Root‐knot nematodes are destructive phytopathogens that damage agricultural crops globally, and there is growing interest in the use of biocontrol based on rhizobacteria such as Bacillus to combat ...Meloidogyne species. It is hypothesized that nematicidal activity of Bacillus can be attributed to the production of secondary metabolites and hydrolytic enzymes. Yet, few studies have characterized these metabolites and their identities remain unknown. Others are speculative or fail to elaborate on how secondary metabolites were detected or distinguished from primary metabolites. Metabolites can be classified based on their origin as either intracellular or extracellular and based on their function, as either primary or secondary. Although this classification is in general use, the boundaries are not always well defined. An understanding of the secondary metabolite and hydrolytic enzyme classification of Bacillus species will facilitate investigations aimed at bionematicide development. This review summarizes the significance of Bacillus hydrolytic enzymes and secondary metabolites in bionematicide research and provides an overview of known classifications. The importance of appropriate cultivation conditions for optimum metabolite and enzyme production is also discussed. Finally, the use of metabolomics for the detection and identification of nematicidal compounds is considered.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Meloidogyne enterolobii is an emerging destructive pathogen. The aim of this manuscript is to help growers be aware of the symptom, distribution, destructiveness and management measures of this ...nematode.
Root-knot nematodes differentiate highly specialized feeding cells in roots (giant cells, GCs), through poorly characterized mechanisms that include extensive transcriptional changes. While global ...transcriptome analyses have used galls, which are complex root structures that include GCs and surrounding tissues, no global gene expression changes specific to GCs have been described. We report on the differential transcriptome of GCs versus root vascular cells, induced in Arabidopsis by Meloidogyne javanica at a very early stage of their development, 3 days after infection (d.p.i.). Laser microdissection was used to capture GCs and root vascular cells for microarray analysis, which was validated through qPCR and by a promoter-GUS fusion study. Results show that by 3 d.p.i., GCs exhibit major gene repression. Although some genes showed similar regulation in both galls and GCs, the majority had different expression patterns, confirming the molecular distinctiveness of the GCs within the gall. Most of the differentially regulated genes in GCs have no previously assigned function. Comparisons with other transcriptome analyses revealed similarities between GCs and cell suspensions differentiating into xylem cells. This suggests a molecular link between GCs and developing vascular cells, which represent putative GC stem cells. Gene expression in GCs at 3 d.p.i. was also found to be similar to crown galls induced by Agrobacterium tumefaciens, a specialized root biotroph.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Summary
Taxonomy
Superkingdom Eukaryota; Kingdom Metazoa; Phylum Nematoda; Class Chromadorea; Order Tylenchida; Suborder Tylenchina; Infraorder Tylenchomorpha; Superfamily Tylenchoidea; Family ...Meloidogynidae; Subfamily Meloidogyninae; Genus Meloidogyne.
Biology
Microscopic non‐segmented roundworm. Plant pathogen; obligate sedentary endoparasitic root‐knot nematode. Reproduction: facultative meiotic parthenogenetic species in which amphimixis can occur at a low frequency (c. 0.5%); relatively fast life cycle completed in 19–27 days on rice depending on the temperature range.
Host range
Reported to infect over 100 plant species, including cereals and grass plants, as well as dicotyledonous plants. Main host: rice (Oryza sativa).
Symptoms
Characteristic hook‐shaped galls (root swellings), mainly formed at the root tips of infected plants. Alteration of the root vascular system causes disruption of water and nutrient transport, stunting, chlorosis and loss of vigour, resulting in poor growth and reproduction of the plants with substantial yield losses in crops.
Disease control
Nematicides, chemical priming, constant immersion of rice in irrigated fields, crop rotation with resistant or non‐host plants, use of nematode‐free planting material. Some sources of resistance to Meloidogyne graminicola have been identified in African rice species (O. glaberrima and O. longistaminata), as well as in a few Asian rice cultivars.
