Building soil suppressiveness against plant-parasitic nematodes

Damage caused by plant-parasitic nematodes (PPNs) represents significant losses in agriculture worldwide. Sustainable and non-agrochemical practices have been sought out for the last few years aiming the reduction of PPN outbreaks, as such practices represent less interference in the soil health. In addition, certain soils naturally show high levels of suppressiveness against nematodes. Natural suppressive soils do not allow PPN increment by a balance in soil biotic and abiotic conditions. Such soils must be better understood by which components are responsible for their natural suppressiveness. Hence, keeping, stimulating or and even creating suppressive conditions in agricultural rhizosphere has been studied and applied to reduce PPN populations. There are many aspects that implicate in soil suppressiveness against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution. However, any of those conditions is a single driver in suppressive soils against PPN. In this context, we intend to bring up an overview concerning the natural occurrence of suppressive soils against the most devastating PPNs worldwide and discuss the means used to induce suppressiveness in agricultural fields by sustainable management practices.     

具杀线虫活性植物内生细菌的筛选和活性产物

【目的】植物寄生线虫是危害植物的重要病原物,为了筛选到能在植物体内稳定定殖并且对植物寄生线虫具有较高杀线虫活性的植物内生细菌生防菌。【方法】以松材线虫为靶标,用直接触杀法进行筛选。对高活性菌株采用正交实验优化发酵条件,测定发酵液杀线虫活性的稳定性,并对菌株进行鉴定。【结果】从6种植物中分离筛选出13株对松材线虫具有较高杀线虫活性的植物内生细菌菌株,这些菌株的发酵上清液对松材线虫处理24h杀线虫率均达到了100%;其中BCM2、SZ5、CCM7和DP1这4个菌株的杀线虫活性较高,发酵上清液稀释3倍处理24h杀线虫率均达到95%以上,DP1和SZ5菌株达到了100%;并发现部分菌株发酵液能使线虫虫体发生渗漏或消解。发酵条件优化后能使发酵液杀线虫效果提高4倍。4株高活性菌株产生的杀线虫物质均对蛋白酶稳定、耐热不耐酸碱且长时间保藏活性不下降。经过鉴定DP1和CCM7是枯草芽孢杆菌(Bacillus subtilis),BCM2和SZ5是蜡样芽孢杆菌(Bacillus cereus)。【结论】经济作物体内存在一定数量的能产生杀线虫活性物质的内生细菌,其中一些细菌产生的杀线虫物质具有较强的稳定性。认为杀线虫活性的植物内生细菌具有很大的生防潜力。     

Use of chitin for controlling plant-parasitic nematodes

Cabbage plants were grown in soil amended with Clandosan (CLA) prepared from crustacean chitin (0.3% w/w). The plants were maintained in constant temperature tanks set to 15° or 30°C, in soils naturally infested with cyst nematodeHeterodera schachtii, or inoculated with the root-knot nematode,Meloidogyne javanica, respectively. At 30°C, after the first month following inoculation, CLA caused an increase in top fresh weight of plants but no reduction in nematode—induced root galling was recorded. However, when fresh plants were planted, CLA induced a large reduction in gall formation and caused an increase in top fresh weight of nematode-inoculated plants. At 15°C, CLA significantly affected the plants only after 60 days: an increase in top fresh weight and a reduction in the number of eggs per cyst were recorded. Ammonium was not detected in soil after 30 days, at 30°C, whereas at 15°C, CLA-treated soil contained twice as much ammonium as non-treated soil. After 60 days, ammonium was not detected at all. After 30 days nitrate concentrations in soil attained higher values at 30°C than at 15°C, whereas after 60 days high levels were detected only at 15°C. At 30°C, CLA induced an increase in the number of fungi, chitinolytic bacteria, and total amount of bacteria; at 15°C, such an increase was detected only with the chitinolytic microorganisms.Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel No. 2196-E, 1987 series.     

