Histopathology of Oil Palm Seedlings Infected by, Pathogenic Fusarium oxysporum Isolates from Africa

Oil palm seedlings (one-leaf stage) grown from Malaysian seed were inoculated with six African isolates of Fusarium oxysporum f. sp. elaeidis and one African isolate of Fusarium oxysporum var. redolens. All the isolates induced similar symptoms and anatomical responses in the inoculated palms. The pathogen invaded the root, bulb, leaf bases and leaves in that sequence. In the root and bulb, infection resulted in plugging of xylem elements with mycelium, conidia, tyloses and gums, disintegration and plugging of phloem tissues, disintegration of plugged vascular elements forming gaps and cavities, and collapse of cortical tissues leading to the isolation of the infected vascular tissues. Formation of hypertrophic or hyperplastic cells in the xylem parenchyma was not observed. Anatomical changes in the infected leaf bases and petioles were similar to those occurring in the infected bulb; except that tyloses were formed less frequently. Generally there was no sign of the pathogen in the wilted leaf blade, but the epidermal, hypodermal and mesophyll cells appeared shrunken or to have collapsed. No hyphae or anatomical changes were observed m the tissues of symptomless inoculated palms.     

Pathogenicity of Fusarium oxysporum Isolates from Malaysia and F. oxysporuin f. sp. elaeidis from Africa to Seedlings of Oil Palms (Elaeis guineensis)

Pathogenicity tests with Fusarium oxysporum isolated form Malaysian oil palm were made with oil palms seedlings raised form Malaysian seed as well s with wilt-susceptible seedlings gown from African seed. Oil palm seedlings grown form Malaysian seed were also inoculated with African isolates of F. oxysporum f. sp. elaeidis and F. oxysporum var. redolens. The experiments were made under normal soil moisture conditions and under water stress. F. oxysporum f. sp. elaeidis isolates form Africa were pathogenic to oil palm seedlings from Malaysian seeds but the Malaysian F oxysporum isolates were non-pathogenic to plams grown from Malaysian seed or the wilt-susceptible palms from African seed. Seedlings from Malaysian seed proved to be highly susceptible to the vascular wilt disease caused by F. oxysporum f. sp. elaeidis as 75–90% of the palms were infected. The susceptibility of the palms from Malaysian seed varied with different African isolates tested. The Yaligimba isolate from Zaire which was found to be F. oxysporum var. redolens was the most virulent. Disease was more severe when oil palm seedlings were subjected to a period of water stress. The incidence of death in the seedlings under stress conditions was 45% as compared with only 15% for palms grown under normal conditions.     

Pathogenicity of Geographic Isolates of Fusarium oxysporum from Crucifers on a Differential Set of Crucifer Seedlings

Pathogenicity tests with 103 isolates of Fusarium oxysporum from crucifers worldwide were conducted using a standard set of six differential crucifer cultivars. Based on their reaction to the standard differentials, all isolates could be grouped into the five major pathotypes in the three formae speciales, f. sp. conglutinans. f. sp. raphani and f. sp. matthioli. When two additional crucifers, Brassica nigra and B. campestris were added to the differe, ntial set, and the reactions of the host differentials were analyzed, an increased range of virulence profiles was observed, implying the existence of more virulence factors in the F. oxysporum population. An isolate from the U.S.S.R., was identified with virulence capable of overcoming dominant monogenic “type A” resistance in Brassica oleracea suggestive of a potentially new location for this pathotype.     

Pathogenicity of Fusarium oxysporum to Easter lily, narcissus and gladiolus

Isolates of Fusarium oxysporum from roots, bulbs and stems of Easter lilies (Lilium longiflorum) differed widely in pathogenicity and also, apparently, in tissue specificity. Virulent isolates caused a typical basal rot and root rot (but not a wilt) in which the mycelium advanced intercellularly through the scales and basal plates. Mildly pathogenic isolates became established in mature or senescent outer scales, at first producing only superficial effects, but further growth of mycelium occurred as the outer scales died and sometimes continued until the dead tissues were permeated and chlamydospores were formed. The underlying scales were then colonized. The modes of pathogenicity and survival in Easter lily were compared with those of the F. oxysporum formae causing bulb rots of gladiolus and narcissus. It is suggested that advance of hyphae by penetration between the cells of the vascular parenchyma, which is common in isolates causing rots in bulbs and corms, represents a stage in the evolution of the truly vascular habit among fusaria.     

