Multiple species-specific controls of root-feeding nematodes in natural soils

One of the major limitations to enhance sustainability of crop production systems is the inability to control root-feeding nematodes without using chemical biocides. In soils under wild vegetation, however, root-feeding nematodes affect plant performance and plant community composition varying from substantially to insignificantly. Previous studies in natural ecosystems have already shown that mutualistic symbionts, such as arbuscular mycorrhizal fungi and endophytes, may influence plant exposure to root-feeding nematodes. In order to learn more from natural systems, we examined nematode control in the root zone of a wild coastal foredune grass by microorganisms, other nematodes and microarthropods. We cultured all eight root-feeding nematode species that occur in the root zone of marram grass (Ammophila arenaria) in coastal foredunes of the Netherlands. Then, in an indoor growth experiment we exposed each nematode species to the potential natural antagonists collected from the same dune soil. Most of the eight dominant root-feeding nematode species could be controlled to some extent by more than one group of soil organisms added. The effectiveness of control varied among nematode species, which seemed to be controlled in a species-specific way. We conclude that in a natural soil the effectiveness of control by microorganisms, other nematodes or microarthropods varies among root-feeding nematode species. Most are controlled, at least to some extent, by soil microbes. However, some root-feeding nematode species are controlled only by microarthropods. Our results strongly suggest that sustainable agriculture will benefit from using a range of biological control mechanisms when controlling root-feeding nematodes, rather than relying on single control agents. Our suggestion also implies that conserving soil biodiversity is crucial in order to enhance the reliability of biological crop protection against soil-borne pests and diseases.     

Local variation in belowground multitrophic interactions

A growing number of studies point at the involvement of root herbivores in influencing plant performance, community composition and succession. However, little is known about the factors that control root herbivore abundance and the role of local variation in the effectiveness of these factors. Here, we performed a full factorial experiment with plants, root-feeding nematodes and rhizosphere microbial communities from two dune sites, to test the hypothesis that the outcome of belowground multitrophic interactions depends on local differences between the interacting organisms. The organisms included the marram grass Ammophila arenaria, the cyst nematode Heterodera arenaria, microbial plant pathogens and natural enemies of the nematodes from two coastal foredune systems, one in The Netherlands and one in Wales. The two plant populations differed at the molecular and phenotypic level, and the microbial communities from the two dune sites differed in the composition of the dominant soil fungi but not of the dominant bacteria. Plants were negatively affected by the rhizosphere microorganisms from one of the sites. Nevertheless, nematode performance was not affected by the origin of both the host plants and the microbial communities. The reproductive output of the cyst nematode depended on the presence of microorganisms, as well as on inter-population variability in the response of the nematode to these natural enemies. In the absence of microorganisms, the two nematode populations differed in the number and size of the produced cysts, although maternal effects cannot be excluded. Inter-population differences in the host plant were a secondary factor in the nematode-microorganisms interactions, and did not influence bottom-up control of the cyst nematodes. Our results did not reveal strong signals of coevolution in belowground multitrophic interactions of plants, cyst nematodes and soil microbial communities. We conclude that the interactions between the studied organisms do not necessarily depend on their local vs. non-local origin. Nevertheless, we were able to show that local variation in soil organism community composition can be an important factor in determining the outcome of interactions in belowground multitrophic systems.     

