Selection of rhizobacteria able to produce metabolites active against Meloidogyne exigua

This work aimed to select potentially useful rhizobacteria for the control of Meloidogyne exigua, a widely disseminated root-knot nematode found in Brazilian coffee fields. Initially, crude metabolites produced in liquid medium by 69 isolated rhizobacteria strains (previously obtained from several plants collected in the south of Minas Gerais State, Brazil) were tested in vitro for lethality towards M. exigua second stage juveniles (J₂). Substances produced by strains of Bacillus cereus, B. megaterium, B. pumilus, B. thuringiensis, Enterobacter asburiae, E. cloacae and Paenibacillus macerans caused high mortality in J₂. Subsequently, the ten most active crude metabolites were selected and assessed for nematicidal activity in a biotest with M. exigua-inoculated coffee plants. Although strains of B. cereus, B. pumilus and P. macerans caused a significant reduction in the number of root galls and/or nematode eggs per plant 90 days after treatment, the best results were obtained with the application of B. megaterium strain 54-06.     

Characterisation of volatiles produced from <Emphasis Type="Italic">Bacillus megaterium</Emphasis> YFM3.25 and their nematicidal activity against <Emphasis Type="Italic">Meloidogyne incognita</Emphasis>

A member of plant growth-promoting rhizobacteria, Bacillus megaterium YMF3.25, was demonstrated to be an efficient biocontrol agent (BCA) against root-knot nematode Meloidogyne incognita. Results from three-compartmented Petri dish tests and a pot experiment indicated that the bacterial culture could significantly inhibit the hatch of eggs and reduce infection of the nematode through production of nematicidal volatiles. After analysis by gas chromatograph/mass spectrometer and confirmation with commercial pure compounds, the nematicidal volatiles produced by the bacterium were characterised to include mainly the benzeneacetaldehyde, 2-nonanone, decanal, 2-undecanone and dimethyl disulphide, which were active against to both juveniles and eggs at the concentration of 0.5 mmol. Six compounds (phenyl ethanone, nonane, phenol, 3,5-dimethoxy-toluene, 2,3-dimethyl- butanedinitrile and 1-ethenyl-4-methoxy- benzene) with nematicidal activityies of 30%–63% also contributed to nematicidal efficacy of the bacterium.     

Effect of <Emphasis Type="Italic">Meloidogyne ethiopica</Emphasis> parasitism on water management and physiological stress in tomato

Root-knot nematodes (RKN) are obligate endoparasites that severely damage the host root system. Nutrient and water uptake are substantially reduced in infested plants, resulting into altered physiological processes and reduced plant growth. The effect of nematode infestation on the morphological changes of roots and subsequent physiological plant responses of infested tomatoes with the RKN Meloidogyne ethiopica was studied in a pot experiment. Plants were infested with two inoculum densities (10 or 50 eggs per cm³ substrate) and its effect was evaluated 74 and 102 days post inoculation (DPI). Morphological changes and root growth was determined by analysing scanned images of the whole root system. Nematode infestation reduced the portion of fine roots and increased that of coarse roots due to gall formation. Fine roots of non-infested control plants represented around 51% of the area of the whole root system at 74 and 102 DPI. In comparison to controls, plants inoculated with low and high nematode density had 2.1 and 3.2-times lower surface area of fine roots at 102 DPI. Root analyses revealed that plants had a very limited ability to mitigate the effects of the root-knot nematodes infestation by altering root growth. Root galls had a major influence on the hydraulic conductivity of the root system, which was significantly reduced. The low leaf water potential of infested plants coincided with decreased stomatal conductivity, transpiration and photosynthesis. The latter two were reduced by 60–70% when compared to non-infested control plants.     

Suppression of Meloidogyne incognita by the endophytic fungus Acremonium implicatum from tomato root galls

Specific endophytes with biocontrol potential might occur in diseased plant tissues. We isolated an endophytic fungus from tomato root galls infected with Meloidogyne incognita and identified it as Acremonium implicatum based on morphology and internal transcribed spacer sequences. Its biocontrol potential was tested in vitro and in pot and field experiments. In the in vitro test, 96.0% of second-stage juveniles of M. incognita were killed by a culture filtrate of A. implicatum after 48 h. The fungus also suppressed egg hatching, with only 36.3% of treated eggs hatching compared with 87.3% of control eggs. Pot experiments showed that A. implicatum inhibited the formation of root galls, with 40.6 galls per treated plant compared with 121.6 on control plants. A. implicatum reduced the nematode population in soil, with 151.1 nematodes per 100 g treated soil and 375.1 in control soil. Field experiments demonstrated that the root gall index of treated plants (25) was markedly lower than that of control plants (96). In conclusion, A. implicatum has excellent potential for the biocontrol of M. incognita.     

