Identification of Fusarium species causing basal rot of onion in East Azarbaijan province,Iran and evaluation of their virulence on onion bulbs and seedlings

One of the economically important diseases of onion is the basal rot caused by various Fusarium species. Identification of the pathogenic species prevalent in a region is indispensable for designing management strategies, especially to develop resistant cultivars. Eighty Fusarium isolates are obtained from red onion bulbs on infected fields of East Azarbaijan province. Inoculating the onion bulbs with 38 selective isolates indicated that 17 isolates were pathogenic on onion. According to the morphological and molecular characteristics, these isolates were identified as F. oxysporum, F. solani, F. proliferatum and F. redolens. This is the first report of F. redolens on onion in Iran. On the other hand, the virulence of each pathogenic isolate was evaluated on onion bulbs and seedlings. F. oxysporum which causes severe rot and damping-off was considered as a highly virulent species in both conditions. While, F. proliferatum was considered as the most destructive on onion bulbs. Rot ability of F. solani was not considerable, and only the 4S isolate caused pre- and post-emergence damping-off more than 50%. Finally, F. redolens with less pathogenicity on onion bulbs was identified as the most virulent isolate on onion seedlings, which was explanatory of its importance on farm.     

cDNA cloning of mRNAs induced in resistant barley during infection by Erysiphe graminis f.sp. Hordei

Summary Near-isogenic cultivars of Hordeum vulgare which differ for the Mlp gene for resistance to Erysiphe graminis f.sp. hordei were inoculated with race 3 of this pathogen and in vitro translation products of mRNA populations compared by 2-dimensional gel electrophoresis and fluorography. This revealed the presence of new mRNA species in infected leaves compared to non-inoculated controls. These new mRNA species were more abundant in resistant leaves than susceptible leaves. A cDNA library was prepared from poly(A)⁺RNA isolated from infected leaves carrying the Mlp gene for resistance (cvMlp). The library was screened by differential hybridization using [³²P]-labelled cDNA prepared from poly(A)⁺RNA of both control and infected leaves. Six cDNA clones showing greater hybridization to cDNA prepared from infected leaves were selected. These six cDNA clones hybridized to DNA isolated from barley leaves but not to DNA from conidia of the fungus. In Northern blot analysis of RNA from infected leaves the six cDNA clones each hybridized to mRNA species of different size. Translation products for three of the cDNA clones corresponded to infection-related translation products identified on 2-dimensional fluorograms. The cDNA clones were used to study the kinetics of host mRNA induction during infection of the near-isogenic cultivars of barley. The host mRNA species corresponding to the cDNA clones were induced prior to 24 h after inoculation during the primary penetration processes. In addition the mRNAs corresponding to four of the cDNA clones increased to greater amounts in cvMlp than in the near-isogenic susceptible cultivar (cvmlp) over a 2-d period following inoculation. These results suggest that the Mlp gene has a regulatory role in host gene expression resulting in enhanced expression of several host mRNA species following infection by the powdery mildew fungus.     

Influence of Exogenous Salicylic Acid on the Level of Phytohormones in Tissues of Phlox paniculata and Phlox setacea Leaves with Special Reference to Resistance against the Powdery Mildew Causative Agent Erysiphe cichoracearum DC. f. phlogis Jacz

We studied the effects of exogenous salicylic acid on the level of endogenous cytokinins and abscisic and salicylic acids in the tissues of leaves of phloxes contrasting in resistance against the powdery mildew causative agent: susceptible Phlox paniculata L. and resistant Ph. setacea L. Studies were carried out under the conditions of biotic stress. The initial level of salicylic and abscisic acids and cytokinins is the highest in the resistant phlox species. After treatment with salicylic species, the total level of cytokinins and endogenous salicylic acid increased in both species. When the treated phlox species were infected by the powdery mildew causative agent, the level of abscisic and salicylic acids increased in the susceptible Ph. paniculata, while that of cytokinins increased in the resistant Ph. setacea. The role of salicylic acid in the induction of plant defense reactions against phytopathogens is discussed.     