Interactions between root-feeding nematodes depend on plant species identity

Root-feeding nematodes play an important role in structuring the composition of natural plant communities. Little is known about the role of intra- and interspecific interactions in determining the abundance of root-feeding nematodes in natural ecosystems. We examined interactions between two ectoparasitic root-feeding nematodes on two plant species: a good host plant for both nematode species and a good host for only one of the nematodes. We tested the hypothesis that root herbivore competitiveness depends on host suitability and related the experimental results to field data. In a greenhouse, we added different densities of the nematodes Tylenchorhynchus microphasmis and Tylenchorhynchus ventralis to Ammophila arenaria (the good host for both) and Carex arenaria (a good host for T. microphasmis only). Addition of T. ventralis did not significantly affect multiplication of T. microphasmis on both plant species. In contrast, on A. arenaria, T. ventralis experienced interspecific competition. However, on C. arenaria, T. microphasmis facilitated multiplication of T. ventralis. To explain this effect, we studied systemic plant-mediated effects in a split-root experiment. Nematode addition to one root compartment did not significantly influence nematode multiplication in the other root compartment, irrespective of nematode species identity. Therefore, the observed nematode interactions were not related to induced changes in the roots. In a two-choice experiment we tested whether host suitability was related to root attractiveness. Both nematode species were attracted to seedlings of A. arenaria, but not to C. arenaria. The low multiplication of T. ventralis on C. arenaria could be related to poor attraction to the roots. However, the poor attraction of T. microphasmis cannot be related to poor host suitability. Adding T. ventralis reduced shoot biomass of A. arenaria more than T. microphasmis did, whereas for C. arenaria the effect was the reverse. The interaction of the two nematodes on A. arenaria and C. arenaria shoot biomass was insignificant. However, the effect on root biomass of A. arenaria was interactive; adding T. ventralis to plants with high inoculation densities of T. microphasmis further decreased root biomass. Adding T. microphasmis further decreased root biomass of plants inoculated with low levels of T. ventralis. Depending on host plant identity, interactions between root-feeding nematodes may lead to competition or facilitation. Our results suggest that facilitation by T. microphasmis contributes to persistence of T. ventralis on C. arenaria. Thus, the population dynamics of root-feeding nematodes is influenced both by host plant identity and the presence of other root-feeding nematodes.     

Effects of earthworms on above- and belowground herbivores

Earthworms affect plant performance and can influence plant–herbivore interactions. Both primary and secondary metabolites and the expression of stress-responsive genes of plants can be affected by earthworms. Plant-mediated effects of earthworms on aboveground herbivore performance range between positive and negative. These indirect, plant-mediated effects likely depend on the altered resource uptake of plants or changes in the soil microbial community composition in presence of earthworms. Studies on belowground interactions between earthworms and root herbivores focussed almost exclusively on root-feeding nematodes. These interactions can be either direct (e.g. ingesting of nematodes) or indirect, mediated by changes in host plant performance or biotic and abiotic soil characteristics. Earthworms were documented to counteract the negative effects of root-feeding nematodes on plants. Consistently, earthworm-worked soils (vermicompost) have been reported to reduce numbers of root-feeding nematodes and plant damage by aboveground herbivores. The results suggest context dependent impacts of earthworms on herbivore performance and an alleviation of herbivore damage of plants by earthworms, besides their well-known effects on plant growth. This knowledge is crucial for understanding the impact of earthworms on plants in natural environments, and may be applied as alternative plant protection in sustainable agriculture.     

Soil feedback effects to the foredune grass Ammophila arenaria by endoparasitic root-feeding nematodes and whole soil communities

In coastal foredunes, the grass Ammophila arenaria develops a soil community that contributes to die-back and replacement by later successional plant species. Root-feeding nematodes and pathogenic soil microorganisms are involved in this negative feedback. Regular burial by wind-blown beach sand results in vigorous growth of A. arenaria, probably because of enabling a temporary escape from negative soil feedback. Here, we examine the role of root-feeding nematodes as compared to the whole soil community in causing negative feedback to A. arenaria. We performed a 3-year sand burial experiment in the field and every year we determined the feedback of different soil communities to plant growth in growth chamber bioassays.In the field, we established A. arenaria in tubes with beach sand, added three endoparasitic root-feeding nematode species (Meloidogyne maritima, Heterodera arenaria and Pratylenchus penetrans) or root zone soil to the plants, and created series of ceased and continued sand burial. During three subsequent years, plant biomass was measured and numbers of nematodes were counted. Every year, bioassays were performed with the field soils and biomass of seed-grown A. arenaria plants was measured to determine the strength of feedback of the established soil communities to the plant.In the field, addition of root zone soil had a negative effect on biomass of buried plants. In the bioassays, addition of root zone soil also reduced the biomass of newly planted seedlings, however, only in the case when the field plants had not been buried with beach sand. Addition of the three endoparasitic root-feeding nematodes did not influence plant biomass in the field and in the bioassays. Our results strongly suggest that the negative feedback to A. arenaria is not due to the combination of the three endoparasitic nematodes, but to other components in the soil community, or their interactions with the nematodes.     

