Management Of Plant Parasitic Nematodes Research Articles

Extracts and purified substances of Cabralea canjerana inhibit hatching and extracts of Schinus terebinthifolius kill juveniles of meloidogyne incognita

Nematicidal substances have been identified from plants and are potentially useful for the management of plant-parasitic nematodes. Cabralea canjerana, (Meliaceae) and Schinus terebinthifolius (Anacardiaceae) produce bioactive compounds during their secondary metabolism and little is known about the effect of such substances on plant-parasitic nematodes. In the present study, we assessed the effect of aqueous and ethanolic extracts of C. canjerana and S. terebinthifolius at 1% (m:v) and purified substances from C. canjerana (gedunin, ocotillone, cabraleadiol, a mixture of ocotillone + cabraleadiol and a mixture of shoreic acid + eichlerianic acid) on hatching and mortality of Meloidogyne incognita juveniles. Aqueous extracts of C. canjerana fruits and seeds reduced hatching by 70.3 to 95.7%. Aqueous extracts of S. terebinthifolius fruits killed 42.8 to 77.1% of juveniles. The purified substances of C. canjerana inhibited the hatching of M. incognita from 57 to 90% and did not increase the mortality of juveniles. Therefore, C. canjerana extracts and its purified substances reduce M. incognita hatching and aqueous extracts of S. terebinthifolius kill J2 of this nematode.

Nematode assemblages, food web indices and metabolic footprints in maize-pigeon pea agro-ecosystems

Pigeon pea (Cajanus cajan L.) and maize (Zea mays L.) are important food crops in developing countries due to their multiple benefits. However, their production is constrained by plant-parasitic nematodes (PPN) which cause significant yield losses. Understanding the nematode-based soil food web structure in maize-pigeon pea agro-ecosystems will allow sustainable PPN management by improving soil health. This study explored nematode community assemblages, indices and metabolic footprints in maize-pigeon pea agroecosystems in Mbeere South, Embu County, Kenya. Soil samples were collected from Gachuriri, Irabari, Kanduu, Kangeta, Kangungi, Kaninwathiga, Karimari and Mutugu regions. The recovered nematodes were identified to the genus level. There were 41 nematode genera across the eight regions. Longidorus spp., Heterocephalobus spp., Cervidellus spp., Mesorhabditis spp. and Mononchus spp. differed significantly across the regions. Meloidogyne spp., Scutellonema spp., Rotylenchulus spp. and Pratylenchus spp. were the most prevalent genera although their abundance was not statistically different across the regions. Using the structure and enrichment indices, soil food web in Irabari was degraded, whereas the other seven regions were structured. The main energy channel of organic matter decomposition in the studied regions was dominated by fungivores. There were no differences in metabolic footprints expect for bacterivore footprint. The occurrence of Hoplolaimus spp. and Xiphinema spp. showed a negative correlation with N, C, Mg and Na. This work provides useful insights into the maize-pigeon pea nematode soil food web structure and function which can be used in improving their yields and soil health.

Production of Purpureocillium lilacinum and Pochonia chlamydosporia by Submerged Liquid Fermentation and Bioactivity against Tetranychus urticae and Heterodera glycines through Seed Inoculation.

Pochoniachlamydosporia and Purpureocillium lilacinum are fungal bioagents used for the sustainable management of plant parasitic nematodes. However, their production through submerged liquid fermentation and their use in seed treatment have been underexplored. Therefore, our goal was to assess the effect of different liquid media on the growth of 40 isolates of P. lilacinum and two of P. chlamydosporia. The most promising isolates tested were assessed for plant growth promotion and the control of the two-spotted spider mite (Tetranychus urticae) and the soybean cyst nematode (Heterodera glycines). Most isolates produced > 108 blastospores mL−1 and some isolates produced more than 104 microsclerotia mL−1. Microsclerotia of selected isolates were used to inoculate common bean (Phaseolus vulgaris L.) seeds in greenhouse trials. All fungal isolates reduced the T. urticae fecundity in inoculated plants through seed treatment, while P. chlamydosporia ESALQ5406 and P. lilacinum ESALQ2593 decreased cyst nematode population. Purpureocillium lilacinum was more frequently detected in soil, whereas P. chlamydosporia colonized all plant parts. Pochonia chlamydosporia ESALQ5406 improved the root development of bean plants. These findings demonstrate the possibility of producing submerged propagules of P. chlamydosporia and P. lilacinum by liquid culture, and greenhouse trials support the applicability of fungal microsclerotia in seed treatment to control P. vulgaris pests.

