A Fusarium Wilt Resistance Gene in Gossypium barbadense and Its Effect on Root-Knot Nematode-Wilt Disease Complex

ABSTRACT Fusarium wilt, caused by the soilborne pathogen Fusarium oxysporum f. sp. vasinfectum race 1, is a vascular disease in cotton (Gossypium spp.), and is a component of a disease complex with root-knot nematodes (Meloidogyne incognita). Genetic analysis of two interspecific crosses (G. barbadense Pima S-7 x G. hirsutum Acala NemX and Pima S-7 x Acala SJ-2) showed that one major gene (designated Fov1) with allele dosage effect conferred resistance to F. oxysporum f. sp. vasinfectum race 1 in Pima S-7. Two amplified fragment length polymorphism (AFLP) markers were linked to Fov1 in Pima S-7, with genetic distance from the gene of 9.3 and 14.6 centimorgans. Less severe wilt symptoms in Acala NemX than Acala SJ-2 indicated that Acala NemX possesses one or more minor genes contributing to delay of wilt symptoms. Highly resistant plants in F(2) and F(3) (Pima S-7 x NemX) families indicated transgressive segregation effects of minor genes in Acala NemX combined with Fov1 from Pima S-7. The effects of wilt and nematode resistance on the nematode-wilt disease complex were assayed with two inoculation methods. In the presence of both pathogens, wilt damage measured as shoot and root weight reductions was greatest on wilt- and nematode-susceptible Acala SJ-2 and least in root-knot nematode-resistant and wilt-susceptible Acala NemX. Intermediate damage occurred in wilt-resistant and root-knot nematode-susceptible Pima S-7. The results indicated that nematode resistance was more effective than wilt resistance in suppressing wilt symptoms when either resistance was present alone. Nematode resistance combined with intermediate wilt resistance, as in the F(1) (Pima S-7 x NemX), was highly effective in protecting plants from root-knot nematodes and race 1 of Fusarium wilt as a disease complex.     

Identification of a major gene (Mex-1) from Coffea canephora conferring resistance to Meloidogyne exigua in Coffea arabica

Among the most damaging root-knot nematode species, Meloidogyne exigua is especially common in Latin America and constitutes a major agronomic constraint in all major coffee-growing ( Coffea arabica ) areas. Growing nematode-resistant coffee represents the most promising option for control of the pest. The present study aimed to determine the mode of inheritance of the M. exigua resistance transferred into C. arabica from a related species, Coffea canephora , and to identify associated molecular markers. Segregation data analysis of F ₂ progeny derived from a cross between the resistant introgression line T5296 and the susceptible accession Et6 showed that the resistance to M. exigua is controlled by a simply inherited major gene (designated the Mex -1 locus). The gall index distribution exhibited by the F ₂ individuals suggested incomplete dominant expression. Fourteen AFLP markers were found associated with the resistance to M. exigua and a localized genetic map of the chromosome segment carrying Mex -1 was constructed. Furthermore, the association of the identified AFLP markers with Mex -1 was confirmed by analysis of a set of genotypes involving 28 introgression Arabica lines either resistant or susceptible to M. exigua in field conditions. These results represent an important starting point to enhance backcross breeding programmes and to perform an early selection of resistant seedlings.     

Histological Characterization of Resistance to Different Root-Knot Nematode Species Related to Phenolics Accumulation in Capsicum annuum

