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.     

Interaction between Meloidogyne incognita and Agrobacterium tumefaciens or Fusarium oxysporum f. sp. lycopersici on Tomato

Agrobacterium tumefaciens stimulated and Fusarium oxysporum f. sp. lycopersici inhibited development and reproduction of Meloidogyne incognita when applied to the opposite split root of tomato, Lycopersicon esculentum cv. Tropic, plants. The lowest rate of nematode reproduction occurred after 2,000 juveniles were applied and the fungus was present in the opposite split root. The effects of all three pathogens alone on the growth of roots and shoots of tomato plants were evident, but M. incognita had a greater effect alone than did either of the other pathogens. The length of split roots was reduced by the infection of M. incognita and A. tumefaciens or F. oxysporum f. sp. lycopersici. The number of galls induced by nematodes on roots was higher where the bacterium was applied and lower where the fungus was applied to the opposite split root.     

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.     

In vitro selection of alfalfa plants resistant to Fusarium oxysporum f. sp. medicaginis

Summary From two lines of Medicago sativa characterized by a high regeneration capability, calli resistant to culture filtrate of Fusarium oxysporum f. sp. medicaginis have been selected. In these calli regeneration capability was greatly reduced and only one plant per callus was recovered. Regenerated plants have been evaluated for resistance to culture filtrate and for in vivo resistance to the pathogen. Three plants out of eight were resistant to the fungus and a high correlation between resistance to culture filtrate and in vivo resistance was observed.Research work supported by C.N.R., Italy. Special grant I.P.R.A. Subproject 1, paper no. 1468     

Somaclonal variation in celery: screening for resistance to Fusarium oxysporum f. sp. apii

Summary Two methods were used to screen putative Fusarium-resistant celery (Apium graveolens L.) plantlets from cell culture: placing plantlets on a mycelial mat for one month or planting them directly in Fusarium-infested soil. Resistant phenotypes were identified with both methods, but the plants grown on the mycelial mat died before they reached reproductive maturity. Four plants, K, T-2, T-3, and R-R₁ from the soil screen, survived and produced viable seed. Tests of self-pollinated progeny, in field and greenhouse conditions, showed that T-2, T-3, and R-R₁ were superior to the original cultivar, 5270R, with respect to disease resistance, as measured by vascular discoloration and plant height. Chi-square analysis of progeny scores for root and crown decay showed that the new variation was heritable and appeared to be conditioned by more than one locus.     

Two granular formulations of Fusarium oxysporum f.sp. orthoceras to mitigate sunflower broomrape Orobanche cumana

Fusarium oxysporum Schlecht. f.sp. orthoceras (Appel & Wollenw.) Bilai, a potential biocontrol agent against Orobanche cumana Wallr.,was formulated into two granular forms, wheatflour kaolin (`Pesta') granules and sodium alginatepellets. The formulations were compared in terms ofeffectiveness for mitigating O. cumanaparasitism in sunflower and shelf-life forstorage. `Pesta' granules reduced the emergence of O. cumana shoots by 64% while sodium alginatepellets did not reduce the emergence rate but increased thepercentage of diseased O. cumana plants.Calculated efficacy of the application was better for`Pesta' granules. Viability of the formulatedmaterial tested in the laboratory was higher in sodium alginatepellets than in the `Pesta' formulation.However, a loss of virulence after six months of storage wasalso observed in sodium alginate pellets in agreenhouse experiment.     

Chemical-Mediated Toxicity of N-Viro Soil to Heterodera glycines and Meloidogyne incognita

N-Viro Soil (NVS) is an alkaline-stabilized municipal biosolid that has been shown to lower population densities and reduce egg hatch of Heterodera glycines and other plant-parasitic nematodes; but the mechanism(s) of nematode suppression of this soil amendment are unknown. This study sought to identify NVS-mediated changes in soil chemical properties and their impact upon H. glycines and Meloidogyne incognita mortality. N-Viro Soil was applied to sand in laboratory assays at 0.5%, 1.0%, 2.0%, and 3.0% dry w/w with a nonamended treatment as a control. Nematode mortality and changes in sand-assay chemical properties were determined 24 hours after incubation. Calculated lethal concentration (LC₉₀) values were 1.4% w/w NVS for second-stage juveniles of both nematode species and 2.6 and >3.0% w/w NVS for eggs of M. incognita and H. glycines, respectively. Increasing rates of NVS were strongly correlated (r² = 0.84) with higher sand solution pH levels. Sand solution pH levels and, to a lesser extent, the production of ammonia appeared to be the inorganic chemical-mediated factors responsible for killing plant-parasitic nematodes following amendment with NVS.     