Agronomic importance
Major threat to rice agriculture, particularly in Asia. Adapted to flooded conditions, Meloidogyne graminicola causes problems in all types of rice agrosystems.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
The guava root-knot nematode (Meloidogyne enterolobii) has become one of the greatest enemies of agricultural production as current nematode management methods are not effective against this ...nematode. Summer cover crops can be an alternative solution for sustainable nematode management as they have a great potential to suppress nematode reproduction in addition to providing other usual benefits. Greenhouse experiments were conducted to evaluate ten commercially available summer cover crops against M. enterolobii. Sunflower and cowpea supported a high reproduction of M. enterolobii and had significantly greater biomass relative to the susceptible control (tomato cv. Rutgers). Buckwheat and sunn hemp had lower nematode reproduction but produced greater biomass compared to the susceptible control. Sesame supported significantly lower nematode reproduction and produced the lowest biomass among all cover crops employed in this study. Three millets (pearl millet, brown top millet and Japanese millet), grain sorghum and sorghum-sudangrass did not support any nematode reproduction and produced significantly higher plant biomass when compared with the control. Results from this study suggest that the three millets, grain sorghum and sorghum-sudangrass are promising summer cover crops for managing M. enterolobii.
•Current nematode management methods are not effective for managing M. enterolobii.•Ten summer cover crops were evaluated against M. enterolobii in greenhouse environment.•Sunflower and cowpea were excellent hosts.•Buckwheat, sunn hemp and sesame were poor hosts.•Millets (pearl, brown top and Japanese), grain sorghum and sorghum-sudangrass were non-hosts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A two-year field study was established in August 2008 at the USDA-ARS, U.S. Horticultural Research Laboratory in Fort Pierce, FL to examine the impact of anaerobic soil disinfestation (ASD) combined ...with soil solarization as an alternative to methyl bromide (MeBr) fumigation for control of plant–parasitic nematodes and introduced inoculum of soilborne plant pathogens. A complete factorial experiment in a split-split plot was established to evaluate three levels of applied initial irrigation (10, 5, or 0cm), two levels of partially-composted poultry litter (CPL; amended or unamended), and two levels of molasses (amended or unamended) in combination with solarization in a raised-bed bell pepper-eggplant double crop production system. Untreated and MeBr controls were established in each block for comparison to ASD treatments. Survival of Phytophthora capsici inoculum, introduced prior to ASD treatment, was equal to that with MeBr and less than the untreated control for all solarized treatments regardless of applied soil amendments during both seasons. Survival of introduced inoculum of Fusarium oxysporum f. sp. lycopersici was least (and equivalent to the MeBr control) in treatments with applied molasses during the second season. While endemic plant-parasitic nematode populations were generally low throughout the first season, by the end of the second eggplant double crop, root-knot nematode (Meloidogyne incognita) populations in treatments not receiving molasses and/or CPL (solarization only) or not receiving irrigation at treatment averaged more than 200 nematodes per 100cm3 of soil compared to an average of 10 nematodes per 100cm3 in ASD treatments where molasses or molasses+CPL was applied and irrigated with 5 or 10cm of water. Anaerobic soil disinfestation combined with solarization may provide an alternative to chemical soil fumigation for control of soilborne plant pathogens and plant–parasitic nematodes in Florida raised-bed vegetable production systems.
► Examine anaerobic soil disinfestation (ASD) combined with soil solarization. ► Two-year, double-crop field study in Florida raised-bed vegetable production. ► ASD+solarization effective for management of plant-parasitic nematodes. ► ASD+solarization comparable to MeBr for plant pathogen inoculum survival.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Priority effects shape the assembly of free‐living communities and host‐associated communities. However, the current literature does not fully incorporate two features of host–symbiont interactions, ...correlated host responses to multiple symbionts and ontogenetic changes in host responses to symbionts, leading to an incomplete picture of the role of priority effects in host‐associated communities. We factorially manipulated the inoculation timing of two plant symbionts (mutualistic rhizobia bacteria and parasitic root‐knot nematodes) and tested how host age at arrival, arrival order, and arrival synchrony affected symbiont colonization success in the model legume Medicago truncatula. We found that host age, arrival order, and arrival synchrony significantly affected colonization of one or both symbionts. Host age at arrival only affected nematodes but not rhizobia: younger plants were more heavily infected than older plants. By contrast, arrival order only affected rhizobia but not nematodes: plants formed more rhizobia nodules when rhizobia arrived before nematodes. Finally, synchronous arrival decreased colonization both symbionts, an effect that depended on host age. Our results demonstrate that priority effects compromise the host's ability to control colonization by two major symbionts and suggest that the role of correlated host responses and host ontogeny in the assembly of host‐associated communities deserve further attention.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The ability of
to reproduce on selected sweetpotato (
) cultivars (Beauregard, Covington, Evangeline, Hernandez, and Orleans (LA 05-111)) was evaluated in two greenhouse experiments, each with 10 ...replicates. All cultivars, except Beauregard (control) and Orleans, were reported previously as moderately resistant or resistant to
f. sp.