ABSTRACT In the pepper Capsicum annuum CM334, which is used by breeders as a source of resistance to Phytophthora spp. and potyviruses, a resistance gene entirely suppresses reproduction of the root-knot nematode (Meloidogyne spp.). The current study compared the histological responses of this resistant line and a susceptible cultivar to infection with the three most damaging root-knot nematodes: M. arenaria, M. incognita, or M. javanica. Resistance of CM334 to root-knot nematodes was associated with unidentified factors that limited nematode penetration and with post-penetration biochemical responses, including the hypersensitive response, which apparently blocked nematode migration and thereby prevented juvenile development and reproduction. High-performance liquid chromatography analysis suggested that phenolic compounds, especially chlorogenic acid, may be involved in CM334 resistance. The response to infection in the resistant line varied with root-knot nematode species and was correlated with nematode behavior and pathogenicity in the susceptible cultivar: nematode species that quickly reached the vascular cylinder and initiated feeding sites in the susceptible cultivar were quickly recognized in CM334 and stopped in the epidermis or cortex. After comparing our data with those from other resistant pepper lines, we suggest that timing of the resistance response and the mechanism of resistance vary with plant genotype, resistance gene, and root-knot nematode species.     

Hypersensitive-like reaction conferred by the Mex-1 resistance gene against Meloidogyne exigua in coffee

The response of a susceptible coffee cultivar (Caturra) to infection by the root-knot nematode Meloidogyne exigua was compared histologically with that of cv. Iapar 59 possessing the recently identified Mex-1 resistance gene. The reproductive behaviour of the nematode was also compared in the two cultivars. Penetration and development in resistant plants were reduced in comparison with susceptible plants. Several cell features, including dark-stained cytoplasm and altered organelle structure, were observed in the resistant cultivar, indicating a hypersensitive-like (HR) response of the infested host cells. Features of giant cells were sometimes found beside necrotic-like areas, but the corresponding feeding sites were frequently associated with nematodes displaying abnormal shape. Six weeks after inoculation, root systems of cv. Caturra contained significantly more nematodes than those of cv. Iapar 59 (mean values 1574 and 41, respectively). The susceptible cultivar presented a minimum of 11 galls per plant, compared with only one or two galls per plant in the resistant cultivar. The findings are discussed in the context of plant–pathogen interactions.     

Infection by Meloidogyne artiellia does not break down resistance to races 0, 1a, and 2 of Fusarium oxysporum f. sp. ciceris in chickpea genotypes

Fusarium oxysporum f. sp. ciceris, and the root-knot nematode Meloidogyne artiellia, coinfect chickpea crops in several countries of the Mediterranean Basin. The influence of root infection by M. artiellia on the reactions of chickpea genotypes with different reaction to infection with F. oxysporum f. sp. ciceris races 0, 1A, and 2 was investigated under controlled environmental conditions. Results demonstrated that co-infection of chickpea genotypes resistant to specific fungal races by M. artiellia did not influence the Fusarium wilt reaction of the plant, irrespective of the F. oxysporum f. sp. ciceris race assayed. However, in some of the assayed combinations, coinfection by both pathogens significantly affected the level of colonization by the fungus or reproduction of the nematode in the root system. Thus, coinfection of chickpea plants with Foc-0 and M. artiellia significantly decreased the level of colonization of the root system by F. oxysporum f. sp. ciceris in genotypes 'CA 336.14.3.0' and 'PV 61', but not in 'ICC 14216 K' and 'UC 27'. Similarly, the nematode reproduction index was also significantly reduced by coinfection with Foc-0 in the four chickpea genotypes tested and inoculated with this race. Conversely, coinfection of chickpea plants with Foc-1A and M. artiellia significantly increased colonization of the root system by the fungus in all genotypes inoculated with this race, except for line BG 212. Altogether, we confirmed the complete resistance phenotype of 'UC 27' and 'ICC 14216 K' to Foc-0, and of 'ICC 14216 K' to Foc-1A and Foc-2, and demonstrated that this resistance was not modified by coinfection of the resistant plant with M. artiellia.     

