Comparative transcriptome analysis reveals distinct responsive biological processes in radish genotypes contrasting for Plasmodiophora brassicae interaction.

Plasmodiophora brassicae is a protozoan pathogen that causes clubroot disease, which is one of the most destructive diseases for Brassica crops, including radish. However, little is known about the molecular mechanism of clubroot resistance in radish. In this study, we performed a comparative transcriptome analysis between resistant and susceptible radish inoculated with P. brassicae. More differentially expressed genes (DEGs) were identified at 28 days after inoculation (DAI) compared to 7 DAI in both genotypes. Gene ontology (GO) and KEGG enrichment indicated that stress/defense response, secondary metabolic biosynthesis, hormone metabolic process, and cell periphery are directly involved in the defense response process. Further analysis of the transcriptome revealed that effector-triggered immunity (ETI) plays key roles in the defense response. The plant hormones jasmonic acid (JA), ethylene (ET), and abscisic acid (ABA) related genes are activated in clubroot defense in the resistant line. Auxin (AUX) hormone related genes are activated in the developing galls of susceptible radish. Our study provides a global transcriptional overview for clubroot development for insights into the P. brassicae defense mechanisms in radish.

'Bottom-up' effects in a tritrophic plant-aphid-parasitoid system: Why being the perfect host can have its disadvantages.

In this study the host plant genotype effect on cabbage aphid, Brevicoryne brassicae (L.)(Hemiptera: Aphididae) preference and performance, the effect of aphid genotype on parasitoids performance, as well as the indirect effects of plant genotypes on aphid parasitoid performance, were tested using different population samples of the aphid and its primary endoparasitoid wasp, Diaeretiella rapae (M'Intosh) (Hymenoptera: Braconidae). Experiments were run as fully-factorial randomized block design in a greenhouse. Accordingly, host plant cultivar had significant effects on the total number of aphids and aphid-load whilst the fitness of the aphid genotypes were also influenced by plant cultivar. The effect of parasitism on cabbage aphids was significantly different between plant cultivars. Overall, the results revealed that cabbage aphid is under different selective pressures arising from both higher (parasitoid) and lower (host plant cultivar) trophic levels. The host plant cultivar had a significant effect on both aphid fitness and parasitism rate on particular aphid genotypes. This indicates that host-plant-adapted aphid species can create much context-dependency in the nature and strength of 'fitness benefits parasitism', which may in turn alter the costs and benefits of host specialization.

Risk factors for human fascioliasis in schoolchildren in Baños del Inca, Cajamarca, Peru.

Background: The aim of the investigation was to determine the risk factors for human fascioliasis in schoolchildren in five localities of the Baños del Inca district in Cajamarca, Peru. Secondarily, the prevalence of infection among this population was also studied. Methods: A questionnaire was applied to 270 schoolchildren from 6-12 years of age and to their parents with the aim of collecting information related to risk factors predisposing the children to Fasciola hepatica infection. Faecal samples from all the children were tested for F. hepatica using the modified rapid sedimentation method of Lumbreras and the technique of Kato-Katz for egg counts. Results: Risk factors were identified as follows-raising cattle, consumption of radishes and chewing grass. The prevalence of F. hepatica in Baños del Inca was 6.30%; there was no significant difference by sex or age. Conclusion: Risk factors associated with this parasitosis in children in this area of Cajamarca were the raising of cattle, the consumption of radish and the habit of chewing grass. The prevalence results in this district suggest a mesoendemic level of infection, with local variations between meso- and hyper-endemic levels.

Assessments of iodoindoles and abamectin as inducers of methuosis in pinewood nematode, Bursaphelenchus xylophilus.

