Absence Of Host Plant Research Articles

Composition of soil Frankia assemblages across ecological drivers parallels that of nodule assemblages in Alnus incana ssp. tenuifolia in interior Alaska.

In root nodule symbioses (RNS) between nitrogen (N)-fixing bacteria and plants, bacterial symbionts cycle between nodule-inhabiting and soil-inhabiting niches that exert differential selection pressures on bacterial traits. Little is known about how the resulting evolutionary tension between host plants and symbiotic bacteria structures naturally occurring bacterial assemblages in soils. We used DNA cloning to examine soil-dwelling assemblages of the actinorhizal symbiont Frankia in sites with long-term stable assemblages in Alnus incana ssp. tenuifolia nodules. We compared: (1) phylogenetic diversity of Frankia in soil versus nodules, (2) change in Frankia assemblages in soil versus nodules in response to environmental variation: both across succession, and in response to long-term fertilization with N and phosphorus, and (3) soil assemblages in the presence and absence of host plants. Phylogenetic diversity was much greater in soil-dwelling than nodule-dwelling assemblages and fell into two large clades not previously observed. The presence of host plants was associated with enhanced representation of genotypes specific to A. tenuifolia, and decreased representation of genotypes specific to a second Alnus species. The relative proportion of symbiotic sequence groups across a primary chronosequence was similar in both soil and nodule assemblages. Contrary to expectations, both N and P enhanced symbiotic genotypes relative to non-symbiotic ones. Our results provide a rare set of field observations against which predictions from theoretical and experimental work in the evolutionary ecology of RNS can be compared.

Enrichment of bacteria involved in the nitrogen cycle and plant growth promotion in soil by sclerotia of rice sheath blight fungus

Rice sheath blight pathogen, Rhizoctonia solani, produces numerous sclerotia to overwinter. As a rich source of nutrients in the soil, sclerotia may lead to the change of soil microbiota. For this purpose, we amended the sclerotia of R. solani in soil and analyzed the changes in bacterial microbiota within the soil at different time points. At the phyla level, Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, Chloroflexi and Firmicutes showed varied abundance in the amended soil samples compared to those in the control. An increased abundance of ammonia-oxidizing bacterium (AOB) Nitrosospira and Nitrite oxidizing bacteria (NOB) i.e., Nitrospira was observed, where the latter is reportedly involved in the nitrifier denitrification. Moreover, Thiobacillus, Gemmatimonas, Anaeromyxobacter and Geobacter, the vital players in denitrification, N2O reduction and reductive nitrogen transformation, respectively, depicted enhanced abundance in R. solani sclerotia-amended samples. Furthermore, asymbiotic nitrogen-fixing bacteria, notably, Azotobacter as well as Microvirga and Phenylobacterium with nitrogen-fixing potential also enriched in the amended samples compared to the control. Plant growth promoting bacteria, such as Kribbella, Chitinophaga and Flavisolibacter also enriched in the sclerotia-amended soil. As per our knowledge, this study is of its kind where pathogenic fungal sclerotia activated microbes with a potential role in N transformation and provided clues about the ecological functions of R. solani sclerotia on the stimulation of bacterial genera involved in different processes of N-cycle within the soil in the absence of host plants.

Long-Term Persistence of Arbuscular Mycorrhizal Fungi in the Rhizosphere and Bulk Soils of Non-host Brassica napus and Their Networks of Co-occurring Microbes.

Arbuscular mycorrhizal fungi (AMF) are obligate plant symbionts that improve the nutrition and health of their host. Most, but not all the crops form a symbiosis with AMF. It is the case for canola (Brassica napus), an important crop in the Canadian Prairies that is known to not form this association. From 2008 to 2018, an experiment was replicated at three locations of the Canadian Prairies and it was used to assess the impact of canola on the community of AMF naturally occurring in three cropping systems, canola monoculture, or canola in two different rotation systems (2-years, canola-wheat and 3-years, barley-pea-canola). We sampled canola rhizosphere and bulk soils to: (i) determine diversity and community structure of AMF, we expected that canola will negatively impact AMF communities in function of its frequency in crop rotations and (ii) wanted to assess how these AMF communities interact with other fungi and bacteria. We detected 49 AMF amplicon sequence variants (ASVs) in canola rhizosphere and bulk soils, confirming the persistence of a diversified AMF community in canola-planted soil, even after 10 years of canola monoculture, which was unexpected considering that canola is among non-mycorrhizal plants. Network analysis revealed a broad range of potential interactions between canola-associated AMF and some fungal and bacterial taxa. We report for the first time that two AMF, Funneliformis mosseae and Rhizophagus iranicus, shared their bacterial cohort almost entirely in bulk soil. Our results suggest the existence of non-species-specific AMF-bacteria or AMF-fungi relationships that could benefit AMF in absence of host plants. The persistence of an AMF community in canola rhizosphere and bulk soils brings a new light on AMF ecology and leads to new perspectives for further studies about AMF and soil microbes interactions and AMF subsistence without mycotrophic host plants.