Protein and Esterase Patterns of Pathogenic, Fusarium oxysporum f. sp. elaeidis and F. oxysporum var. redolens from Africa, and Non-Pathogenic K oxysporum from Malaysia

Protein and esterase patterns of eleven isolates of F. oxysporum f. sp. elaeidis, one isolate of F. oxysporum var. redolens pathogenic to oil palm from Africa and six non-pathogenic isolates of F. oxysporum from oil palm soils in Malaysia were studied by vertical disc-electrophoresis and isoelectric focusing, to determine whether the pathogenic and saprophytic forms of F. oxysporum could be distinguished using these two methods. The protein patterns of all the isolates studied by the two methods were almost identical qualitatively and it was impossible to distinguish between the pathogenic isolates of F. oxysporum f. sp. elaeidis and F. oxysporum var. redolens from Africa and saprophytic isolates of F. oxysporum from Malaysia. Esterase zymograms of the isolates produced by the two methods were different. Esterase zymograms produced by vertical disc-electrophoresis showed great variations between and within the African and Malaysian isolates, but the esterase patterns produced by isoelectric focusing were almost identical qualitatively.     

The Saprophytic Status of Fusarium oxysporum Schl: Causing Vascular Wilt of Oil Palm

The droplet plating method described, especially when used inconjunction with a baiting technique, facilitates the demonstrationof Fusarium oxysporum in soil. This fungus was present in soilfrom wilt-free areas of oil palm plantations as well as in soilabout wilt-diseased palms. Hyphal fusions between soil isolatesand isolates from wilted palms could be demonstrated. The funguspersisted for periods of at least ¹ year in naturally infestedsoils under a variety of moisture conditions; it also survivedin inoculated alien soil forms of Ieast ¹year. Soil forms ofthe fungus had a high competitive saprophytic ability, competitivelycolonizing sterilized soils and sand, and organic materialsadded to soils and mixed cultures. The pathogenic isolate, aswell as the soil isolates, exhibited characters belonging tosoil-inhabiting fungi, namely continued persistance in soil:tolerance, in respect of growth and reproduction, to antagonism:and the ability competitively to colonize dead organic materialin soils. The pathogenic form is considered to be a soil inhabitant.     

Clonal Diversity of Escherichia Coli Isolates from Marketed Beef in East Malaysia

Summary Escherichia coli, including Shiga-like toxin producing E. coli (STEC), serogroup O157:H7 and E. coli O157, were isolated from raw beef marketed in Sarawak and Sabah, East Malaysia. Molecular subtyping by pulsed-field gel electrophoresis (PFGE) was performed on 51 confirmed E. coli isolates. Of the 51 isolates, five were E. coli O157:H7, four E. coli O157, two non-O157 STEC and 40 other E. coli isolates (non-STEC). Digestion of chromosomal DNA from these E. coli isolates with restriction endonuclease XbaI (5′-TCTAGA-3′), followed by PFGE, produced 45 restriction endonuclease digestion profiles (REDPs) of 10–18 bands. E. coli O157:H7 isolates from one beef sample were found to have identical PFGE profiles. In contrast, E. coli serogroup O157 from different beef samples displayed considerable differences in their PFGE profiles. These suggested that E. coli isolates of both serogroups were not closely related. A large variety of PFGE patterns among non-STEC isolates were observed, demonstrating a high clonal diversity of E. coli in the beef marketed in East Malaysia. The distance matrix values (D), calculated showed that none of the pathogenic E. coli strains displayed close genetic relationship with the non-STEC strains. Based on the PFGE profiles, a dendrogram was generated and the isolates were grouped into five PFGE clusters (A–E). From the dendrogram, the most related isolates were E. coli O157:H7, grouped within cluster B. The STEC O157:H7 beef isolates were more closely related to the clinical E. coli O157:H7 isolate than the E. coli O157:H7 reference culture, EDL933. Cluster A, comprising many of other E. coli isolates was shown to be the most heterogeneous. PFGE was shown to possess high discriminatory power in typing pathogenic and non-pathogenic E. coli strains, and useful in studying possible clonal relationship among strains.     

Pathogenicity of Fusarium avenaceum Isolates from Cereals and their Ability to Produce Substance with Yellow Fluorescence

Fusarium avenaceum isolates from wheat, rye, barley, triticale, corn and potato formed substance with yellow fluorescence with properties similar to citrinin. Pathogenicity of 17 isolates tested against cereals seedlings was weaker than F. culmorum isolates; one isolate only was strong, two medium and the remaining 82 % were very weak or non pathogenic.     

