Cabbage Roots Research Articles

Piriformospora indica confers drought tolerance in Chinese cabbage leaves by stimulating antioxidant enzymes, the expression of drought-related genes and the plastid-localized CAS protein

Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance against biotic and abiotic stress. The fungus strongly colonizes the roots of Chinese cabbage, promotes root and shoot growth, and promotes lateral root formation. When colonized plants were exposed to polyethylene glycol to mimic drought stress, the activities of peroxidases, catalases and superoxide dismutases in the leaves were upregulated within 24 h. The fungus retarded the drought-induced decline in the photosynthetic efficiency and the degradation of chlorophylls and thylakoid proteins. The expression levels of the drought-related genes DREB2A, CBL1, ANAC072 and RD29A were upregulated in the drought-stressed leaves of colonized plants. Furthermore, the CAS mRNA level for the thylakoid membrane associated Ca 2+-sensing regulator and the amount of the CAS protein increased. We conclude that antioxidant enzyme activities, drought-related genes and CAS are three crucial targets of P. indica in Chinese cabbage leaves during the establishment of drought tolerance. P. indica-colonized Chinese cabbage provides a good model system to study root-to-shoot communication.

ハクサイ黄化病罹病根及び植物体各部における Verticillum dahliae の微小菌核形成

ハクサイ黄化病罹病根及び植物体各部における Verticillum dahliae の微小菌核形成

ツケナ根こぶ病に対するPCNB粉剤・同液剤の効果試験 (続3)

ツケナ根こぶ病に対するPCNB粉剤・同液剤の効果試験 (続3)

Effects of plant competition and herbivore density on the development of the turnip root fly (Delia floralis) in an intercropping system

In this study, interactive effects of plant competition and herbivory on plant quality and herbivore development were examined in a greenhouse experiment where cabbage plants [Brassica oleracea L. var. capitata (Brassicaceae)] were intercropped with red clover [Trifolium pratense L. (Fabaceae)]. Cabbages were grown with two red clover densities and attack rates by the root feeding herbivore the turnip root fly, Delia floralis Fall. (Diptera: Anthomyiidae). Above ground and below ground cabbage biomass was reduced through intercropping and larval damage. Intercropping also resulted in lower nitrogen and higher carbon root levels compared with levels in the roots of monocultured cabbage. Furthermore, both root nitrogen and carbon levels increased with herbivory. Root neutral detergent fibre (NDF) and lignin content increased in response to both increased plant competition and higher egg densities. For lignin, an interaction effect was observed in the form of elevated levels in intercropped plants subjected to larval damage, while levels in roots of monocultured cabbage remained unchanged. The quality changes brought about by clover competition affected D. floralis development negatively, which resulted in reduced pupal weight. In addition, increased egg density also decreased larval growth. The effects on the development of D. floralis in relation to host plant quality are discussed.

Isolation and Characterization of Endophytic Actinomycetes from Chinese Cabbage Roots as Antagonists to Plasmodiophora brassicae

This study was conducted to select endophytic actinomycetes as biocontrol agents against Chinese cabbage clubroot caused by Plasmodiophora brassicae. A total of 81 endophytic actinomycetes were isolated from surface-sterilized roots of Chinese cabbage that was grown on paddy field and upland soils collected from various locations in Korea. By using 16S ribosomal DNA (rDNA) gene sequencing, they were classified to 8 actinobacterial genera. The genus Microbispora (67%) was most frequently isolated, followed by Streptomyces (12%) and Micromonospora (11%). Three of the 81 isolates, when inoculated in germinated Chinese cabbage seeds and then transplanted to pots, effectively suppressed the occurrence of a post-inoculated strain of P. brassicae in the pots. They showed control values of 58% for strain A004, 33% for strain A004, and 42% for strain A018. Based on cell wall components, morphological characteristics, and phylogenetic analyses, the three antagonistic isolates were identified as Microbispora rosea subsp. rosea (A004 and A011) and Streptomyces olivochromogenes (A018). Further researches on the field efficacy and action modes of the three actinomycetes are in progress.