Interactions Between Meloidogyne artiellia, the Cereal and Legume Root-Knot Nematode, and Fusarium oxysporum f. sp. ciceris Race 5 in Chickpea

ABSTRACT In the Mediterranean Basin, Fusarium oxysporum f. sp. ciceris and the root-knot nematode Meloidogyne artiellia coinfect chickpea. The influence of root infection (after inoculation with 20 nematode eggs and second-stage juveniles per gram of soil) by two M. artiellia populations, from Italy and Syria, on the reaction of chickpea lines and cultivars with partial resistance to Fusarium wilt (CA 252.10.1.OM, CA 255.2.5.0, CPS 1, and PV 61) and with complete resistance to F. oxysporum f. sp. ciceris race 5 (CA 334.20.4, CA 336.14.3.0, ICC 14216 K, and UC 27) was investigated under controlled conditions. In genotypes with partial resistance, infection by M. artiellia significantly increased the severity of Fusarium wilt, irrespective of the fungal inoculum density (3,000 or 30,000 chlamydospores per gram of soil), except in cultivar CPS 1 at the lower fungal inoculum density. In genotypes with complete resistance to Fusarium wilt, infection by M. artiellia overcame the resistance to F. oxysporum f. sp. ciceris race 5 in CA 334.20.4 and CA 336.14.3.0 but not in ICC 14216 K, irrespective of the fungal inoculum density, and overcame the resistance in UC 27 only at the higher inoculum density. Infection by the nematode significantly increased the number of propagules of F. oxysporum f. sp. ciceris race 5 in root tissues of genotypes with complete resistance to Fusarium wilt, compared with roots that were not inoculated with the nematode, irrespective of the fungal inoculum density, except in ICC 14216 K, in which this effect occurred only at the higher inoculum density. Reproduction of an M. artiellia population from Syria in the absence of F. oxysporum f. sp. ciceris race 5 was significantly higher than that of a population from Italy in all tested chick-pea genotypes except ICC 14216 K. However, there was no significant difference between the reproduction rates of the two nematode populations in plants infected with F. oxysporum f. sp. ciceris race 5, irrespective of the fungal inoculum density and the reaction of the genotypes to the fungus.     

Distribution analyses of Meloidogyne spp. and Pratylenchus coffeae sensu lato in coffee plots in Costa Rica and Guatemala

The distribution of the plant-parasitic nematodes Pratylenchus coffeae sensu lato and Meloidogyne spp. were studied in two plots, one in Guatemala ( P. coffeae and M. paranaensis ) and the other in Costa Rica ( P. coffeae and M. exigua ). The quantity of nematodes per g fresh weight root were counted for each coffee tree sampled. The distributions were aggregated, and generally fitted well to negative binomial distributions. Population aggregation was greater when a smaller number of nematodes were involved, suggesting that initial colonization develops in foci. Analyses of the relationships between population levels of the species suggested that there was competition between Pratylenchus coffeae and Meloidogyne spp. This competition was expressed differently depending on the relative population density of the different species.     

A high-throughput method for early screening of coffee (<Emphasis Type="Italic">Coffea</Emphasis> spp.) genotypes for resistance to root-knot nematodes (<Emphasis Type="Italic">Meloidogyne</Emphasis> spp.)

Root-knot nematodes (Meloidogyne spp.) threaten the livelihood of millions of farmers producing coffee worldwide. The use of resistant plants either as cultivars or rootstocks appears to be the single most effective method of control. A screening method was developed to evaluate large populations of plants for resistance to root-knot nematodes. Two coffee cultivars, one susceptible and the other resistant to Meloidogyne paranaensis, were grown under controlled conditions in two substrates: a commercial sieved potting compost and an inert substrate containing sand with a water-absorbent synthetic polymer. Plant growth and development and nematode multiplication were compared for two inoculation dates (2 and 8 weeks after planting) and two evaluation dates (eight and 13 weeks after inoculation). Root growth, but not nematode multiplication, was influenced by the choice of substrate. Evaluation of the differences in root weight and nematode numbers between the different cultivars, substrates and dates of inoculation suggested that an optimal condition could be defined. The best discrimination between susceptible and resistant plants was found in the experiment where inoculation occurred at 2 weeks after planting and evaluation occurred at 8 weeks after inoculation. Because the total duration of this experiment was only 3 months, high-throughput evaluation was possible, opening up new possibilities for screening large germplasm collections and studying the genetic control of root-knot nematode resistance in coffee.     