Identification of resistance to Peanut bud necrosis virus (PBNV) in wild Arachis germplasm

Eighty three wild Arachis germplasm accessions, belonging to 24 species of five sections and one natural hybrid derivative of a cross between the cultivated and a wild Arachis species, were evaluated along with a susceptible groundnut cultivar for resistance to Peanut bud necrosis virus (PBNV) in a replicated field trial at ICRISAT, Patancheru, India. Thirty days after sowing, the percentage of infected plants were recorded for all the accessions and subsequently young leaflets from all these accessions were tested for the presence of the virus by enzyme linked immunosorbent assay (ELISA). One accession each of A. benensis and A. cardenasii, and two accessions of A. villosa, in the section Arachis, two accessions of A. appressipila in the section Procumbentes, and one accession of A. triseminata under section Triseminatae were not infected by PBNV. These seven field‐resistant accessions were tested under glasshouse conditions for virus resistance by mechanical sap inoculations. One accession of A. cardenasii and two accessions of A. villosa did not show systemic infection. Similarly, in another glasshouse test, where 13 A. cardenasii accessions of section Arachis were evaluated, two accessions did not show systemic infection. In all these resistant accessions, the inoculated leaves showed infection, but the systemic leaves did not show the presence of virus in spite of repeated mechanical sap inoculations. So, the resistance in these accessions appears to be due to a block in systemic movement of the virus. To our knowledge this is the first report on the identification of resistance to PBNV in wild Arachis species. Since both A. cardenasii and A. villosa are the progenitors of cultivated groundnut and can be hybridised with the latter, the resistant accessions are being utilised in conventional breeding programmes to transfer PBNV resistance to widely adapted groundnut cultivars.     

The elimination of viruses from Narcissus tazetta cv. Grand Soleil d''Or, and rapid multiplication of virus-free clones

Arabis mosaic virus and narcissus degeneration virus were eliminated from Narcissus tazetta L. cv. Grand Soleil d'Or by meristem-tip culture. Cultures grew equally well in two liquid nutrient media, but tubes 25times75 mm size and temperature c. 12 ^oC were optimal for growth and survival. Virus-free bulbs grew more vigorously than infected bulbs, and gave more and larger flowers with a better colour. To increase the normal multiplication rate, either sector cuts were made in the basal plate, or bulbs were divided into chips (c. 1 g), before planting. Multiplication was greater by chip-cutting. Five virus-free bulbs were propagated to over 2000 in 8 years; theoretically, 20000000 bulbs should be produced in a further 5–6 years, sufficient to replant the Isles of Scilly with virus-free stock.     

Effects of Alternaria alternata f.sp. lycopersici toxins on pollen

Summary Effects of the phytotoxic compounds (AAL-toxins) isolated from cell-free culture filtrates of Alternaria alternata f.sp. lycopersici on in vitro pollen development were studied. AAL-toxins inhibited both germination and tube growth of pollen from several Lycopersicon genotypes. Pollen from susceptible genotypes, however, was more sensitive for AAL-toxins than pollen from resistant plants, while pollen of species not belonging to the host range of the fungus was not significantly affected by the tested toxin concentrations. AAL-toxins elicit symptoms in detached leaf bioassays indistinguishable from those observed on leaves of fungal infected tomato plants, and toxins play a major role in the pathogenesis. Apparently, pathogenesis-related processes and mechanisms involved in disease resistance are expressed in both vegetative and generative tissues. This overlap in gene expression between the sporophytic and gametophytic level of a plant may be advantageously utilized in plant breeding programmes. Pollen may be used to distinguish susceptible and resistant plants and to select for resistances and tolerances against phytotoxins and other selective agents.     

Resistenzinduktion gegen systemische Virusinfektionen durch Kulturfiltrate von Stachybotrys chartarum (Ehrenb. ex Link) Hughes

Induced resistance in systemic host-virus combinations by culture filtrates of Stachybotrys chartarum (Ehrenb. ex Link) Hughes Culture filtrates of the fungus Stachybotrys chartarum sprayed on systemic hosts decreased the development of symptoms of different elongated and isometric viruses. The degree of induced resistance depended on the host-virus system. An interval of three or five days between application of the filtrate and virus inoculation was sufficient to induce resistance. High inoculum concentration reduced the efficiency of induced resistance in cucumber against CMV. The content of CMV in inoculated andsystemically infected, induced resistant cucumber leaves was decreased. TMV inoculated leaves of induced resistant tobacco plants contained higher, systemically infected leaves lower virus amounts as comparable untreated control leaves. Reduced virus content and distribution in induced resistant plants obviously resulted from inhibition of multiplication and spread of viruses.     