Combined Effect of Intercropping and Turnip Root Fly (Delia floralis) Larval Feeding on the Glucosinolate Concentrations in Cabbage Roots and Foliage

The effects of plant competition and herbivory on glucosinolate concentrations in cabbage root and foliage were investigated in a cabbage-red clover intercropping system. Cabbage plants were grown under different competitive pressures and with varying degrees of attack by root-feeding Delia floralis larvae. Glucosinolate concentrations in cabbage were affected both by intercropping and by D. floralis density. Glucosinolate concentrations in foliage generally decreased as a response to intercropping, while the responses to insect root damage of individual glucosinolates were weaker. Root glucosinolates responded more strongly to both intercropping and egg density. Total root glucosinolate concentration decreased with clover density, but only at high egg densities. Increased egg density led to opposite reactions by the indole and aliphatic glucosinolates in roots. The responses of individual root glucosinolates to competition and root damage were complex and, on occasion, nonlinear. Reduced concentrations of several glucosinolates and the tendency towards a decrease in total concentration in cabbage foliage caused by intercropping and larval damage suggest that competing plants or plants with root herbivory do not allocate the same resources as unchallenged plants towards sustaining levels of leaf defensive compounds. This could also be true for root glucosinolate concentrations at high egg densities. In addition, the results suggest that changes occurring within a structural group of glucosinolates may be influenced by changes in a single compound, e.g., glucobrassicin (indol-3-ylmethyl) in foliage or sinigrin (2-propenyl) in roots.

국내 배추 뿌리혹병균, Plasmodiophora brassicae의 race와 그 우점 양상

국내의 여러 배추 생산지로부터 뿌리혹을 채집하여 단포자 균주(SSI)를 분리하였다. 분리한 단포자를 접종한 후 총 321개의 뿌리를 수거하여 병징 발현 여부를 관찰하였다. 접종한 개체 중 단 한 개체에서만 작은 혹이 형성되었고, 70개 개체에서 미약한 기형 증상을 보였다. 이들 이상 증상을 보인 개체를 마쇄하여 단포자 균주의 안정적 증식을 위한 접종원으로 사용하였다. 단포자를 접종하여 발병시킨 개체로부터 얻은 포자들을 재접종하였을 때가 1차 단포자 접종하였을 때보다 병징이 훨씬 확대되었고, 이후 실험에 사용할 수 있을 정도로 증식된 개체는 15균주였다. 이 15균주들을 Williams의 판별기주에 접종하여 분석하였을 때, race 1이 4균주, race 4는 7균주, race 9는 2균주, race 11이 2균주로 각각 판별되어, race 4가 국내에 가장 우점하는 것으로 밝혀졌다. 이들 race들은 모두 배추, 무, 순무에 단포자 접종하여 얻어진 균주들로, 병원성 검정에서도 4종의 판별품종 중 Rutabaga 계열(스페인산 순무)에 속하는 'Laurentian'과 'Wilhelmsburger' 두 품종에만 병원성을 보였다. 따라서 이 race들이 배추, 무, 순무에 대해 강한 병원성을 보이는 것으로 보아 국내의 P. brassicae 군집은 배추와 무, 순무 등에 강한 병원성을 나타내는 race가 우점하는 것으로 판단된다. 이는 이들 작물이 병 발생량에 따른 국내 십자화과 채소 감수 비율과도 연관이 있으리라 생각된다. Single spores were isolated from infected roots of Chinese cabbage with a typical clubroot symptom, collected from different Chinese cabbage cultivation areas in Korea. When the single spore isolates were inoculated on Chinese cabbage, radish, turnip, kale, leaf mustard and Williams' differential varieties, among 321 roots harvested two weeks after inoculation, a visual symptom was observed on only one root and light/uncommon symptoms were done on 70 roots. These 71 individuals were homogenized and used as inocula. These inocula caused generally higher pathogenicity than that of single spore. Finally 15 isolates, with enough growth for conducting further experiment, were selected. These 15 individuals were grouped four, seven, two and two into race 1, race 4, race 9 and race 11, respectively, using Williams' differential set. It was confirmed that race 4 were dominantly present in Korea. These 15 had been obtained from roots of Chinese cabbages, radishes and turnips inoculated with single resting spores and had shown pathogenicity to Laurentian and Wilhelmsburger belong to Rutabaga in Williams' differential variety set. Therefore, we assume that such characteristic pathotypes including race 4, especially, of P. brassicae showing strong pathogenicity to Chinese cabbage, radish and turnip may be dominant in Korea.