Influence of reduced agrochemical inputs on plant-parasitic nematodes

Plant-parasitic nematodes were monitored in the multidisciplinary TALISMAN (Towards a Lower Input System Minimising Agrochemicals and Nitrogen) experiment undertaken at ADAS experimental sites at Boxworth, Drayton and High Mowthorpe, England (1990–1994). The treatments compared standard and alternative rotations, reduced and full herbicide application and full and half rate nitrogen at all three sites. After 6 yr, results snowed no evidence of either a positive or negative impact of the reduced application of agrochemicals on the non-target plant-parasitic nematode populations. Greatest differences were the unexplained year to year variability in nematode numbers.     

Use of chitin for controlling plant plant-parasitic nematodes

Summary Bean and tomato seedlings, treated with different amounts of ammonia and chitin, and inoculated with the root-knot nematode,Meloidogyne javanica, were reared in two consecutive 35-day growth of shoot and root and the condition of the root systems of both plant species and degree of infection byM. javanica were decreased by increasing amounts of ammonia. Chitin caused a relatively small reduction in gall formation but almost no changes in fresh shoot weights. The effect of chitin on plant growth and nematode attack were also compared in irradiated and non-irradiated soil. In the first cycle galling index of the chitin treated plant was similar to that of untreated plants maintained in the irradiated soil conditions, while in the non-irradiated soil, chitin treatment reduced galling index. In the second cycle, chitin treatment reduced galling index in both irradiated and non-irradiated soils, especially in the latter, where galling index greatly decreased compared with the non-treated plants. Differences in fresh shoot weight between nematode-infected and nematode-free plants amended with chitin were greater under non-irradiated than irradiated conditions, especially in the second cycle. In non-irradiated soil, a higher level of chitinolytic microorganisms, particularly actinomycetes, was found in the second cycle. Contribution from the Agricultural Research Organization (ARO), Bet Dagan, Israel. No. 1520-E, 1985 series.     

Migratory plant-parasitic nematodes associated with cereals in Scotland

Ninety-eight soil samples were collected from cereal farms on mainland Scotland and examined for migratory plant-parasitic and predatory nematodes. Soil analysis was also carried out on each sample. Of the 25 parasitic nematode species identified Longidorus elongatus was the most frequently found and while populations were generally low, populations great enough to cause damage were detected. Populations of other plant-parasites were usually low. Individual species were unlikely to cause economic losses but their combined effect could possibly reduce yields. Analysis of the relationships between nematode species suggested that neither competition nor predation were important factors limiting population size. With few exceptions, none of the soil factors measured influenced the occurrence or abundance of the nematodes identified.     

Microbial control of plant-parasitic nematodes: a five-party interaction

Plant-parasitic nematodes cause significant economic losses to a wide variety of crops. Chemical control is a widely used option for plant-parasitic nematode management. However, chemical nematicides are now being reappraised in respect of environmental hazard, high costs, limited availability in many developing countries or their diminished effectiveness following repeated applications. This review presents progress made in the field of microbial antagonists of plant-parasitic nematodes, including nematophagous fungi, endophytic fungi, actinomycetes and bacteria. A wide variety of microorganisms are capable of repelling, inhibiting or killing plant-parasitic nematodes, but the commercialisation of these microorganisms lags far behind their resource investigation. One limiting factor is their inconsistent performance in the field. No matter how well suited a nematode antagonist is to a target nematode in a laboratory test, rational management decision can be made only by analysing the interactions naturally occurring among “host plant–nematode target–soil–microbial control agent (MCA)–environment”. As we begin to develop a better understanding of the complex interactions, microbial control of nematodes will be more fine-tuned. Multidisciplinary collaboration and integration of biological control with other control methods will␣also contribute to more successful control practices.     