Systemic nematicidal activity of fluensulfone against the root-knot nematode Meloidogyne incognita on pepper

BACKGROUND: Fluensulfone, a new nematicide of the fluoroalkenyl group, has proved to be very effective in controlling root‐knot nematodes, Meloidogyne spp., by soil application. The systemic activity of this compound against M. incognita on peppers via soil drenching and foliar spray was evaluated. RESULTS: Root application of fluensulfone via soil drenching showed slight and no nematode control activity when applied 4 and 10 days, respectively, after inoculation. A single foliar spray of peppers with a fluensulfone solution at 3.0 g L^?1 prior to inoculation reduced the galling index by 80% and the number of nematode eggs by 73–82% of controls. The reduction in these parameters by fluensulfone was much higher than that obtained with oxamyl or fenamiphos at the same concentration. This activity was also observed when the plants were sprayed 21 days before inoculation. A series of experiments suggested that foliar spray with fluensulfone prior to inoculation reduces nematode invasion. However, foliar spray after inoculation did not inhibit nematode development inside roots. CONCLUSION: Fluensulfone showed relatively high nematode control activity when sprayed on the foliage before inoculation. Fluensulfone may be used as a foliar application, in addition to soil application, for root‐knot nematode control. Copyright © 2011 Society of Chemical Industry     

Metabolic profiling in the roots of coffee plants exposed to the coffee root-knot nematode, Meloidogyne exigua

To understand the effect of nematode Meloidogyne exigua infestation on coffee plants, resistant and susceptible coffee seedlings were inoculated with second-stage juveniles of M. exigua, and root metabolites were studied for four time intervals at 0, 24, 48 and 96 h. During this important period for parasite establishment, the concentrations of phenols, carbohydrates, amino acids and alkaloids in the roots were measured, and hydrogen nuclear magnetic resonance spectra of the root extracts were used to identify and quantify other metabolites. One of the most striking changes was the concentration of fumaric acid on resistant plants, which varied from 59 μg g(of root)^?1 to 138 μg g(of root)^?1 during the first 24 h of the nematode inoculation. The same level of variation was observed much later (96 h) in susceptible plants. Similarly, formic and quinic acid concentrations increased more rapidly in the resistant plants compared to the susceptibles. Sucrose concentrations increased to 370 % in the first 48 h in the resistant plants but showed no significant variation in the susceptible plant. Besides, the concentration of alkaloids was much higher at 24 and 48 h in the susceptibles compared to the resistant plants. These results suggest that the higher production of sucrose as well as formic, fumaric and quinic acids, and the lower production of alkaloids by the resistant cultivar in the first 48 h after the nematode inoculation are associated with the resistance of coffee plants to M. exigua.     

Methods of assessing the efficacy of non-volatile nematicides

In-vivo tests of non-volatile nematicides using a fungal-feeding nematode Aphelenchus avenae were shown to be more reliable than in-vitro tests. Phoxim and carbofuran were as effective as thionazin against the stem nematode Ditylenchus dipsaci in preventing eggs being laid, but they did not prevent nematodes from migrating from treated plants. Aldicarb and phoxim delayed the emergence of second-stage juveniles from cysts of the potato cyst nematode Globodera rostochiensis; phoxim at 8 mg kg^?1 of soil gave the same results as aldicarb at 2 mg kg^?1 of soil and both chemicals altered the sex ratio in the final population. A simple pot-test with G. rostochiensis in foul soil types was used to demonstrate the comparative effectiveness of non-volatile nematicides.     