Salt Stress Inhibits Germination and Early Seedling Growth in Cabbage (Brassica oleracea capitata L.)

Salinity induced inhibition in germination and early stages of cabbage (Brassica oleracea capitata L.) [two varieties (autumn cabbage and spring cabbage)] were measured in response to increasing NaCl concentration. The salinity (NaCl) concentrations in solution were 0 (control), 4.7, 9.4 and 14.1 dS m(-1). Different concentrations of salt stress had considerable effect on germination, germination rate (1/t50, where t50 is the time to 50% of germination), root and shoot lengths, root, shoot and plant fresh weight of cabbage. Final germination in cabbage (autumn cabbage and spring cabbage) showed significant inhibition with increasing salt stress up to 14.1 dS m(-1) NaCl. The required time for germination increased with increasing concentration of salt. The seedling growth was strongly inhibited by all salt levels, particularly at 14.1 dS m(-1). Furthermore Root growth was more affected then shoots growth by salt stress. Fresh weights of root, shoot and plant were also severely affected by different salinity treatments. Linear regression revealed a significant negative relationship between salinity and final germination, germination rate, root and shoot lengths and fresh weights of roots, shoots and plants.

Increase in BrAO1 gene expression and aldehyde oxidase activity during clubroot development in Chinese cabbage (Brassica rapa L.)

SUMMARY In clubroot disease, gall formation is induced by infection with the obligate biotroph Plasmodiophora brassicae due to increased levels of auxins and cytokinins. Because aldehyde oxidase (AO) may be involved in auxin biosynthesis in plants, we isolated two AO genes (BrAO1 and BrAO2) from Chinese cabbage (Brassica rapa ssp. pekinensis cv. Muso), which are the most similar to AAO1 among Arabidopsis AO genes, and examined their expressions during clubroot development. The expression of BrAO1 was enhanced in inoculated roots from 15 days post-inoculation (dpi) when visible clubroots were still undetectable. Thereafter, BrAO1 expression increased with clubroot development compared with uninoculated roots, although BrAO2 expression was repressed. In situ hybridization revealed that BrAO1 was strongly expressed in tissues that were invaded by immature plasmodia at 35 dpi, suggesting that BrAO1 expression was enhanced by the pathogen in order to establish its pathogenesis. In addition, we detected AO activity, as evidenced by the occurrence of at least six bands (BrAO-a to BrAO-f) in the roots of Chinese cabbage using an active staining method with benzaldehyde and indlole-3-aldehyde as the substrate. Coincidental with BrAO1 expression, the signals of BrAO-a and BrAO-d increased with inoculation by P. brassicae during clubroot development compared with healthy roots, resulting in an increase in total AO activity. By contrast, the band BrAO-b decreased post-inoculation, in parallel with the expression of BrAO2. The other bands of activity were not clearly influenced by the infection. Based on these results, we discuss the involvement of AO in auxin-overproduction during clubroot development in Chinese cabbage.