Effect of differential addition of water on mobility of fluopyram in two different soils of Kerala

ABSTRACT Fluopyram, a pyridyl ethyl benzamide broad-spectrum fungicide and nematicide, used for the management of plant parasitic nematodes and soil-borne fungi, is recommended for use in crops like tomato, potato and tobacco. Fluopyram being a pesticide used for drenching soil, there is every possibility of it getting leached down with water, ultimately leading to contamination of waterbodies. An experiment was conducted to study the downward movement of fluopyram in laterite and red loam soils in Kerala, India. Fluopyram and fluopyram benzamide, each at150 µg, were loaded separately on top of the respective soil column and were eluted separately with 20, 40, 80 and 160 mL each of water equivalent to 50, 100, 200 and 400 mm rainfall. It was observed that 76.84% and 74.85% of fluopyram and 73.48% and 64.24% of fluopyram benzamide were confined to the top 0–10 cm soil with application of 20 mL water in laterite and red loam soil, respectively. More than 50% of fluopyram and fluopyram benzamide were detected in the top 0–10 cm layer of soil with the application of 40 and 80 mL water. With the application of 160 mL water, considerable reduction in the concentration of both compounds was observed and the residues moved beyond 30 cm. Leaching of residues was more in laterite soil than in red loam soil, and they are in direct relation to the volume of water applied and the residues moved beyond 30 cm depth with 160 mL water.

Bionematicides in Brazil: an emerging and challenging market

Management of plant parasitic nematodes in Brazil is a challenge and bionematicides are an important tool in the Integrated Nematode Management in several crops. There are 47 commercial bionematicides with 11 microorganisms as active ingredient available for growers in Brazil; Bacillus spp. are the main biological control agents, but fungi are also important for nematode management. Bionematicides reached 82% of the total market of nematicides in 2019/2020 in Brazil and, in soybean, they represented 90% of the area treated with nematicides. Although, the use of bionematicides is considered an emerging market worldwide, some challenges involve the correct use and formulation of organisms with different modes of action, difficulties in laboratory culturing, and the existence of non-regulated bionematicides, which do not ensure the quality, the purity, and the efficiency in the nematode control under field conditions, leading to lack of control and discredit of this tool. Considering the Brazilian biodiversity richness, a universe of new macroand microorganisms can be explored, as well as the metabolites produced by these organisms as the active ingredient of bionematicides. Expectations of an increase in this market are optimistic and may materialize in light of the increasing demand for biological products in Brazil.

A Review of Bio-Role Fumigation's in Plant Parasitic Nematode (PPNs) Control

Worldwide there are greater than 4,100 species of PPNs. The most common opponent of agricultural production is PPNs. Plant parasitic nematodes (PPN) cause substantial economic destruction to an extensive range of crops. Nematicide Chemicals are considered the furthermost operative method in reducing nematodes population. Increasing concern over chemical nematicides has increased interest in safe alternative methods to minimize these losses. This review focuses on the role of bio-fumigation against PPNs in sustainable agroecosystems. Bio-fumigation is a long-term approach for controlling diseases, nematodes, insects, and weeds in the soil. It was originally defined as the pest-controlling effect of decomposing Brassica tissues, but it was later broadened to include animal and plant leftovers. Glucosinolates are the principal active molecule responsible for the bio-fumigation process in various plants. Plant age and tissue type influence glucosinolate accumulation and myrosinase activity, which are influenced by environmental factors such as planting density and herbivory. Glucosinolates are sulphur-containing chemicals produced by the secondary metabolism of plants in the order Capparales, which includes the Brassicacea family among others. Natural antimicrobials and anti-carcinogenic agents, glucosinolates are well-known. Therefore, researchers should have to focus on environmentally save methods of plant parasitic nematode management like bio-fumigation. This biofumigation may be replace the fumigant nematicides for future.