Ferulic acid may prevent infection of Cicer arietinum by Sclerotium rolfsii

High performance liquid chromatography analysis of different parts of Sclerotium rolfsii-infected and healthy seedlings of chickpea (Cicer arietinum) was carried out to examine the status of phenolic compounds. Three major peaks that appeared consistently were identified as gallic, vanillic and ferulic acids. Gallic acid concentrations were increased in the leaves and stems of infected plants compared to healthy ones. Vanillic acid detected in stems and leaves of healthy seedlings was not detected in infected seedlings. There was a significant increase of ferulic acid in those stem portions located above the infected collar region compared to minimal amounts in the roots of healthy seedlings. In vitro studies of ferulic acid showed significant antifungal activity against S. rolfsii. Complete inhibition of mycelial growth was observed with 1000 g of ferulic acid/ml. Lower concentrations (250, 500 and 750 g/ml) were also inhibitory and colony growth was compact in comparison with the fluffy growth of normal mycelium. Higher amounts of phenolics were found in the stems and leaves of S. rolfsii-infected seedlings in comparison to the healthy ones. A role for ferulic acid in preventing infections by S. rolfsii in the stems and leaves of chickpea plants above the infection zone is therefore feasible.     

Relationships between initial population densities of Meloidogyne incognita race 2 and nematode population development in terms of variable soybean resistance

The effect of increasing initial population density levels (Pi) of Meloidogyne incognita race 2 on nematode population development and yield of a susceptible (Prima2000) and resistant (LS5995) soybean cultivar was investigated. Two experiments, one in a hail net cage and one in microplots, were conducted one each during two consecutive growing seasons at Potchefstroom in the North West Province of South Africa. Nematode reproduction was assessed by determining the number of eggs and second-stage juveniles (J2) in the rhizosphere and roots, egg masses, egg-laying females (ELF) and reproduction factor (Rf) values per root system at harvesting 110 days after planting. Percentage yield reduction in the two cultivars was also calculated. Strong non-linear relationships existed between all nematode variables as well as between Pi and percentage yield loss in both cultivars for both experiments in this study. Significantly higher numbers of eggs and J2, egg masses and ELF were maintained in the roots of the nematode-susceptible Prima2000 than in the resistant LS5995 from Pi = 100 and higher in both experiments. Rf values were inversely related to Pi for both cultivars and were lowest on LS5995, with Prima2000 maintaining significantly higher Rf values in both experiments. Yield loss in LS5995 was at least six times higher than that of Prima2000. The difference in monetary terms is demonstrated, although it is suggested that host plant resistance to plant-parasitic nematodes may not be sufficient as the only management tool in highly infested soils or in rotation systems including nematode susceptible crops.     

Rhizosphere bacteria antagonistic to soybean cyst (Heterodera glycines) and root-knot (Meloidogyne incognita) nematodes: Identification by fatty acid analysis and frequency of biological control activity

Rhizosphere bacteria were isolated from roots of young and mature plants with known antagonism to phytopathogenic nematodes, including velvet bean (Mucuna deeringiana), castor bean (Ricinus communis), sword bean (Cannavalia ensiformis), and Abruzzi rye (Secale cereale). Isolates from antagonistic plants were compared to soybean isolates for the frequency of antagonism to the root-knot (Meloidogyne incognita) and soybean cyst (Heterodera schachtii) nematodes in a disease assay with soybean. Bacterial isolates were identified using fatty acid analysis, and isolates which exhibited a significant reduction in incidence of soybean damage from both nematodes were characterized physiologically. The bacterial taxa associated with antagonistic plants were markedly different from soybean bacteria. Isolates from soybean were predominantly Bacillus spp., while those from antagonistic plants included more coryneform and Gram-negative genera. Pseudomonas cepacia and Pseudomonas gladioli were predominant among Gram-negative bacteria on antagonistic plants but were not isolated from soybean. Four to six times the number of bacteria from antagonistic plants, compared to soybean, significantly reduced disease incidence of both nematodes. No single pattern of physiological reactions was common among all these bacteria, suggesting that multiple mechanisms accounted for the observed biological control. The results suggest that rhizospheres of antagonistic plants may be useful sources of potential biological control agents for phytopathogenic nematodes.     

