Free-living Nematode Populations Research Articles

Temporal dynamics of soil nematode population in an Acacia saligna invaded Mediterranean sand dune ecosystem

Summary The invasive Australian tree, Acacia saligna, has been the subject of numerous studies investigating its ecological impact. However, the effect of its invasion on the soil free-living nematode population has yet to be researched. In this study, we examined the impact of A. saligna on the soil free-living nematode population in a coastal dune site with a Mediterranean climate during three sampling periods. Soil samples were collected from beneath the canopies of A. saligna trees, the native dominant shrub Retama raetam, and bare soil plots as a control. Our findings reveal that A. saligna increases the density of the soil free-living nematode population and changes its trophic and taxonomic composition. While the nematode diversity and functional index scores did not significantly differ between sampling locations, they did differ between the different sampling times, highlighting the seasonal dynamics of the soil nematode population in Mediterranean sand dunes.

Abundance and diversity of terrestrial free-living nematodes in potato agroecosystem

Abstract. Mutala’liah, Manan A, Bayyinah LN. 2023. Abundance and diversity of terrestrial free-living nematodes in potato agroecosystem. Nusantara Bioscience 15: 129-136. The presence of terrestrial free-living nematodes in agroecosystems is frequently overlooked. However, these microorganisms in agroecosystems soil are beneficial for supporting plant growth. These microorganisms could recycle the nitrogen in soil, decomposition and mineralization of organic matter, and suppress the densities of plant parasitic nematodes through their life strategy. Terrestrial free-living nematodes are classified according to trophic groups such as bacterivores, fungivores, predators, and omnivores. Reports on the abundance and diversity of terrestrial free-living nematode populations in agroecosystems, especially on potato plantations, were limited. They usually focused on the plant parasitic nematode’s attack on potatoes. Therefore, this study aimed to examine the diversity and abundance of terrestrial free-living nematodes in potato agroecosystems. The current study was conducted in two potato fields in Pratin Village, Serang, Purbalingga, Central Java, Indonesia. Soil samples were collected from two potato fields planted with different varieties (Granola and Atlantik) and extracted using the Whitehead-tray method. The variables observed were the diversity of genera and the abundance of terrestrial free-living nematode populations from each field. Population density data were analyzed by T-test, and diversity (H'), evenness (E), and dominance index (D) were also calculated. The results showed that the mean population densities of terrestrial free-living nematodes in the two fields were significantly higher at 918.40 individuals/ 100 g of soil in the Atlantik field than in the Granola field 76.53 individuals/ 100 g of soil. However, the diversity, evenness, and dominance index were not significantly different in both fields. Genera of nematode found in the Granola field were Diplogaster, Dorylaimus, Trypilla, and Lotonchus, while in the Atlantik field were Rhabditis and Dorylaimus.

Seasonal fluctuations attenuate stimulatory or inhibitory impacts of colonial birds on abundance, structure and diversity of soil biota.

Soil microorganisms and free-living nematodes were investigated in association with the nesting and roosting habitats of the following piscivorous and omnivorous colonial birds: black kite (Milvus migrans), great cormorant (Phalacrocorax carbo), black-crowned night heron (Nycticorax nycticorax) and little egret (Egretta garzetta), in Israel's Mediterranean region. Abiotic variables, abundance, trophic structure, sex ratio and genus diversity of soil free-living nematodes, and total abundance of bacteria and fungi, were measured during the wet season, following our previous study conducted during the dry season. The observed soil properties were important drivers of soil biota structure. Presence of the most efficient elements for soil organisms, such as phosphorus and nitrogen, was strongly dependent on the diet of the compared piscivorous and omnivorous bird colonies; levels of these nutrients were notably higher in the bird habitats than in their respective control sites during the study period. Ecological indices showed that the different species of colonial birds can have different (stimulatory or inhibitory) impacts on abundance and diversity of the soil biota, affecting the structure of the soil free-living nematode population at the generic, trophic and sexual levels during the wet season. A comparison with results from the dry season illustrated that seasonal fluctuations can change, and even attenuate the effect of bird activity on the abundance, structure and diversity of the soil communities.

On-Farm Evaluations of Nonfumigant Nematicides on Nematode Communities of Peach.

