Interaction between Meloidogyne incognita and Fusarium oxysporum f. sp. phaseoli on Selected Bean Genotypes

Four bean genotypes (IPA-1, A-107, A-211, and Calima), representing all possible combinations of resistance and susceptibility to Fusarium oxysporum f. sp. phaseoli (Fop) and Meloidogyne incognita, were each inoculated with three population densities of these pathogens. Calima and A-107 were resistant to Fop; A-107 and A-211 were resistant to M. incognita; and IPA-1 was susceptible to both pathogens. In Fop-susceptible lines (IPA-1 and A-211), the presence of M. incognita contributed to an earlier onset and increased severity of Fusarium wilt symptoms and plant stunting. However, the Fop-resistant Calima developed symptoms of Fusarium wilt only in the presence of M. incognita. Genotype A-107 (resistant to both M. incognita and Fop) exhibited Fusarium wilt symptoms and a moderately susceptible reaction to Fop only after the breakdown of its M. incognita resistance by elevated incubation temperatures (27 C). Root galling and reproduction of M. incognita was generally increased as inoculum density of M. incognita was increased on the M. incognita susceptible cultivars. However, these factors were decreased as the inoculum density of Fop was increased. It was concluded that severe infections of bean roots by M. incognita increase the severity of Fusarium wilt on Fop-susceptible genotypes and may modify the resistant reaction to Fop.     

Effect of flavonoids on the development of Fusarium oxysporum f. sp. lycopersici

Abstract

In the present study the effect of flavonoid compounds on the germination and fungal growth of the soil-borne tomato pathogen Fusarium oxysporum f. sp. lycopersici was studied. Out of 12 flavonoid compounds only myricetin and luteolin exhibited a low stimulating activity on microconidia germination of Fusarium oxysporum f. sp. lycopersici, whereas the other flavonoids tested were inactive when applied at five different concentrations. In our study the tested flavonoids affect fungal growth differently to microconidia germination. Individual flavonoid concentrations resulted in a small increase of fungal growth, but the lowest flavonoid concentrations showed an inhibiting effect on fungal growth for all flavonoids tested. There is evidence to suggest, that low flavonoid concentrations exhibit slight antimicrobial properties against Fusarium oxysporum f. sp. lycopersici.     

Purification and characterization of an exopolygalacturonase produced by Fusarium oxysporum f. sp. radicis lycopersici

Abstract An exopolygalacturonase produced by Fusarium oxysporum f. sp. radicis lycopersici , a fungus that produces root rot, was purified by gel filtration and ion exchange chromatography. It had a M _r 68 K, a pH optimum of 5.6 and an optimum temperature of 60°C. This polygalacturonase was inhibited by calcium ions and had a K _m of 0.64 mM using sodium polypectate as substrate. The exo mode of action of this enzyme was revealed by thin-layer chromatography of hydrolysed substrate.     

Biological Control of Fusarium Wilt in Tomato Caused by Fusarium oxysporum f. sp. lycopersici by AMF Glomus intraradices and some Rhizobacteria

In the present study, the effects of the arbuscular mycorrhizal fungus (AMF) Glomus intraradices Schenck & Smith and four rhizobacteria (RB; 58/1 and D/2: Pseudomonas fluorescens biovar II; 17: P. putida; 21: Enterobacter cloacae), which are the important members of the rhizosphere microflora and biological control agents against plant diseases, were examined in the pathosystem of Fusarium oxysporum f. sp. lycopersici [(Sacc) Syd. et Hans] (FOL) and tomato with respect to morphological parameters (fresh and dry root weight) and phosphorous (P) concentration in the roots. Treatments with single and dual inoculation with G. intraradices and RB strains reduced disease severity by 8.6–58.6%. Individual bacteria inoculations were more effective than both the single AMF and dual (G. intraradices + RB) inoculations. In addition, the RB and G. intraradices enhanced dry root weight effectively. Significant increases in root weights were recorded particularly in the triple inoculations compared with single or dual inoculations. Compared with the non‐treated controls all biological control agents increased P‐content of treated roots of plants. Colonization with RB increased especially in triple (FOL + G. intraradices + RB) inoculations whereas colonization of G. intraradices was significantly decreased in treatment of FOL + G. intraradices compared with triple inoculations. The results suggest that suitable combinations of these biocontrol agents may ameliorate plant growth and health.     