Effect of root-knot nematodes on cajanol accumulation in the vascular tissues of pigeonpea after stem inoculation with Fusarium udum

The effect of root-knot nematodes ( Meloidogyne javanica and M. incognita ) on production of the isoflavonoid phytolexin, cajanol, was investigated in pigeonpea ( Cajanus cajan ) plants infected with Fusarium udum , the causal organism of Fusarium wilt. Seven-day-old seedlings of a wilt-resistant pigeonpea cultivar, ICP 9145 and a wilt-susceptible cultivar, Malawi Local, both of which were moderately susceptible to the nematode, were grown in soil infested with 2000 Meloidogyne juyeniles per plant. A duplicate set of plants remained free from nematodes. Twenty-one days later, all the plants were inoculated with F. udum by stem puncture. Quantitative estimates of cajanol in the vascular tissues were made at intervals up to 15 days after inoculation with the fungus. No external symptoms of wilt appeared in any plants of the wilt-resistant cultivar in the absence of the nematode. However, when inoculated with the nematode, two thirds of the plants developed wilt symptoms. Cajanol levels were lower in both the wilt-resistant and wilt-susceptible plants in the presence of the nematode than in its absence, although this effect was considerably more marked in the wilt-resistant cultivar. These results indicate that the root-knot nematode is capable of breaking resistance of ICP 9145 to Fusarium wilt and that at least part of the mechanism of this effect is retarded cajanol accumulation.     

Race 3, a new race of<Emphasis Type="Italic"> Fusarium oxysporum</Emphasis> f. sp. <Emphasis Type="Italic">lactucae </Emphasis>determined by a differential system with commercial cultivars

 Pathogenic variation among 26 Japanese isolates of Fusarium oxysporum f. sp. lactucae (FOL) was tested using 21 lettuce cultivars to select commercial lettuce cultivars as race differential indicators. Cultivar Costa Rica No. 4 was resistant to race 1 but susceptible to race 2, consistent with the conventional standard differential line VP1010. Cultivar Banchu Red Fire was susceptible to race 1 but resistant to race 2, which showed an opposite type of reaction as another differential line VP1013. Cultivar Patriot was susceptible to both races. The resistance reactions of the three cultivars under field conditions were identical with that observed in the seedlings. Thus cv. Costa Rica No. 4 and cv. Banchu Red Fire can be used as differential hosts to identify pathogenic races of FOL. This differential system showed that all FOL isolates obtained from diseased butterhead lettuce in Fukuoka, Japan were new races (i.e., pathogenic to three cultivars). We propose that the new race be designated race 3. Isolates of FOL, the pathogen of Fusarium wilt in lettuce, obtained from California showed the same reaction as that of race 1. Furthermore, the Japanese isolate SB1-1 (race 1) and California isolate HL-2 belonged to the same vegetative compatibility group. Our results suggest that both of the fungi are the same forma specialis. Received: March 25, 2002 / Accepted: August 26, 2002     

番茄抗性品种与黄瓜轮作对根结线虫的防治作用

通过室内盆栽试验探讨对根结线虫具有不同抗性的番茄品种与黄瓜轮作减轻根结线虫病危害的可行性。试验结果表明:抗性品种多菲亚能极大降低土壤中根结线虫2龄幼虫和卵的密度,减轻黄瓜根结线虫病的危害;抗性砧木Beaufort也能显著地降低土中根结线虫和卵的密度,但下茬黄瓜根结线虫的危害与对照相比没有显著差异。表明抗性品种与感病品种轮作能有效地防止根结线虫的发生。     

