Greenhouse and field screening of wild<Emphasis Type="Italic">Lycopersicon</Emphasis> germplasm for resistance to the whitefly<Emphasis Type="Italic">Bemisia argentifolii</Emphasis>

Thirty-two accessions of wild tomato (Lycopersicon spp.) germplasm were evaluated for resistance to the whiteflyBemisia argentifolii Bellows ⇐p; Perring in a greenhouse choice bioassay. Density data were recorded for the adaxial and abaxial leaf surfaces for (i) all life stages ofB. argentifolii and (ii) types I, IV, V and VI trichomes. Individual plant selections (33 from 22 wild tomato accessions) with high resistance were subsequently tested in the field to verify the resistance found in the greenhouse screening. Resistance was defined by the density of all life stages of the whitefly observed on the eight leaflets sampled at nodes 5 and 7. Only type IV trichomes had a consistent (but low) and significant negative correlation between trichome density and whitefly density for various life stages. The highest whitefly resistance was observed inLycopersicon pennellii accessions LA 716, LA 1340 and LA 2560. The most resistantL. hirsutum f.typicum accessions were LA 1777 and LA 1353. http://www.phytoparasitica.org posting Dec. 9, 2002.     

Partial stem and leaf resistance against the fungal pathogen <Emphasis Type="Italic">Botrytis cinerea</Emphasis> in wild relatives of tomato

Tomato (Solanum lycopersicum) is one of many greenhouse crops that can be infected by the necrotrophic ascomycete Botrytis cinerea. Commercial cultivation of tomato is hampered by the lack of resistance. Quantitative resistance has been reported in wild tomato relatives, mostly based on leaf assays. We aimed to identify wild tomato relatives with resistance to B. cinerea based on quantitative assays both on leaves and stem segments, monitoring infection frequency and disease expansion rate as parameters. A quantitative tomato stem segment assay was developed. This stem assay and a previously described leaf assay were used to screen a collection of 22 Solanum accessions. Significant differences in disease parameters were observed among accessions. Resistance to B. cinerea was observed in a number of wild Solanum species, including accessions of S. chilense, S. habrochaites and S. neorickii, both in the leaf assay and the stem segment assay. A number of resistant and susceptible accessions were evaluated as adult plants under greenhouse conditions. The data obtained in greenhouse assays confirmed the leaf and stem disease data. The expression of several defence-related genes was studied in a subset of accessions. There was no apparent correlation between the expression levels of the genes tested and the quantitative resistance level to B. cinerea. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Is the parasitization rate of<Emphasis Type="Italic">Diaeretiella rapae</Emphasis> influenced when<Emphasis Type="Italic">Brevicoryne brassicae</Emphasis> feeds on<Emphasis Type="Italic">brassica</Emphasis> plants?

The development time and parasitization rate ofDiaeretiella rapae (M’Intosh) onBrevicoryne brassicae (L.) feeding on differentBrassica cultivars was studied in the laboratory at 20°C. The shortest development time from egg to adult parasitoid was 11.6 days on cabbage cv. ‘Yalova 1’ and the longest was 12.1 days on turnip cv. ‘Antep’ and rapeseed cv. local variety. Females lived significantly longer than males on the host plants used in the study. Females and males had the shortest longevity on rapeseed at 11.1 and 5.1 days, respectively. The highest percent parasitism ofB. brassicae byD. rapae was found on cabbage (40.20%), and the lowest was recorded on turnip (32.64%). Our results demonstrate that parasitism rate could be influenced by the plant quality, probably due to the nutritional status of the aphids or to toxic compounds ingested through the plant. Cabbage, cauliflower and broccoli were found to be suitable plants for the parasitoid, considering the development time of pre-adults, and the parasitization rate ofD. rapae onB. brassicae. http://www.phytoparasitica.org posting Jan. 23, 2007.     