Experiments were established to evaluate the efficacy of currently available nonfumigant chemical and biological nematicides against nematode communities in peach orchards in two different geographic regions of South Carolina: the Upstate and Ridge. The treatments included sole or mixed application of two chemical nematicides (oxamyl and fluopyram) and a biological nematicide (Majestene) plus an untreated control. Ring nematode and lesion nematode were predominant in Upstate and Ridge orchards, respectively. Fluopyram was the most effective nematicide in the Upstate orchard, and it reduced plant-parasitic nematodes by 69% relative to the untreated control at 3months postapplication. Similarly, fluopyram and oxamyl suppressed 74 to 87% of plant-parasitic nematodes in the Ridge orchard at 2months postapplication. Significant effects of Majestene on plant-parasitic nematodes was not observed. Mixed applications of nematicides were also effective in suppressing plant-parasitic nematodes although the suppressions were not always significant from sole applications or the control. The chemical nematicides significantly reduced free-living nematodes in the first 2months following their applications in the Ridge orchard, the reductions ranging from 60 to 79% relative to the control. However, free-living nematode populations quickly rebounded to the highest level in 3months following the nematicide applications. Free-living nematode communities in the Upstate orchard did not experience any significant effects of nematicides until 4 months following nematicide application; at that time there was a 60 to 68% decline in populations. Results from this study suggest that the nonfumigant nematicides can only provide a short-term management of plant-parasitic nematodes in peach.

A Biochar Improves the Efficacy of Green Manure-Based Strategies to Suppress Soybean Cyst Nematode (Heterodera glycines) and Promotes Free-Living Nematode Populations

A Biochar Improves the Efficacy of Green Manure-Based Strategies to Suppress Soybean Cyst Nematode (Heterodera glycines) and Promotes Free-Living Nematode Populations

Distribution of plant-parasitic nematodes and comparative effects of fadama (hydromorphic) fields and upland fields on plant-parasitic nematodes and free-living nematodes on three indigenous vegetables commonly grown in Osun State Nigeria

Surveys were conducted in 2016 and 2017 to investigate the distribution of plant-parasitic nematodes and the effects of fadama fields and upland fields on plant-parasitic and free-living nematodes. A total of 84 soil samples were collected from seven Local Government Areas visited in Osun State. Soil samples were collected from two fadama fields and two upland fields in all the LGAs visited. Nematodes were extracted, counted and identified under a compound microscope according to the morphological characteristics of the nematodes. The results showed that sixteen genera of plant-parasitic nematodes were found associated with Solanum macrocarpon, Amaranthus cruentus and Telfairia occidentalis. Meloidogyne\\ Helicotylenchus and Rotylenchulus were the most abundant nematodes associated with the vegetables. Fadama fields significantly had lower populations of plant-parasitic nematodes and higher populations of free-living nematodes in comparison with upland fields in fields sown to the vegetables. Farmers are advised to take full advantage of fadama fields in vegetable production.

Toxic effects of phenanthrene intensify with an increase of temperature for the populations of a free-living nematode

Phenanthrene is one of the most common Polycyclic Aromatic Hydrocarbons (PAHs) in the marine environment. It has high lipoafinity and environmental persistence and tends to accumulate in benthic ecosystems. Exposure to phenanthrene can have severe impacts on a wide range of marine organisms, from nematodes to fish. These effects can be exacerbated with concurrent warming associated with climate change. In this study we investigated the response of free-living nematode populations of the species Diplolaimelloides delyi following exposure to different phenanthrene concentrations under normal and increased temperature conditions (from 25 °C up to 35 °C). Phenanthrene was toxic to D. delyi, causing a decrease in population growth (at concentrations ≥1 μg ml−1) and negatively affecting their development times and reproduction (at concentrations ≥2.5 μg ml−1). The observed effects intensified with increasing temperature, leading to further reduced development and population growth rate, arrested reproduction, and even mortality in 100% of the populations exposed to phenanthrene concentrations over 5 μg ml−1 at the highest temperature used (30 °C). Thermal-induced toxicity effects on marine populations can be significant, and current climate change and warming may have substantial implications for marine food webs and ecosystem functioning.