西南部分地区荞麦根结线虫种类与地理分布

近年来,随着我国荞麦面积的迅速增加,根结线虫病呈逐年加重趋势,严重影响了荞麦的产量与品质。本研究于2014年对西南10个地区17个乡镇秋播苦荞麦根结线虫的分布、发生种类以及危害程度进行了调查。结果表明,西南地区危害荞麦的根结线虫种类有南方根结线虫(Meloidogyne incognita)、爪哇根结线虫(M.javanica)和花生根结线虫(M.arenaria)3种,其中南方根结线虫为优势种群。田间根结线虫种群大多数为单一种群,23.5%的样品为南方根结线虫与爪哇根结线虫(或花生根结线虫)组成的混合种群。调查发现前作为烟草或马铃薯的地块,荞麦根结线虫发生危害严重,平均被害株率为6.0%~77.5%,病情指数为1.4~26.1,而前作为玉米的荞麦根结线虫则较轻,被害株率最高为16.0%,相应病情指数为2.3。     

重庆市草坪草病害种类调查及病原鉴定初报

为了明确重庆草坪草主要病害及其病原菌的种类,作者调查了重庆草坪草病害种类,并分离鉴定了病原。结果表明：重庆草坪草常见病害有锈病、结缕草炭疽病、褐斑病、镰刀枯萎病、结缕草弯孢霉叶枯病和结缕草根结线虫等病害,分别由柄锈菌（Puccinia spp.）、尾状炭疽菌（Colletotrichum caudatum）、立枯丝核菌（Rhizoctonia solani）、镰刀菌（Fusarium sp.）、弯孢霉（Curvularia spp.）和根结线虫（Meloidogyne sp.）危害所致。     

The genetic analysis of resistance to fusarium crown and root rot of tomato

The tomato line IRB-301-31, resistant to fusarium crown and root rot ( Fusarium oxysporum f.sp. radicis-lycopersici ) was crossed with two susceptible cultivars, Motelle and Earlypak No. 7. When F₁, F₂ and backcross progenies were inoculated at the one-leaf stage with a suspension of spores of the pathogen, all could be classified as either resistant (healthy) or susceptible (dead). The ratios of resistant to susceptible plants indicated that resistance was conferred by a single dominant gene, designated Fr1.     

Suppression of pre- and postemergence damping-off in corn by Burkholderia cepacia

Burkholderia cepacia (syn. Pseudomonas cepacia) strain PHQM100 applied as a seed coating was tested in growth chamber experiments for its ability to suppress preemergence damping-off, and postemergence damping-off in corn induced by Pythium and Fusarium spp. The symptoms observed in bioassays with soils naturally infested with the fungal pathogens were seed rot with Pythium spp. and mesocotyl and root tissue necrosis in the presence of Fusarium spp. Three corn cultivars that differed in their susceptibility to damping-off pathogens were used. Cultivar L was susceptible to pre- and postemergence damping-off, whereas cv. LPDP and cv. LG11 were moderately resistant and resistant to the damping-off diseases respectively. In the presence of Pythium spp., seed treatment with B. cepacia reduced seed rot, as compared to the untreated seeds, and this reduction was more consistent in the cv. LPDP than in the resistant cv. LG11 or the susceptible cv. L. In soils infested with Fusarium spp., seed treatment significantly reduced root and mesocotyl necrosis as compared to the untreated seeds, and this reduction was more consistent in the resistant cultivars LG11 and LPDP than in the susceptible cv. L. Root colonization levels by B. cepacia were similar in the three corn cultivars tested. Biocontrol efficiency of B. cepacia varied among cultivars mainly due to the differences in their susceptibility to the fungal pathogens. In spite of variability and also irrespective of the soil characteristics, B. cepacia increased seedling emergence and decreased mesocotyl and root necrosis when used as a seed coating.     