Identification of Repellents from Four Non-Host Asteraceae Plants for the Root Knot Nematode, Meloidogyne incognita

Olfactory cues guide plant parasitic nematodes (PPNs) to their host plants. We tested the hypothesis that non-host plant root volatiles repel PPNs. To achieve this, we compared the olfactory responses of infective juveniles (J2s) of the PPN Meloidogyne incognita to four non-host Asteraceae plants, namely, black-jack (Bidens pilosa), pyrethrum (Chrysanthemum cinerariifolium), marigold (Tagetes minuta), and sweet wormwood (Artemisia annua), traditionally used in sub-Saharan Africa for the management of PPNs. Chemical analysis by coupled gas chromatography-mass spectrometry (GC/MS) combined with random forest analysis, followed by behavioral assays, identified the repellents in the root volatiles of B. pilosa, T. minuta, and A. annua as (E)-β-farnesene and 1,8-cineole, whereas camphor was attractive. In contrast, random forest analysis predicted repellents for C. cinerariifolium and A. annua as β-patchoulene and isopropyl hexadecanoate. Our results suggested that terpenoids generally account for the repellency of non-host Asteraceae plants used in PPN management.

Effect of crop sequences in combination with other ecofriendly practices for management of plant parasitic nematodes infecting jute (Corchorus olitorius L.)

Among the different biotic stress, plant parasitic nematodes are considered to be real menace to successful and profitable cultivation of crops. This tiny microscopic organism can effectively manage by application of chemical pesticides, but frequent use of chemical pesticides may induce residual effect, phytotoxicity, health hazards to human and live stocks including ground water contamination. To overcome these hazards, effort is being made to reduce the nematode infestation by some non chemical methods. Use of proper crop sequences seems to be one of the best methods to counter nematode problem. Incorporation of non host or poor host crop between two susceptible host crops can successfully reduce nematode infestation. In the present study four crop rotation sequences were tested for their efficacy to reduce the incidence of plant parasitic nematodes on jute in a naturally infested field of Biswanth College of Agriculture, Biswanath Chariali, Assam during 2019–20. Other ecofriendly nematode management practices like application of compost and crop residue, soil incorporation of dhaincha as green manure, application of bioagents were also combined with different crop sequence. Among the different crop sequences, Jute-Toria-Dhaincha-Jute was found to be most effective in reducing the final nematode population in soil and increasing the seed yield of jute followed in order of efficacy by the crop sequence Jute-Toria- Fallow- Jute. These crop sequences may be recommended for future record.

Efficacy of Beneficial Microbes in Sustainable Management of Plant Parasitic Nematodes: A Review

The soil inhabits many microbes, including plant parasitic nematodes. Plant parasitic nematodes are reported to cause substantial damage to crops which results in yield and economic losses. Chemical control is the most widely used method to control plant parasitic nematodes. However, the consequences of synthetic chemicals are detrimental to human health, animals, and the environment and face so many strict regulatory measures. Synthetic chemicals are also not reliable with their inability to provide long-term protection. Many studies have shown that the use of beneficial fungi and bacteria has the potential to prevent and suppress plant parasitic nematodes while keeping the environment safe. Several experiments have demonstrated that bioproducts of microbial origin are cheap, safe, and provide long-lasting biocontrol effects against pathogens both in vitro and field conditions. Therefore, this review aims to discuss mechanisms that beneficial microbes and their products use to successfully suppress plant parasitic nematodes. The review also explains the importance of using commercial bionematicides in the sustainable management of plant parasitic nematodes. The existing challenges that are limiting the full application of beneficial microbes, and what needs to be done to fully utilize biocontrol agents in the management of plant parasitic nematodes have also been discussed. To the best of our knowledge, this review has come at the right time to give researchers and plant growers more options when several synthetic chemical nematicides are being banned by regulatory authorities due to their hazardous effects.