A database for ITS2 sequences from nematodes

BackgroundMarker gene surveys have a wide variety of applications in species identification, population genetics, and molecular epidemiology. As these methods expand to new types of organisms and additional markers beyond 16S and 18S rRNA genes, comprehensive databases are a critical requirement for proper analysis of these data.ResultsHere we present an ITS2 rDNA database for marker gene surveys of both free-living and parasitic nematode populations and the software used to build the database. This is currently the most complete and up-to-date ITS2 database for nematodes and is able to reproduce previous analysis that used a smaller database.ConclusionsThis database is an important resource for researchers working on nematodes and also provides a tool to create ITS2 databases for any given taxonomy.

Evaluation of Nematicidal Activity of Fluensulfone against Non-Target Free-Living Nematodes under Field Conditions

The use of nematicides with reduced toxic side-effects against non-target free-living nematodes is a favorable option for farmers to control plant-parasitic nematodes. The nematicide fluensulfone was registered in several countries for the control of the root-knot nematodes, Meloidogyne spp. among other plant-parasitic nematodes. This study aimed to evaluate the nematicidal activity of fluensulfone against non-target nematode fauna in four field experiments, each under different conditions (soils types and plant hosts). Nematodes extracted from soil samples were classified and counted based on their morphological characters. Fluensulfone significantly reduced damage caused by root-knot nematodes to tomato and sweet potato plants, while overall non-target free-living nematode population densities were maintained at the same level as those in control. Different diversity indices (e.g., Shannon-Wiener H’, Simpson’s D, species richness, evenness J’, maturity indices) and principal component analyses in the four experiments showed that fluensulfone treatment kept a similar diversity level of non-target free-living nematode fauna to that of the non-treated control. The results suggested that fluensulfone may have minimal impact to free-living nematode fauna in both population density and diversity when the nematicide was applied to control Meloidogyne spp.

Evaluation of non-fumigant chemical and biological nematicides for strawberry production in Florida

In Florida, strawberry is an economically important horticultural crop. Plant-parasitic nematodes present a significant obstacle for strawberry growers in the sandy soils found in this state. Historically, nematodes have been controlled through the application of soil fumigants; however, there is interest in exploring the use of non-fumigant nematicides that can provide similar levels of control and at the same time be more environmentally friendly than fumigants. Using two field experiments, the effects of non-fumigant chemical and biological nematicides on plant vigour and fruit yield, populations of plant-parasitic nematodes, and populations of free-living nematode feeding groups were evaluated. In experiment 1, soil fumigation with metam potassium, as well as all non-fumigant chemical nematicides (fluopyram, fluensulfone, fluazaindolizine) failed to increase plant vigour, fruit yield, or suppress populations of plant-parasitic nematodes. In experiment 2, fluopyram increased fruit yield and suppressed Belonolaimus longicaudatus populations by the end of the growing season. Biological nematicides (Dazitol®, Majestene®, and Nemakill®) did not enhance crop establishment or suppress plant-parasitic nematode populations. Soil fumigation with 1,3-dichloropropene + chloropicrin provided consistent enhancement of plant vigour and fruit yield, as well as suppressed populations of B. longicaudatus; however, populations of free-living nematodes were also reduced. Overall, soil application of fluopyram shows potential to be a component of an integrated pest management strategy for the control of B. longicaudatus populations on strawberry in Florida.

Long-term farming systems modulate multi-trophic responses

Soil microbiome and multi-trophic relationships are essential for the stability and functioning of agroecosystems. However, little is known about how farming systems and alternative methods for controlling plant pathogens modulate microbial communities, soil mesofauna and plant productivity. In this study, we assessed the composition of eukaryotic microbial groups using a high-throughput sequencing approach (18S rRNA gene marker), the populations of parasitic and free-living nematodes, plant productivity and their inter-relationships in long-term conventional and organic farming systems. The diversity of the fungal community increased in the organic farming system compared to the conventional farming system, whereas the diversity of the protist community was similar between the two farming systems. Compared to conventional farming, organic farming increased the population of free-living nematodes and suppressed plant parasitic nematodes belonging to Meloidogynidae and Pratylenchidae. Fungal diversity and community structure appeared to be related to nematode suppression in the system receiving organic fertilizer, which was characterized by component microbial groups known to be involved in the suppression of soil pathogens. Unraveling the microbiome and multi-trophic interactions in different farming systems may permit the management of the soil environment toward more sustainable control of plant pathogens.