宁夏葡萄苗圃根结线虫病发病症状、为害程度及种类

为有效防治葡萄苗圃根结线虫病,采用拔根百分法和直接解剖法调查宁夏永宁县玉泉营镇葡萄苗圃葡萄苗木根结线虫病的发病症状、为害程度,并通过形态学和分子生物学对其种类进行鉴定。结果表明:15个葡萄品种的病害症状之间有一定差异。除抗砧3号外,其余14个葡萄品种均受根结线虫侵染,且不同葡萄品种受根结线虫为害的严重度差异明显,其中西拉、红芭拉蒂、爱神玫瑰、阳光玫瑰、马瑟兰、贝达和黑比诺上根结线虫病较严重,病情指数介于51.67～78.33之间,大青的病情指数最低,为21.67。不同葡萄品种的每根段雌成虫数量之间、每根段根结数量之间差异明显,其中葡萄品种贝达的每根段雌成虫数量和每根段根结数量最多,分别为12.47条和4.27个,葡萄品种黑比诺的每根段雌成虫数量和每根段根结数量较少,分别为3.60条和1.73个;每根段雌成虫数量随着每根段根结数量的增加而增加。根据根结线虫2龄幼虫、雌成虫和会阴花纹的形态学特征及分子生物学鉴定结果确定为害葡萄苗圃的根结线虫主要为南方根结线虫Meloidogyne incognita和花生根结线虫M. arenaria。除抗砧3号外,其它14个葡萄品种均不同程度的感染了南方根结线虫和花生根结线虫,且所有葡萄品种感染南方根结线虫的比例均较高。     

A New Root-Knot Nematode, Meloidogyne baetica n. sp. (Nematoda: Heteroderidae), Parasitizing Wild Olive in Southern Spain

ABSTRACT High infection rates of wild olive (Olea europaea sp. sylvestris) feeder roots and soil infestation by a new root-knot nematode were found in sandy soil at Vejer de la Frontera (Cádiz), southern Spain. Morphometric traits and analyses of the nematode esterase electrophoretic pattern as well as of the internal transcribed spacer 1 (ITS1)-5.8S gene and D2-D3 fragment of the 28S gene of rDNA showed that specimens differed clearly from known root-knot nematodes. Studies of host-parasite relationships showed a typical susceptible reaction in naturally infected wild olive plants and in olive planting stocks (cvs. Arbequina and Picual) artificially inoculated with the nematode. However, the nematode did not reproduce in artificially inoculated chickpea, pea, and tomato. Because of the ability of this new nematode to infect wild and cultivated olives only, we suggest the common name, "Mediterranean olive root-knot nematode." The species is herein described and illustrated, and named as Meloidogyne baetica n. sp. The new root-knot nematode can be distinguished from other Meloidogyne spp. by (i) the perineal pattern, which is almost similar to that of M. artiellia, characterized by distinct inner striae forming two distinct longitudinal bands, extending throughout the perineum to just below the vulva; (ii) female excretory pore anterior to the level of stylet knobs, excretory pore distance from anterior end/length of stylet ratio extremely small (0.5 to 0.8); and (iii) second-stage juveniles with elongate-conoid tail. Phylogenetic trees derived from maximum parsimony analyses showed that M. baetica is closely related to M. artiellia, the cereal and legume root-knot nematode.     

A new root-knot nematode, Meloidogyne silvestris n. sp. (Nematoda: Meloidogynidae), parasitizing European holly in northern Spain

High infection rates of European holly ( Ilex aquifolium ) feeder roots by an unknown root-knot nematode were found in a holly forest at Arévalo de la Sierra (Soria province) in northern Spain. Holly trees infected by the root-knot nematode showed some decline and low growth. Infected feeder roots were distorted and showed numerous root galls of large (8–10 mm) to moderate (2–3 mm) size. Morphometry, esterase and malate dehydrogenase electrophoretic phenotypes and phylogenetic trees of sequences within the ribosomal DNA (rDNA) demonstrated that this nematode species differs clearly from other previously described root-knot nematodes. Studies of host-parasite relationships showed a typical susceptible reaction in naturally infected European holly plants, but did not reproduce on a number of cultivated plants, including tomato, grapevine, princess-tree and olive. The species is described here, illustrated and named as Meloidogyne silvestris n. sp. The new root-knot nematode can be morphologically distinguished from other Meloidogyne spp. by: (i) roundish perineal pattern, dorsal arch low, with fine, sinuous cuticle striae, lateral fields faintly visible; (ii) female excretory pore level with stylet knobs, or just anterior to them, EP/ST ratio about 0·8; (iii) second-stage juveniles with hemizonid located 1 to 2 annuli anterior to excretory pore and short, sub-digitate tail; and (iv) males with lateral fields composed of four incisures, with areolated outer bands. Phylogenetic trees derived from maximum parsimony analysis based on 18S, ITS1-5·8S-ITS2 and D2–D3 of 28S rDNA showed that M. silvestris n. sp. can be differentiated from all described root-knot nematode species, and it is clearly separated from other species with resemblance in morphology, such as M. ardenensis , M. dunensis and M. lusitanica .     