The marksman: Bioactivated nematicides selectively kill plant-parasitic nematodes

<正>Plant-parasitic nematodes(PPNs) are destructive pathogens that cause great damage to crops and severely limit food production, hindering our ability to meet the growing worldwide demand for food(Topalovi? and Vesterg?rd,2021). The global crop losses caused by PPNs are estimated to be about 8.8%–14.6% of total crop production and 100–157 billion USD annually(Singh et al., 2013).     

Vertical distribution of plant-parasitic nematodes in sandy soil under maize

Distribution of plant-parasitic nematode species at soil depths of 0–15 cm, 15–30 cm, and 30–45 cm was examined in two maize fields in Florida during 1987 and 1988. Soil type in both fields was an Arredondo fine sand, consisting of 94–96% sand at all three depths. On most sampling dates, more than 50% of the Belonolaimus longicaudatus collected occurred at the 0–15 cm depth. Only 20–30% of Criconemella sphaerocephala were present at this depth, and the depth distribution of this nematode differed in the two fields. The greatest densities of Pratylenchus brachyurus often occurred at 15–30 cm. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed marked seasonal variation. For all species examined except B. longicaudatus, a diagnostic soil sample collected 15 cm deep would recover only a minority of the nematode population present in the soil profile.     

Infection of plant-parasitic nematodes by Paecilomyces lilacinus and Monacrosporium lysipagum

Studying the mode of infection of a biocontrol agent is important in order to assess its efficiency. The mode and severity of infection of nematodes by a soil saprophyte Paecilomyces lilacinus (Thom) Samson and a knob-producing nematode trapping fungus Monacrosporium lysipagum (Drechsler) Subram were studied under laboratory conditions using microscopy. Infection of stationary stages of nematodes by P. lilacinus was studied with three plant-parasitic nematodes Meloidogyne javanica (Treub) Chitwood, Heterodera avenae Wollenweber and Radopholus similis (Cobb) Thorne. Paecilomyces lilacinus infected eggs, juveniles and females of M. javanica by direct hyphal penetration. The early developed eggs were more susceptible than the eggs containing fully developed juveniles. As observed by transmission electron microscopy, fungal hypha penetrated the M. javanica female cuticle directly. Paecilomyces lilacinus also infected immature cysts of H. avenae including eggs in the cysts and the eggs of R. similis. Trapping and subsequent killing of mobile stages of nematodes by M. lysipagum were studied with the above three nematodes. In addition, plant-parasitic nematodes Pratylenchus neglectus (Rensch) Chitwood and Oteifa and Ditylenchus dipsaci (Kuhn) Filipjev were tested with M. lysipagum. This fungus was shown to infect mobile stages of all the plant-parasitic nematodes. In general, juveniles except those of P. neglectus, were more susceptible to the attack than adults.     

Nematicidal effect of rhizobacteria on plant-parasitic nematodes associated with vineyards

The action of metabolites and exoenzymes from rhizobacteria on different plant-parasitic nematodes has an influence on the nematicidal efficacy of the microbe. Seven rhizobacteria, divided into two bacterial groups, were evaluated in vitro for nematicidal activity on Meloidogyne ethiopica and Xiphinema index. The direct effect of their filtrates on egg hatching and juveniles of M. ethiopica as well as mobile stages of X. index was evaluated during a 72-h period. The production of four exoenzymes and two metabolites associated with nematode mortality was investigated. Molecular characterization of three isolates was performed, and the physiological profiles and lipase activity of all isolates were obtained using the BIOLOG EcoPlate system. While chitinase and collagenase were measured using the BIOLOG MT2 plate system, protease, hydrogen cyanide and hydrogen sulphide were directly determined in Petri dishes. Nematode mobile stages exposure to the bacterial filtrate revealed a nematicidal effect up to 93.7% on X. Index and up to 83.3% on M. ethiopica. The control of egg hatching varied between 35 and 85%. A positive correlation was found between the mortality of both nematode mobile stages and the concerted activities of the bacterial enzymes as well as the level of the volatile metabolites. The nematicidal effect of rhizobacteria strains varies by nematode genera and among the developmental stages evaluated.     