Survival and infectivity of second-stage root-knot nematode Meloidogyne incognita juveniles depend on lysosome-mediated lipolysis

Adaptation to nutrient deprivation depends on the activation of metabolic programs to use reserves of energy. When outside a host plant, second-stage juveniles (J2) of the root-knot nematode (Meloidogyne spp.), an important group of pests responsible for severe losses in the production of crops (e.g., rice, wheat, and tomato), are unable to acquire food. Although lipid hydrolysis has been observed in J2 nematodes, its role in fitness and the underlying mechanisms remain unknown. Using RNA-seq analysis, here, we demonstrated that in the absence of host plants, the pathway for the biosynthesis of polyunsaturated fatty acids was upregulated, thereby increasing the production of arachidonic acid in middle-stage J2 Meloidogyne incognita worms. We also found that arachidonic acid upregulated the expression of the transcription factor hlh-30b, which in turn induced lysosomal biogenesis. Lysosomes promoted lipid hydrolysis via a lysosomal lipase, LIPL-1. Furthermore, our data demonstrated that blockage of lysosomal lipolysis reduced both lifespan and locomotion of J2 worms. Strikingly, disturbance of lysosomal lipolysis resulted in a decline in infectivity of these juveniles on tomato roots. Our findings not only reveal the molecular mechanism of lipolysis in J2 worms but also suggest potential novel strategies for the management of root-knot nematode pests.

Impact of the genetic diversity of three cyst nematodes on the effectiveness of root exudates to induce hatching

Cyst nematodes are sedentary endoparasites of plants which cause important economic losses worldwide. New nematode control measures are needed since the removal of effective chemical nematicides from the market due to their negative impact on environment and human health. Induced hatching of second-stage juveniles in the absence of host plant using root exudates, also named “suicide hatching”, could be a sustainable alternative method to reduce nematode population densities in infested soils. Unfortunately, biocontrol methods are often less effective in agricultural fields than in laboratory or greenhouse and this could be due to, among other reasons, a different susceptibility of nematode populations to root exudate stimulation. Testing this intra-specific variability would help to anticipate any drop in the efficiency of this new biocontrol strategy. A selection of root exudates from different plant species, maximizing the hatching level highlighted in a previous study, was tested on the hatching of representative populations of the genetic diversity for Globodera pallida, Heterodera schachtii and Heterodera carotae. Results showed significant differences between populations for given nematode species but not correlated with the genetic structure. Overall, root exudates tested provide a high level of hatching of these three nematode species. Surprisingly, the root exudate from broccoli induces hatching of European populations of the potato cyst nematode G. pallida.

Moments of weaknesses - exploiting vulnerabilities between germination and encystment in the Phytomyxea.

Attempts at management of diseases caused by protozoan plant parasitic Phytomyxea have often been ineffective. The dormant life stage is characterised by long-lived highly robust resting spores that are largely impervious to chemical treatment and environmental stress. This review explores some life stage weaknesses and highlights possible control measures associated with resting spore germination and zoospore taxis. With phytomyxid pathogens of agricultural importance, zoospore release from resting spores is stimulated by plant root exudates. On germination, the zoospores are attracted to host roots by chemoattractant components of root exudates. Both the relatively metabolically inactive resting spore and motile zoospore need to sense the chemical environment to determine the suitability of these germination stimulants or attractants respectively, before they can initiate an appropriate response. Blocking such sensing could inhibit resting spore germination or zoospore taxis. Conversely, the short life span and the vulnerability of zoospores to the environment require them to infect their host within a few hours after release. Identifying a mechanism or conditions that could synchronise resting spore germination in the absence of host plants could lead to diminished pathogen populations in the field.

Hatching Induction of Cyst Nematodes in Bare Soils Drenched With Root Exudates Under Controlled Conditions.