Ultrastructural Changes Caused by Fusarium oxysporum f. sp. lycopersici in Meloidogyne javanica Induced Giant Cells in Fusarium Resistant and Susceptible Tomato Cultivars

Tomato (Lycopersicon esculentum Mill.) seedlings, susceptible (cv. Pearson A-I Improved) and resistant (cv. Pearson Improved) to race 1 Fusarium oxysporum f. sp. lycopersici (Sacc.) Snyd &Hans., were inoculated with Meloidogyne javanica (Trueb) Chitwood second-stage juveniles and 3 weeks later with race 1 F. oxysporum f. sp. lycopersici spores. One week after fungal inoculation, no fungus was visible in root tissue of the tomato cultivars and the giant cells were normal. Two weeks after fungal inoculation, abundant hyphae were visible in xylem tissues of Fusarium-susceptible but not of Fusarium-resistant plants. In susceptible plants, giant cell degeneration occurred, characterized by membrane and organelle disruption. In addition, where hyphae were in direct contact with the giant cell, dissolution of the giant cell wall occurred. Three weeks after fungal inoculation, fungal hyphae and spores were visible inside xylem tissues and giant cells in Fusarium-susceptible plants and in xylem tissue of the resistant plants. In susceptible and resistant plants, giant cell degeneration was apparent. Giant cell walls were completely broken down in Fusarium-susceptible tomato plants. In both cultivars infected by Fusarium, giant cell nuclei became spherical and dark inclusions occurred within the chromatin material which condensed adjacent to the fragmented nuclear membrane. No such ultrastructural changes were seen in the giant cells of control plants inoculated with nematode alone. Giant cell deterioration in both cultivars is probably caused by toxic fungal metabolites.     

Tomato root colonization by fluorescent-tagged pathogenic and protective strains of Fusarium oxysporum in hydroponic culture differs from root colonization in soil

The colonization process of tomato roots inoculated separately or/and simultaneously by a pathogenic Fusarium oxysporum f. sp. lycopersici strain Fol8 and the protective F. oxysporum strain Fo47, genetically tagged with the red and green fluorescent protein genes, respectively, was studied in a hydroponic culture. Plants were coinoculated with Fol8 and Fo47 at two conidial concentration ratios of 1/1 and 1/100, in which biological control was not effective or effective, respectively. First observation of fungi on root was possible 48 h after inoculation at a high inoculum level and 5 days post inoculation at the lower concentration of inoculum. The pattern of root colonization was similar for both strains with the initial development of hyphal network on the upper part of taproot, followed by the growth of hyphae towards the elongation zone, lateral roots and root apices. Finally, the whole elongation zone and root apex were invaded by both strains but no specific infection sites were observed. When coinoculated, both strains could grow very closely or even at the same spot on the root surface. At the nonprotective ratio, Fol8 was the successful colonizer, but application of Fo47 at a concentration 100 times >Fol8 delayed vessel colonization by the pathogen.     

Biomass Partitioning in Tomato Plants Infected with Meloidogyne incognita

Tomato plants were inoculated with Meloidogyne incognita at initial populations (Pi) of 0, 1, 10, 50, 100, and 200 (x 1,000) eggs per plant and maintained in a growth chamber for 40 days. Total fresh biomass (roots + shoots) at harvest was unchanged by nematode inoculation with Pi of 1 x 10⁵ eggs or less. Reductions in fresh shoot weight with increasing Pi coincided with increases in root weight. Total fresh biomass declined with Pi above 1 x 10⁵ eggs, whereas total dry biomass declined at Pi above 1 x 10⁴ eggs. The greatest reduction percentages in fresh shoot biomass induced by root-knot nematodes occurred in the stem tissue, followed by the petiole + rachis; the least weight loss occurred in the leaflets. Although biomass varied among shoot tissues, the relationship between biomass of various shoot tissues and Pi was described by quadratic equations. The linear and quadratic coefficients of the equations (stem, petiole + rachis, or leaflets on Pi) did not differ among tissues when calculations were based on standardized values. Meloidogyne incognita-infected plants had thinner leaves (leaf area/leaf weight) than did uninfected plants. Reductions in leaf weight and leaf area with nematode inoculation occurred at nodes 5-15 and 4, 6-14, respectively. Losses in plant height and mass due to nematodes reflected shorter internodes with less plant mass at each node.     