Pathogenicity of Fusarium Isolates from Wheat, Rye and Triticale Towards Seedlings and their Ability to Produce Trichothecenes and Zearalenone

37 Fusarium isolates (F. culmorum 20, F. graminearum 4, F. avenaceum 3, F. solani 4, and F. equiseti 6 from wheat, rye and triticale) were examined for pathogenicity and tested for zearalenone (F-2) and trichothecenes production in vitro. Strong pathogens (F. culmorum and F. graminearum) produced deoxynivalenol and 3-acetyl-deoxynivalenol and zearalenone in considerable quantities.     

Relationship between Cell Wall Susceptibility to Cellulases and Pectinases of Fusarium oxysporum and Susceptibility of Date Palm Cultivars

Fusarium oxysporum f. sp. albedinis, the bayoud disease agent of date palm, grows on a mineral medium containing the cell walls of date palm roots as a sole carbohydrate source. The growth and development of pathogen under these conditions was related to the production of extracellular cell wall-degrading enzymes (CWDE): cellulases, polygalacturonases, polygalacturonate transeliminases, and pectinmethylesterases. The mycelial growth and the sporulation of pathogen were higher in the presence of cell walls of susceptible cultivars (BFG, JHL, BSK) than in the presence of those of resistant cultivars (IKL, SLY, BSTN). After 8 d of fungal culture, the activity of CWDE was equal whatever is the origin of the cell walls (resistant or susceptible cultivars). After 16 d of culture, the activity of these CWDE was higher when the parasite was cultivated on the cell walls of the susceptible cultivars than on those of the resistant cultivars. A positive correlation was observed between CWDE activities and the growth and the sporulation of F. oxysporum after 16 d of culture. These results clearly show a relation between the susceptibility/resistance of the cell walls of the roots of the date palm to the parasitic CWDE and the susceptibility/resistance of the cultivars.     

Windborne displacements of Desert Locusts from Africa to the Caribbean and South America

The Desert Locust is a major pest of agriculture in Africa, the Middle East and South-West Asia and swarms are known to make downwind flights over hundreds and thousands of kilometres between seasonal breeding areas. At the end of summer in 1988, swarms of locusts were moving north and south along the western margins of North Africa and in October and November, swarms crossed the Atlantic Ocean and invaded the Caribbean and neighbouring parts of South America for the first recorded time. Because of the extent of the migration and the evolutionary significance of linkages between Old and New World species of locusts, the weather associated with the migrations was studied and trajectory analysis was used to identify the source areas and estimate the flight times. Locusts were moving offshore from western North Africa throughout the autumn and on three occasions migrated west of 40° W with easterly Trade winds. Two trans-Atlantic crossings coincided with the passage of easterly waves. Over 100 trajectories were constructed at 950 and 850 hPa and within the time limit used ( 144-h), 28% successfully linked source and receptor areas. Minimum trajectory duration was 93-h, which is one-and-a-half times longer than the previously longest flight duration, derived for a similar migration to the British Isles in 1954. Upwind trajectories from the arrival areas, identified sources between 27 and 6° N in Africa, with most end-points located in Mauritania, Senegal, Gambia and Guinea-Bissau. Interspersed with the Atlantic crossings were a northward movement of locusts and an incursion of Saharan dust into Europe within the circulations of frontal depressions. While offshore migrations from northern Africa are common in autumn, the immigrants in the Caribbean and South America were probably at the extreme limits of flight endurance for the species. The results tend to confirm earlier hypotheses that New World species of locusts may have evolved from ancestral migrants from Africa.     

Comparisons of Isolates of Fusarium avenaceum from White Lupin and Other Crops by Pathogenicity Tests,DNA Analyses and Vegetative Compatibility Tests

Isolates of Fusarium avenaceum, mostly from crops of white lupin or wheat, were tested for pathogenicity on white lupin and wheat plants and compared by DNA tests and, in a limited study, vegetative compatibility. Most of the 80 isolates were pathogenic on both plant species after inoculation on shoot bases. Disease severity was greater at higher incubation temperatures that ranged from 15/10°C to 25/20°C (day/night temperatures). Isolates from lupin crops tended to be more pathogenic, on average, on lupins than on cereals. Polymerase chain reaction (PCR)‐restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of the rDNA distinguished two groups of isolates that occurred in different proportions among isolates from lupins and cereal crops. Random amplified polymorphic DNA (RAPD)‐PCR analyses indicated considerable genetic variation among isolates, but there was some similarity among groups of isolates from populations in the same field. Genetic diversity was confirmed by a high degree of vegetative incompatibility among 20 isolates using nitrate nonutilizing mutants. There were no relationships among pathogenicity, RFLP group, RAPD group and vegetative compatibility group.     