Cyst nematodes account for substantial annual yield losses in crop production worldwide. Concerns over environmental and health issues due to the use of chemical nematicides mean alternative sustainable and integrated solutions are urgently required. Hatch induction of encysted eggs in the absence of host plants, i.e., ‘suicide-hatching,’ could be a sustainable alternative in reducing population densities of cyst nematodes in infested soils. Here we examined in situ hatching of encysted eggs of Globodera pallida, Heterodera carotae, and Heterodera schachtii at varying soil depths, following exogenous applications of host root exudates in repeated glasshouse experiments. Cysts were retrieved 30 or 43 days post-incubation depending on the nematode species and assessed for hatching rates relative to the initial number of viable eggs per cyst. Hatching of the potato cyst nematode G. pallida depended on both soil moisture and effective exposure to root exudates, and to a lesser extent on exudate concentration. The carrot cyst nematode H. carotae had over 75% hatched induced by root exudate irrespective of the concentration, with better hatch induction at 20 cm as compared with 10 cm soil depth. Hatching of the beet cyst nematode H. schachtii largely depended on the soil moisture level at constant temperature, rather than the type or concentration of root exudates applied. As a conclusion, exogenously applied host root exudates may play a major role in inducing in situ hatch of encysted eggs of potato and carrot cyst nematodes in the absence of host plant under favorable soil temperature/moisture conditions. To improve such strategy, the characterization of chemical profiles of the root exudate composition and field validation are currently ongoing.

Regulators of nitric oxide signaling triggered by host perception in a plant pathogen

The rhizosphere interaction between plant roots or pathogenic microbes is initiated by mutual exchange of signals. However, how soil pathogens sense host signals is largely unknown. Here, we studied early molecular events associated with host recognition in Fusarium graminearum, an economically important fungal pathogen that can infect both roots and heads of cereal crops. We found that host sensing prior to physical contact with plant roots radically alters the transcriptome and triggers nitric oxide (NO) production in F. graminearum We identified an ankyrin-repeat domain containing protein (FgANK1) required for host-mediated NO production and virulence in F. graminearum In the absence of host plant, FgANK1 resides in the cytoplasm. In response to host signals, FgANK1 translocates to the nucleus and interacts with a zinc finger transcription factor (FgZC1), also required for specific binding to the nitrate reductase (NR) promoter, NO production, and virulence in F. graminearum Our results reveal mechanistic insights into host-recognition strategies employed by soil pathogens.

Survival of Meloidogyne javanica during the summer season under semiarid conditions

One of the survival mechanisms of root-knot nematodes (Meloidogyne spp.) in the absence of host plants during hot and dry summer seasons is anhydrobiosis of second-stage juveniles (J2). Another strategy might be migration of J2 to deeper soil to avoid high soil temperatures and low humidity. Wetting infested soil during such seasons is sometimes suggested as a nematode control method that prevents anhydrobiosis, leading to exhaustion of their energy reserves. Population densities of Meloidogyne javanica at five soil depths (0–50 cm) in irrigated and nonirrigated field plots were estimated during three summer months in two successive years after uprooting infected tomato plants. The number of J2 in the soil was estimated by counting J2 extracted by Baermann funnel extraction and number of root galls on lettuce seedlings grown in the soil samples. Significant factors for J2 survival were number of days after plant removal and soil depth, probably due to lower maximum daily soil temperatures and higher water contents at depth. Irrigation did not consistently affect the number of extracted J2 or root galls. No obvious evidence of J2 migration from the upper to deeper soil layers or nematode-control effects of the irrigation were observed.

Suicidal germination as a control strategy for Striga hermonthica (Benth.) in smallholder farms of sub‐Saharan Africa

Societal Impact StatementInfestation by the parasitic plant Striga hermonthica is a severe threat to food security in sub‐Saharan Africa, impacting the production of the major staple crops pearl millet and sorghum, equating to 7–10 billion $ losses. Using Striga seed dependency on host‐released germination stimulants, we have developed and validated a method for addressing the problem of accumulated parasite seedbanks—the major obstacle in combating Striga infestation in African rain‐fed fields. Application of our method promises to alleviate the problem posed by this pernicious weed by increasing crop production for smallholder farmers. Summary The root parasitic plant Striga hermonthica is a major threat to global food security, causing enormous losses in yields of the main staple crops in sub‐Saharan Africa, which include pearl millet, sorghum, maize and rice. Sustainable Striga control should ideally lead to the depletion of the vast, long‐lived Striga seedbank, and this can be achieved by inducing suicidal seed germination through application of strigolactone (SL) analogs in the absence of host plants. However, this “suicidal germination” strategy has not been evaluated under the natural rain‐fed conditions that prevail in Striga‐prone regions. We have developed and validated a protocol for suicidal germination in laboratory and natural conditions in Striga‐infested rain‐fed African fields. Three SL analogs were tested and these resulted to between 65% and 55% reduction in Striga emergence in pearl millet and sorghum fields, respectively. We conclude that suicidal germination is an effective method for reducing the Striga seedbank. Moreover, the minimal demands of our protocol, in terms of water consumption and amount of selected SL analogs, make it affordable and applicable at a large scale in African rain‐fed agriculture, holding promise for sustainable cleaning of heavily Striga‐infested fields in sub‐Saharan Africa.