Genetic dissection of resistance to root-knot nematodes Meloidogyne spp. in plum, peach, almond, and apricot from various segregating interspecific Prunus progenies

Sources of resistance in Prunus spp. exhibit different spectra to the root-knot nematodes (RKN) Meloidogyne incognita, Meloidogyne javanica and Meloidogyne floridensis. In this Prunus genus, two dominant genes, Ma with a complete spectrum from the heterozygous Myrobalan plums P.2175 and P.2980 (section Euprunus; subgenus Prunophora) and RMia with a more restricted spectrum from the peaches Nemared and Shalil (subgenus Amygdalus), have been identified. This study characterizes the resistance spectra of interspecific crosses involving (1) previous Myrobalan and peach sources, (2) two Alnem almonds (subgenus Amygdalus) resistant to M. javanica, and (3) the apricot A.3923, representing a species considered RKN-resistant (section Armeniaca; Prunophora). For both latter species, genetic data could be obtained through F1 crosses with genetically characterized Myrobalans that conferred their rooting ability for clonal multiplication of the hybrids and permitted their simultaneous evaluation to the three RKN. Crosses involving either Ma or RMia or both generated the expected resistance spectra. Nemared confirmed the species-specific resistance to M. incognita conferred by RMia. This rootstock, also previously considered resistant to M. javanica, was susceptible to the M. javanica isolate used, what illustrates an isolate-specific resistance to this species. Alnem accessions were shown homozygous resistant to M. javanica. In the progeny P.2980 × A.3923, Ma markers allowed to distinguish resistant individuals carrying that gene from resistant individuals lacking it. Distribution of non-Ma individuals in this cross suggested, in the apricot parent, (1) the absence of a major gene allelic to Ma and (2) the presence of a non RKN specific polygenic resistance.     

The seasonal carry-over of Botrytis tulipae (Lib.) Lind., the cause of tulip fire

Damage done by Botrytis tulipae developed in a variety of ways after planting naturally and artificially inoculated bulbs, the fungus sometimes rapidly invading developing shoots, preventing their emergence. In other instances (a) leaves emerged above ground, but not before being severely infected (the traditional ‘primaries’), (b) leaves emerged uninfected but the flower stalks were attacked at a later stage causing mechanical weakness (and hence frequent snapping), or (c) leaves and flower stalks remained uninfected, with the development of B. tulipae being restricted to its spread from mother to daughter bulbs, which also occurred in (a) and (b). More emerging shoots were infected when inoculated bulbs were grown at 10° and 15.5° than at 4 °C—an effect suggesting that greater numbers of foliar primaries would develop in mild winters. The underground transmission of B. tulipae indicates the need for eradicating infections in the bulb, the primary sources of this pathogen.     

Interactions of the Solanum spp. of the Etuberosa group and nine potato-infecting viruses and a viroid

All 26 accessions of Solanum brevidens, one accession of S. etuberosum and one accession of S. fernandezianum tested were all extremely resistant to potato leafroll virus (PLRV) and potato viruses Y (PVY) and A (PVA). S. brevidens and S. etuberosum were also resistant to Andean potato mottle virus (APMV) and moderately resistant to potato virus X (PVX), whereas S. fernandezianum was susceptible to these viruses. Additionally, S. brevidens was resistant to sap-inoculated potato viruses M (PVM) and S (PVS). All the Etuberosa accessions were susceptible by graft-inoculation to PVM, PVS, potato virus T (PVT) and Andean potato latent virus (APLV). Infections by the above mentioned viruses were symptomless in all of the Etuberosa spp. S. etuberosum and S. fernandezianum were infected by mechanical inoculation with potato spindle tuber viroid, S. etuberosum developing severe stunting and leaf-curl symptoms, but S. brevidens was infected only by graft-inoculation. The genes conferring resistance to PVY and PVX in S. brevidens and S. etuberosum appeared to be different from those currently utilised by plant breeders.     