Ethylene biosynthesis in Fusarium oxysporum f. sp. tulipae proceeds from glutamate/2-oxoglutarate and requires oxygen and ferrous ions in vivo

Liquid cultures of the deuteromycete, Fusarium oxysporum f. sp. tulipae, a tulip pathogen, produced high amounts of ethylene during stationary phase. 1-Aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene in plants, was not present in the fungus. Radioactivity from [3,4-³H]glutamate as well as [U-¹⁴C]glutamate was incorporated into ethylene, indicating that it was derived from C3 and C4 of glutamate or 2-oxoglutarate. Ferrous ions markedly stimulated the rate of ethylene formation in vivo, whereas Fe³⁺, Cu²⁺ or Zn²⁺ had little or no effect. Ethylene biosynthesis was strongly inhibited by the heavy metal chelator ,-dipyridine. The effect of ,-dipyridine was fully reversed by Fe²⁺ ions and partially by Cu²⁺ and Zn²⁺ ions but not by the supply of glutamate or 2-oxoglutarate, suggesting that a step in the ethylene biosynthetic pathway downstream of 2-oxoglutarate is dependent on Fe²⁺. When stationary phase cultures were supplied with arginine, ornithine, or proline, ethylene production increased dramatically while addition of glutamate or 2-oxoglutarate had little effect. Tracer studies were performed to test the possibility that an intermediate in the catabolism of arginine to glutamate was the direct precursor of ethylene. In cultures supplied with [U-¹⁴C]arginine or [U-¹⁴C]glutamate, the specific radioactivity of ethylene was closely similar to the specific radioactivity of the endogenous glutamate pool, indicating that glutamate was on the pathway between arginine and ethylene. An enzyme system converting 2-oxoglutarate to ethylene in a reaction dependent on oxygen, ferrous ions and arginine has previously been described in extracts from Penicillium digitatum (Fukuda et al. 1986). The present results suggest that a similar enzyme system catalyzes the final step of ethylene biosynthesis in F. oxysporum.Non-standard abbreviations AdoMet S-adenosyl methionine - ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme     

The determination of physiological race of Fusarium oxysporum f. sp. lycopersici of tomato in Zhejiang, China

A group of differential tomato lines was used to identify the races of Fusarium oxysporum f. sp. lycopersici in Zhejiang, China. Marmande verte carries no resistant genes and Marporum carries gene I-1. Both lines Motelle and Mogeor have Gene I-1 and I-2. Tomato seedlings of eighteen days after sowing were inoculated with an isolate of Fusarium oxysporum f. sp. lycopersici, No. 98-2 and kept in a growth chamber. The seedlings were evaluated at fourteen days after inoculation. Results showed that Marmande verte and Marporum were severely infected by the pathogen and established as susceptible. Motelle and Mogeor were not infected and established as resistant. These results indicated that the isolate No. 98-2 represented the race 2 of Fusarium oxysporum f. sp. lycopersici and gene I-2 is necessary for obtaining resistance to this pathogen in the Zhejiang region.     