Observations on the Influence of Temperature Of Second Stage Juveniles (Meloidogyne Spp.) in the Absence of the Host Plant

Abstract The knowledge of root-knot nematodes behavior in different habitats and especially the knowledge of their reaction to major ecologic factors (humidity, temperature) are important for the assessment of pathogen potential in a specific area, being at the same time an important criterion for understanding the behavior towards host plants. The temperature is the most important factor, not just in the development of the entire biological cycle of root-knot nematodes, but at the same time it also affects their distribution, spread and survival under thermic stress conditions (excessive heat or cold). Alongside with the water and oxygen, the temperature is the triggering factor of hatching and running all stages until the adult stage. The articles aims to determine the survival of juveniles stages for Meloidogyne species, in the absence of host plants, and by exposing second stage juveniles to different temperatures. The juveniles survival and mobility decreases quite much at relative low temperatures (4°C and 10°C). Forward movements, mobility, hatching and lifetime were accentuated at higher temperatures (20°C) for a few weeks, so that after a period to decrease drastically (in 10 and 12 week) for the species considered for the study.

Germinate to exterminate: chemical stimulation of Spongospora subterranea resting spore germination and its potential to diminish soil inoculum

Hoagland's solution (HS), a defined nutrient supplement for plants, has been previously reported to stimulate zoospore release from resting spores of the potato pathogen Spongospora subterranea f. sp. subterranea. This study obtained direct empirical evidence for an increase in zoospore release with HS treatment, and identified Fe‐EDTA as the stimulant component of HS. Stimulation of resting spores by HS and Fe‐EDTA resulted in greater and earlier zoospore release compared to a distilled water control, and in the presence of a susceptible tomato host plant resulted in enhanced root infection. Given the labile nature of S. subterranea zoospores, it was postulated that stimulation of premature release of zoospores from the dormant resting spores in absence of susceptible hosts could reduce soil inoculum levels. In two glasshouse trials in the absence of host plants, both Fe‐EDTA and HS soil treatments reduced S. subterranea soil inoculum levels, providing proof of concept for the ‘germinate to exterminate’ approach to inoculum management.

In vitro Antagonistic Activity of Trichoderma harzianum against Rhizoctonia solani The Causative Agent of Potato Black Scurf and Stem Canker

IN EGYPT Potato (Solanum tuberosum L.) is considered one of the most important vegetable crops as well as many others countries in the world. It plays an important role in the Egyptian agricultural economy, not for local consumption but also for exportation especially to Europe, Russia and Arabic countries. However, potato crop suffer from more than 40 pests and diseases caused by insects, nematodes, viruses, bacteria and fungi, of which black scurf and stem canker induced by Rhizoctonia solani is probably the most serious disease. The world yield losses caused by R. solani were estimated to 5-15%. R. solani is an unspecialized parasite, survive in soil in the absence of host plant and make itself a very difficult pathogen to manage. Reduction or elimination of soil borne inoculum is the only effective solution to overcome the problem and this may be achieved through the application of various control measures of which fungal antagonists consider among the most important tactic. Although R. solaniis usually controlled through the application of chemicals, the serious ecological and financial toll of this fungus has prompted for research on biopesticides as a viable alternative. Trichoderma spp. were well-known fungi often used for the biological control of crop pests, whose anti-fungal mechanisms include competition for the substrate, antibiosis and/or mycoparasitism. Five isolates of Trichoderma harzianum were tested in vitro for their antagonistic potential against Rhizoctonia solani. Both Trichoderma harzianum and Rhizoctonia solani were identified by molecular and morphological methods. In dual culture of all isolates were found antagonistic to the growth of R. solani. The hyphal interaction studied using light microscopy revealed destructive mycoparasitism of R. solani by T. harzianum. The method of mycoparasitism was sparse to intense coiling of R. solani followed by disintegration, disorganization and death of R. solani mycelium.