Arabidopsis thaliana as a new model host for plant-parasitic nematodes

We have established culture conditions for successful infection and development of several economically important cyst-forming and root-knot nematodes on Arabidopsis thaliana under monoxenic conditions. Complete life cycles were obtained with the sedentary cyst nematodes Heterodera schachtii, H. trifolii, H. cajani and the root-knot nematodes Meloidogyne incognita and M. arenariaas well as with the migratory nematode Pratylenchus penetrans. In contrast, H. goettingiana and Globodera rostochiensis were unable to develop on Arabidopsis roots. Tissue-culture quality agar and medium conditions optimized for hydroponic root culture were essential for successful infections. Detailed in-vivo observations were made inside Arabidopsis roots during the early infection stages of M. incognita and during complete development of H. schachtii. Seventy-four different ecotypes of Arabidopsis were screened for their susceptibility towards H. schachtii resulting in a range of infection rates. None of the ecotypes tested showed complete resistance in vitro. The use of Arabidopsis as a host for plant-parasitic nematodes will provide a new model system for the molecular genetic analysis of this interaction.     

Overview of organic amendments for management of plant-parasitic nematodes, with case studies from Florida

Organic amendments have been widely used for management of plant-parasitic nematodes. Relatively rapid declines in nematode population levels may occur when decomposing materials release toxic compounds, while longer-term effects might include increases in nematode antagonists. Improved crop nutrition and plant growth following amendment use may lead to tolerance of plant-parasitic nematodes. Results depend on a great variety of factors such as material used, processing/composting of material, application rate, test arena, crop rotation and agronomic practices, soil type, climate, and other environmental factors. Reasons for variable performance and interpretation of results from amendment studies are discussed. Case studies of amendments for nematode management are reviewed from Florida, where composts and crop residues are the most frequently used amendments. Plant growth was often improved by amendment application, free-living nematodes (especially bacterivores) were often stimulated, but suppression of plant-parasitic nematodes was inconsistent. Amendments were generally not as effective as soil fumigation with methyl bromide for managing root-knot nematodes (Meloidogyne spp.), and often population levels or galling of root-knot nematodes in amended plots did not differ from those in non-amended control plots. While amendments may improve plant growth and stimulate soil food webs, additional study and testing are needed before they could be used reliably for management of plant-parasitic nematodes under Florida conditions.     

Nematicidal activity of 5-hydroxymethyl-2-furoic acid against plant-parasitic nematodes

A nematicide, 5-hydroxymethyl-2-furoic acid (1), was isolated from cultures of the fungus Aspergillus sp. and its structure was identified by spectroscopic analysis. Compound 1 showed effective nematicidal activities against the pine wood nematode Bursaphelenchus xylophilus and the free-living nematode Caenorhabditis elegans without inhibitory activity against plant growth, but 1 did not show any effective nematicidal activity against Pratylenchus penetrans.     

Extraction of nematodes from Dry Valley Antarctic soils

Nematode density and taxonomic composition from Dry Valley soil processed by the sugar centrifugation (SC) method in Antarctica was compared to those extracted from soils shipped frozen to the USA and processed by either the SC or Baermann Funnel (BF) (at 5°C and 10°C) techniques. Soil selected for the extraction comparisons represented a wide range of soil properties found in the Dry Valleys. More nematodes were recovered from freshly collected Antarctic soil and from stored frozen soil using the SC technique than from BF at either temperature (P<0.05). Temperature had no effect on nematode densities extracted by the BF. Scottnema lindsayae was the most abundant species recovered by all extraction methods, but recovery was significantly lower from stored soils. Thus, nematodes can be extracted qualitatively following frozen storage using SC, but quantitative studies of nematode populations should be based on soils extracted following field sampling.