Dynamics of plant parasitic and free living nematode populations in sugarcane <i>Saccharum officinarum</i> in Fiji


 
 
 Parasitic nematodes are one of the main constraints in the production of sugarcane, Saccharum officinarum, in Fiji and other sugarcane-growing countries. Both plant parasitic and free-living nematodes are associated with roots of the plant, and the level of infestation affects both soil health and cane yield. This study examined the dynamics of plant parasitic and free-living nematode populations in sugarcane crops in Drasa Estate, Lautoka, Fiji. Soil samples to quantify nematode populations were collected ve times during the crop cycle. There was an exponential increase in the plant parasitic nematode population with time after planting (nematode population=64.316e0.0112x; R2=0.56, x=days after planting). However, the increase was not consistent among the different nematode groups. Significant increases in Lesion (P<0.05), Rootknot (P<0.05), Spiral (P<0.01), and Ring (P<0.03) nematode populations were found but not for Reniforms (P>0.05). Populations of free-living nematodes built up 90 days after planting and remained elevated in the ratoon crop. Populations of parasitic nematodes increased with the growth of cane (as measured by cane height) with increases occurring faster in the ratoon than in the plant crop (P=0.001). The number of free-living nematodes may have affected population growth of parasitic nematodes.
 
 

The Mesostigmatid Mite Protogamasellus mica, an Effective Predator of Free-Living and Plant-Parasitic Nematodes

Protogamasellus mica was extracted from a sugarcane field in Australia and cultured on bacterial-feeding nematodes. Studies with various nematodes in laboratory arenas showed that one mite and its progeny reduced nematode numbers by between 26 and 50 nematodes/day. A bacterivore (Mesorhabditis sp.), a fungivore (Aphelenchus avenae), and two plant parasites (root-knot nematode, Meloidogyne javanica and root-lesion nematode, Pratylenchus zeae) were all reduced at much the same rate despite the fact that the nematodes are quite different in size and motility and belong to different trophic groups. When sugarcane was grown in the greenhouse for 8 wk, stunt nematode (Tylenchorhynchus annulatus), a plant parasite that feeds ectoparasitically on roots, was almost eliminated from pots inoculated with the mite, and numbers of microbivores and root-lesion nematode were markedly reduced. Huge reductions in nematode populations were also observed when mites were added to microcosms containing small quantities of defaunated soil. These results show that P. mica multiplies rapidly when nematodes are available as a food source and has the capacity to play a role in regulating populations of both plant-parasitic and free-living nematodes. Future research should focus on understanding the crop and soil management practices required to enable this mite and other predatory species to thrive.

Carbon-rich organic fertilizers to increase soil biodiversity: Evidence from a meta-analysis of nematode communities

Organic fertilizer applications that boost soil fertility and crop production are expected to enhance soil biodiversity, making ecosystems more resilient to stress. Numerous studies have compared biodiversity in soil receiving organic fertilizer to soil under other fertilizer regimes (inorganic fertilizers, unfertilized), yet the data were not analyzed systematically across studies. We evaluated fertilizer effects on soil nematode communities with a meta-analysis of more than 229 data points from 54 studies around the world that were published between 1996 and 2015. Data were from cropland and considered five fertilizer regimes. These regimes include unfertilized soils and those receiving inorganic fertilizers (2 regimes), as well as organic fertilizers (2 regimes). Species richness and total nematode abundance increased with increasing carbon (C) inputs from fertilizers, whereas greater nitrogen (N) application rates from fertilizers significantly reduced the species richness, Shannon⿿s diversity (H⿲), maturity index (MI) and omnivore-predator nematode abundance. This could indicate that high fertilizer N inputs simplifies the nematode community structure and functions. Species richness, omnivore-predator nematode abundance and structural index (SI) increased with the organically-fertilized regime and declined in inorganically-fertilized regimes, suggesting that organic fertilizers can buffer stresses and sustain soil food web functions. Furthermore, organic fertilizers differed in their impact on soil nematodes, as those with C-rich crop residues supported larger free-living nematode populations and greatly promoted H⿲, SI and enrichment index (EI), whereas N-rich animal manure was more effective in controlling plant-feeding nematodes. Our review suggests that the application of C-rich crop residues is the most effective practice to enhance soil biodiversity in intensively managed agroecosystems, highlighting the importance of regular applications of straw and other C-rich residues to preserve the ecological resilience of cropland.