Systemically induced resistance and microbial competitive exclusion: implications on biological control

The root-knot nematode, Meloidogyne incognita, is among the most damaging agricultural pests, particularly to tomato. The mutualistic endophytes Fusarium oxysporum strain Fo162 (Fo162) and Rhizobium etli strain G12 (G12) have been shown to systemically induce resistance toward M. incognita. By using triple-split-root tomato plants, spatially separated but simultaneous inoculation of both endophytes did not lead to additive reductions in M. incognita infection. More importantly, spatially separated inoculation of Fo162 and G12 led to a reduction in Fo162 root colonization of 35 and 39% when G12 was inoculated on a separate root section of the same plant in two independent experiments. In an additional split-root experiment, spatial separation of Fo162 and G12 resulted in a reduction of Fo162 root colonization of approximately 50% over the water controls in two independent experiments. The results suggested that the suppressive activity of G12 on Fo162 and M. incognita is possibly related to the induction of specific plant defense mechanisms. Thus, although Fo162 and G12 have the ability to systemically repress M. incognita infection in tomato, they can be considered incompatible biocontrol agents when both organisms are present simultaneously on the same root system.     

Biological impact of divergent land management practices on tomato crop health

Development of sustainable food systems is contingent upon the adoption of land management practices that can mitigate damage from soilborne pests. Five diverse land management practices were studied for their impacts on Fusarium wilt (Fusarium oxysporum f. sp. lycopersici), galling of roots by Meloidogyne spp. and marketable yield of tomato (Solanum lycopersicum) and to identify associations between the severity of pest damage and the corresponding soil microbial community structure. The incidence of Fusarium wilt was >14% when tomato was cultivated following 3 to 4 years of an undisturbed weed fallow or continuous tillage disk fallow rotation and was >4% after 3 to 4 years of bahiagrass (Paspalum notatum) rotation or organic production practices that included soil amendments and cover crops. The incidence of Fusarium wilt under conventional tomato production with soil fumigation varied from 2% in 2003 to 15% in 2004. Repeated tomato cultivation increased Fusarium wilt by 20% or more except when tomato was grown using organic practices, where disease remained less than 3%. The percent of tomato roots with galls from Meloidogyne spp. ranged from 18 to 82% in soil previously subjected to a weed fallow rotation and 7 to 15% in soil managed previously as a bahiagrass pasture. Repeated tomato cultivation increased the severity of root galling in plots previously subjected to a conventional or disk fallow rotation but not in plots managed using organic practices, where the percentage of tomato roots with galls remained below 1%. Marketable yield of tomato exceeded 35 Mg ha(-1) following all land management strategies except the strip-tillage/bahiagrass program. Marketable yield declined by 11, 14, and 19% when tomato was grown in consecutive years following a bahiagrass, weed fallow, and disk rotation. The composition of fungal internal transcribed spacer 1 (ITS1) and bacterial 16S rDNA amplicons isolated from soil fungal and bacterial communities corresponded with observed differences in the incidence of Fusarium wilt and severity of root galling from Meloidogyne spp. and provided evidence of an association between the effect of land management practices on soil microbial community structure, severity of root galling from Meloidogyne spp., and the incidence of Fusarium wilt.