Assessment of early blight (<Emphasis Type="Italic">Alternaria solani</Emphasis>) resistance in tomato using a droplet inoculation method

A droplet inoculation method was used for evaluation of tomato resistance to early blight, a destructive foliar disease of tomato caused by Alternaria solani (Ellis and Martin) Sorauer. In this test method, leaflets are inoculated with small droplets of a spore suspension in either water or a 0.1% agar solution. Early blight resistance was evaluated based on lesion size. The droplet method better discriminated the level of resistance (P < 0.001) for a range of spore densities in comparison with the more commonly used spray inoculation method. Lesions generated by droplet inoculation at 7 days after inoculation ranged from small flecks to almost complete blight with an exponential-like distribution of lesion sizes. Significant correlations (r = 0.52, 0.58, and 0.63, P < 0.001) were observed across three glasshouse tests of 54 accessions including wild species using the droplet method. The most resistant accessions included wild species: one accession of Solanum arcanum, three accessions of Solanum peruvianum, one accession of Solanum neorickii, and one of Solanum chilense. Solanum pennellii and Solanum pimpinellifolium accessions were susceptible, whereas Solanum habrochaites and Solanum lycopersicum accessions ranged from susceptible to moderately resistant. The droplet test method is simple to apply, offers a fine discrimination of early blight resistance levels, and allows objective evaluation.     

Host status and reaction of <Emphasis Type="Italic">Medicago truncatula</Emphasis> accessions to infection by three major pathogens of pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>) and alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis>)

Ditylenchus dipsaci, the stem nematode of alfalfa (Medicago sativa), Mycosphaerella pinodes, cause of Ascochyta blight in pea (Pisum sativum) and Aphanomyces euteiches, cause of pea root rot, result in major yield losses in French alfalfa and pea crops. These diseases are difficult to control and the partial resistances currently available are not effective enough. Medicago truncatula, the barrel medic, is the legume model for genetic studies, which should lead to the identification and characterization of new resistance genes for pathogens. We evaluated a collection of 34 accessions of M. truncatula and nine accessions from three other species (two from M. italica, six from M. littoralis and one from M. polymorpha) for resistance to these three major diseases. We developed screening tests, including standard host references, for each pathogen. Most of the accessions tested were resistant to D. dipsaci, with only three accessions classified as susceptible. A very high level of resistance to M. pinodes was observed among the accessions, none of which was susceptible to this pathogen. Conversely, a high level of variation, from resistant to susceptible accessions, was identified in response to infection by A. euteiches.     

Inheritance of resistance to <Emphasis Type="Italic">Mycosphaerella pinodes</Emphasis> in two wild accessions of <Emphasis Type="Italic">Pisum</Emphasis>

Mycosphaerella pinodes is one of the most devastating pea pathogens. Pea cultivars with adequate levels of resistance to control the disease are not so far available. However, promising levels of resistance have been identified in wild accessions of pea. In the present investigation the inheritance of resistance to M. pinodes was studied in two crosses between the susceptible pea cv. ‘Ballet’ and the partially wild resistant accessions P665 (Pisum sativum subsp. syriacum) and P42 (P. sativum subsp. sativum var. arvense). Both additive and dominant effects were important in control of resistance and susceptibility dominated over resistance.     

Biotype Q of<Emphasis Type="Italic">Bemisia tabaci</Emphasis> identified in Israel

The biotype status of samples of the whiteflyBemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) collected from several field and greenhouse sites in Israel during 1999–2000 was determined by polyacrylamide gel electrophoresis (PAGE) for general esterases, and by RAPD-PCR using primers of arbitrary sequence. Results of this survey provide the first published evidence for the occurrence of theB. tabaci Q biotype, alongside the more widely distributed B biotype. Based on the collected samples, it appears that both the B and Q biotypes are present in Israel, and that field populations consist of a mixture of the two biotypes. A possible link betweenB. tabaci biotypes and insecticide resistance is discussed. Contribution no. 508/02 from the Inst. of Plant Protection, ARO, The Volcani Center, Bet Dagan, Israel. http://www.phytoparasitica.org posting Dec. 5, 2002.     