Effects of organic and inorganic fertilization with bio-inoculants on the sustainable management of plant-parasitic nematodes infesting okra (Abelmoschus esculentus)

Root-knot nematodes are believed to be amongst the biological constraints causing severe damage and a great reduction in the productivity of okra. The purpose of this study was to apply organic matter and non-symbiotic nitrogen-fixing bacteria to minimize the addition of chemical fertilizers that constantly pollute the environment. Experimental studies were conducted in the field for two summers to determine the effect of inoculations of non-symbiotic nitrogen-fixing bacteria, such as Azotobacter chroococcum and Azospirillum brasilense singly and in combinations, with different recommended doses of inorganic nitrogen as well as organic matter such as neem seed cake on the growth, yield, and organic parameters of the okra crop towards the management of plant-parasitic nematodes. The results show a significant reduction in nematode multiplication through soil application of nitrogen-fixing bacteria and neem seed cake along with different recommended doses of nitrogen inoculated plants. Azotobacter was found to be less effective than Azospirillum in agronomic parameters and nematode control. The most pronounced increases were observed in the yield and growth parameters such as plant height, fresh as well as dry weights, fruit weights/plant, number of total fruits/plant and primary branches, chlorophyll content, and ascorbic acid content when A. chroococcum and A. brasilense were added concomitantly in various combinations. Agronomic parameters such as NPK content in the plant as well as in residual soil increased considerably in almost all the combinations irrespective of these biofertilizers and neem seed cake. In conclusion, the combined application of a 100% recommended dose of nitrogen fertilizer along with Azospirillum and neem seed cake is recommended for better growth and yield of okra with better control of nematodal population.

Optimizing Safe Approaches to Manage Plant-Parasitic Nematodes.

Plant-parasitic nematodes (PPNs) infect and cause substantial yield losses of many foods, feed, and fiber crops. Increasing concern over chemical nematicides has increased interest in safe alternative methods to minimize these losses. This review focuses on the use and potential of current methods such as biologicals, botanicals, non-host crops, and related rotations, as well as modern techniques against PPNs in sustainable agroecosystems. To evaluate their potential for control, this review offers overviews of their interactions with other biotic and abiotic factors from the standpoint of PPN management. The positive or negative roles of specific production practices are assessed in the context of integrated pest management. Examples are given to reinforce PPN control and increase crop yields via dual-purpose, sequential, and co-application of agricultural inputs. The involved PPN control mechanisms were reviewed with suggestions to optimize their gains. Using the biologicals would preferably be backed by agricultural conservation practices to face issues related to their reliability, inconsistency, and slow activity against PPNs. These practices may comprise offering supplementary resources, such as adequate organic matter, enhancing their habitat quality via specific soil amendments, and reducing or avoiding negative influences of pesticides. Soil microbiome and planted genotypes should be manipulated in specific nematode-suppressive soils to conserve native biologicals that serve to control PPNs. Culture-dependent techniques may be expanded to use promising microbial groups of the suppressive soils to recycle in their host populations. Other modern techniques for PPN control are discussed to maximize their efficient use.

Management of Pests and Pathogens Affecting Citrus Yield in Egypt with Special Emphasis on Nematodes

Although citriculture ranks high in Egypt as a superior orange producer and exporter country, citrus yield should be further optimized viamanagement of pests and pathogens that adversely affect citrus orchards. We throw light on the various groups of these citrus-damaging organisms to alarm for the significance of adopting adequate programs for their control. As many plant-parasitic nematode (PPN) species in Egypt and abroad; all but one, the citrus nematode Tylenchulus semipenetrans, of which are of limited distribution, this species was addressed herein in details. The citrus nematode could significantly reduce lemon yield. Before nematicidal application, growers and stakeholders should adopt strict quarantine and seedling certification programs, consider the limiting factor principle, and use appropriate nematode sampling and extraction methods. Moreover, bionematicides should be earnestly tried among other PPN management options in order to avoid human health hazards and attain pollution-free environment. Yet, holistic management should include not only nematodes but also other pests and pathogens of citrus in Egypt. We highlighted general production practices that should adequately tackle relevant citrus problems.

