Morphological Characteristics, Distribution, And Mycotoxin Profiles Of Fusarium Species From Soils In Peninsular Malaysia [QK625.T8 I98 2008 f rb].

Fusarium merupakan salah satu genus kulat yang paling dikenali dan penting kerana kepelbagaian, kosmopolitan, dan keupayaannya sebagai penyebab kepada sebilangan penyakit yang parah terhadap tumbuhan, manusia, haiwan, dan juga mikotoksikosis. Fusarium is considered as one of the most interesting and important group of fungi, because of the diversity, cosmopolitan, and ability to cause serious diseases on plants, humans, animals, as well as mycotoxicoses. Fusarium species is commonly found in the soils in all major geographic regions of the world

Genetics of Southeast Asian populations and interspecific hybrids of Fusarium spp.

Doctor of PhilosophyDepartment of Plant PathologyJohn F. LeslieMembers of the genus Fusarium are widely distributed in many geographic regions of the world. This genus includes plant pathogens of many important cereal crops, e.g., wheat, maize, rice and sorghum, and of other native and economically important plants. From culture collections at Kansas State University and Universiti Sains Malaysia, strains from Southeast Asia, primarily from Malaysia and Thailand, associated with mango malformation disease, bakanae disease of rice, and stalk rot of sorghum were analyzed in sexual crosses and molecular diagnostics, e.g., Amplified Fragment Length Polymorphisms (AFLPs). Fusarium proliferatum was recovered from all three crops, with each crop also yielding some species unique to the crop, e.g. F. fujikuroi from rice, F. thapsinum from sorghum, and F. mangiferae from mango. These results are consistent with hypotheses that F. proliferatum has a wide host range while other species have much more limited host preferences. The absence from our samples of species associated with these diseases in other parts of the world suggests policies should be developed to reduce the chances of introduction of novel pathogens into Southeast Asia. Fusarium fujikuroi and F. proliferatum are closely related. They usually can be separated by sexual cross-fertility and DNA sequence analysis. However, some strains can cross irregularly and with poor fertility to produce viable interspecific hybrids. From a laboratory cross between F. fujikuroi FGSC8932 and F. proliferatum FGSC7615, 533 progeny were collected. These progeny were characterized for their AFLP genotype, mating type, gibberellic acid production, and pathogenicity on rice, onions, and apples. A recombination-based map from this interspecific cross was constructed. QTLs associated with gibberellic acid production, rice pathogenicity, and onion pathogenicity were identified. Gene segregation amongst the progeny of the F. fujikuroi × F. proliferatum cross was distorted towards F. proliferatum. Both novel and transgressive pathogenicity phenotypes were detected. Overall, this research demonstrates the potential threats that can result from an interspecific cross. These threats include pathogens with novel toxin profiles, new pathogenicity phenotypes, and more virulent strains. The variation observed among the progeny may enable isolation and characterization of genetic factors that have a role in pathogenicity, toxin production, and host specificity

Characterization of Fusarium proliferatum and Fusarium verticillioides based on species-specific gene and microsatellites analysis

Fusarium species are known to cause various diseases on plantations including fruits and vegetables. The most common Fusarium that can cause plant diseases are Fusarium proliferatum and Fusarium verticillioides. Ear rot disease on maize, wilt disease on cucurbits and fruit rot disease on tomato as well as banana are example of diseases caused by these two species. The objectives of this study were to identify F. proliferatum and F. verticillioides based on species-specific primers and polymerase chain reaction (PCR) amplification and to evaluate the genetic diversity of both species based on microsatellite markers. Fifty isolates of Fusarium species that were previously collected throughout Malaysia from different hosts were identified by using species-specific PCR amplification. Twenty-nine isolates were identified as F. proliferatum and 21 isolates were identified as F. verticillioides based on species-specific primer. The genetic diversity of all the fungal isolates was evaluated by using microsatellite analysis with six established primers. Five out of six primers amplified polymorphic bands with the most effective primer showing high polymorphism were (AG)7C and (TCC)5 meanwhile one primer (TTTC)4 gave negative result with no band amplified. The phylogenetic tree that was constructed showing two different clades distinguished between F. proliferatum and F. verticillioides

Mycotoxin production by Fusarium proliferatum and Fusarium fujikuroi causing stem rot of hylocereus polyrhizus in Malaysia