Differing susceptibility to<Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> formulations of<Emphasis Type="Italic">Thaumetopoea wilkinsoni</Emphasis> populations between forests with different<Emphasis Type="Italic">Bt</Emphasis> management in Israel

The susceptibility ofThaumetopoea wilkinsoni larvae toBacillus thuringiensis (Bt) formulations was screened in 2003 and 2004. Eggs and larvae were collected from pine forests in 11 geographical locations in Israel. Larval mortality bioassays were conducted with commercial formulations (Delfin WG, Dipel DF and Foray 48B) at concentrations ranging from 0.001% to 0.1%. Significant differences in susceptibility toBt were recorded among populations that were treated withBt intensively, frequently, or never. The mortality recorded in a population that was never treated withBt was twice that in an intensivelyBt-treated population. The correlation between susceptibility toBt and the possible resistance to the microbe is discussed. http://www.phytoparasitica.org posting Jan. 31, 2007.     

Identification of a CAPS marker tightly linked to the Tomato yellow leaf curl disease resistance gene <Emphasis Type="Italic">Ty-1</Emphasis> in tomato

During the process of breeding programmes, several resistance genes have been introgressed into tomato (Solanum lycopersicum) cultivars from different wild tomato relatives. A number of these resistance genes have been mapped to chromosome 6. Among them, Ty-1 and Mi, which confer resistance to Tomato yellow leaf curl disease and to Meloidogyne spp., respectively, are in most cases incorporated in commercial hybrids. Several molecular markers tightly linked to Mi have been identified. This study was conducted in order to find an informative molecular marker linked to Ty-1. Six markers mapped in the same region as Ty-1 were analysed in plant material carrying different combinations of Ty-1 and Mi alleles. Three of the six markers revealed polymorphism among the assayed accessions. One allele of JB-1 marker showed association with Ty-1. Furthermore, the presence of Mi did not interfere with the results. The analysis of several accessions of wild tomato relatives with the three polymorphic markers allowed the establishment of the origin of the alleles found in cultivated plant material, showing that introgressions from S. lycopersicum, S. pimpinellifolium and S. habrochaites will not interfere with the results of this marker which tags Ty-1. Furthermore this analysis enabled the location of CT21, the RFLP marker from which JB-1 was designed.     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

Effect of temperature on development,mortality, fecundity and reproduction of<Emphasis Type="Italic">Tuberolachnus salignus</Emphasis> on weeping willow (<Emphasis Type="Italic">Salix babylonica</Emphasis>) and corkscrew willow (<Emphasis Type="Italic">Salix matsudana</Emphasis>)

The development time, survivorship and reproduction ofTuberolachnus salignus (Gmelin) (Hemiptera: Aphididae) [Lachninae, Lachnini] were studied onSalix babylonica (weeping willow) andSalix matsudana (corkscrew willow) at five constant temperatures (17.5, 20, 22.5, 25 and 27.5°C). The development time of immature stages ofT. salignus ranged from 14.56 days at 17.5°C to 12.50 days at 25°C onS. babylonica, and 16.47 days at 20°C to 12.28 days at 25°C onS. matsudana. The total survivorship of immature stages ofT. salignus varied from 28% to 85% at 22.5 and 17.5°C, respectively, onS. babylonica, and from 13% to 63%, respectively, at 17.5 and 25°C onS. matsudana. The greatest intrinsic rate of increase occurred at 25°C onS. babylonica (0.2691) and also onS. matsudana (0.2607). The mean generation time of the aphid population ranged from 14.15 days at 25°C to 16.24 days at 17.5°C onS. babylonica, and from 14.33°C days at 25°C to 19.86 days at 20°C onS. matsudana. The optimal temperature forS. babylonica growth, development time, reproduction and percent survival was 25°C.     