Bursaphelenchus xylophilus is a quarantined migratory endoparasite known to cause severe economic losses in pine forest ecosystems. The study presents the nematicidal effects of halogenated indoles on B. xylophilus and their action mechanisms. 5-Iodoindole and abamectin (positive control) at low concentration (10 µg/mL) presented similar and high nematicidal activities against B. xylophilus. 5-Iodoindole diminished fecundity, reproductive activities, embryonic and juvenile lethality and locomotor behaviors. Molecular interactions of ligands with invertebrate-specific glutamate gated chloride channel receptor reinforced the notion that 5-iodoindole, like abamectin, rigidly binds to the active sites of the receptor. 5-Iodoindole also induced diverse phenotypic deformities in nematodes including abnormal organ disruption/shrinkage and increased vacuolization. These findings suggest the prospective role of vacuoles in nematode death by methuosis. Importantly, 5-iodoindole was nontoxic to two plants, Brassica oleracea and Raphanus raphanistrum. Henceforth, the study warrants the application of iodoindoles in ecological environments to control the devastating pine destruction by B. xylophilus.

Pollinator-mediated interactions in experimental arrays vary with neighbor identity.

PREMISE OF THE STUDY: Local ecological conditions influence the impact of species interactions on evolution and community structure. We investigated whether pollinator-mediated interactions between coflowering plants vary with plant density, coflowering neighbor identity, and flowering season. METHODS: We conducted a field experiment in which flowering time and floral neighborhood were manipulated in a factorial design. Early- and late-flowering Clarkia unguiculata plants were placed into arrays with C. biloba neighbors, noncongeneric neighbors, additional conspecific plants, or no additional plants as a density control. We compared whole-plant pollen limitation of seed set, pollinator behavior, and pollen deposition among treatments. KEY RESULTS: Interactions mediated by shared pollinators depended on the identity of the neighbor and possibly changed through time, although flowering-season comparisons were compromised by low early-season plant survival. Interactions with conspecific neighbors were likely competitive late in the season. Interactions with C. biloba appeared to involve facilitation or neutral interactions. Interactions with noncongeners were more consistently competitive. The community composition of pollinators varied among treatment combinations. CONCLUSIONS: Pollinator-mediated interactions involved competition and likely facilitation, depending on coflowering neighbor. Experimental manipulation helped to reveal context-dependent variation in indirect biotic interactions.

Interplay between parasitism and host ontogenic resistance in the epidemiology of the soil-borne plant pathogen Rhizoctonia solani.

Spread of soil-borne fungal plant pathogens is mainly driven by the amount of resources the pathogen is able to capture and exploit should it behave either as a saprotroph or a parasite. Despite their importance in understanding the fungal spread in agricultural ecosystems, experimental data related to exploitation of infected host plants by the pathogen remain scarce. Using Rhizoctonia solani / Raphanus sativus as a model pathosystem, we have obtained evidence on the link between ontogenic resistance of a tuberizing host and (i) its susceptibility to the pathogen and (ii) after infection, the ability of the fungus to spread in soil. Based on a highly replicable experimental system, we first show that infection success strongly depends on the host phenological stage. The nature of the disease symptoms abruptly changes depending on whether infection occurred before or after host tuberization, switching from damping-off to necrosis respectively. Our investigations also demonstrate that fungal spread in soil still depends on the host phenological stage at the moment of infection. High, medium, or low spread occurred when infection was respectively before, during, or after the tuberization process. Implications for crop protection are discussed.

USE OF GREEN MANURE CROPS AND SUGAR BEET VARIETIES TO CONTROL HETERODERA BETAE.