, and
. Plants were inoculated with
(5,000 eggs/plant) and arranged in a completely randomized design in a greenhouse with an average daily temperature of 24.8°C. Galls and egg masses per root system (0-5 scale), eggs per egg mass, eggs per gram of fresh root (gfr), and reproduction factor (RF) were determined.
infected and reproduced on all the sweetpotato cultivars. The nematode induced galls on both fibrous and storage roots, regardless of the cultivar, as well as induced necrosis and cracks on storage roots. The lesions and cracks on the storage roots were more visually pronounced on Hernandez than those on other cultivars. Cultivar Orleans sustained less root galling and egg masses than other cultivars (
≤ 0.01), and both Orleans and Beauregard cultivars had less eggs per gfr and a lower RF than Covington (5,683 eggs/gfr; RF = 16.92), Evangeline (7,161 eggs/gfr; RF = 30.01), and Hernandez (6,979 eggs/gfr; RF = 22.6). The latter two cultivars sustained the largest amount of reproduction of
. The number of eggs per egg mass ranged from 462 to 503 and was similar among all cultivars. In summary,
reproduced well on all sweetpotato cultivars; however, differences were observed among cultivars (
≤ 0.001). The host status as previously reported for other root-knot nematode species was not a good predictor of host status to
. Some sweetpotato cultivars that were reported as resistant or moderately resistant to
race 3, such as Evangeline and Hernandez, were among the best hosts to
. Root growth of Evangeline and Orleans, but not of the other cultivars, was negatively correlated with nematode eggs per gfr.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Field experiments were conducted during 2018–19, 2019–20 and 2020–21 at ICAR-Central Plantation Crops Research Institute, Kasaragod, Kerala for assessment of biocontrol fungi for the management of ...root-knot nematode (RKN), Meloidogyne incognita damaging turmeric (Cucuma longa L.) (cv. IISR-Prathibha) under coconut (Cocos nucifera L.) cropping system. Treatments included talc-based formulations of Trichoderma harzianum (ICAR- Indian Institute of Spices Research (IISR), Kerala and ICAR-Central Plantation Crops Research Institute (CPCRI), Kerala isolates) and Pochonia chlamydosporia (ICAR-Indian Institute of Spices Research, Kerala isolate), neem cake, marigold and carbosulfan 25 ec (standard check). Talc-based formulations were applied at 50 g/bed, neem cake @1 kg/bed at pre-monsoon and post-monsoon, marigold @30 plants/bed compared with untreated and standard check carbosulfan 25 ec @5 litre/bed at pre-monsoon and post-monsoon against M. incognita. Maximum reduction of RKN in the soil, as well as root, was achieved by either P. chlamydosporia (74 and 86%, respectively) or carbosulfan (67 and 87%, respectively) over the control. A number of the tillers (3.75/plant) for P. chlamydosporia and (3.23/ plant) for carbosulfan were recorded more in comparison to control (1.42/plant). The findings demonstrated that P. chlamydosporia (ICAR-Indian Institute of Spices Research) is a promising alternative to synthetic nematicides for the management of M. incognita due to its high antagonistic and good plant growth promotion activities. However, large scale field trials on these promising fungal biocontrol agents can be considered for evaluation in relation to the management of RKN under field conditions for confirmation.
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