A review on the role of predatory soil nematodes in the biological control of plant parasitic nematodes

Predatory nematodes feed on soil microorganisms including plant parasitic nematodes. They reduce populations of plant parasitic nematodes in virtually all soils because of their constant association with plant parasitic nematodes in the rhizosphere, and also release nutrients in plant-available forms, which may enable plants to better withstand nematode burden on their roots. Predation by nematodes of the orders Mononchida, Diplogasterida, Dorylaimida and Aphelenchida, has been studied but the data available in field/natural conditions are insufficient to conclude whether they are effective biocontrol agents of plant parasitic nematodes. However, among the different types of predators, diplogasterids are the most suited for biocontrol of nematodes, because of their short life cycles, easy culture, prey-specificity, chemotaxis sense and resistance to adverse conditions. This article summarizes progress to date and suggests ways to encourage the use of predatory nematodes as biocontrol agents in the management of plant parasitic nematodes.     

Managing crop root zone ecosystems for prevention of harmful and encouragement of beneficial nematodes

The goal of agricultural nematologists is usually considered to be the prevention of harmful nematode populations from reaching levels that cause noticeable yield losses in field crops. Usually, it is the plant-parasitic nematodes that are attributed with constraining plant growth and development. Not nearly as well understood is the impact on crop plants of the non-plant-parasitic and bacteria-feeding nematodes. This latter group can interact with plant-growth-promoting bacteria to improve soil fertility and improve crop productivity. The challenge has become finding methods to develop and maintain those systems that build-up beneficial nematode populations while simultaneously suppressing plant-parasitic nematodes and associated plant pathogens. Beneficial soil nematodes are usually more abundant in crop management systems subjected to sophisticated crop sequences, cultivation practices and organic amendments. Models to predict the population dynamics of a nematode species have been developed. However, the inadequacies of nematode identification, compounded by the irregular distribution of nematodes in soil, have made it difficult to obtain reliable data on nematode distribution and abundance with which to refine these simulation models. Since many different nematode extraction methods are in use today it also becomes extremely difficult to meaningfully compare quantitative data from different laboratories. As the number of factor variables affecting soil nematode populations is large and monitoring seasonal populations awkward, nematode influence on crop health and yield determination is seldom fully recognized. Thus, it is usually only those catastrophic nematode outbreaks that are recognized, while systematic benefits are rarely recognized or appreciated. Perhaps, with the utilization of molecular biotechnology it will become possible to better elucidate nematode plant–host interactions. Clearly, these root zone relationships will increasingly become a key component in understanding soil ecosystem function and lead to better cropping system design.     

Microcosm experiments on the development of different plant parasitic nematode fauna in two soils from the Soudanese-Sahelian zone of West Africa

To test the hypothesis that the structure of plant parasitic nematode communities is affected by soil characteristics, experiments were conducted in a greenhouse with two soils with different physical and chemical characteristics and land management histories (fallow and a cultivated field) from adjacent plots. The cultivated soil was more sandy and had lower organic matter and nutrient contents than the fallow soil. Four nematode assemblages of Scutellonema cavenessi, Helicotylenchus dihystera and Tylenchorhynchus gladiolatus were inoculated in the soils. The pot experiment was conducted on millet during 2 months. Multiplication rates of H. dihystera were not significantly different in the two soils. T. gladiolatus had a lower multiplication rate in the fine-textured soil. S. cavenessi seemed to reproduce better in the coarse-textured soil when inoculated in low density with H. dihystera. The presence of plant parasitic nematodes in the cultivated soil caused a significant decrease of millet biomass, whereas plants in the fallow soil were less sensitive to nematode damage and were only affected when the soil was inoculated with T. gladiolatus alone. This experiment did not explain the distribution of plant parasitic species observed in the field. However, parameters other than the presence of a favourable host plant and micro-climatic conditions were found to induce differences in the reproductive rates of several species of plant parasitic nematodes. Received: 14 January 1996     