Effects of Heterodera glycines and Meloidogyne incognita on Early Growth of Soybean

Greenhouse and field microplot studies were conducted to compare soybean shoot and root growth responses to root penetration by Heterodera glycines (Hg) and Meloidogyne incognita (Mi) individually and in combination. Soybean cultivars Centennial (resistant to Hg and Mi), Braxton (resistant to Mi, susceptible to Hg), and Coker 237 (susceptible to Hg and Mi) were selected for study. In the greenhouse, pot size and number of plants per pot had no effect on Hg or Mi penetration of Coker 237 roots; root weight was higher in the presence of either nematode species compared with the noninoculated controls. In greenhouse studies using a sand or soil medium, and in field microplot studies, each cultivar was grown with increasing initial population densities (Pi) of Hg or Mi. Interactions between Hg and Mi did not affect early plant growth or number of nematodes penetrating roots. Root penetration was the only response related to Pi. Mi penetration was higher in sand than in soil, and higher in the greenhouse than in the field, whereas Hg penetration was similar under all conditions. At 14 days after planting, more second-stage juveniles were present in roots of susceptible than in roots of resistant plants. Roots continued to lengthen in the greenhouse in the presence of either Mi or Hg regardless of host genotype, but only in the presence of Mi in microplots; otherwise, responses in field and greenhouse studies were similar and differed only in magnitude and variability.     

Changes in the populations of microorganisms associated with the application of soil amendments to control Sclerotium rolfsii Sacc.

Populations of microorganisms from soil treated with guanidine thiocyanate, guanylurea sulfate, thiourea, or furfural were compared with those of untreated soil. The materials effected quantitative and/or qualitative changes in composition of the soil microflora depending on the compound used. Guanidine thiocyanate (Gt) significantly (p0.05) increased total fungal populations relative to populations of other treatments. Populations of Penicillium purpurogenum were markedly higher in Gt-treated soil. Gt also increased total bacterial populations, and was the only compound that increased actinomycete populations. The relative percentage of Trichoderma harzianum was significantly higher in soil treated with thiourea than in the other treatments. Furfural increased the percentage of P. purpurogenum with respect to total fungi, and was as effective as guanylurea sulfate in increasing chitinolytic bacteria and those in the Pseudomonas cepacia-group. Thiourea most effectively promoted proliferation of coryneform bacteria. Chitinolytic fungi increased synergistically when Gt and guanylurea sulfate were applied in combination.     

The effects of inoculum density and physical factors on the assessment of disease caused by Sclerotium rolfsii

Greenhouse and laboratory experiments were conducted to determine the effects of various physical factors on the assessment of disease caused by Sclerotium rolfsii using field and artificially infested soils. Lentil(Lens esculenta Moench) seedlings growing in trays or pots with sand were inoculated by surrounding them with a layer of soil infested with the pathogen. The number of dead plants was maximal within a 10-day period following inoculation. Seedling mortality increased with the number of sclerotia in the soil to a maximum that depended on seedling spacing, depth of the soil layer, and soil type.     

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.     

Interrelationships of Meloidogyne arenaria and M. incognita on Tolerant Soybean

Reproduction of Meloidogyne arenaria race 2 was excellent on Centennial, Govan, and Kirby soybeans, the latter two of which have tolerance to this species. The M. incognita race 1 isolate reproduced poorly on Centennial, especially at the higher of two temperature regimes. Numbers of galls and egg masses of M. arenaria plus M. incognita in simultaneous equivalent infestations on Centennial did not differ from sequential infestations in which M. arenaria was added first and M. incognita was added to the same pots, 1,2, or 3 weeks later. However, at both 25 and 30 C, suppression of galls and egg masses occurred when inoculation of M. incognita preceded that of M. arenaria by 2 weeks. Generally, M. arenaria reproduced well at 25 or 30 C, whereas M. incognita reproduced better at 30 C. Kirby was tolerant to either nematode species at 25 and 30 C, but in combined infestations of M. arenaria and M. incognita there was evidence of synergistic growth suppression. Govan was tolerant of M. arenaria at 25 C but not at 30 C. Moreover, general plant growth was less vigorous for Govan at the higher temperature, whereas Centennial was much more vigorous at this temperature. Kirby grew equally well at both temperatures.     