长枝木霉菌株TL16防治南方根结线虫的作用机理

为探明长枝木霉Trichoderma longibrachiatum菌株TL16防治南方根结线虫Meloidogyne incognita的作用机理,采用原生质体转化法获得绿色荧光蛋白(green fluorescent protein,GFP)标记菌株GFP-TL16,通过测定菌株TL16和GFP-TL16对南方根结线虫卵和2龄幼虫(2nd-stage juvenile,J2)的寄生与致死作用,其发酵液对卵孵化的抑制作用和对J2的致死作用,以及菌株GFP-TL16在黄瓜根系的定殖情况和菌株TL16对番茄根结形成的抑制作用来综合分析其作用机理。结果显示:菌株TL16菌丝对南方根结线虫卵无寄生作用,处理19 d后卵降解率为26.33%,致死作用较低;菌株TL16分生孢子悬浮液处理南方根结线虫J2后72 h的致死率为1.65%,且无寄生作用。菌株TL16发酵液处理南方根结线虫J2后48 h的校正死亡率为10.71%,处理卵15 d后对卵孵化的相对抑制率为77.11%。菌株GFP-TL16可定殖于黄瓜根系中,经菌株TL16处理后接种南方根结线虫J2,番茄根结减退率为55.88%。表明长枝木霉菌株TL16可通过抑制根结线虫卵孵化和诱导番茄产生抗病性来防治根结线虫病。     

Nematicidal activity of some essential plant oils from tropical West Africa

Abstract

Plant parasitic nematodes are among the most destructive plant pathogens worldwide and their control is very challenging. Plant essential oils (EOs) have showed a great potential in nematode control. In this work, EOs from 10 aromatic plants acclimatized in Togo were assessed in vitro for their nematicidal activity on the root-knot nematode Meloidogyne incognita. EOs were subsequently analyzed by GC-MS and compounds were tested individually on nematodes. The most potent EOs were: Ocimum sanctum L., Cymbopogon schoenanthus (L.) Spreng and Cinnamomum zeylanicum Blume with EC_50/72h values of 282?±?53, 288?±?30 and 355?±?126?mg/L, respectively. The EC_50/48h values of tested compounds were 81?±?14, 117?±?33, 128?±?42, 141?±?47, 168?±?40, 216?±?86 and 235?±?43?mg/L for cinnamyl acetate, methyl eugenol, cinnamyl alcohol, acetyl eugenol, isoeugenol, eugenol and benzyl benzoate, respectively. Furthermore, we found a synergistic nematicidal activity when we combined phenylpropanoids compounds with carvone. EOs and their constituents described herein merit further studies, especially in pot experiments before serving as nematicides.     

Thermal time requirements of root-knot nematodes on zucchini-squash and population dynamics with associated yield losses on spring and autumn cropping cycles

The present research was undertaken to evaluate the effects of soil temperature on the life cycle of root-knot nematodes (RKN) on zucchini-squash in growth chambers and to assess the relationship between Meloidogyne incognita soil population densities at planting (Pi), its multiplication rate, and crop losses of zucchini in field conditions. Thermal requirements for M. incognita and M. javanica were determined by cultivating zucchini plants in pots inoculated with 200 second stage juveniles (J2) of each Meloidogyne species at constant temperatures of 17, 21, 25, and 28 °C. Number of days from nematode inoculation until appearance of egg laying females and until egg hatching were separately recorded. For life cycle completion, base temperatures (Tb) of 12?ºC and 10.8?ºC and accumulated degree-days above Tb (S) of 456 and 526, were estimated for M. incognita and M. javanica, respectively. The relationship between fruit weight and M. incognita Pi fits the Seinhorst damage function, but differed accordingly to the cropping season, spring or autumn. Tolerance limits for M. incognita on zucchini were 8.1 J2 per 250 cm³ of soil in spring and 1.5 in autumn cropping cycles, and the minimum relative yields were 0.61 in spring and 0.69 in autumn. Zucchini-squash was a poorer host for M. incognita in spring than in autumn, since maximum multiplication rates (a) and equilibrium densities (E) were lower in spring (a?=?16–96; E?=?274–484) than in autumn (a?=?270–2307; E?=?787–1227).     

Host suitability of Vitis rootstocks to root‐knot nematodes (Meloidogyne spp.) and the dagger nematode Xiphinema index,and plant damage caused by infections

The host suitability of commercial Vitis rootstocks commonly used in Spain (161‐49C, 41B, 1103P, 110R, 140Ru and SO4) to root‐knot nematodes (Meloidogyne arenaria, M. incognita, M. javanica) and Xiphinema index, and damage caused by nematode infection were determined under controlled conditions. The three root‐knot nematodes reproduced with a rate higher than one in all rootstocks, indicating that they are suitable hosts for these nematodes. Growth of rootstocks infected with the root‐knot nematodes was less vigorous than that of nematode‐uninfected controls in the majority of the rootstocks studied. Root infection resulted in moderate to severe root galling in all rootstocks. The shoot and main stem diameters appeared to be the most sensitive variables of damage caused by infection by Meloidogyne spp., with reduction rates from 36% and 53% in 161‐49C to 57% and 66% in 140Ru, respectively. The shoot height was not significantly affected by the root‐knot nematodes and the root fresh weight generally increased as a consequence of intensive galling. The nematode X. index caused significant root damage with a reproduction factor higher than one in all rootstocks. However, reproduction factor was significantly influenced by the rootstock and significantly decreased by about 12‐fold (5·7 to 18·1‐fold) with the increase in inoculum density from 100 to 1000 nematodes per plant. The root dry weight was reduced by X. index infections, and was the plant growth variable most affected by the nematode infection in all rootstocks at both inoculum densities. Meloidogyne arenaria, M. incognita, M. javanica and X. index, prevalent in many world vineyards, are all shown to have a damaging effect on the six tested rootstocks.     