Antibiotic resistance and protease production by Photorhabdus luminescens and Xenorhabdus poinarii bacteria symbiotic with entomopathogenic nematodes: variation among species and strains

Bacteria in the genera Photorhabdus and Xenorhabdus are highly pathogenic to insects and are symbiotically associated with nematodes in the genera Heterorhabditis and Steinernema, respectively. We compared extracellular protease production and resistance to antibiotics (chloramphenicol, erythromycin, neomycin and tetracycline) for 32 isolates of P. luminescens and 11 isolates of X. poinarii taken from nematodes isolated from soil in southern New Jersey. P. luminescens produced greater amounts of protease, and was more resistant to erythromycin and less resistant to neomycin than X. poinarii. No interspecific differences in resistance to chloramphenicol or tetracycline were detected. Variability within species was not related to the site, habitat or soil core from which the isolates were obtained, and was not associated with variation in the color of the host cadaver for P. luminescens. Resistance to erythromycin was positively correlated with resistance to both neomycin and tetracycline for P. luminescens, but was negatively correlated with resistance to neomycin for X. poinarii. Antibiotic resistance profiles and extracellular protease production might be useful characteristics for distinguishing among species and strains of these bacteria, probably have ecological significance with respect to intra- and interspecific competition within host cadavers, and could have implications for the utility of these organisms for biological control.     

Plant parasitic nematodes and spatio-temporal variation in natural vegetation

In this paper, the possible role of plant parasitic nematodes as a driving force of change in natural vegetation is analysed using the succession at coastal foredunes as a model. In pot trials, when grown in natural substrates from mature stands, seedlings of dominant foredune plants showed poor growth when compared to sterilised substrates. In natural substrates from preceding stages, growth reduction was far less, or even non-significant. Chemical soil treatment with nematicides resulted in enhanced growth of the seedlings. Inoculation of ectoparasitic nematodes reduced plant growth, but only at densities much higher than those occurring in control pots with unsterilised field soil. Identification at species level showed that endoparasitic nematodes are specifically associated with particular plant species. Therefore, it is hypothesised that the distribution of endoparasitic nematodes may be an important factor leading to the specific nature of soil pathogen complexes in coastal foredunes. We discuss the role of endoparasitic nematodes as possible key species in soil communities and compare the possible effects of specific vs. generalistic plant parasitic nematodes in soil communities on vegetation processes.     

Influence of soil and host plant crop on the genetic diversity of Azospirillum amazonense isolates

The genetic structure of Azospirillum amazonense populations isolated from the rhizosphere soil and washed and surface-sterilised roots of rice, maize and sorghum plants, cropped simultaneously in two different soils (clay loam and sandy loam) was characterised. Genetic diversity was measured by restriction fragment length polymorphism of the amplified 16S–23S rDNA intergenic spacer region (RISA-RFLP) and cluster analysis. Four genetically distinct clusters of isolates were observed with 78% similarity, suggesting that the A. amazonense population was heterogeneous at the strain level regardless of the soil type or host plant. Analysis of molecular variance (AMOVA) demonstrated that the host plant had a highly significant selective effect on the genetic structure of this species, especially on those isolates intimately associated with them, but also to a lesser extent on isolates from the rhizosphere and washed roots. The soil type also had a highly significant selective effect on A. amazonense genetic diversity, especially for those isolates from the rhizosphere soil. The selective effect of the soil type combined with that of the host plant suggests that environmental factors, such as soil texture and composition of exudates provided by C₃ or C₄ plants, play major roles in the overall genetic structure of A. amazonense populations associated with these cereals.     