Eradication of Plasmodiophora brassicae during composting of wastes

Survival of infectious inoculum of the clubroot pathogen Plasmodiophora brassicae was assessed following bench‐scale flask composting experiments and large‐scale composting procedures. Clubroot‐affected material was provided by artificial inoculation of Chinese cabbage or naturally infected Brussels sprout and cabbage roots. Both sets of diseased material were used in flask experiments, and the latter in large‐scale windrow and aerated tunnel experiments. Municipal green wastes, onion waste and spent mushroom compost were evaluated in flask experiments with varying temperature, aeration and moisture conditions. Green wastes were used in larger‐scale composts. Within the limits of a Chinese cabbage seedling bioassay, both temperature and moisture content were critical for eradication of P. brassicae spores extracted from composted clubroot‐affected residues. Incubation in compost at 50°C for 7 days or 1 day at 60°C with high moisture levels (= −5 kPa matric potential or 60% w/w moisture content) eradicated inoculum from artificially inoculated Chinese cabbage roots. In large‐scale windrows and aerated tunnels, the pathogen was eradicated from naturally infected brassica wastes after 6–7 days at 54–73°C.

Molecular Cloning of PbSTKL1 Gene from Plasmodiophora brassicae Expressed during Clubroot Development

AbstractInfection of crucifers by the obligate plant pathogen Plasmodiophora brassicae Woron. results in the formation of clubroot disease in these plants. Plasmodiophora brassicae gene expression during disease development was studied by differential display analysis of total RNA extracted from the roots of Chinese cabbage inoculated with the pathogen. In a series of experiments, 30 differentially expressed bands of cDNA were detected, and the expression of clone no. 17 was confirmed in clubbed roots. Southern blot analysis showed that this clone was a single‐copy gene in the P. brassicae genome. Putative amino acid sequence analysis of the full‐length cDNA of clone no. 17 (4.6 kb, designated PbSTKL1) revealed a serine/threonine kinase‐like domain at the C‐terminal region and a coiled‐coil structure in the middle region of the putative protein. PbSTKL1 expression increased strongly beginning 30 days after inoculation and was coincident with resting spore formation.

The development and endophytic nature of the fungus Heteroconium chaetospira

The root endophytic fungus Heteroconium chaetospira was isolated from roots of Chinese cabbage grown in field soil in Japan. This fungus penetrates through the outer epidermal cells of its host, passes into the inner cortex, and grows throughout the cortical cells, including those of the root tip region, without causing apparent pathogenic symptoms. There are no ultrastructural signs of host resistance responses. H. chaetospira has been recovered from 19 plant species in which there was no disruption of host growth. H. chaetospira has a symbiotic association with Chinese cabbage. The fungus provides nitrogen in exchange for carbon. These associations are beneficial for the inoculated plants, as demonstrated by increased growth rate. When used as a preinoculum, H. chaetospira suppresses the incidence of clubroot and Verticillium yellows when the test plant is post-inoculated with the causal agents of these diseases. H. chaetospira is an effective biocontrol agent against clubroot in Chinese cabbage at a low to moderate soil moisture range and a pathogen resting spore density of 10 5 resting spores per gram of soil in situ. Disease caused by Pseudomonas syringae pv. macricola and Alternaria brassicae on leaves can be suppressed by treatment with H. chaetospira. The fungus persists in the roots and induces systemic resistance to the foliar disease.

Anatomical study on the interaction between the root endophytic fungus Heteroconium chaetospira and Chinese cabbage

Chinese cabbage roots colonized by the dematiaceous fungal taxon Heteroconium chaetospira were previously found to become highly resistant to clubroot and Verticillium yellows. The dematiaceous fungus possesses an endophytic nature, but no detailed anatomical studies on endophyte–host plant interactions have so far been provided. Light and electron microscopy revealed that hyphae of H. chaetospira were abundant on and inside the root epidermal cells by 3 weeks following inoculation. The penetration pegs easily breached into epidermal cells, and the infection hyphae penetrated into cortical cells. Some appressorium-like swollen structures formed from intracellular hyphae, but no visible degradation of the host cell walls was evident where the hyphae contacted. No visible signs of host reactions and no invagination of the host plasma membrane around the hyphae were seen in the host cells. By 8 weeks following inoculation, masses of closely packed fungal cells had been formed in some cells of the epidermis and cortical layers, but further hyphal ingress was halted, mostly in the inner cortical cell layer. Thus, root vascular cylinders remained intact.