The response of tomato seedling roots to infection by Verticillium albo-atrum or Fusarium oxysporum f. sp. lycopersici

The response of seedling roots of near-isogenic tomato varieties to infection by Verticillium albo-atrum or Fusarium oxysporum f. sp. lycopersici was investigated. Studies of the infection of seedling roots not artificially damaged indicated that there was an extra-vascular expression of resistance towards V. albo-atrum but not to F. oxysporum. Roots of resistant tomato seedlings infected by V. albo-atrum contained the fungus in the epidermis and outer cortex while susceptible roots became heavily colonised. Observations made by transmission electron microscopy showed that the fungus appeared to be abnormal in growth and appearance in the epidermal and cortical cells of resistant seedling roots but normal in susceptible roots. Two preformed antifungal terpenoids were detected in seedling roots in greater amounts in resistant that in susceptible varieties. The possible mechanisms of seedling root resistance to vascular wilts are discussed.     

Wyerone Acid Phytoalexin Synthesis and Peroxidase Activity as Markers for Resistance of Broad Beans to Chocolate Spot Disease

Infection of broad bean (Vicia faba L.) leaves with Botrytis fabae (Sard.) resulted in wyerone acid phytoalexin accumulation and increase in peroxidase activities in resistant and susceptible broad bean cultivars. Rapid wyerone acid accumulation was observed in leaves of resistant cultivars that reached levels greater than twofold of the susceptible cultivars. Following infection of broad bean cultivars, either resistant or susceptible to B. fabae, wyerone acid synthesis in resistant cultivars peaked at 5 days then declined, whereas in susceptible cultivars synthesis gradually decreased. While the ethanol‐extract of wyerone acid significantly reduced B. fabae spore germination with increased concentrations, the phytoalexin had no effect on in vitro B. fabae germ‐tube growth. Peroxidase activity in infected leaves of resistant was 10 times higher than the susceptible cultivars and eight times higher in uninfected leaves of the resistant than the susceptible cultivars. Peroxidase activity in infected leaves was greater than twofold in resistant cultivars and less than twofold in susceptible cultivars, when compared with uninfected leaves. The ratio of peroxidase activity in infected to uninfected leaves increased over time in susceptible cultivars but remained unchanged in resistant cultivars. Peroxidase activity in uninfected and infected leaves and wyerone acid biosynthesis in infected broad bean plants were successfully used to ascertain the resistance and susceptibility of four broad bean cultivars to B. fabae. Using wyerone acid synthesis and peroxidase activity as preliminary markers for resistance of broad bean to chocolate spot disease, caused by B. fabae, is suggested in this study.     

<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of <Emphasis Type="Italic">Hyacinthus orientalis</Emphasis> with thaumatin II gene to control fungal diseases

Transgenic plants of hyacinth (Hyacinthus orientalis L.) cvs. Edisson and Chine Pink have been obtained by Agrobacterium-mediated transformation. Leaf explants of the both hyacinth cultivars regenerated shoots on MS medium containing 2.2 μM BAP and 0.3 μM NAA at a frequency of 95%. A. tumefaciens strain CBE21 carrying binary vector pBIThau35 was used for transformation. Plasmid pBIThau35 has been produced by cloning preprothaumatin II cDNA into pBI121 instead of uidA gene. Inoculated leaf explants formed calli and shoots at high frequency on selective medium with 100 mg l⁻¹ kanamycin. Four hyacinth transgenic lines of cv. Chine Pink and one line of cv. Edisson have been selected on medium containing 200 mg l⁻¹ kanamycin. The insertion of thaumatin II gene into hyacinth genome has been confirmed by PCR-analysis. All transgenic plants expressed substantial amounts of thaumatin II (between 0.06 and 0.28% of the total soluble protein). Hyacinth transgenic lines were assayed for resistance to the pathogenic fungi Fusarium culmorum and Botrytis cinerea. There were no significant differences between nontransformed control and transgenic leaves of both cultivars. At the same time the bulbs of the transgenic line Н7401 cv. Chine Pink showed the higher level of resistance to B. cinerea, the bulbs of the transgenic line Н7404 were more resistant to F. culmorum. In both cases the signs of the fungal disease were developed more slowly. The resistance of the bulbs cv. Edisson line to these fungi was not changed. All transgenic hyacinth plant were successfully transferred to soil for further evaluation.     