Nematodes as indicators of soil recovery in tailings of a lead/zinc mine

Trophic groups and functional guilds of soil nematodes were measured under four mine tailing subsystems in the Baoshan lead/zinc mine, Hunan Province, southern China to test the indicator value of nematodes for heavy metal pollution. No obvious correlation was found between heavy metal concentration and the total number of nematodes. However, the densities of c–p3, c–p4 and c–p5 nematodes were negatively correlated with Pb and Zn concentrations, suggesting that the abundance of nematode groups of high c–p values is useful indicators of heavy metal contamination. The “weighted faunal analysis” provided a better assessment of soil health condition than Maturity Index (MI) in situations where there were extremely low numbers of soil nematodes. Results showed that the effect of heavy metal contamination on soil nematodes might be strongly influenced by plants. Although the abundance of plant-feeding nematodes did not reflect the heavy metal conditions in the soil, it might be used as an index for assessing the soil remediation potential of pioneering plants. Patrinia villosa seems superior to Viola baoshanensis as a pioneer plant species for soil remediation based on analysis of rhizosphere nematode community.     

Productivity parameters and soil health dynamics under long-term 2-year potato rotations in Atlantic Canada

Crop rotation effects, due to emerging soil ecological interactions and processes that occur with time, can have a major impact on crop productivity and soil health. 2-year potato (Solanum tuberosum L.) rotation studies were conducted during an 11-year period on a fine sandy loam (Orthic Podzol) under a cool, humid climate in Prince Edward Island in eastern Canada. Rotation partners included Italian ryegrass (Lolium multiflorum Lam.), red clover (Trifolium pratense L.), and barley (Hordeum vulgare L.). The study objective was to assess trends in yield parameters, populations and diversity in nematodes and soil-borne pathogens, and soil structural stability and organic matter retention with time. Italian ryegrass had the largest biomass of both herbage (6.5 Mg ha⁻¹) and roots (4.8 Mg ha⁻¹), compared to red clover or barley. Averaged across 9 years, potato tuber yield was highest under Italian ryegrass (35.0 Mg ha⁻¹) and lowest under red clover (31.1 Mg ha⁻¹) rotations. Differences in tuber yield among rotations was associated with soil N limitation and nematode activity, but was not evident until Year 6. Population densities of specific plant parasitic nematodes recovered from roots and soil were generally low and varied according to host plant. Root lesion (Pratylenchus spp.) and root-knot (Meloidogyne spp.) nematodes were more prevalent under red clover compared to other rotational crops. Stunt (Merlinius spp. and Tylenchorhynchus spp.) nematodes were more common under Italian ryegrass. The main organisms associated with tuber-borne disease were Rhizoctonia solani, Streptomyces spp., Fusarium spp., and Helminthosporium solani. The greatest reduction in tuber-borne diseases occurred with the potato–red clover rotation but significant differences were infrequent. Soil structural form throughout the soil profile (to 30 cm depth) was not adversely affected by the rotational treatments during the duration of the study, while soil structural stability at the soil surface (0–10 cm) was significantly improved. Losses of soil organic C, during the 11-year period ranged from marginal (4%) for rotations with Italian ryegrass, to significant (16%) under the barley rotation. Computer simulations, using the Century model, illustrated the importance of C inputs to maintain soil organic matter levels. Overall, potato crop productivity and soil organic C were generally maintained in rotations that contained Italian ryegrass, but declined under rotations with red clover and barley.     

Nematode assemblages in the rhizosphere of spring barley (Hordeum vulgare L.) depended on fertilisation and plant growth phase

Nematodes from rhizosphere soil of barley grown at three fertiliser treatments (control (0), NK and NPK) were studied in a field experiment. Sampling was done twice, during vegetative growth and flowering, respectively, to determine how fertiliser effects on nematode assemblages depended on plant growth phase. At the growth stage the proportion of fungal feeding nematodes (dominated by Aphelenchoides spp. and Aphelenchus sp.) was highest in NK. During flowering, the abundance and proportion of fungal feeders in the 0 and NPK plots had increased and reached a level similar to the NK plot. Overall densities of bacterial feeders (mainly Cephalobidae and Rhabditidae) were similar, but opportunistic bacterial feeders constituted a higher proportion in the fertilised plots compared to the unfertilised. Ectoparasitic plant feeders (Tylenchorhynchus sp.) were more numerous in NK and NPK than in the control at both sampling dates. Endoparasite (Pratylenchus spp.) numbers were lower in the NPK plot at the growth stage. Numbers of Tylenchidae increased between samplings. The classification of Tylenchidae as epidermal cell and root hair feeders as opposed to hyphal feeders is discussed. Results thus indicate that: (i) bacterial and especially fungal feeding nematodes are stimulated by unbalanced fertilisation; (ii) ectoparasitic plant feeders are stimulated by N-fertilisation, while migratory endoparasites are inhibited at high and balanced fertilisation; (iii) nutrient effects diminish after plants reach the flowering stage.     