The use of fast protein liquid chromatography with ICP-OES and ES–MS–MS detection for the determination of various forms of aluminium in the roots of Chinese cabbage

The distribution of aluminium (Al) species was investigated in the roots of Al-tolerant Chinese cabbage ( Brassica rapa L. ssp. pekinensis) by employing fast protein liquid chromatography (FPLC) with inductively coupled plasma optical emission spectrometry (ICP-OES) and electrospray tandem mass spectrometry (ES–MS–MS) detection. The cabbage was exposed to a nutrient solution that contained 10 μg cm −3 of Al 3+. The results demonstrated that after 24 h of exposure, Al was quantitatively taken up by the cabbage and was distributed in different parts of the plant. 36 ± 6% of total Al was located in the roots, while the remaining 64 ± 10% was transferred to the leaves. It was found that in the roots Al was partially present in the root sap (15.5%), while the majority (84.5%) was accumulated in its apoplasmic compartments. It was further demonstrated that the proportion of Al that entered the symplasm formed a complex with organic acid. Speciation analysis by FPLC with ICP-OES detection and ES–MS–MS identification of the binding ligand indicated that Al-citrate complex was the prevailing species in the root sap. The results of the present study showed that both immobilization of Al in the apoplasmic compartments of the roots and transformation of Al 3+ to Al-citrate are most likely responsible for the tolerance of Chinese cabbage ( B. rapa L. ssp. pekinensis) to the toxic effects of Al 3+.

Exudation of organic anions by roots of cabbage, carrot, and potato as influenced by environmental factors and plant age

AbstractA previous study demonstrated that cabbage was P efficient compared to carrot and potato. However, calculating plant P uptake by a mechanistic simulation model based on P transport by diffusion and mass flow, P uptake of roots according to the Michaelis‐Menten kinetics, and morphological root characteristics including root hairs, revealed that these parameters could explain only 2/5 of the total P uptake of cabbage, but 4/5 of that of carrot and potato (Dechassa et al., 2003). Therefore, it was hypothesized that a higher root exudation of organic anions may enhance P mobilization and hence P uptake of cabbage. The objective of this research was to determine root exudation of organic anions by the three species, and to investigate the influence of plant age and dark/light period on organic‐anion exudation by cabbage. Experiments were conducted in a growth chamber in nutrient solution with or without P. Organic anions were determined in root exudates and in root tissue. With cabbage and potato, P deficiency induced exudation of citrate and succinate, respectively. Citrate‐exudation rate of P‐deficient cabbage plants was correlated with accumulation of citrate in root tissue. In contrast, high succinate‐exudation rates in potato were not correlated with an increased concentration in root tissue. For carrot, no change was observed in the exudation of any of the organic anions in response to P deficiency. The results also showed that succinate‐ and citrate‐exudation rates of cabbage roots increased with increased plant age. There was also a significant increase in exudation rates of organic anions of cabbage roots during the light period of the day. It was concluded that cabbage had the ability to exude large amounts of citrate in response to P deficiency by which it can additionally enhance its P‐uptake efficiency, whereas carrot and potato showed little evidence of possessing such a mechanism.