Seed treatments associated with resistance inducers for management of <Emphasis Type="Italic">Pratylenchus brachyurus</Emphasis> in soybean

Pratylenchus brachyurus is one of the main limiting factors of soybean yield in Brazil, particularly because of inefficiency of the control methods when used individually. The present study aimed to assess the effect of associated methods, using seed treatment with nematicides (ST) and resistance inducers (RI), on nematode control in soybean plant in both field and greenhouse conditions. A field assay was conducted in an infested field and nematode population was assessed at sowing, 45, 75, and 100 days after sowing and the yield measured at end of crop cycle. The experiment was repeated in greenhouse. In another experiment, that was conducted in two different periods in a greenhouse, seed treatments and resistance inducers, alone or combined, were assessed under two initial populations of P. brachyurus (low IP = 500 specimens and high IP = 2000 specimens). The treatments did not reduce the number of nematodes g^?1 of root in field assay, but all seed treatments effectively controlled nematode population in the greenhouse assay. Most treatments reduced the number of nematodes g^?1 of root when nematode initial population was low (IP = 500) but when initial nematode population was high (IP = 2000) combinations of treatments which includes abamectin inhibited P. brachyurus reproduction. Chemical products did not affect yield but acibenzolar-S-methyl, alone or associated with other products, generally inhibit plant growth.     

Biological control of Otiorrhynchus sulcatus with Heterorhabditid nematodes in the glasshouse

AHeterorhabditis species, found in dead larvae ofOtiorrhynchus sulcatus, was tested for its efficacy as a biological control agent of this insect in glasshouse experiments. In a preliminary test all weevil larvae were killed in pots with primula, 88% in strawberry and 50% in cyclamen. In a second test with strawberry plants good results were obtained when the nematodes were applied about the hatching time of the weevil eggs. At a dosage of 100 nematodes per cm² of soil area, 90–97% of the larvae were killed and 90% of the plants remained undamaged. A dosage of 50 nematodes per cm² produced roughly the same level of larval mortality, but left 30% of the plants damaged. Both early and late application of nematodes protected the plants insufficiently, because too many larvae survived. In a third test with strawberry, cyclamen and primula, soil treatment with 50 and 100 nematodes per cm² gave comparable results at both application times, i.e. one and three weeks after hatching of the weevil eggs. In strawberry 100% of the larvae were killed and all plants remained in good condition. Also in cyclamen nearly all larvae were killed and the plants remained in good condition, although the root systems had, less fine roots in comparison with control plants without insects. In primula 4–12% of the weevil larvae survived, whereas up to 20% of the plants died, indicating that soil structure, soil moisture, and condition of the plants have an important impact on the control results. A dosage of 25 nematodes per cm² appeared to be too low in all cases. The results of these experiments open new perspectives for control of the black vine weevil in glasshouses.Samenvatting Een inheemse, nematode van het geslachtHeterorhabditis werd door middel van potproeven in kassen getoetst op zijn werkzaamheid als biologisch bestrijdingsmiddel tegen larven van de gegroefde lapsnuitkever,Otiorrhynchus sulcatus. In een oriënterende proef werden in potten met primula's alle keverlarven gedood, bij aardbeiplanten werden 88% gedood en bij cyclamen 50%. In een tweede proef met alleen aardbeiplanten werden goede resultaten verkregen als de aaltjes werden toegediend in de periode dat de kevereieren uitkwamen. Bij een dosering van 100 aaltjes per cm² grondoppervlak werd 90–97% van de keverlarven gedood en bleef 90% van de planten onbeschadigd. Bij een dosering van 50 aaltjes per cm² was de doding van de keverlarven weliswaar vrijwel hetzelfde, maar de schade aan de planten was te groot; 30% van de planten ging dood. Ook bij een eerder of later bestrijdingstijdstip was de schade aan de planten aanzienlijk en was de doding van de keverlarven onvoldoende. In een derde proef werd in zowel aardbei als in cyclamen vrijwel 100% van de keverlarven gedood bij een dosering van zowel 50 als 100 aaltjes per cm² en op beide bestrijdingstijdstippen, te weten toen de keverlarven circa 1 en 3 weken oud waren. Alle aardbeiplanten en cyclamen bleven in goede staat, hoewel bij cyclamen het aantal fijne wortels minder was dan bij de controle planten zonder keverlarven. De resultaten met primula's waren in deze proef iets minder goed. Het percentage overlevende keverlarven variëerde van 4 tot 12, terwijl tot 20% van de planten dood ging. Een dosering van 25 aaltjes per cm² was in alle gevallen te laag. De resultaten van deze proeven bieden gunstige perspectieven voor toepassing van dit aaltje bij de bestrijding van de gegroefde lapsnuitkever in kassen.     