Spatial association between entomopathogenic and other free-living nematodes and the influence of habitat

Spatial association between entomopathogenic and free-living nematode populations in soil were analyzed at the landscape scale. GPS coordinates were obtained for 479 locations where soil samples were collected to extract nematodes. Habitats sampled included vegetable and agronomic crop fields, grassy borders adjacent to fields, residential lawns, meadow and forested wetlands in a vegetable growing region in northwest Ohio. Free-living nematodes were classified according to trophic level (bacterivores, fungivores, carnivores, and omnivores) and life history characteristics (r-selected colonizing versus K-selected persisting species on a 1–5 scale). Spatial associations based on spatial analysis of distance indices (SADIE) were analyzed and compared among entomopathogenic nematodes and free-living nematode functional guilds defined by the classifications described above. Spatial aggregation indices (Ia) revealed that each functional guild's spatial pattern varied among habitats. Considering all data regardless of habitat, spatial aggregation indices showed that functional guilds with K-selected persisting life history traits were less aggregated, whereas those with r-selected colonizer life history traits were more aggregated. The spatial aggregation index of entomopathogenic nematodes was similar to that of the r-selected colonizer type free-living nematodes, which share several life history traits including bacteriophagy, high reproductive rates, insect phoresy, and greater abundance in grassy borders, where spatial associations between entomopathogenic and r-selected colonizing functional guilds of free-living nematodes were particularly strong. The spatial aggregation patterns of entomopathogenic and free-living nematodes, suggest that these species associate over larger areas than previously measured and that the extent of these spatial associations might be predicted by the nematode life history traits.

Efeito da aplicação de herbicidas dessecantes na soja sobre as populações de nematoides no solo

The use of herbicides is the main method of weed control in soybeans. Desiccants are also being used routinely to anticipate the harvest and / or minimize the deterioration of seed quality. There is the possibility of direct or indirect contact with such pesticides, affect the community of nematodes in the soil. However, such effects and their magnitudes are yet to be clarified, especially in the case of selective herbicides. Thus, the objective of this study was to evaluate the use of selective herbicides in soybean on nematodes harmful to the crop. The experiment was conducted with transgenic soybean (‘M-SOY 7908RR’). The experimental design was a randomized block design with the following treatments: paraquat (400 g a.i ha-1), diquat (200 g a.i ha-1), a mixture of paraquat and diquat (300 + 150 g a.i ha-1), two doses of carfentrazone ethyl (20 g a.i ha-1 and 30 g a.i ha-1) and control (without desiccant application). The nematode community in the area was monitored in four periods. In none of those was found significant variation in the populations of nematodes harmful to soybeans, due to the application of any of desiccants. However, especially in the last sampling time, the desiccant application always resulted in increased populations of free-living nematodes and parasites those considered weak for soybean.

Efeito da aplicação de herbicidas dessecantes na soja sobre as populações de nematoides no solo

The use of herbicides is the main method of weed control in soybeans. Desiccants are also being used routinely to anticipate the harvest and / or minimize the deterioration of seed quality. There is the possibility of direct or indirect contact with such pesticides, affect the community of nematodes in the soil. However, such effects and their magnitudes are yet to be clarified, especially in the case of selective herbicides. Thus, the objective of this study was to evaluate the use of selective herbicides in soybean on nematodes harmful to the crop. The experiment was conducted with transgenic soybean (‘M-SOY 7908RR’). The experimental design was a randomized block design with the following treatments: paraquat (400 g a.i ha-1), diquat (200 g a.i ha-1), a mixture of paraquat and diquat (300 + 150 g a.i ha-1), two doses of carfentrazone ethyl (20 g a.i ha-1 and 30 g a.i ha-1) and control (without desiccant application). The nematode community in the area was monitored in four periods. In none of those was found significant variation in the populations of nematodes harmful to soybeans, due to the application of any of desiccants. However, especially in the last sampling time, the desiccant application always resulted in increased populations of free-living nematodes and parasites those considered weak for soybean.

Biocontrol of the Reniform Nematode by Bacillus firmus GB-126 and Paecilomyces lilacinus 251 on Cotton.