Nematode Genera Associated with Selected Vegetable Crops in a Tropical Region

A survey was conducted in a tropical region under continuous crop production for more than a century in the Dominican Republic, to determine the incidence of nematode genera in the soil and in tomato, eggplant, okra, carrot, cabbage, onion, Sweetpotato, squash, and cucumber roots. Typical crop sequences in the region were tomato, eggplant, or beans, followed by either corn, sorghum, cassava, squash or Sweetpotato, followed by either onion, carrot or cabbage, all the crops being grown with medium to high agrichemical input levels. The genera Meloidogyne, Rotylenchulus, Pratylenchus, Aphelenchus, Helicotylenchus, Tylenchus, and Criconemoides were found in soil and/or crop root samples. Meloidogyne was the most prevalent genus in the soil (41% of the samples) and in roots of squash, cucumber, tomato, Sweetpotato, and carrot (50% of the samples). Rotylenchulus was found in 27% of the soil samples, and in 33% of the tomato, okra, and carrot root samples. Aphelenchus was isolated from 2.5% of the eggplant, onion, and cabbage root samples, and from 11% of the soil samples. Pratylenchus was found only in cucumber roots (13% of the samples) and soil samples (10%). Helicotylenchus, Tylenchus, and Criconemoides were isolated from soil (5%, 4%, and 1% of the samples, respectively), but were not found in crop roots. The incidence of Meloidogyne, Rotylenchulus, Pratylenchus, and Aphelenchus tended to be higher in plots where cucurbits and/or solanaceaous crops were grown more frequently, whereas the presence of Criconemoides seemed to be associated with plots where cassava, corn or sorghum had been grown recently.

Control of Verticillium Yellows in Chinese Cabbage by the Dark Septate Endophytic Fungus LtVB3

ABSTRACT Three hundred forty-nine fungal endophytes were obtained from a total of 1,214 root segments of eggplant, melon, barley, and Chinese cabbage grown as bait plants in a mixed soil made up of samples from different forest soils in Alberta and British Columbia, Canada. Three of the 349 isolates, when inoculated in axenically reared Chinese cabbage seedlings grown in petri dishes, almost completely suppressed the effects of a postinoculated and virulent strain of Verticillium longisporum. Two isolates effective against the pathogen were Phialocephala fortinii, which had been obtained from the roots of eggplant and Chinese cabbage. The third isolate was a dark septate endophytic (DSE) fungus obtained from barley roots. Hyphae of P. fortinii grew along the surface of the root and formed microsclerotia on or in the epidermal layer. Hyphae of the DSE fungus heavily colonized root cells of the cortex. Seedlings grown for 1 week in the presence of the endophytes were then challenged with the Verticillium pathogen. In DSE-treated roots, some of cell walls in the epidermal and cortical layers showed cell wall appositions and thickenings, which appeared to limit the ingress of the pathogen into adjacent cells. Such marked host reactions were not observed in the root cells colonized by P. fortinii. Chinese cabbage preinoculated with the above endophytes and, for comparison, a previously reported disease-suppressive fungal endophyte, Heteroconium chaetospira, were transplanted into the field and disease symptoms were assessed. The DSE could most effectively inhibit the development of Verticillium yellows, with reductions in the percentages of external and internal disease symptoms of 84 and 88%, respectively. The protective values against the disease are extremely high compared with those of other isolates. Most of the DSE-treated plants in the plots achieved marketable quality.

Cloning and expression of a cDNAAAPT3 encoding aminoalcoholphosphotransferase Isoform from Chinese Cabbage

Aminoalcoholphosphotransferase catalyzes the synthesis of phosphatidylcholine and phosphatidylethanolamine from diacylglycerol plus a CDP‐aminoalcohol such as CDP‐choline or CDP‐ethanolamine. Previously we suggested the presence of possible isoforms of this enzyme from Chinese cabbage roots and now report the cDNA cloning and expression analysis of AAPT3 encoding a third isoform of aminoalcoholphosphotransferase (AAPT3). AAPT3 contains an open reading frame of 1,176 bp coding for a protein of 392 amino acids. It shares 96 and 95% identity with Chinese cabbage AAPT1 and AAPT2, respectively, at the deduced amino acid level. The results from reverse transcriptase‐polymerase chain reaction analysis indicate that expression of AAPT3 is up‐regulated by low temperature as well as AAPT1 and AAPT2.