Interaction of Fusarium oxysporum f. sp. ciceri and Meloidogyne javanica on Cicer arietinum

Interaction of Meloidogyne javanica and Fusarium oxysporum f. sp. ciceri was studied on Fusarium wilt-susceptible (JG 62 and K 850) and resistant (JG 74 and Avrodhi) chickpea cultivars. In greenhouse experiments, inoculation of M. javanica juveniles prior to F. oxysporum f. sp. ciceri caused greater wilt incidence in susceptible cultivars and induced vascular discoloration in roots of resistant cultivars. Nematode reproduction was greatest (P = 0.05) at 25 °C. Number of galls and percentage of root area galled increased when the temperature was increased from 15 °C to 25 °C. Wilt incidence was greater at 20 °C than at 25 °C. Chlorosis of leaves and vascular discoloration of plants did not occur at 15 °C. The nematode enhanced the wilt incidence in wilt-susceptible cultivars only at 25 °C. Interaction between the two pathogens on shoot and root weights was significant only at 20 °C, and F. o. ciceri suppressed the nematode density at this temperature. Wilt incidence was greater in clayey (48% clay) than in loamy sand (85% sand) soils. The nematode caused greater plant damage on loamy sand than on clayey soil. Fusarium wilt resistance in Avrodhi and JG 74 was stable in the presence of M. javanica across temperatures and soil types.     

Interaction of Population Levels of Fusarium oxysporum f. sp. vasinfectum and Meloidogyne incognita on Cotton

In autoclaved greenhouse soil without Fusarium oxysporum f. sp. vasinfectum, Meloidogyne incognita did not cause leaf or vascular discoloration of 59-day-old cotton plants. Plants had root galls with as few as 50 Meloidogyne larvae per plant. Root galling was directly proportional to the initial nematode population level. Fusarium wilt symptoms occurred without nematodes with 77,000 fungus propagules or more per gram of soil. As few as 50 Meloidogyne larvae accompanying 650 fungus propagules caused Fusarium wilt. With few exceptions, leaf symptoms appeared sooner as numbers of either or both organisms increased. In soils infested with both organisms, the extent of fungal invasion and colonization was well correlated with the extent of nematode galling and other indications of the Fusarium wilt syndrome.     

Interaction Studies Between Meloidogyne Javanica and Fusarium Oxysporum f. Sp. lycopersici (Fol) Race 3 on Different Isolines of Tomato Cv. Tasti Lee

The Mi gene in tomato confers resistance to Meloidogyne javanica, M. incognita, and M. arenaria, the most common tropical root-knot nematode (RKN) species found in Florida. Fusarium wilt (Fol) is another major problem in Florida tomatoes which may interact with RKN and cause more plant damage. To study the interactions between RKN, Fusarium, and Mi in tomato, two greenhouse experiments were conducted. Both experiments used different isolines (with and without I-3 and Mi genes) of the tomato cultivar Tasti Lee^®. In the first experiment, all four isolines were subjected to two levels of RKN (~10,000 eggs/pot and no eggs) and two levels of Fol (1000 cc soil with 1,000 cfu/g at planting and no Fol), both applied at planting. In the second experiment, the two isolines without I-3 were exposed to the same two levels of RKN as described above and three levels of Fol (50 ml Fol with 1×10⁶ cfu/m at planting, at 10 DAT, and no Fol). Fol reduced root-knot infection and reproduction when both Fol and RKN were inoculated at planting but not when Fol was inoculated 10 days later. Plant damage from Fol was exacerbated in the presence of RKN, especially when both pathogens were present at planting. Isolines with I-3 grew better in Fol-inoculated soil but had no effect when Fol and RKN were both present. Isolines with Mi gene reduced RKN infection and reproduction but did not affect plant damage caused by Fol. In summary, while RKN reproduction was reduced in the presence of Fol, the overall plant damage was more severe when both pathogens were present.     

Induction of Isoperoxidases in Resistant and Susceptible Tomato Cultivars by Meloidogyne incognita

Isoperoxidases were detected in resistant Rossol and susceptible Roma VF tomato roots uninfected and infected by Meloidogyne incognita. Syringaldazine, guaiacol, p-phenylenediamine-pyrocatechol (PPD-PC), and indoleacetic acid (IAA) were used as substrates, and the corresponding peroxidative activities were detected either in cytoplasmic or in cell wall fractions, except for IAA oxidase, which was measured in soluble and microsomal fractions. Isoperoxidase activities and cellular locations were induced differently in resistant and susceptible cultivars by nematodes. Nematode infestation markedly enhanced syringaldazine oxidase activity in cell walls of the resistant cultivar. This isoperoxidase is involved in the last step of lignin deposition in plants. Conversely, the susceptible cultivar reacted to M. incognita infection with an increase in cytoplasmic PPD-PC oxidase activity, which presumedly is involved in ethylene production; no changes in cell wall isoperoxidases were observed. IAA oxidase was inhibited in susceptible plants after nematode inoculation, whereas in resistant plants this activity increased in the soluble fraction and decreased in the microsomal fraction.     

