestion of tomato yellow leaf curl virus

In transmitting plant viruses, insect vectors undergo physiological and behavioral alterations. The whitefly Bemisia tabaci is a vector of tomato yellow leaf curl virus (TYLCV), causing severe damages to various horticultural crop plants. To determine whether whitefly alteration is specific to vector species, the responses to TYLCV ingestion were compared between B. tabaci and Trialeurodes vaporariorum, a nonvector for TYLCV. The two species were reared on TYLCV‐infected and noninfected tomato, a host of TYLCV, and their longevity and fecundity were determined while rearing in either tomato or eggplant, a nonhost of TYLCV. TYLCV‐ingested B. tabaci increased their developmental rates but reduced fecundity when they were reared in either tomato or eggplant compared with those of TYLCV‐free ones. In contrast, TYLCV‐ingested T. vaporariorum did not show any of the aforementioned changes when reared on both plant species. In addition, TYLCV‐ingested B. tabaci increased their levels of three heat shock protein genes ( hsp20, hsp70, and hsp90) against thermal stress, whereas TYLCV‐ingested T. vaporariorum did not. The presence of TYLCV virions was identified in two colonies of both species via polymerase chain reaction analysis. TYLCV was detected in the whole body, saliva, and eggs of B. tabaci, while TYLCV was detected only in the whole body but not in the saliva and eggs of T. vaporariorum. The present results strongly indicated that TYLCV specifically manipulate physiological processes of the vector species, B. tabaci.     

Isolation and characterization of microsatellite loci in Bemisia tabaci (Hemiptera: Aleyrodidae)

Microsatellite‐enriched genomic libraries were obtained from the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) using a magnetic/biotin capture of repetitive sequences. Ten dinucleotide markers were successfully isolated and characterized from these libraries. Variability was assessed in six populations of B. tabaci collected from different localities of the island of Crete, Greece. The number of alleles per locus in approximately 105 individuals screened across populations ranged from two to 13. Averaged observed heterozygosity over the six populations ranged from 0.001 to 0.58.     

Hygienic quality of traditional processing and stability of tomato (Lycopersicon esculentum) puree in Togo

Microbiological and physicochemical qualities of a tomato (Lycopersicon esculentum) puree production line (ripe tomato, washing, cutting, pounding, bleaching, straining, bottling and pasteurization) and its preservation in Togo, West Africa, were studied using the HACCP method. Samples generated during the steps described previously were analyzed by determining sensory, chemical and microbiological characteristics. Samples were analyzed using MPN for coliform populations and plate count methodology for other bacteria. The microorganisms involved in spoilage of the opened products were moulds of genera Penicillium, Aspergillus, Fusarium, Geotrichum, Mucor and gram-positive Bacillus bacteria. The preserved tomato puree exhibited a pH value of 4.3, 90% water content, 0.98 water activity (aw) and an average ascorbic acid level of 27.3mg/100g. Results showed that the critical control point (CCP) of this tomato puree processing line is the pasteurization stage. The analysis of selected microbiological and physicochemical parameters during the preservation of bottled tomato puree indicated that this product was stable over 22 months at 29 degrees C. But the stability of the opened product stored at 29 degrees C did not exceed two months.