Nematicidal Effects of Various Fractions of Curcuma longa against Meloidogyne incognita (root knot nematodes)

Parasitism is an important limiting factor responsible to cause damage to agricultural production. Plant parasitic root knot nematodes attack several economic crops in Pakistan. Plant- parasitic nematodes considerably add huge losses to economies in the top tomatoes crop producing countries throughout the world, instead of controlling the main pathogenic nematode species as usual; one of the innovative strategies to control plant-parasitic nematodes would be to manage diversity in communities in order to lead them to be less pathogenic. The plants and their materials are one of the potential remedies for nematodes management. Turmeric (Curcuma longa) along with its several biological applications may serve as a biopesticide against Meloidogyne incognita, a nematode species. A bioassay guided isolation of various fractions of turmeric was subjected to nematicidal activity in comparison with Azadirachta indica against Meloidogyne incognita larvae at the concentration of 0.25, 0.5, and 1% for 48 hours. Alongside, Larvae and eggs of nematodes were inoculated around the tomato seedlings in experiments with turmeric in a growth chamber. The control contains water instead of turmeric. Root gall severity and final nematode population were suppressed significantly. It was observed that the use of turmeric is very important for selected plant parasitic nematodes management.

NEMATODE PARASITES OF WATERLEAF (Talinum triangulare) IN OBIO-AKPOR AND IKWERRE LOCAL GOVERNMENT AREAS OF RIVERS STATE, NIGERIA

Waterleaf, Talinum triangulare is cultivated in home gardens and fields to improve nutritional quality for the family and a source of livelihood for farmers. However, the role of T. triangulare is often counteracted by plant-parasitic nematodes (PPNs). Effective management of PPNs will depend on the identification and determination of their population and distribution. A survey was conducted in two Local Government Areas (LGAs), Ikwerre and Obio-Akpor of Rivers State to identify plant-parasitic nematodes associated with waterleaf. Multistage random sampling technique was employed in the collection of 60 bulked soil and root samples across six waterleaf monoculture farming communities. The nematodes were extracted, identified and their population determined using standard procedures. Occurrences, relative importance values (RIV) and diversity indices were determined. Other data were analysed using descriptive statistics and analysis of variance. Six plant-parasitic nematodes genera were encountered in this study, Helicotylenchus, Pratylenchus, Paratylenchus, Meloidogyne, Scutellonema and Tylenchulus. Pratylenchus and Helicotylenchus were the most frequently occurring nematode pest genera with equal relative frequency of occurrence of 38.89%. Pratylenchus species with RIV of 61.34% was the most important nematode pest associated with waterleaf across the six farm communities. The dominance index of 0.71 for the nematode genera showed that some nematode species dominated others. Alakahia farms had the highest population of plant-parasitic nematodes (2,780) across the six farm communities, whereas Omagwa farms had the lowest (250). The study showed that nematode pests are associated with waterleaf and could be contributing to yield losses in this crop

Association of Duddingtonia flagrans with microorganisms for management of Meloidogyne javanica and acquisition of nutrients in soybean

The use of beneficial microorganisms in agricultural production systems has been growing due to the worldwide demand for more sustainable crops. Biological control has thus gained prominence in the management of plant parasitic nematodes, as the result of the efficiency in reducing their population densities, improving plant development. The objectives of this study were to evaluate the association of the nematophagous fungi Duddingtonia flagrans and Pochonia chlamydosporia to reduce the population of Meloidogyne javanica in soybean, and to check if D. flagrans promotes the acquisition of nutrients in soybean. The plant-parasitic nematode biocontrol experiment was carried out twice, at 20 and 27 °C. In the nutrient acquisition test, plants grown in soil infested by D. flagrans and/or Bradyrhizobium japonicum were compared with plants grown in soil without the application of these organisms. All treatments with fungi resulted in reductions in the numbers of eggs and galls per g of root, when compared to the control. A compatible association between D. flagrans and P. chlamydosporia was verified in the experiment. For the nutrition test, the fungus, combined or not with B. japonicum, promoted an increase in the nutrient content in the soybean roots. In this study, we found that D. flagrans may be associated with other microorganisms to control nematodes and to promote the acquisition of nutrients.