Influence of Meloidogyne incognita on Fusarium Wilt of Tomato at or below the Minimum Temperature for Wilt Development

''Bonny Best'' tomato plants were grown at 16, 21, or 24 C for 28 d in soil infested with either of two isolates of Fusarium oxysporum f. sp. lycopersici race 1 and Meloidogyne incognita. Significant levels of fusarium wilt occurred at all temperatures including 16 C, which has not been reported previously. One Fusarium isolate resulted in the highest levels of disease incidence at 21 and 24 C in the presence of root-knot nematodes, and at 24 C when the nematodes were not present. At 16 C there was no significant difference in the number of plants infected by the second Fusarium isolate alone or in combination with root knot nematodes, although the presence of nematodes resulted in a significant increase in the percentage of disease occurrence and vessel infection at 21 C.     

Genetic Diversity of Fusarium oxysporum Populations Isolated from Tomato Plants in Tunisia

Fusarium crown and root rot of tomato (Lycopersicon esculentum) caused by Fusarium oxysporum f. sp. radicis‐lycopersici is a new devastative disease of tomato greenhouse crops in Tunisia. Nothing is known neither about the population of this pathogen in this region, nor about the population of F. oxysporum f. sp. lycopersici the causal agent of Fusarium wilt of tomato. In order to examine the genetic relatedness among the F. oxysporum isolates by intergenic spacer restriction fragment length polymorphism (IGS‐RFLP) analysis and to elucidate the origin of the formae specialesradicis‐lycopersici in Tunisia by looking for genetic similarity of Tunisians isolates with isolates from a foreign source, the genetic diversity among F. oxysporum f. sp. radicis‐lycopersici and F. oxysporum f. sp. lycopersici populations was investigated. A total of 62 isolates of F. oxysporum, obtained from symptomless tomato plants, were characterized using IGS typing and pathogenicity tests on tomato plants. All Fusarium isolates were highly pathogenic on tomato. Fusarium oxysporum f. sp. radicis‐lycopersici isolates were separated into five IGS types. From the 53 F. oxysporum f. sp. radicis‐lycopersici isolates, 34 isolates have the same IGS types (IGS type 25), and the remaining 19 isolates were distributed into four IGS types. However, the only nine isolates of F. oxysporum f. sp. lycopersici have six different IGS types. This difference of diversity between the two formae speciales suggests that F. oxysporum f. sp. radicis‐lycopersici isolates have a foreign origin and may have been accidentally introduced into Tunisia.     

Survival of Paecilomyces lilacinus in Selected Carriers and Related Effects on Meloidogyne incognita on Tomato

Laboratory and microplot experiments were conducted to determine the influence of carrier and storage of Paecilomyces lilacinus on its survival and related protection of tomato against Meloidogyne incognita. Spores of P. lilacinus were prepared in five formulations: alginate pellets (pellets), diatomaceous earth granules (granules), wheat grain, soil, and soil plus chitin. Fungal viability was high in wheat and granules, intermediate in pellets, and low in soil and chitin-amended soil stored at 25 ± 2 C. In 1985 P. lilacinus in field microplots resulted in about a 25% increase in tomato yield and 25% gall suppression, compared with nematodes alone. Greatest suppression of egg development occurred in plots treated with P. lilacinus in pellets, wheat grain, and granules. In 1986 carryover protection of tomato against M. incognita resulted in about a threefold increase in tomato fruit yield and 25% suppression of gall development, compared with plants treated with nematodes alone. Higher numbers of fungus-infected egg masses occurred in plots treated with pellets (32%) than in those treated with chitin-amended soil (24%), wheat (16%), granules (12%), or soil (7%). Numbers of fungal colony-forming units per gram of soil in plots treated with pellets were 10-fold greater than initial levels estimated at planting time in 1986.     

Colored Mulches Affect Yield of Fresh-market Tomato Infected with Meloidogyne incognita

The effects of different-colored polyethylene mulches on the quantity and spectra of reflected light, earliness of fruit set, fruit yield and quality, and root-knot disease were studied in field-grown, staked tomato (Lycopersicon esculentum). White mulch reflected more photosynthetic light and a lower far-red-to-red ratio than red mulch, whereas black mulch reflected less than 5 percent of any color. Soil temperatures and fruit yields were recorded for tomato plants inoculated with Meloidogyne incognita race 3 at initial populations of 0, 1,000, 10,000, 50,000, or 100,000 eggs/plant and grown over black, white, or red plastic mulch in both spring and fall. Soil temperatures were lower under white mulch than under red or black mulch. Tomato yields declined as inoculum level increased. Plants grown over red mulch in the spring and inoculated with 50,000 eggs of M. incognita had greater early marketable yields than similarly inoculated plants grown over black or white mulch. Tomato plants inoculated with 100,000 eggs and grown over white mulch or red mulch in the spring had greater total yields per plot than similar plants grown over black mulch (7.39 kg and 7.71 kg vs. 3.65 kg, respectively).     