Pathogenicity and host‐parasite relationships of the root‐knot nematode Meloidogyne incognita on celery

Pathogenicity and host‐parasite relationships in root‐knot disease of celery (Apium graveolens ) caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Naturally and artificially infected celery cv. D’elne plants showed severe yellowing and stunting, with heavily deformed and damaged root systems. Nematode‐induced mature galls were spherical and/or ellipsoidal and commonly contained more than one female, males and egg masses with eggs. Feeding sites were characterized by the development of giant cells that contained granular cytoplasm and many hypertrophied nuclei. The cytoplasm of giant cells was aggregated along their thickened cell walls and consequently the vascular tissues within galls appeared disrupted and disorganized. The relationship between initial nematode population density (Pi) and growth of celery plants was tested in glasshouse experiments with inoculum levels that varied from 0 to 512 eggs and second‐stage juveniles (J₂) mL^?1 soil. Seinhorst's model y = m + (1 – m)z^P–T was fitted to height and top fresh weight data of the inoculated and control plants. The tolerance limit with respect to plant height and fresh top weight of celery to M. incognita race 1 was estimated as 0·15 eggs and J₂ mL^?1 soil. The minimum relative values (m) for plant height and top fresh weight were 0·37 and 0·35, respectively, at Pi ≥ 16 eggs and J₂ mL^?1 soil. The maximum nematode reproduction rate (Pf/Pi) was 407·6 at an initial population density (Pi) of 4 eggs and J₂ mL^?1 soil.     

Inheritance of resistance to Meloidogyne enterolobii in <Emphasis Type="Italic">Psidium guajava</Emphasis> x <Emphasis Type="Italic">P. guineense</Emphasis> hybrid

Inheritance of the resistance to nematodes has been studied on many different crops, however to our knowledge, no data are available for guava species. The basic genetic resistance parameters to Meloidogyne enterolobii are estimated in the current research in order to guide the development of genotypes resistant to the pathogen. The parental plants, F1 and F2 from a Psidium guajava x P. guineense cross were assessed for the presence or absence of galls and for the number of eggs and juveniles in the root system at the 120th and 240th days after inoculation with 10,000 eggs and juveniles of the nematode. At the age of nine years, the P. guineense plant remained without nematode attack symptoms, whereas the maternal plant was destroyed by the pathogen. The F1 generation showed 270 plants with reproduction factor (RF) <0.322, and there were tiny galls in only 16 plants. The segregation for the presence or absence of galls in the root system in generation F2 was 9:7, wherein the χ² values were 0.78 and 2.66, respectively, at the 120th and 240th days after inoculation, whereas the segregation for RF was 15:1, wherein the χ² values were 2.76 and 1.18, respectively, at the 120th and 240th days. These results indicate epistatic interaction between two genes: in RF < 1 only one allele sets the resistance to the pathogen. The broad sense heritability of RF, estimated to the two assessments was 0.97, and it also indicates a simple inheritance of resistance to M. enterolobii.     