Marine Organisms for the Sustainable Management of Plant Parasitic Nematodes.

Plant parasitic nematodes are annually responsible for the loss of 10%–25% of worldwide crop production, most of which is attributable to root-knot nematodes (RKNs) that infest a wide range of agricultural crops throughout the world. Current nematode control tools are not enough to ensure the effective management of these parasites, mainly due to the severe restrictions imposed on the use of chemical pesticides. Therefore, it is important to discover new potential nematicidal sources that are suitable for the development of additional safe and effective control strategies. In the last few decades, there has been an explosion of information about the use of seaweeds as plant growth stimulants and potential nematicides. Novel bioactive compounds have been isolated from marine cyanobacteria and sponges in an effort to find their application outside marine ecosystems and in the discovery of new drugs. Their potential as antihelmintics could also be exploited to find applicability against plant parasitic nematodes. The present review focuses on the activity of marine organisms on RKNs and their potential application as safe nematicidal agents.

Short-Time Impact of Soil Amendments with Medicago Plant Materials on Soil Nematofauna.

Soil amendments with plant materials from Medicago species are widely acknowledged for a suppressive effect on plant-parasitic nematodes but their impact on beneficial components of soil nematofauna is still unknown. A study on potted tomato was carried out to investigate the short-time effects on the overall nematofauna of dry biomasses from six different Medicago species, i.e., M. sativa, M. heyniana, M. hybrida, M. lupulina, M. murex and M. truncatula, incorporated to natural soil at 10, 20, or 40 g kg−1 soil rates. All amendments resulted in a significant decrease of the total nematofauna biomass, whereas total abundance was significantly reduced only by M. heyniana, M. hybrida, and M. lupulina biomasses. Almost all the Medicago amendments significantly reduced the relative abundance of plant-parasites and root fungal feeders. All amendments significantly increased the abundance of bacterivores, whereas fungivores significantly increased only in soil amended with M. heyniana, M. lupulina and M. sativa plant materials. Mesorhabditis and Rhabditis were the most abundant genera of bacterivores, whereas Aphelenchoides and Aphelenchus prevailed among the fungivores. Predators were poorly influenced by all the tested Medicago biomasses, whereas the abundance of omnivores was negatively affected by M. heyniana and M. lupulina. Values of the Maturity Index and Sum Maturity Index were reduced by treatments with M. heyniana, M. hybrida, M. lupulina and M. sativa plant materials, whereas most of the tested amendments decreased values of the Channel Index while increasing those of the Enrichment Index. Enrichment and bacterivore footprints raised following soil addition with Medicago biomasses, whereas composite and fungivore footprints were significantly reduced. According to their overall positive effects on soil nematofauna, amendments with Medicago plant materials or their formulated derivatives could represent an additional tool for a sustainable management of plant-parasitic nematodes.

Evaluation of a new chemical nematicide, fluazaindolizine (ReklemelTM active), for plant-parasitic nematode management in bermudagrass.

Plant-parasitic nematodes are a major pest of turfgrass in the United States, yet there are few options for successful management. Most current management strategies rely on the use of a limited number of chemical nematicides, so finding a new management option for nematode suppression would be extremely valuable for turfgrass managers. The aim of this study is to evaluate a new nematicide, fluazaindolizine (Reklemel™ active), for its ability to reduce plant-parasitic nematode population density and improve turfgrass quality. Separate research trials were conducted on bermudagrass infested with Belonolaimus longicaudatus and Meloidogyne incognita in greenhouse, microplot, and field settings over 2018 and 2019. Both greenhouse evaluations demonstrated multiple rates of fluazaindolizine reduced B. longicaudatus population density, and one of the two M. incognita trials showed multiple rates of fluazaindolizine reduced nematode population density. Fluazaindolizine was also effective at reducing population density of both B. longicaudatus and M. incognita in microplot settings for both 2018 and 2019, and a significant improvement in turf quality was observed for both visual turfgrass ratings and NDVI. Field trials demonstrated a significant reduction for both B. longicaudatus and M. incognita population density by multiple rates of fluazaindolizine, but no significant differences in turf quality ratings were observed. Overall, fluazaindolizine shows promise as a chemical nematicide for plant-parasitic nematode management on turfgrass.