Pathogenic analyses of fungus strains isolated from medicinal Fritillaria przewalskii Maxim. bulb rot

Bulb rot causes a great loss of rare perennial medicinal Fritillaria przewalskii Maxim., which is exacerbated with growth year and seriously constrains the plant productivity, but the pathogens responsible for the disease were still unknown. In this paper, we attempted to explore the potential pathogens leading to bulb rotting and their occurrence patterns in artificial domesticated F. przewalskii. Fungus strains were isolated from the bulb rot spot of the 3‐ to 5‐year‐old diseased F. przewalskii plants by tissue separation, further assayed for pathogenicity according to Koch's law and finally identified by both morphological and molecular methods. Seven pathogenic strains (F1‐F7) were detected in 5‐year‐old rot bulbs, six (F1‐F6) in 4‐year‐old rot bulbs and four (F1, F2, F5, F6) in 3‐year‐old rot bulbs. All of the strains were able to infect bulbs by stabbing and some exhibited varying levels of aggressiveness. Relative to the non‐stabbing controls, the bulbs stab‐inoculated with F5, F2, F7, F4, F1, F6, and F3 showed 76.65%, 75.15%, 71.44%, 40.37%, 39.09%, 36.87%, and 34.93% rot after 8 days, respectively. Phylogenetic analysis revealed that these seven strains were clustered into Bionectria ochroleuca (F1, F3, F4), Fusarium oxysporum (F2, F7), Fusarium tricinctum (F5), and Clonostachys rosea (F6). The two species of Fusarium had the strongest pathogenicity, followed by Bionectria ochroleuca and Clonostachys rosea. Although leading to low bulb rot incidence by stab inoculation, F1 showed the highest isolation rate (48.9%) among all strains. Thus, the edible and medicinal bulbs of F. przewalskii are susceptible to synergetic contamination by these seven pathogens at some point after their third year of growth, which has contributed to the species endangered status, with the two strains of Fusarium being the predominant pathogens. To our knowledge, this is the first report on the seven strains of four fungal species causing F. przewalskii bulb rot in China.     

3种百合鳞茎中多酚类物质的抗氧化活性分析

以野生百合渥丹、山丹和传统食用的兰州百合为研究对象,对其鳞茎中多酚类物质、11种单体酚的含量及抗氧化活性(ABTS自由基、超氧阴离子、羟自由基的清除能力,铜离子还原能力以及抑制脂质过氧化活性)进行了分析。结果表明:两种野生百合鳞茎中的多酚类物质含量及抗氧化活性均显著高于兰州百合。3种百合鳞茎中单体酚的种类也有所不同,但均含有没食子酸、矢车菊素-3-芸香糖苷、儿茶素、表儿茶素、杨梅酮、芦丁、对香豆酸、山奈酚。相关性分析显示,除对羟自由基的清除力外,各酚类物质总量与不同抗氧化指标之间呈显著正相关关系。试验结果认为,野生百合鳞茎可作为天然抗氧化资源应用于食品和医药业,具有一定的开发应用前景。     

Genetic variation in resistance to Fusarium oxysporum f.sp. lilii in the genus Lilium

Genetic variation in Fusarium resistance in 82 Lilium genotypes was studied. A high level of resistance was found in the Asiatic hybrids (section Sinomartagon) and to a lesser extent in cultivars of L. longiflorum (section Leucolirion). The Oriental hybrids (section Archelirion) showed only moderate resistance. In the sections Sinomartagon, Leucolirion and Martagon species were detected with high levels of resistance. An accession of L. dauricum (section Sinomartagon) was the most resistant source. Possibilities for introgression of Fusarium resistance into cultivars by interspecific hybridisation, using the resistance found in Lilium genotypes, are discussed.     

Resistance to three thrips species in Capsicum spp. depends on site conditions and geographic regions