Greenhouse propagation of the endangered hemiparasiteSchwalbea americana(American chaffseed): experimentation and botanical studies

American chaffseed ( Schwalbea americana L. [Scrophulariaceae]) is a federally endangered, hemiparasitic species that primarily occurs in fire-maintained pinelands in the Atlantic and Gulf coastal plains of the US. Efforts to propagate S. americana for re -introduction into the wild have been met with mixed results. Discrepancies in our understanding of host requirements, soil ecology, and growing conditions need to be resolved in order to develop a successful ex situ propagation program. We conducted a series of greenhouse experiments to address the impact that growth media, soil microbes, mycorrhizal associations, and autoparasitism may have on successful propagation of seedlings. We also tested the effectiveness of storing bareroot plants at 4°C (39 °F) relative to plants overwintering outside or being maintained in the greenhouse. We confirmed that cold-moist stratification is necessary to achieve the high germination rates needed for ex situ propagation. Soil microbes and growth media affected S. americana survivorship. We successfully grew plants in the absence of host plants by supplementing nursery media with organic hydrolized fish fertilizer. We did not observe S. americana forming mycorrhizal associations or parasitizing its own roots (no autoparasitism). Finally, we demonstrated that 1-y-old bareroot plants stored for 3 mo at 4°C exhibited survival rates that rivaled plants that overwinter outdoors or in the greenhouse.

Divergent host plant preference causes assortative mating between sympatric host races of the ladybird beetle,Henosepilachna diekei

Divergent host preference (i.e. host fidelity) plays a significant role in the speciation process in phytophagous insects. However, how and to what extent this divergence reduces gene flow between populations has rarely been measured. Here, we estimated the intensity of assortative mating caused solely by host fidelity in two host races of the phytophagous ladybird beetle Henosepilachna diekei, specialized on Mikania micrantha (Asteraceae) and Leucas lavandulifolia (Lamiaceae) in West Java, Indonesia. These host races mated randomly in the absence of host plants under laboratory conditions, but demonstrated nearly complete assortative mating in field cages with the two host plants, by spending almost all of their time on their respective host plants. The frequency of assortative mating in the field cages was not affected drastically by host plant patch structure. These results suggest that fidelity to the different host plants yields directly almost complete reproductive isolation between the host races by limiting the habitat on the respective host plant. In addition, the high host fidelity also ensures female oviposition on the original host plant. As larvae cannot survive on non-host plants, a positive association between female oviposition preference and larval performance on the host plant on which the beetles are specialized will further facilitate the evolution of host fidelity. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 606–614.

Arbuscular mycorrhizal fungi reduce growth and infect roots of the non‐host plant Arabidopsis thaliana

The arbuscular mycorrhizal (AM) symbiosis is widespread throughout the plant kingdom and important for plant nutrition and ecosystem functioning. Nonetheless, most terrestrial ecosystems also contain a considerable number of non-mycorrhizal plants. The interaction of such non-host plants with AM fungi (AMF) is still poorly understood. Here, in three complementary experiments, we investigated whether the non-mycorrhizal plant Arabidopsis thaliana, the model organism for plant molecular biology and genetics, interacts with AMF. We grew A. thaliana alone or together with a mycorrhizal host species (either Trifolium pratense or Lolium multiflorum) in the presence or absence of the AMF Rhizophagus irregularis. Plants were grown in a dual-compartment system with a hyphal mesh separating roots of A. thaliana from roots of the host species, avoiding direct root competition. The host plants in the system ensured the presence of an active AM fungal network. AM fungal networks caused growth depressions in A. thaliana of more than 50% which were not observed in the absence of host plants. Microscopy analyses revealed that R. irregularis supported by a host plant was capable of infecting A. thaliana root tissues (up to 43% of root length colonized), but no arbuscules were observed. The results reveal high susceptibility of A. thaliana to R. irregularis, suggesting that A. thaliana is a suitable model plant to study non-host/AMF interactions and the biological basis of AM incompatibility.