Note: Pyrethroid resistance and possible involvement of glutathione<Emphasis Type="Italic">S</Emphasis>-transferases in<Emphasis Type="Italic">Helicoverpa armigera</Emphasis> from Turkey

An introductory study was conducted to investigate the pyrethroid resistance ofHelicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) strains in Turkey, collected from cotton fields in the Adana and Antalya provinces, through two different synthetic pyrethroid insecticides: lambda-cyhalothrin and esfenvalerate. In addition, the roles of glutathioneS-transferases (GSTs) in this resistance mechanism were analyzed. It was found that whereas resistance ratios for lambda-cyhalothrin (LD₅₀ levels) were 3- and 98-fold increased in the Adana and Antalya strains, respectively, esfenvalerate ratios were 3.3- and 92.3-fold increased in the Adana and Antalya strains, respectively, with respect to the susceptible strain. Furthermore, Adana and Antalya strains showed 2.4- and 2.9-fold higher GST activities than the susceptible strain, respectively. In the Antalya field strain, the minor increase in GST activity compared with the resistance levels implies that GSTs may be not greatly involved in this resistance. It also provides evidence that they could not be the only metabolic mechanism responsible for resistance to lambda-cyhalothrin and esfenvalerate inH. armigera from Turkey. http://www.phytoparasitica.org posting Nov. 16, 2006.     

Fumigant toxicity of<Emphasis Type="Italic">Eucalyptus blakelyi</Emphasis> and<Emphasis Type="Italic">Melaleuca fulgens</Emphasis> essential oils and 1,8-cineole against different development stages of the rice weevil<Emphasis Type="Italic">Sitophilus oryzae</Emphasis>

Essential oils extracted fromEucalyptus blakelyi (1,8-cineole, 77.5%),Melaleuca fulgens (1,8-cineole, 56.9%) and 1,8-cineole were shown to have fumigant toxicity against different development stages ofSitophilus oryzae. The eggs ofS. oryzae were the most tolerant, followed by pupae, larvae and adults in that order.M. fulgens oil,E. blakelyi oil and 1,8-cineole at 100 μl per liter of air gave, respectively, LT₅₀ values of 16.2, 17.4 and 9.1 h for adults, 31.1, 19.3 and 17.5 h for larvae, 55.6, 75.2 and 39.7 h for pupae, and required >7 days for eggs. Only 1,8-cineole (200 μl ⁻¹ air) gave a significant egg kill by 7 days and the LT₉₅ was 134.5 h. 1,8-Cineole could be a useful new fumigant. http://www.phytoparasitica.org posting Oct. 3, 2004.     

Genetics of host-pathogen interactions in the <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> (net form) – barley (<Emphasis Type="Italic">Hordeum vulgare)</Emphasis> pathosystem

The genetics of host-pathogen interactions in the Hordeum vulgare – P. teres f. teres pathosystem was studied in twelve resistant barley accessions, i.e. CI 9825, CI 9819, Diamond, CI 4922, CI 5401, Harbin, c-8755, c-21849, c-8721 c-23874, c-19979, c-15811. F₂ analyses of crosses with susceptible genotypes employing various isolates (from Europe, USA, Canada, and Australia) revealed that resistance is mostly isolate-specific and controlled by one or two genes. Segregation in ascospore progeny from two crosses between isolates of different origin revealed that avirulence in P. teres is also determined by one or two genes. An epistatic effect of suppressor genes on avirulence genes is proposed for the genetics of virulence to Diamond, Harbin, CI 5401 and c-8721 in the fungal crosses D (181-6 × A80) and F (H-22 × 92-178/9). Segregation in F₂ of crosses of three new sources of resistance (c-23874, c-19979, c-15811) to the susceptible cv. Pirkka was studied in laboratory and greenhouse tests by using seven P. teres isolates, i.e. 181-6, d8-3, d8-4, d9-1, d9-4, F4 and F74. In addition, virulence to these barley accessions of ascospore progeny from crosses of the same isolates was studied. Based on these studies it was concluded that depending on the isolate used, resistance of c-23874 is determined at least by two genes and in c-19979 and c-15811 by three genes. The results of this parallel analyses of genetics of resistance and genetics of virulence allows the postulation of a gene–for–gene interaction in the P. teres – H. vulgare pathosystem.     