Although it is less studied than the white beet cyst nematode (Heterodera schachtii), the yellow beet cyst nematode (H. betae) has been found in many countries in Europe. For example in The Netherlands, France and Spain. H. betae causes yield losses on sandy soils. A high infestation can result in loss of complete plants. In The Netherlands, this nematode is especially found in the south eastern and north eastern part, where it occurs on 18% and 5% of the fields, respectively. From a project of the Dutch Sugar beet Research Institute IRS (SUSY) on factors explaining differences in sugar yield, this nematode was one of the most important factors reducing sugar yields on sandy soils. Until 2008, the only way to control H. betae was by reducing the number of host crops in the crop rotation. Host crops are crops belonging to the families of Cruciferae, Chenopodiaceae, Polygonaceae, Caryophyllaceae and Leguminosea. In order to find more control measures, research was done to investigate the host status of different green manure crops and the resistance and tolerance of different sugar beet varieties to H. betae. White mustard (Sinapis alba) and oil seed radish (Raphanus sativus spp. oleiferus) varieties resistant to H. schachtii were investigated for their resistance against H. betae. A climate room trial and a field trial with white mustard and oil seed radish were conducted in 2007 and 2008, respectively. Results show that H. betae could multiply on susceptible white mustard and susceptible oil seed radish, but not on the H. schachtii resistant varieties. In climate room trials in 2009, 2010 and 2011 and field trials in 2010, 2011 and 2012, the effect of different sugar beet varieties on the multiplication of H. betae and the effect of H. betae on yield at different infestation levels was investigated. Sugar beet varieties with resistance genes to H. schachtii (from Beta procumbens or B. maritima) were selected. Varieties with resistance genes from these sources were not totally resistant to H. betae, but limited the multiplication of this nematode in comparison with susceptible varieties considerably. Only the varieties with resistance genes from B. maritima gave higher yields in comparison with susceptible varieties. Growing these varieties was already profitable from very light infestation levels (75 eggs and larvae/100 ml soil) of H. betae. Therefore, resistant cruciferous green manure crops and resistant and tolerant sugar beet varieties are good tools for growers to control H. betae.

[Interrelations of infusoria with Azotobacter and their influence on plants].

Symbiotic coexistence of infusoria Colpoda steinii with bacteria of Azotobacter genus has been investigated. It is shown that when infusoria are incubated during 3 days with the cells of A. vinelandii IMV D-7076 selected in the logarithmic phase of growth, the number of colpods increased 19 times, and with A. chrooccum 20--only 1.8 times. After 6 days of incubation with bacteria selected in the phase of stationary growth the number of infusoria increased with A. vinelandii 10 times, and with A. chrooccum 20 - 9.2 times. Treatment of seeds by the bacterial mix of A. vinelandii and C. stenii stimulates their germination, growth of roots and sprouts at early stages of plants development as compared with the use of cultures of monobacteria. It is evident that infusoria Colpoda steinii as well as the bacteria of Azotobacter genus secrete biologically active substances which accelerate growth and development of plants.

Insecticide resistance mechanisms in the green peach aphid Myzus persicae (Hemiptera: Aphididae) II: Costs and benefits.

BACKGROUND: Among herbivorous insects that have exploited agro-ecosystems, the peach-potato aphid, Myzus persicae, is recognized as one of the most important agricultural pests worldwide. Uses over 400 plant species and has evolved different insecticides resistance mechanisms. As M. persicae feeds upon a huge diversity of hosts, it has been exposed to a wide variety of plant allelochemicals, which probably have promoted a wide range of detoxification systems. METHODOLOGY/PRINCIPAL FINDINGS: In this work we (i) evaluated whether insecticide resistance mutations (IRM) in M. persicae can give an advantage in terms of reproductive fitness when aphids face two hosts, pepper (Capsicum annuum) a suitable host and radish (Raphanus sativus) the unfavorable host and (ii) examined the transcriptional expression of six genes that are known to be up-regulated in response to insecticides. Our results show a significant interaction between host and IRM on the intrinsic rate of increase (r(m)). Susceptible genotypes (not carrying insensitivity mutations) had a higher r(m) on pepper, and the transcriptional levels of five genes increased on radish. The r(m) relationship was reversed on the unfavorable host; genotypes with multiple IRM exhibited higher r(m), without altering the transcriptional levels of the studied genes. Genotypes with one IRM kept a similar r(m) on both hosts, but they increased the transcriptional levels of two genes. CONCLUSIONS/SIGNIFICANCE: Although we have studied only nine genotypes, overall our results are in agreement with the general idea that allelochemical detoxification systems could constitute a pre-adaptation for the development of insecticide resistance. Genotypes carrying IRM exhibited a higher r(m) than susceptible genotypes on radish, the more unfavorable host. Susceptible genotypes should be able to tolerate the defended host by up-regulating some metabolic genes that are also responding to insecticides. Hence, our results suggest that the trade-off among resistance mechanisms might be quite complex, with a multiplicity of costs and benefits depending on the environment.