Due to increased restrictions on the use of chemical nematicides, alternative nematode management strategies, including biocontrol, are needed. The objectives of this study were to evaluate the potential of Bacillus firmus GB-126 and Paecilomyces lilacinus 251 in commercial formulations applied separately or concomitantly to manage Rotylenchulus reniformis in cotton grown under greenhouse, microplot, and field conditions. In the greenhouse, seed treated with B. firmus (1.4 × 107 CFU/seed), an application of P. lilacinus (0.3% vol/vol of water), or the combination of B. firmus and P. lilacinus reduced the number of females, eggs, and vermiforms of R. reniformis (P ≤ 0.02) and increased populations of free-living nematodes (P ≤ 0.01). In microplots and field conditions, populations of R. reniformis vermiforms decreased when exposed to B. firmus and P. lilacinus biocontrol agents at midseason (P ≤ 0.04). Furthermore, stem diameter and free-living nematode numbers increased (P ≤ 0.01) with the combination of B. firmus and P. lilacinus. In the field, numbers of females, eggs, and vermiform life stages at the end of the growing season decreased in the presence of the biocontrol agents applied individually or concomitantly (P ≤ 0.01). Cotton yields from the application of B. firmus GB-126 and P. lilacinus 251 were similar to those from aldicarb, the chemical nematicide standard.

The effect of free-living nematodes on nitrogen mineralisation in undisturbed and disturbed soil cores

Soil fauna, particularly nematodes, are considered to strongly contribute to nitrogen mineralisation through grazing on microflora during decomposition. Demonstration of this effect has mostly relied on calculation-based soil food web analyses or experiments involving simplified and artificially constructed food webs. We carried out an incubation experiment in which defaunated soil cores were reinoculated with entire soil nematode populations extracted from bulk soil and during which nitrogen mineralisation was measured. Both undisturbed and disturbed cores were prepared to investigate whether a representative pore structure influences the effect of entire free-living nematode populations on nitrogen mineralisation. Cores were subjected to a 5 kGy gamma irradiation dose sufficient to eliminate all soil fauna while leaving the microbial biomass largely intact. Half of the irradiated cores were reinoculated with nematodes extracted from a corresponding volume of bulk soil and incubated for 82 days. The microbial biomass was not strongly affected by gamma irradiation or nematode addition but declined strongly in all treatments during incubation. Reinoculation of nematodes was successful in establishing populations of a similar size and composition as in the control samples. Net nitrogen mineralisation from indigenous soil organic matter was observed in all treatments throughout the incubation, but was always more pronounced in irradiated cores. Total mineral nitrogen concentrations did not differ significantly between simply irradiated and irradiated then reinoculated cores. However by the end of the incubation period nematode addition resulted in 87% and 23% more NO3−–N g−1 dry soil in undisturbed and disturbed cores respectively, while NH4+–N g−1 dry soil decreased by 50% in both core types. We found no convincing evidence for a contribution of free-living nematodes on total nitrogen mineralisation, but the activity of nitrifying organisms was clearly stimulated by nematode grazing.

89 % reduction of a potato cyst nematode population using biological control and rotation

A major issue of potato cultivation in temperate zones is the potato cyst nematode Globodera rostochiensis. Population density of G. rostochiensis is high in Mexican potato fields. Control currently consists of the inefficient application of high doses of chemical nematicides. We evaluated the population density of G. rostochiensis in potato production plots in central Veracruz, Mexico. Plots were treated with the biocontrol agent Paecilomyces sp. and rotation with two different leguminous crop plants, Pisum sativum and Vicia faba. A random block experimental design was used with four different treatments over two crop cycles: (1) biological control with crop rotation, (2) crop rotation only, (3) biological control applied to soil left in fallow, and (4) soil left in fallow only. We measured the number and content of cysts, and the number of J2 juveniles of G. rostochiensis in the soil. We then estimated the infestation level in soil and the multiplication rate (Pf/Pi). The number of free-living nematodes was also quantified. Results show that the highest mitigation of G. rostochiensis was observed for the biological control rotation, with 89.2 % reduction, and for the biological control fallow treatments with 84.4 % reduction. In rotation plots, infestation level decreased by 30.7 %. In the biological control rotation and biological control fallow treatments, the Pf/Pi was 0.1 and 0.15, respectively. The highest Pf/Pi of 0.93 was found in the fallow plots. The biological control agent did not significantly affect the free-living nematode populations. In this study, the nematophagous fungus Paecilomyces sp. was used for the first time to efficiently reduce the population of G. rostochiensis in two crop cycles.