Constitutive expression, purification and characterization of a phosphoglucomutase from Fusarium oxysporum

The phosphoglucomutase gene from a wild type Fusarium oxysporum strain (F3), was homologously expressed, under the control of the constitutive promoter of gpdA of Aspergillus nidulans. The transformant produced elevated levels of phosphoglucomutase activity compared to the wild type, a fact that facilitated the subsequent purification procedure. The enzyme (FoPGM) was purified to homogeneity applying three anion exchange and one gel filtration chromatography steps. The native enzyme revealed a monomeric structure with a molecular mass of 60 kDa, while the isoelectric point was 3.5. FoPGM was active in pH ranged from 6.0 to 8.0, with an optimum using 3-(N-morpholino)propanesulfonic acid buffer at 7.0, while loss of activity was observed when phosphate buffer was used in the above mentioned pH range. The optimal temperature for activity was 45°C but the enzyme became unstable at temperatures above 40°C. FoPGM requires the presence of a divalent cation for its function with maximum activity being obtained with Co(2+). The apparent K(m) for Co(2+) was found to be 10 μM. The enzyme was also active with other divalent metal ions such as Mn(2+), Mg(2+), Ni(2+) and Ca(2+) but to a lesser extent. The following kinetic constants were determined: v(max), 0.74 μmol mg(protein)(-1)min(-1); k(cat), 44.2 min(-1); K(m)(G1P), 0.10mM; K(m)(G1,6 diP), 1.03 μM; k(cat)/K(m)(G1P), 443 mM(-1)min(-1) and k(cat)/K(m)(G1,6 diP), 42,860 mM(-1)min(-1). The enzyme was considered to follow a Ping Pong substituted enzyme or enzyme isomerization mechanism.     

Induction, purification, and characterization of two extracellular alpha-L-arabinofuranosidases from Fusarium oxysporum

In the presence of L-arabinose as sole carbon source, Fusarium oxysporum produces two alpha-L-arabinofuranosidases (ABFs) named ABF1 and ABF2, with molecular masses of 200 and 180 kDa, respectively. The two F. oxysporum proteins have been purified to homogeneity. The purified enzymes are composed of three equal subunits and are neutral proteins with pIs of 6.0 and 7.3 for ABF1 and ABF2, respectively. With p-nitrophenyl alpha-L-arabinofuranoside (pNPA) as the substrate, ABF1 and ABF2 exhibited Km values of 0.39 and 0.28 mmol.L(-1), respectively, and Vmax values of 1.6 and 4.6 micromol.min(-1).(mg of protein)(-1), respectively, and displayed optimal activity at pH 6.0 and 50-60 degrees C. ABFs released arabinose only from sugar beet arabinan and not from wheat soluble and insoluble arabinoxylans. The enzymes were not active on substrates containing ferulic acid ester linked to C-5 and C-2 linkages of pNPA showing that phenolic substituents of pNPA sterically hindered the action of ABFs.     

Fuel Characteristics of Solid Biofuel Derived from Oil Palm Biomass and Fast Growing Timber Species in Malaysia

The fuel characteristics of solid biofuels derived from biomass that is abundantly available in Malaysia are presented. The objectives of the study were to characterize fuel properties of oil palm biomass (empty fruit bunch (EFB) and oil palm trunk (OPT)) and wood from a range of fast growing timber species (Albizia falcataria, Acacia spp., Endospermum spp. and Macaranga spp.), inclusive and exclusive of bark. Among the fast-growing timber species, the higher heating values ranged from 4288 cal g^-1 to 4383 cal g^-1 for wood inclusive of bark, and 4134 cal g^-1 to 4343 cal g^-1 for wood exclusive of bark. The inclusive of bark portion in the biomass sample generally increased the heating value except for Macaranga spp. Empty fruit bunch and oil palm trunk had heating values of 4315 cal g^-1 and 4104 cal g^-1, respectively. Ash-forming elements and trace elements were much higher in the timber species samples inclusive of bark than samples exclusive of bark. On the other hand, oil palm biomass contained higher ash-forming elements and trace elements than the wood from the fast growing timber species. The European energy crops show higher HHV, Cl and Si content but lower K, Mg, Na and P compared to the local biomass used in this study. The data obtained from this study can serve as a foundation for the selection of suitable biomass to be used as solid fuel, or as a reference on the fabrication of conversion systems for the selection of biomass solid fuel.