[Relationship of bacteria of Bacillus genus with ciliate Colpoda steinii and their impact on germination of plant seeds].

Features of symbiotic coexistence of bacteria of the genus Bacillus with ciliates Colpoda steinii have been studied. In their mutual cultivation during 10 days the number of bacteria B. subtilis IMV V-7023 was reduced 4.4 times, B. pumilus 3 - 3.4 times, B. megaterium 12 - 2.5 times. In the mixed culture with B. pumilus 3 the number of the ciliates increased gradualluy while under availability of the other two bacilli strains the number of protozoan increased in the first two days, after that their amount decreased. Treatment of some plants seeds by suspension of B. subtilis IMV V-7023 with the protozoan increased their germination and stimulated the growth of plants at the early stages of development.

Residual toxicity and sublethal effects of chlorantraniliprole on Plutella xylostella (lepidoptera: plutellidae).

BACKGROUND: The diamondback moth (DBM), Plutella xylostella (L.), is the most important pest of cruciferous vegetables in the world. Chlorantraniliprole is a novel anthranilic diamide insecticide registered for the control of lepidopteran pests. The dose response, residual toxicity and sublethal effects of chlorantraniliprole applied for 48 h at LC10 (0.02 mg L(-1) ) and LC25 (0.06 mg L(-1) ) on P. xylostella were investigated. RESULTS: Leaf-dip bioassays showed that chlorantraniliprole had a high level of toxicity against larvae of P. xylostella, and the 48 h LC50 values were 0.23 and 0.25 mg L(-1) for a susceptible and field strain respectively. Chlorantraniliprole also had a long-lasting effect when the larvae were exposed to chlorantraniliprole field sprayed on radish seedlings. Sublethal effects of chlorantraniliprole were indicated by reduced pupation, pupal weight and adult emergence rates. There was also an increase in the duration of female preoviposition period, decreased fecundity and egg hatch and decreased survival rates of the offspring. The mean values of the net reproductive rate (R0), intrinsic rate of increase (r(m)), finite rate of increase (λ) were significantly lower in the treatment than in control groups. CONCLUSIONS: These results indicate that chlorantraniliprole is effective against P. xylostella. The sublethal concentrations of chlorantraniliprole may reduce the population growth of P. xylostella by decreasing its survival and reproduction, and by delaying its development.

Spatial variation in foliar chemicals within radish (Raphanus sativus) plants and their effects on performance of Spodoptera litura.

Foliar chemicals are variable within a plant and this may affect herbivore feeding preference. This study was carried out to quantify concentrations of primary (nitrogen, water, and total nonstructural carbohydrates) and secondary substances (sinigrin) in young and old leaves of Raphanus sativus L. and to evaluate performance and survival of a generalist herbivore Spodoptera litura F. feeding on them. Forty to 50-d-old R. sativus plants were used in both foliar chemical analysis and insect performance bioassays. Leaves located on the third to the sixth node from the base of the plant were defined as old leaves and the remaining leaves (from seventh node to the plant apex) of the plant were referred as young leaves in this study. All foliar chemicals except water differed significantly between young and old leaves. Moreover, young leaves were more nutritious but much more defended, based on sinigrin content, against S. litura than old leaves. Performance and survival of S. litura were reduced on young leaves as compared with old leaves. Male and female larval duration only differed significantly on young leaves. Female larval development time was longer than male development time on young leaves, but not on older leaves. Therefore, this study revealed that defenses in young leaves have differential effects upon male and female S. litura.