Effects of six grassland plant species on soil nematodes: A glasshouse experiment

The effects of six individual plant species on the abundance and composition of nematode communities were studied in a glasshouse experiment during 16 weeks. The effect of the presence of plants, the correlation between nematode abundance and plant biomass, the response of plant-feeding nematodes and other nematode groups to different plant species was examined and also whether the effect differed between plant species within a plant functional group. The total number of nematodes increased during the study period in all treatments, although in some treatments, the increase levelled off after 8 or 12 weeks. The identity of the plant species affected both the total abundance of nematodes and the nematode community composition. The number of bacterial-feeding nematodes was greatest under grasses and legumes and was positively correlated with shoot biomass and negatively with root biomass. The response of the plant-feeding nematodes, which differed in abundance under both the investigated legume and the forb species, suggests that the identity of the plant species is more important than the plant functional group. A possible explanation could be related to differences in plant secondary metabolites. Despite some differences in the nematode species pool, the effects of plant species appear quite consistent between the present glasshouse study and previous field experiments.     

Using marigold (Tagetes spp.) as a cover crop to protect crops from plant-parasitic nematodes

A plethora of research has been conducted on the use of marigolds (Tagetes spp.) for nematode suppression, yet limited cover cropping with marigold is being practiced in commercial operations. Marigold is well known among nematologists for its ability to produce compounds such as α-terthienyl that are allelopathic to many species of plant-parasitic nematodes. However, there are contradictory reports on how this compound is released. The uncertainty centers on whether allelopathic compounds are released from root or shoot tissues, by growing live plants or soil-amended tissues, as a response to nematode penetration, or as a non-specific repellent. Other mechanisms by which marigold suppresses plant-parasitic nematodes include acting as a poor host, enhancing nematode-antagonistic microorganisms, or acting as a “dead-end” trap crop. Interpretation is complicated because multiple mechanisms may operate simultaneously. Understanding the exact mechanisms responsible for the nematode-suppressive effects of marigold could lead to further/broader incorporation into nematode management programs. This literature review revealed variable findings from marigold use. For example, in some instances using marigold was reported to be more effective than nematicides or soil fumigants and in other instances it had a negative impact on cash crop growth and yield. This variation has been attributed to differences in the way marigolds were used (e.g. intercrop/cover crop/soil amendment, seeding rate, time between marigold and cash crop), marigold cultivar, species or races of target nematodes, temperature, or age of marigold plant. Thus, future research should focus on determining the exact causes of this variability and on developing field IPM programs that take advantage of the nematode-suppressive potential of marigold.     

Evidence for a transient increase of rhizodeposition within one and a half day after a severe defoliation of Plantago arenaria grown in soil

Plants are often grazed resulting in a sudden and significant removal of shoot tissue, which decreases photosynthesis and changes C allocation between within the plant. From results obtained in percolated sand it is possible to demonstrate an increase of rhizodeposition within few days after defoliation followed by a decrease of rhizodeposition. The aim of our study was to test if this pattern can be also observed for plants grown in soil. We grew Plantago arenaria in microcosms and defoliated half of them after 45 d. Half of the defoliated and non-defoliated microcosms were harvested 1.5 d, and the other half 8.5 d, after defoliation. We observed an increase of microbial biomass 1.5 d after defoliation followed by a decrease assessed 8.5 d after the treatment. In parallel, soil soluble C and the metabolic quotient of the microbial biomass first decreased and then increased at the second harvest reaching values equivalent to those of the non-defoliated treatment. Based on these results together with results obtained in artificial soil, we conclude that the defoliation of P. arenaria grown in soil leads to a transient peak of root exudation.     