Role of salicylic acid in systemic resistance induced by Pseudomonas fluorescens against Fusarium oxysporum f. sp. ciceri in chickpea

Selected isolates of Pseudomonas fluorescens (Pf1-94, Pf4-92, Pf12-94, Pf151-94 and Pf179-94) and chemical resistance inducers (salicylic acid, acetylsalicylic acid, DL-norvaline, indole-3-carbinol and lichenan) were examined for growth promotion and induced systemic resistance against Fusarium wilt of chickpea. A marked increase in shoot and root length was observed in P. fluorescens treated plants. The isolates of P. fluorescens systemically induced resistance against Fusarium wilt of chickpea caused by Fusarium. oxysporum f.sp. ciceri (FocRs1), and significantly (P = 0.05) reduced the wilt disease by 26-50% as compared to control. Varied degree of protection against Fusarium wilt was recorded with chemical inducers. The reduction in disease was more pronounced when chemical inducers were applied with P. fluorescens. Among chemical inducers, SA showed the highest protection of chickpea seedlings against wilting. Fifty two- to 64% reduction of wilting was observed in soil treated with isolate Pf4-92 along with chemical inducers. A significant (P = 0.05; r = -0.946) negative correlation was observed in concentration of salicylic acid and mycelial growth of FocRs1 and at a concentration of 2000 microg ml(-1) mycelial growth was completely arrested. Exogenously supplied SA also stimulated systemic resistance against wilt and reduced the disease severity by 23% and 43% in the plants treated with 40 and 80 microg ml(-1) of SA through root application. All the isolates of P. fluorescens produced SA in synthetic medium and in root tissues. HPLC analysis indicated that Pf4-92 produced comparatively more SA than the other isolates. 1700 to 2000 nanog SA g(-1) fresh root was detected from the application site of root after one day of bacterization whereas, the amount of SA at distant site ranged between 400-500 nanog. After three days of bacterization the SA level decreased and was found more or less equal at both the detection sites.     

Additive Effects of Meloidogyne arenaria and Sclerotinin rolfsii on Peanut

Field observations have suggested that infection of peanut by Meloidogyne arenaria increases the incidence of southern blight caused by Sclerotium rolfsii. Three factorial experiments in microplots were conducted to determine if interactions between M. arenaria and S. rolfsii influenced final nematode population densities, incidence of southern blight, or pod yield. Treatments included four or five initial population densities of M. arenaria and three inoculum rates of S. rolfsii. Final nematode population densities were affected by initial nematode densities in all experiments (P = 0.01) and by S. rolfsii in one of three experiments (P = 0.01). Incidence of southern blight increased with increasing inoculum rates of S. rolfsii in all experiments and by the presence of the nematodes in one experiment (P = 0.01). Pod yield decreased with inoculation with S. rolfsii in all experiments (P = 0.05) and by M. arenaria in two of three experiments (P = 0.05). In no experiment was the interaction among treatments significant with respect to final nematode population densities, incidence of southern blight, or pod yield (P = 0.05). The apparent disease complex between M. arenaria and S. rolfsii on peanut is due to additive effects of the two pathogens.     

Pathogenicity of Pratylenchus penetrans,Heterodera glycines,and Meloidogyne incognita on Soybean Genotypes

The pathogenicity of Heterodera glycines, Meloidogyne incognita, and Pratylenchus penetrans on H. glycines-resistant ''Bryan,'' tolerant-susceptible ''G88-20092,'' and intolerant-susceptible ''Tracy M'' soybean cultivars was tested using plants grown in 800 cm³ of soil in 15-cm-diam. clay pots in three greenhouse experiments. Plants were inoculated with 0, 1,000, 3,000, or 9,000 H. glycines race 3 or M. incognita eggs, or vermiform stages of P. penetrans/pot. Forty days after inoculation, nmnbers of all three nematodes, except H. glycines on Bryan, generally increased with increasing inoculum levels in Experiment I. Heterodera glycines and M. incognita significantly decreased growth only of Tracy M. At 45 and 57 days after inoculation with 6,000 individuals/pot in experiments II and III, respectively, significantly more P. penetrans and M. incognita than H. glycines were found on Bryan. However, H. glycines and M. incognita population densities were greater than P. penetrans on G88-20092 and Tracy M. Growth of Tracy M infected by H. glycines and M. incognita and growth of G88-20092 infected by M. incognita decreased in Experiment III. Pratylenchus penetrans did not affect plant growth. Reduction in plant growth differed according to the particular nematode species and cultivar, indicating that nematodes other than the species for which resistance is targeted can have different effects on cultivars of the same crop species.