QTL mapping of clubroot resistance in radish (Raphanus sativus L.).

A QTL analysis for clubroot resistance (CR) of radish was performed using an F(2) population derived from a crossing of a CR Japanese radish and a clubroot-susceptible (CS) Chinese radish. F(3) plants obtained by selfing of F(2) plants were used for the CR tests. The potted seedlings were inoculated and the symptom was evaluated 6 weeks thereafter. The mean disease indexes of the F(3) plants were used for the phenotype of the F(2). The results of two CR tests were analyzed for the presence of QTL. A linkage map was constructed using AFLP and SSR markers; it spanned 554 cM and contained 18 linkage groups. A CR locus was observed in the top region of linkage group 1 in two tests. Therefore, the present results suggest that a large part of radish CR is controlled by a single gene or closely linked genes in this radish population, although minor effects of other genomic areas cannot be ruled out. The CR locus was named Crs1. Markers linked to Crs1 showed sequence homology to the genomic region of the top of chromosome 3 of Arabidopsis, as in the case of Crr3, a CR locus in Brassica rapa. These markers should be useful for breeding CR cultivars of radish. As Japanese radishes are known to be highly resistant or immune to clubroot, these markers may also be useful in the introgression of this CR gene to Brassica crops.

Challenges to grow oilseed rape Brassica napus in sugar beet rotations.

The study was carried out in 1989-1991 and repeated in 2003-2006 to compare life cycle and dynamics of Heterodera schachtii Schm. on sugar beet, oilseed rape, fodder radish and to work out recommendations on how to decrease the risk of yield reduction while it grows in sugar-beet rotations. Research was carried out in plot experiment in natural conditions. Nematode community on rape, fodder radish and sugar beet was analyzed. Data of nematode community showed that composition of nematode species was very similar. Heterodera shachtii were dominated species with rape and sugar beet. All tested Brassica crops are susceptible to H. schachtii. However there is significant difference in population dynamics. The highest total number of brown cysts, eggs and juveniles of all ages was observed in winter rape. H.schachtii developed two generations on sugar beet and one generation on mustard. The voluntary seed germination after harvest contributes to increasing H. schachtii population. Therefore it is necessary to destroy oilseed rape voluntary chemically or physically. This operation should be done in about 2-4 weeks. The exact time can be calculated using the temperature- based model. Growing regular fodder radish and mustard as the trap crops can significantly reduce population of H. schachtii. The time of sowing is not earlier than August 20th. While estimating the time of destruction of trap crops it should be taken into consideration that H. schachtii can complete life cycle without foliage.

Niche partitioning increases resource exploitation by diverse communities.

Classical ecological theory suggests that the coexistence of consumer species is fostered by resource-use differences, leading to greater resource use in communities with more species. However, explicit empirical support for this idea is lacking, because resource use by species is generally confounded with other species-specific attributes. We overcame this obstacle by co-opting behavioral plasticity in food choice among a group of animal consumers, allowing us to manipulate patterns of resource use while controlling for the effects of species identity and diversity. Within an aphid-parasitoid-radish community, we created a fully factorial manipulation of consumer resource-use breadth (specialist versus generalist) and species diversity (one versus three species) and found that resource exploitation improved with greater specialist, but not generalist, diversity. Therefore, resource partitioning, and not diversity per se, fostered greater overall resource consumption in our multispecies consumer communities.

Competitive exclusion of a worldwide invasive pest by a native. Quantifying competition between two phytophagous insects on two host plant species.