Capsicum species are commercially grown for pepper production. This crop suffers severely from thrips damage and the identification of natural sources of thrips resistance is essential for the development of resistant cultivars. It is unclear whether resistance to Frankliniella occidentalis as assessed in a specific environment holds under different conditions. Additionally, other thrips species may respond differently to the plant genotypes. Screening for robust and general resistance to thrips encompasses testing different Capsicum accessions under various conditions and with different thrips species. We screened 11 Capsicum accessions (C. annuum and C. chinense) for resistance to F. occidentalis at three different locations in the Netherlands. Next, the same 11 accessions were screened for resistance to Thrips palmi and Scirtothrips dorsalis at two locations in Asia. This resulted in a unique analysis of thrips resistance in Capsicum at five different locations around the world. Finally, all accessions were also screened for resistance to F. occidentalis in the Netherlands using a leaf disc choice assay, allowing direct comparison of whole plant and leaf disc assays. Resistance to F. occidentalis was only partially consistent among the three sites in the Netherlands. The most susceptible accessions were consistently susceptible, but which accession was the most resistant differed among sites. In Asia, one C. chinense accession was particularly resistant to S. dorsalis and T. palmi, but this was not the most resistant accession to F. occidentalis. Overall, resistance to F. occidentalis correlated with S. dorsalis but not with T. palmi resistance in the C. annuum accessions. Damage inflicted on leaf discs reflected damage on the whole plant level. Our study showed that identifying broad spectrum resistance to thrips in Capsicum may prove to be challenging. Breeding programmes should focus on developing cultivars suitable for growing in defined geographic regions with specific thrips species and abiotic conditions.     

Comparative study of antioxidant capacity in organs of different Allium species

Cultivated and wild Allium species were investigated in order to compare the antioxidant capacity of their leaves and bulbs. Leaf and bulb anti-oxidative enzymes and scavenger activities, along with quantities of non-enzymic antioxidants, malonyl-dialdehyde and OH radicals were determined. Results obtained suggest that leaves possess higher anti-oxidant and scavenging activities than bulbs in the majority of cultivated and wild Allium species examined. Cultivation of some wild species such as A. flavum L., A. schoenoprasum L. and A. ursinum L. could be conducted in the future in order to produce Allium species with high antioxidant capacity in leaves and bulbs.     

Resistance of roses to pathotypes of Diplocarpon rosae

Colonies of Diplocarpon rosae derived from single conidia were isolated on malt extract agar, multiplied (at 23°C) and stored (at ?20°C) on surface‐sterilised leaf discs of a universally susceptible rose, ‘Frensham’. The resistance of 16 species and cultivars of Rosa to different isolates of D. rosae was assessed using surface‐sterilised leaf discs. Four pathotypes of D. rosae were distinguished on the basis of host range. One species and one hybrid were resistant to all pathotypes. Two species and two cultivars were susceptible to all pathotypes. Four species and six cultivars were interpreted as having vertical resistance because they were strongly resistant to some but not all pathotypes. Only species and hybrids of the section Cinnamomeae were resistant to the pathotype identified as CW1 whereas only roses of other origins were resistant to the pathotype DA2.     

Tuber production,dormancy and resistance against Phthorimaea operculella (Zeller) in wild potato species

The diversification of resistant potato varieties at a landscape level could slow adaptation by Phthorimaea operculella to potato resistance and promote sustainable crop protection. In this study, we assessed wild potato species as novel sources of foliage and tuber resistance against P. operculella. Tuber resistance was quantified for 136 and foliage resistance for 54 potato accessions representing 14 and nine potato species, respectively. Several accessions were highly resistant to moth damage in tubers and/or foliage. In particular, Solanum chiquidenum and Solanum sandemanii were highly resistant to damage in tubers. Several accessions of Solanum multiinterruptum and a small number of accessions of Solanum bukasovii, Solanum berthaultii, Solanum sparsipilum and Solanum wittmackii also had highly resistant tubers. Larval survival on foliage of S. bukasovii and S. chiquidenum was generally low. New resistance sources are listed, and insect performance on the plants is described with possible resistance mechanisms. The study also examined potential trade‐offs associated with resistance. Tuber resistance was negatively correlated with the number and weight of tubers produced per plant, but positively correlated with the length of dormancy across accessions, indicating that, although long dormancy is not a prerequisite for resistance, species and accessions with extended dormancy will have more resistant tubers. Tuber and foliage resistance were generally positively correlated across all accessions; however, among accessions from within a potato species, there were negative (S. berthaultii), positive (S. chiquidenum) and non‐significant (S. bukasovii) relations. These results indicate that, besides identifying novel resistance sources, an improved understanding of the mechanisms and inherent trade‐offs associated with tuber and foliage resistance will improve the efficiency of potato breeding programmes aimed at enhancing resistance against P. operculella.