Fusarium proliferatum and Fusarium fujikuroi are the causative pathogens of stem rot in red-fleshed dragon fruit (Hylocereus polyrhizus). Both species are toxigenic fungi that produce several mycotoxins, including fumonisin B1 (FB1 ), moniliformin (MON), and beauvericin (BEA). These mycotoxins exert phytotoxic effects and are involved in pathogenesis in the host plants. In this study, we investigated the ability of F. proliferatum and F. fujikuroi to produce FB1 , MON, and BEA. Polymerase chain reaction amplification using FUM1-specific primers detected the gene in all 44 isolates tested, indicating that all isolates produced FB1 . Isolates of F. proliferatum and F. fujikuroi produced variable concentrations of FB1 , ranging from 11.97–236.80 µg/g. MON and BEA were also produced at 0.48–174.84 µg/g and 0.28–70.02 µg/g, respectively by isolates of F. proliferatum and F. fujikuroi. These results suggest that the three mycotoxins play roles in stem rot disease development and symptom manifestation, as all isolates tested were pathogenic and led to stem rot in H. polyrhizus

Characterization and mycotoxin analysis of Fusarium spp. from highland areas in Malaysia

Fusarium isolates from highland areas in Malaysia were mostly recovered from two species of grasses, Elyhordeum montanense and Paspalum conjugatum. The isolates were grouped into four morphological groups. Based on TEF-1α sequences, morphotype 1 isolates were molecularly identified as F. graminearum species complex, morphotype 2 as F. venenatum, morphotype 3 as F. avenaceum and morphotype 4 as F. kyushuense. Restriction analysis of the Intergenic Spacer region showed high levels of genetic diversity of isolates in F. graminearum species complex and F. venenatum. For mycotoxin analysis, only F. avenaceum and F. kyushuense produced beauvericin and moniliformin (0.869 & 0.321 µg/kg, respectively). Zearalenone was produced by 32 isolates of F. graminearum species complex (0.002 – 0.437 µg/kg), two isolates of F. venenatum (0.006 - 0.014 µg/kg) and F. kyushuense (0.006 µg/kg). Only F. avenaceum isolate produced fumonisin B1 (0.001 µg/kg). The present study indicates the occurrence of Fusarium species commonly reported in highland areas in Malaysia where the weather is cooler and the temperature is lower than in the lowland areas. To our knowledge, this is the first report on the occurrence of phylogenetic species within F. graminearum species complex, F. venenatum, F. avenaceum and F. kyushuense in Malaysia

Genetic diversity and pathogenicity of Fusarium species associated with fruit rot disease in banana across Peninsular Malaysia

The Malaysian giant prawn is among the most commonly cultured species of the genus Macrobrachium. Stocks of giant prawns from four rivers in Peninsular Malaysia have been used for aquaculture over the past 25 years, which has led to repeated harvesting, restocking, and transplantation between rivers. Consequently, a stock improvement program is now important to avoid the depletion of wild stocks and the loss of genetic diversity. However, the success of such an improvement program depends on our knowledge of the genetic variation of these base populations. The aim of the current study was to estimate genetic variation and differentiation of these riverine sources using novel expressed sequence tag-microsatellite (EST-SSR) markers, which not only are informative on genetic diversity but also provide information on immune and metabolic traits. Our findings indicated that the tested stocks have inbreeding depression due to a significant deficiency in heterozygotes, and FIS was estimated as 0.15538 to 0.31938. An F-statistics analysis suggested that the stocks are composed of one large panmictic population. Among the four locations, stocks from Johor, in the southern region of the peninsular, showed higher allelic and genetic diversity than the other stocks. To overcome inbreeding problems, the Johor population could be used as a base population in a stock improvement program by crossing to the other populations. The study demonstrated that EST-SSR markers can be incorporated in future marker assisted breeding to aid the proper management of the stocks by breeders and stakeholders in Malaysia