Nitrogen mineralization of vegetable root residues and green manures as related to their (bio)chemical composition

Little is known concerning the N mineralization or N immobilization of (vegetable) root residues in soil. The (bio)chemical composition of a range of vegetable root residues (large and fine roots of red cabbage, white cabbage, Brussels sprouts, savoy cabbage, and leek), and plant parts of two green manures (ryegrass and white mustard) was determined by standard chemical analysis (total C, total N, and C:N ratio) and by a modified Stevenson fractionation method (water-soluble, hemicellulose, cellulose, and lignin fraction). Fresh chopped crop residues, homogenously mixed with a sandy loam soil, were incubated during 4 months at constant temperature (21 °C) and constant moisture content (14% w/w). The net N mineralization of each residue was determined by destructive sampling. All fine roots, except these of Brussels sprouts, showed a net N release throughout the incubation. All large roots showed a slight N immobilization at the start of the incubation, but at the end of the incubation a small net N release was observed, except for Brussels sprouts. The roots of Brussels sprouts immobilized N throughout the entire incubation. The leaves of the green manures released more N than both stems (only for white mustard) and roots. It was possible to fit a first-order kinetics model to 8 of the 14 N mineralization patterns: A N( t)= A N(1−exp(− kt)). For the six other residues where the first-order model could not be fitted, the amount of N mineralized at the end of the incubation was taken as an estimate of the A N parameter. Both the mineralization parameters A N and k were correlated to a large number of (bio)chemical parameters. The amount of mineralized N, A N, was best correlated with the C:N ratio ( R=−0.86), and the rate constant k was best correlated with the lignin:N ratio ( R=−0.94). The predictive relationship between the N mineralization of vegetable root residues and green manures and their (bio)chemical composition has the advantage that is independent of the length of the incubation time. The critical C:N ratio, i.e. the break point between net N mineralization and net N immobilization ( A N=0) was found to be 36.6.

The influence of the root‐knot nematode Meloidogyne incognita, the nematicide aldicarb and the nematophagous fungus Pochonia chlamydosporia on heterotrophic bacteria in soil and the rhizosphere

SummaryPlant‐pathogenic nematodes are a major cause of crop damage worldwide, the current chemical nematicides cause environmental damage, but alternatives such as biological control are less effective, so further understanding of the relationship between nematodes, nematicides, biological control agents and soil and rhizosphere microorganisms is needed.Microbial populations from roots of cabbage and tomato plants infested with the root‐knot nematode Meloidogyne incognita were compared with those from plants where the nematode was controlled by the nematicide aldicarb, or a nematophagous fungus with biological control potential, Pochonia chlamydosporia. The total numbers of culturable bacteria and fungi in rhizosphere soil were similar in all three treatments for both plants, around 100‐fold more than in control soil in which there were no plants. However, there were clear differences in the catabolic diversity, assessed by Biolog EcoPlate™ carbon substrate utilization assays, between microbial populations from unplanted soil and the rhizosphere. In cabbage, a poor host for M. incognita, the rhizosphere population from P. chlamydosporia‐treated plants was distinct from the population from untreated and aldicarb‐treated plants. In tomato, a host susceptible to the nematode, the catabolic diversity of populations from aldicarb‐ and P. chlamydosporia‐treated plants was similar and differed from the untreated, nematode‐infested plants. The genetic diversity of the fast‐growing heterotrophic bacteria in the tomato rhizosphere, indicated by PCR fingerprinting with ERIC primers, was very different in the infested roots, whereas the profiles of isolates from both aldicarb‐ and P. chlamydosporia‐treated roots were similar. Evidently, nematodes have a greater impact on the rhizosphere population of a susceptible host, tomato, than a poor one, cabbage, and nematode‐infested roots are colonized by a different subpopulation of soil microbes from that on plants where infection is controlled, illustrating differences in root morphology and physiology.