1. High competitive ability is believed to be an important characteristic of invasive species. Many animal studies have compared the competitive ability of invasive species with a native species that is being displaced, but few have looked at systems where an invasive species has failed to establish itself. These types of studies are important to determine if competition is relevant not only to invading species but also to the biotic resistance of a community. 2. The thrips species F. occidentalis is a highly invasive pest that has spread from its original range (the western states of the USA) to a worldwide distribution. Despite this, F. occidentalis is largely absent or occurs in low numbers in the eastern states of the USA, where the native F. tritici dominates. It is possible that F. tritici is competitively excluding F. occidentalis from this region. 3. Larval competition between these two thrips species was tested on two known plant hosts, Capsicum annuum (a crop plant), and Raphanus raphanistrum (an invasive weed), using a response surface design with number of larvae surviving as the response variable. The response surface design allowed competition models to be fit to data using maximum likelihood estimation, thus generating quantitative values for interspecific competition. 4. On both plant hosts, the native F. tritici did not experience significant interspecific competition from the invasive F. occidentalis. In contrast, F. occidentalis did experience significant interspecific competition from F. tritici. Competition from F. tritici larvae on F. occidentalis larvae was estimated to be 1.72 times (on C. annuum) and 1.76 times (on R. raphanistrum) the effect of intraspecific competition. The invasive F. occidentalis appears to be competitively excluded by the native F. tritici. 5. This study confirms the importance of competition in the biotic resistance of a community and is one of the few animal studies to not only test for competition in an apparently resistant ecosystem but also to quantify the level of interspecific competition between two animal species.

Phaedon cochleariae (F.) performance on different crucifer varieties with different glucosinolate profiles.

The mustard leaf beetle, Phaedon cochleariae (F.) (Coleoptera: Chrysomelidae), is a serious insect pest of cruciferous crops, known especially in Europe. Feeding performances of P. cochleariae on six varieties of crucifer crops (Sinapis alba, Flata and Litember; Raphanus sativus, Münchener Bier and Runder Schwarzer Winter; and Brassica chinensis, Joi Choi and Black Behi) was investigated. The larval performance, measured by weight increase within seven days, was significantly different among six cultivars. The highest larval weight increase observed was on the B. chinensis cultivars with the lowest GS contents, followed by R. sativus and S. alba cultivars. Furthermore, a better larval performance co-insisted with the presence of indolyl and aliphatic GS in cultivars like B. chinensis and R. sativus and was poor on mustard cultivars with aromatic GS. Similar to the weight increase observation, the oviposition performance of P. cochleariae adult beetle was also investigated on three varieties: S. alba: Litember, R. sativus: Muinchener Bier, and B. chinensis: Joi Choi. The female P. cochleoriae laid significantly different numbers of eggs within three days on the different cultivars of crucifers. The highest number of eggs was laid on the B. chinensis cultivar Joi Choi, followed by the radish and mustard cultivars Muinchener Bier and Litember, respectively. Differential oviposition behaviour of P. cochleariae on the different varieties might be explained by their different GS profiles and the dominating group of GS. Indolyl GS, which are abundant in B. chinensis, may have a more stimulatory effect on the oviposition of P. cochleariae than aromatic and aliphatic GS.

Evaluation of entomopathogenic nematode, Steinernema feltiae against field population of mustard sawfly, Athalia lugens proxima (Klug) on radish.

Mustard sawfly, A. lugens proxima, was found to be highly susceptible to entomopathogenic nematode, S. feltiae under laboratory condition. Application of three different doses of S. feltiae, viz. 1.1 x 10(3), 1.1 x 10(4) and 1.1 x 10(5) infective juveniles/ml, at weekly intervals, significantly reduced the field population of mustard sawfly on radish. The mean larval population of A. lugens proxima in all doses of nematode treated plots ranged from 0.42 to 0.48 larvae per plant as against 2.95 larvae / plant in untreated control plots. Similarly, the yield of radish in all the nematode treated plots was significantly higher by way of recording 2.80 to 2.87 tons/ha as compared to 1.63 tons/ha in the case of control.