Occurrence of Plasmodiophora brassicae in Finnish turnip rape and oilseed rape fields

Clubroot, caused by Plasmodiophora brassicae Woronin, is a serious plant disease of cruciferous plants. A field survey of occurrence of clubroot in oilseed fields was conducted in Finland in 2007−2009 and in 1984−1989. At present, the disease is distributed throughout the oilseed cultivation area. Clubroot was found on average from 30% of fields, but its severity was low; fields with high numbers of infected plants and plants with severe symptoms were rare. According to the survey, cultivation frequency of cruciferous plants is the most important factor affecting clubroot occurrence and severity. Clubroot was found in soils with a wide range of pH-values (pH 5-7.6), but symptoms were most severe at low pH. According to the survey, and greenhouse and field trials, high temperature and moisture during the early growth period seem to favour disease development and can cause significant yield losses. In a survival trial, clubroot declined to close to zero after four years in the absence of host plants, but traces of the pathogen were still detectable after a 19-year trial period, making eradication of the pathogen very difficult.

Strigolactone analogues induce suicidal seed germination of Striga spp. in soil

Kgosi RL, Zwanenburg B, Mwakaboko AS & Murdoch AJ (2012). Strigolactone analogues induce suicidal seed germination of Striga spp. in soil. Weed Research52, 197–203.SummaryStriga hermonthica and Striga asiatica are obligate root parasites that cause serious problems in the production of staple cereal crops in Africa. Because of the high levels of infestation, there is an urgent need to control these weeds. A potentially useful control option is depletion of the soil seed bank by suicidal germination, which involves germination of the seeds in the absence of host plants. Suicidal germination is often mentioned in the literature, but not considered realistic, because of the alleged untimely decomposition of the stimulants in the soil, despite the fact that some encouraging results were reported around 1980. The alleged instability has prevented active research in this direction for the past 20–25 years. Five newly designed synthetic germination stimulants were investigated as candidates for suicidal germination. An important issue is the persistence of these stimulants in soil. Packets with Striga spp. seeds were put in pots with soil and then treated with aqueous solutions of the stimulants. All five compounds induced germination under these conditions, with percentages varying between 18% and 98% depending on stimulant and species. There were no noticeable signs of decomposition of the stimulants. The best performing stimulant is derived from 1‐tetralone. We conclude that synthetic strigolactones analogues have excellent prospects for use in combating parasitic weeds. Further testing will be needed to evaluate whether such prospects can be realised in the field.

Plugging into the network: belowground connections between germlings and extraradical mycelium of arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are obligate biotrophs; nevertheless their spores can germinate in the absence of host plants. Such inconsistent behavior is balanced by diverse survival strategies. The ability of AM fungal hyphae to fuse might represent a fundamental survival strategy because germlings could plug into compatible mycorrhizal networks, thus gaining access to plant-derived carbon before asymbiotic growth arrest. An in vivo experimental system was used to grow extraradical mycelium produced by Glomus mosseae colonizing three different plant species and germlings of the same isolate. After symbiotic and asymbiotic mycelia came into contact we showed that germling hyphae fused with symbiotic network hyphae and established protoplasm connections with nuclei occurring in fusion bridges. The frequency of anastomoses between germling and symbiotic hyphae was 4.9–23.9%. Prefusion and postfusion incompatible responses, with protoplasm withdrawal in interacting hyphae, were evident in some hyphal contacts. Given the multigenomic nature of AMF, the mingling of germling nuclei with those of the mycorrhizal network through perfect fusions might represent a means for the maintenance of genetic diversity in the absence of sexual recombination.

Survival of the burrowing nematode Radopholus similis (Cobb) Thorne without food: Why do males survive so long?

The burrowing nematode Radopholus similis is the most damaging banana nematode. To minimize nematicide applications, cropping systems based on fallow, crop rotation, and using clean planting material have been developed in the French West Indies. The survivorship of R. similis in water and soil was evaluated to optimize the collapse of its populations during the intercropping period and to better understand the risk of dissemination of nematodes by run-off water. In both Andosols and Nitisols, survivorship was significantly higher for males than for females. After 180 days, 21.7% of males and 9.8% of females were still alive, whereas no juveniles survived after 150 days. Survivorship was much lower in water and soil solution than in soil. The mean half-life of males was 8.8 days and only 6.2 days for females, but the difference between sexes was less after 1 month: 8% of both males and females in the initial population survived after 35 days. These results suggest that resource allocation for males was directed towards reproduction, whereas females expend energy foraging and laying eggs, and are thus disadvantaged in the absence of host plants. The relatively long survivorship of males of R. similis enables them to fecundate females without competing for food after becoming adults.