Note: Does<Emphasis Type="Italic">Liriomyza cicerina</Emphasis> affect the yield of chickpeas (<Emphasis Type="Italic">Cicer arietinum</Emphasis>)?

Liriomyza cicerina (Rondani, 1875) (Diptera: Agromyzidae) is an important pest on chickpea (Cicer arietinum L.) in some regions of Turkey. The objective of this study was to determine whether the populations ofL. cicerina on different varieties of chickpea plants during the 2004 and 2005 production seasons affected yield in Sanliurfa province. The trials were carried out using eight different varieties of chickpea with three replicates. During each season, larval densities on leaves were assessed weekly. TheL. cicerina larval population was lowest on four varieties for both seasons. There were very minor differences in yield among the eight varieties in the production seasons. There was no correlation found between larval density and yield loss. http://www.phytoparasitica.org posting Jan. 14, 2007.     

Analysis of sources of oxolinic acid-resistant field strains of <Emphasis Type="Italic">Burkholderia glumae</Emphasis> based on rep-PCR analysis and nucleotide sequences of <Emphasis Type="Italic">gyrB</Emphasis> and <Emphasis Type="Italic">rpoD</Emphasis>

Repetitive sequence-based polymerase chain reaction (rep-PCR) analysis using BOX and ERIC as primers showed a highly divergent phylogeny among field strains of Burkholderia glumae. To elucidate the sources of oxolinic acid (OA) resistance in field strains of B. glumae isolated from rice seedlings cultivated in Mie, Toyama, and Iwate prefectures, Japan, the amino acid at position 83 of GyrA (GyrA83), which is involved in OA resistance, and the DNA patterns from the rep-PCR and the partial nucleotide sequences of gyrB and rpoD from various strains were analyzed. The ten Mie strains, in which GyrA83 was isoleucine (Ile), were divided into two groups based on the band patterns in rep-PCR analysis, although the nucleotide sequences of gyrB and rpoD were identical among the strains. Based on the band patterns in the rep-PCR analysis and the gyrB and rpoD sequences, two highly OA-resistant Toyama strains, Pg-13 and Pg-14, for which GyrA83 was serine (Ser) and Ile, respectively, were in the same lineage. This suggests that the bacteria might acquire OA resistance faster than phylogenic diversity as determined with the repetitive sequences BOX and ERIC and with gyrB and rpoD. Furthermore, three Iwate strains (H95, H101, and H104), isolated from seedlings of different cultivars grown in different years and having Ile at GyrA83, are probably in the same lineage, suggesting that OA-resistant bacteria might be transferred among different cultivars.     

Sensitivity of<Emphasis Type="Italic">Botrytis cinerea</Emphasis> from greenhouse vegetables to DMIs and fenhexamid

Two hundred isolates ofBotrytis cinerea were collected from greenhouse vegetables between 2003 and 2006 to determine their baseline sensitivity to triadimefone, penconazole, tebuconazole and fenhexamid. Mean values of 50% effective concentrations (EC₅₀) of inhibiting growth were 4.853±5.102, 0.41±0.215, 0.19±0.099 and 0.36±0.891 mgl ⁻¹, respectively (mean±SD). Individuals ofB. cinerea in the population differed by a factor (EC₅₀ of the least sensitive isolate/EC₅₀ of the most sensitive isolate) of 6625, 20, 603 and 1800, respectively. Naturally fenhexamid-resistant isolates were detected with an unexpected high frequency of 10% although the pathogen population had never been exposed to this fungicide. The resistance level (mean EC₅₀ of resistant isolates / mean EC₅₀ of sensitive isolates) was 19.5. These naturally resistant isolates also were resistantin vivo, and there was no significant difference in growth rate, conidial production or pathogenicity ability between naturally resistant and wild sensitive isolates. These results indicated that there was a potential risk of practical resistance if fenhexamid was applied alone. Negative cross-resistance was observed between fenhexamid and tebuconazole in 90% of the naturally resistant isolates. Moreover, an obvious synergism of the antifungal activity of fenhexamid by tebuconazole was demonstrated in some of the naturally fenhexamid-resistant isolates. http://www.phytoparasitica.org posting May 9, 2007.     