Effects of organic amendments on plant-parasitic nematode populations,root damage,and banana plant growth

Nematodes are major pests for crops, including banana. Environmentally friendly methods for managing plant-parasitic nematodes have to be developed, such as organic material application. Our study focuses on the impacts of several organic amendments on banana plants, considering mainly their effect on soil nitrogen supply and soil microbial biomass, and the consequences on plant-parasitic nematode impacts on the plants. A microcosm experiment for 13 weeks was conducted to evaluate four organic materials: sugarcane bagasse, sugarcane sludge, plant residues, and sewage sludge, compared to a control without organic amendment. Input of organic materials led to an important change on nitrogen resource, and plants grew better when the N availability was the highest, but better growth conditions did not necessarily reduce parasitic nematodes impacts on the roots. Damage on the roots depended on plant-parasitic nematode abundance. Three of four tested amendments exhibited a regulator effect on plant-parasitic nematode populations (bagasse, sugarcane sludge, and plant residues). Root growth was not the explanatory factor for this regulation. Only sugarcane sludge led to an overall positive effect on the plant, increasing its growth and reducing its parasitism pressure. The other organic materials exhibited an antagonism between the promoted plant growth and the reduced nematode populations.     

菲对秀丽隐杆线虫、中杆属和拟丽突属线虫毒性效应研究

采用悉生培养系统,研究不同浓度菲对秀丽隐杆线虫、拟丽突属与中杆属线虫的毒性效应,以及3种线虫对菲的去除作用。结果表明:(1)随着菲浓度的增加,3种线虫存活率逐渐降低。秀丽隐杆线虫在不添加菲的处理中,48 h内出现繁殖,而在添加菲的处理中,即使在最低浓度5 mg/L下,繁殖现象也会消失。中杆属与拟丽突属线虫由于世代时间较长,在本试验周期内均未出现繁殖现象。(2)暴露24 h时,比较不同浓度菲处理下线虫的相对死亡率,得到3种线虫的耐性依次为中杆属线虫≥秀丽隐杆线虫≥拟丽突属线虫,且随菲浓度的增加,秀丽隐杆线虫耐性水平逐渐降低;暴露48 h时中杆属线虫耐性依旧高于拟丽突属,而72 h时中杆属与拟丽突属线虫的耐性趋于一致。(3)3种线虫受菲胁迫后均失去头部正常摆动能力,且秀丽隐杆线虫与拟丽突属线虫体长随菲浓度的增加而逐渐降低。(4)不同种类线虫的添加均能促进菲的去除,不同线虫之间无显著差异。因此,菲会显著抑制3种线虫的存活率和生长发育,抑制秀丽隐杆线虫的繁殖。线虫的存活率受线虫种类、暴露时间、菲浓度及其交互作用的影响显著,其中中杆属线虫对菲的综合耐性最强,3种线虫均能促进溶液中菲的去除。     

Host-status of sweet potato cultivars to South Africa root-knot nematodes

Globally, most of the crop-related developmental projects collapsed due to the existence of aggressive plant-parasitic nematodes. Intensive South African biofortification efforts using exotic and local sweet potato (Ipomoea batatas) cultivars have hardly considered the inclusion of nematode resistance in plant breeding, despite the withdrawal of most nematicides from agrochemical markets. The objective of this study was to screen 12 selected biofortification sweet potato cultivars for host-status to South Africa tropical root-knot (Meloidogyne species) nematodes. Three exotic orange-fleshed, three local orange-fleshed and six cream-fleshed cultivars were used in three separate experiments of M. javanica and races 2 and 4 of M. incognita. In each experiment, 6000 eggs and second-stage juveniles/plant were used for inoculation, with nematode assessment performed at 56 days after inoculation. All tested biofortification exotic (except for cv. ‘W-119’) and local cultivars were hosts to Meloidogyne species and races, whereas three non-biofortication local cultivars, namely, ‘Bosbok’, ‘Blesbok’ and ‘Mvuvhelo’ were non-hosts. In conclusion, the findings suggested the likelihood of the existence of non-host-status in certain exotic and local sweet potato cultivars for use in plant breeding programmes against South African Meloidogyne species and races.