Host-pathogen interaction of root-knot nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> on pepper in the southeast of Spain

The feeder roots of pepper plants (cv. California Wonder) in Campo de Cartagena (southeast Spain) were found to be severely infected by Meloidogyne incognita. Morphometric traits, differential host test and DNA analysis based on PCR were used to characterize the nematode. Naturally and artificially infected pepper plants showed severe yellowing and stunting, with heavily deformed and damaged root systems. Root galls were spherical and commonly contained more than one female and egg masses with eggs. Typical giant cells with a granular cytoplasm and many hypertrophied nuclei were observed in histological preparations. The relationship between initial nematode population density (Pi) and pepper plant growth was tested in greenhouse experiments with inoculum levels that varied from 0 to 64 eggs and second-stage juveniles (J₂) ml⁻¹ soil. A Seinhorst model was fitted to plant height and top fresh weight data of inoculated and non-inoculated plants. The tolerance limit with respect to plant height and fresh top weight of pepper to M. incognita was estimated as 0.85 eggs and J₂ ml⁻¹ soil. The minimum relative values (m) for plant height and top fresh weight were 0.15 and 0.16, respectively, at Pi ≥ 64 eggs and J₂ ml⁻¹ soil. The maximum nematode reproduction rate (Pf/Pi) was 315.4 at an initial population density (Pi) of 4 eggs and J₂ ml⁻¹ soil. The obtained results could be used as a base to establish field experiments that allow strategies to prevent surpassing the threshold of nematodes in fields that are infested.     

Characterization of acetylcholinesterases of acaricide-resistant and susceptible strains of the cattle tick Boophilus microplus (Can.): I. Extraction of the critical component and comparison with enzyme from other sources

The critical acetylcholinesterase component, that is responsible for the resistance mechanism of decreased sensitivity to the inhibitor in the cattle tick Boophilus microplus (Can.), has been isolated from the organophosphorus-susceptible Yeerongpilly and resistant Biarra and Ridgelands strains. With the substrate acetylthiocholine this enzyme component gave a pH activity profile similar for all strains. Optimal substrate concentration for Ridgelands was 1.73.10^?2M compared to 2.70.10^?4M for the other strains. Computed Km values were 1.98.10^?5M, 3.65.10^?5M, and 6.43.10^?6M for Yeerongpilly, Biarra, and Ridgelands strains, respectively, while the corresponding V_max figures were 336, 135, and 21 μmoles acetylthiocholine hydrolyzed per gram of larvae per hour. These results are discussed in relation to the resistance mechanism and compared with similar parameters derived for this enzyme from bovine erythrocytes, the sheep blowfly Lucilia cuprina, and the sheep nematode Trichostrongylus colubtiformis.     

Nematicidal Activity of Chrysanthemum coronarium

Organic amendments and green manure are potential alternatives to the harmful chemical control means currently used against plant-parasitic nematodes. In this work, Chrysanthemum coronarium was applied to the soil as a green manure to control the root-knot nematodes Meloidogyne incognita and M. javanica. Chrysanthemum coronarium significantly reduced nematode infection of tomato roots and improved plant-top fresh weight, both in the greenhouse and in microplots. Other green manures, derived from Anthemis pseudocotula, wild chickpea (Cicer pinnatifidum), Geranium spp. and wheat, were not as effective as C. coronarium. Chrysanthemum coronarium, retained its nematicidal activity even when applied as a dried material. Only mature C. coronarium plants, in their flowering stage, exhibited nematode control activity, but the green plant parts were more effective than the flowers. An aqueous extract of C. coronarium exhibited in vitro, nematostatic activity towards M. incognita and M. javanica second-stage juveniles and inhibited their hatching from eggs and egg-masses; its nematostatic activity was expressed also against other phytonematode species such as Heterodera avenae and Pratylenchus mediterraneus, but did not affect the beneficial entomopathogenic nematode Steinernema feltiae.     

Population dynamics and economic threshold of the nematodes Radopholus similis and Pratylenchus goodeyi on banana in Australia

To help banana growers to decide when to apply nematicide, economic thresholds were determined for tropical north Queensland, subtropical south-east Queensland and northern New South Wales, Australia. This was done by monitoring nematode populations, root damage and growth parameters of bunching pseudostems in several commercial crops for several years. There was no significant consistent change in the disease index in consecutive years in any of the regions, although there was great variation between crops. However, on two crops in the tropics, the disease index of roots increased. To reduce the risk of not applying nematicide when required, the economic threshold was adjusted down to allow for this increase on some crops. In the tropics with a crop value of $25 000 ha^?1 year^?1, the economic threshold occurred at a root disease index = 9.2-15.6. In the subtropics with a crop value of $10 000-15 000, the economic threshold occurred at a root disease index = 20.5-35.5. In the subtropics, Radopholus similis (burrowing nematode) was as pathogenic as Pratylenchus goodeyi (lesion nematode) as measured by root necrosis. However, both nematodes were less pathogenic in the subtropics than was R. similis in the tropics. In the subtropics, R. similis tended to be more numerous in warmer months and P. goodeyi in cooler months.