Meloidogyne incognita and Tomato Response to Thiamine,Ascorbic Acid, L-arginine,and L-glutamic Acid

The influence of solutions of ascorbic acid, thiamine, L-arginine, and L-gtutamic acid on egg hatch, juvenile survival, and development and reproduction of Meloidogyne incognita in susceptible and resistant tomatoes was studied. Maximum inhibition of egg hatch occurred at 2,000, 4,000, and 2,000 ppm for ascorbic acid, L-arginine, and L-glutamic acid, respectively. Larval survival was significantly reduced by concentrations of 2,000 ppm ascorbic acid and 1,000 ppm of L-arginine. Maximum inhibition of egg hatch and mortality of juveniles was achieved at a concentration of 4,000 ppm of ascorbic acid and L-arginine. L-glutamic acid and thiamine had respective moderate and minimal toxic effects. Foliar sprays of ascorbic acid, L-arginine, or L-glutamic acid suppressed the numbers of root galls, females, and egg masses on the susceptible tomato cultivar Tropic. Ascorbic acid and L-arginine had highly significant effects when applied to foliage before inoculation with nematodes. Thiamine had little effect. All sprays suppressed the numbers of root galls and females in roots of the resistant cultivar VFN8 when treatments were applied before inoculation. They were not, however, effective as post-inoculation treatments. Growth of a susceptible cultivar was improved by post-inoculation and pre-inoculation treatments when compared with the control plants which had neither nematode infection nor chemical treatment. No positive growth response to chemical treatment was seen in resistant control plants.     

Meloidogyne incognita Resistance Characteristics in Tomato Genotypes Developed for Processing

Nine resistant processing tomato (Lycopersicon esculentum) cultivars and advanced lines were compared with four susceptible cultivars in 1,3-dichloropropene-fumigated and nontreated plots on Meloidogyne incognita-infested sites over 3 years. Yield of all resistant genotypes grown in nontreated and nematicide-treated plots did not differ and was greater than yield of susceptible genotypes. M. incognita initial soil population densities caused 39.3-56.5% significant (P = 0.05) yield suppressions of susceptible genotypes. Nematode injury to susceptible plants usually caused both fruit soluble solids content and pH to increase significantly (P = 0.05). Only trace nematode reproduction occurred on resistant genotypes in nontreated plots, whereas large population density increases occurred on susceptible genotypes. Slightly greater nematode reproduction occurred on resistant genotypes at the southern desert location, where soil temperature exceeded 30 C, than at other locations. At two locations resistant MOX 3076 supported greater reproduction than other resistant genotypes.     

Characterization of Anionic Peroxidases in Tomato Isolines Infected by Meloidogyne incognita

Changes in peroxidase activity during nematode infection were studied using root extracts of tomato near-isogenic lines differing in resistance to Meloidogyne incognita. Total peroxidase activity increased slightly in crude extracts of four susceptible isolines but doubled in two resistant lines, Monita and Motaci. Nematode infection enhanced levels of both p-phenylenediamine-pyrocatechol oxidase and syringaldazine oxidase 7 days after inoculation, especially in resistant lines. This elevated peroxidase activity in resistant isolines was caused by an increase in anionic peroxidase activity. These enzymes, which likely are involved in lignification, were isolated and purified from tomato isolines by ammonium sulfate precipitation, high performance ion-exchange chromatography, and gel electrophoresis. The purified anionic peroxidase extracts contained an electrophoretic band with Rf 0.51 that was present in extracts of infected but not uninfected roots.     

Impact of Paecilomyces lilacinus Inoculum Level and Application Time on Control of Meloidogyne incognita on Tomato

Microplot experiments were conducted to evaluate the effects of inoculum level and time of application of Paecilomyces lilacinus on the protection of tomato against MeIoidogyne incognita. The best protection against M. incognita was attained with 10 and 20 g of fungus-infested wheat kernels per microplot which resulted in a threefold and fourfold increase in tomato yield, respectively, compared with tomato plants treated with this nematode alone. Greatest protection against this pathogen was attained when P. lilacinus was delivered into soil 10 days before planting and again at planting. Yield was increased twofold compared with yield in nematode-alone plots and plots with M. incognita plus the fungus. Percentages of P. lilacinus-infected egg masses were greatest in plots treated at midseason or at midseason plus an early application, compared with plots treated with the fungus 10 days before planting and (or) at planting time.