Effects of fluopyram and azadirachtin integration with sunn hemp on nematode communities in zucchini, tomato and sweet potato in Hawaii.

Fluopyram (Velum® One) is a synthetic nematicide and azadirachtin (Molt-X®) is a biological nematicide. Both have shown promise against plant-parasitic nematodes on several agriculturally important crops. There is a lack of information on integration of pre-plant sunn hemp (Crotalaria juncea) cover crop with these post-plant nematicides, aiming to improve plant-parasitic nematodes management and mitigate any detrimental effects on free-living nematodes. Three field trials were conducted to investigate the effects of fluopyram alone or in combination with pre-plant sunn hemp cover crop, and azadirachtin combined with pre-plant sunn hemp on Rotylenchulus reniformis and Meloidogyne spp., and free-living nematodes. Zucchini (Cucurbita pepo) and tomato (Solanum lycopersicum) were grown in Trials I and II, and sweet potato (Ipomoea batatas) only was grown in Trial III. In all three trials, early applications of fluopyram at crop planting were effective in suppressing the abundance of Meloidogyne spp. (M. incognita and M. javanica) but it was not effective in reducing R. reniformis in the soil. Combining sunn hemp with fluopyram was suppressive to R. reniformis on short-term zucchini crop, but not on longer term tomato and sweet potato crops. In addition, application of fluopyram at transplanting was the key to successful suppression of Meloidogyne spp. as later fluopyram chemigation (at 2 weeks after planting in Trial II or 1 month after planting in Trial III) had no effect against Meloidogyne spp. On the other hand, planting of sunn hemp followed by monthly post-plant azadirachtin application consistently suppressed R. reniformis, but this treatment did not suppress Meloidogyne spp. Integrating sunn hemp with fluopyram increased zucchini yield by >2.3 folds and that with azadirachtin increased the zucchini yield by >1.7 folds. Although no yield improvement was observed on tomato in Trial II, integrating sunn hemp with azadirachtin and fluopyram increased tomato yield by 0.23 and 1.12 folds, respectively, in Trial I. Marketable yield of sweet potato was increased by 4.5–6.4 folds in all the fluopyram treatments but was only increased 61.5% by sunn hemp plus azadirachtin treatment. While fluopyram alone often reduced the abundance of free-living nematodes, integrating with sunn hemp mitigated the negative impacts of fluopyram on soil health.

Current Utility of Plant Growth-Promoting Rhizobacteria as Biological Control Agents towards Plant-Parasitic Nematodes.

Plant-parasitic nematodes (PPN) are among the most economically and ecologically damaging pests, causing severe losses of crop production worldwide. Chemical-based nematicides have been widely used, but these may have adverse effects on human health and the environment. Hence, biological control agents (BCAs) have become an alternative option for controlling PPN, since they are environmentally friendly and cost effective. Lately, a major effort has been made to evaluate the potential of a commercial grade strain of plant growth-promoting rhizobacteria (PGPR) as BCAs, because emerging evidence has shown that PGPR can reduce PPN in infested plants through direct and/or indirect antagonistic mechanisms. Direct antagonism occurs by predation, release of antinematicidal metabolites and semiochemicals, competition for nutrients, and niche exclusion. However, the results of direct antagonism may be inconsistent due to unknown endogenous and exogenous factors that may prevent PGPR from colonizing plant’s roots. On the other hand, indirect antagonism may occur from the induced systemic resistance (ISR) that primes whole plants to better fight against various biotic and abiotic constraints, actuating faster and/or stronger defense responses (adaption), enhancing their promise as BCAs. Hence, this review will briefly revisit (i) two modes of PGPR in managing PPN, and (ii) the current working models and many benefits of ISR, in the aim of reassessing current progresses and future directions for isolating more effective BCAs and/or developing better PPN management strategy.