First record of the invasive mite<Emphasis Type="Italic">Tetranychus evansi</Emphasis> in Greece

The red spider miteTetranychus evansi (Acari: Tetranychidae) Baker and Pritchard was recorded for the first time in Greece, in the area of Tympaki (south-central Crete) onSolanum nigrum. T. evansi is a pest of crops of the family Solanaceae, which are grown extensively in Crete. The species identification was based on both morphological and molecular data. The second internal transcribed spacer was PCR amplified and sequenced in samples from Crete. Sequences were compared with the sequence ofT. evansi from Brazil and with the ITS2 sequences (retrieved from GenBank) of the two closely related tetranychid species most commonly found in Greece,Tetranychus turkestan andTetranychus urticae.     

Quantification of camalexin in several accessions of<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> following inductions with<Emphasis Type="Italic">Peronospora parasitica</Emphasis> and UV-B irradiation

Five accessions ofArabidopsis thaliana, Ws-3, Nd-1, Ler, Col-5 and Oy-0, were inoculated withPeronospora parasitica isolate Emoy2 and the accumulation of camalexin within infected tissues was measured. The variations in camalexin accumulation in various accessions ofA. thaliana induced by a specific (P. parasitica isolate Emoy2) and a non-specific elicitor (UV-B irradiation) were investigated. Phenotypic examination of Emoy2/Oy-0 revealed that susceptibility was characterized by extensive asexual sporulation of the pathogen, whereas early restriction of the pathogen in infected plant tissues, accompanied by chlorosis and necrosis — which are associated with the hypersensitive response — was observed in Nd-1, Ws-3 and Ler. Partial resistance detected in Col-0 was characterized by low to medium sporulation of the pathogen. Camalexin was monitored by high pressure liquid chromatography (HPLC) and found to accumulate during both compatible and incompatible interactions and also following treatment with the abiotic inducer, UV-B. Among the accessions tested, Ws-3 yielded significantly more camalexin than the other accessions, regardless of which inducers (biotic or abiotic) were used. There was no significant correlation between resistance and camalexin accumulation in theA. thaliana/P. parasitica interaction. The results suggest that there is genetic variation in camalexin biosynthesis among accessions ofA. thaliana, rather than variation in types of induction. http://www.phytoparasitica.org posting Dec. 16, 2002.     

Common resistance to different <Emphasis Type="Italic">Fusarium</Emphasis> spp. causing <Emphasis Type="Italic">Fusarium</Emphasis> head blight in wheat

Different sets of wheat genotypes were tested under field conditions by spraying inocula of isolates of seven Fusarium spp. and Microdochium nivale (formerly F. nivale) in the period 1998–2002. The severity of Fusarium head blight (FHB), Fusarium-damaged kernels (FDK), the yield reduction and the deoxynivalenol (DON) contamination were also measured to describe the nature of the resistance. The degrees of FHB severity of genotypes to F. graminearum, F. culmorum, F. avenaceum, F. sporotrichioides, F. poae, F.␣verticillioides, F. sambucinum and M. nivale were very similar, indicating that the resistance to F.␣graminearum was similar to that for other Fusarium spp. listed. This is an important message to breeders as the resistance relates not only to any particular isolate of F. graminearum, but similarly to isolates of other Fusarium spp. This holds true for all the parameters measured. The DON contamination refers only to DON-producers F. graminearum and F. culmorum. Highly significant correlations were found between FHB, FDK, yield loss and DON contamination. Resistance components such as resistance to kernel infection, resistance to DON and tolerance were identified in the more susceptible genotypes. As compared with western European genotypes which produced up to 700 mg kg⁻¹ DON, the Hungarian genotypes produced only 100 mg kg⁻¹ at a similar FDK level. This research demonstrates the importance of measuring both FDK and DON in the breeding and selection of resistant germplasm and cultivars.