Histopathology of Corn Plants Infected by Endophytic Fungi

Endophytic fungi inhabiting plant tissues show extensive functional diversity, ranging from mutualism to pathogenicity. The present study evaluated the histological responses of corn plants to colonization by three species of endophytic fungi isolated from corn. Corn seedlings were inoculated with 1 × 106 conidia per mL spore suspensions of endophytic Fusarium verticillioides, Fusarium sacchari, and Penicillium citrinum and observed for 14 days for the emergence of disease symptoms. Histological examination of diseased root, stem, and leaf tissues was conducted using light and transmission electron microscopy. The results indicated that the mean diameters of root phloem, stem vascular bundles, and leaf vascular bundles, of corn plants infected with endophytic P. citrinum (18.91 µm, 146.96 µm, and 107.86 µm, respectively), F. verticillioides (18.75 µm, 85.45 µm, and 118.24 µm, respectively), and F. sacchari (24.15 µm root phloem, and 98.90 µm stem vascular bundle diameters), were significantly lower than the root phloem (33.68 µm), stem vascular bundle (186.77 µm), and leaf vascular bundle (155.88 µm) of the uninfected corn plants (p ≤ 0.05). Endophytic F. verticillioides was the most virulent, resulting in severe degradation and the eventual collapse of infected plant tissues. The study showed that endophytic fungi recovered from corn plants are capable of initiating significant disease responses in infected corn tissues

<i>Fusarium</i> Species in Mangrove Soil in Northern Peninsular Malaysia and the Soil Physico-Chemical Properties

Fusarium genus comprises important saprophytic and phytopathogenic fungi and is widespread in nature. The present study reports the occurrence of Fusarium spp. in soils from two mangrove forests in northern Peninsular Malaysia and analyzed physico-chemical properties of the mangrove soil. Based on TEF-1α sequences, nine Fusarium species were identified: Fusarium solani species complex (FSSC) (n = 77), Fusarium verticillioides (n = 20), Fusarium incarnatum (n = 10), Fusarium proliferatum (n = 7), Fusarium lateritium (n = 4), Fusarium oxysporum (n = 3), Fusarium rigidiuscula (n = 2), Fusarium chlamydosporum (n = 1), and Fusarium camptoceras (n = 1); FSSC isolates were the most prevalent. Phylogenetic analysis of the combined TEF-1α and ITS sequences revealed diverse phylogenetic affinities among the FSSC isolates and potentially new phylogenetic clades of FSSC. Soil analysis showed varied carbon content, pH, soil moisture, and salinity, but not nitrogen content, between sampling locations. Regardless of the physico-chemical properties, various Fusarium species were recovered from the mangrove soils. These were likely saprophytes; however, some were well-known plant pathogens and opportunistic human pathogens. Thus, mangrove soils might serve as inoculum sources for plant and human pathogenic Fusarium species. The present study demonstrates the occurrence of various Fusarium species in the extreme environment of mangrove soil, thereby contributing to the knowledge on species diversity in Fusarium

Molecular characterization and mating study of Fusarium proliferatum from various hosts in Malaysia

Fusarium proliferatum is a well-known plant pathogenic fungus-infected many crops. The present study was carried out to molecularly identified and characterized morphologically identified F. proliferatum from various hosts and substrates. The species identity of the isolates was verified as F. proliferatum based on TEF-1α sequences and phylogenetic analysis indicated high intraspecific variations. RFLP-IGS analysis also indicated high intraspecific variations of which the isolates were clustered into three RFLP Groups (I, II, and III) comprising 67 IGS haplotypes. Seventy isolates were crossed-fertile and proven to be members of mating population D (MP-D) of Gibberella fujikuroi while four isolates were infertile. A high level of intraspecific variations is vital for F. proliferatum adaptation and survival in the host and environment. Correct species identification of F. proliferatum is important as the fungus is a well-known plant pathogen and mycotoxin producer. Correct species identity is also essential to strategize suitable disease control methods as well as to predict their host range and mycotoxin production

Laboratory efficacy of mycoparasitic fungi (Aspergillus tubingensis and Trichoderma harzianum) against tropical bed bugs (Cimex hemipterus) (Hemiptera: Cimicidae)

Objective: To test the effectiveness of conidial spore formulations [Aspergillus tubingensis (A. tubingensis) and Trichoderma harzianum (T. harzianum)] against tropical bed bugs, Cimex hemipterus. Methods: Spore formulations were made from two fungal strains, T. harzianum and A. tubingensis. The bed bugs were exposed to the conidial spores placed soaked onto a fabric cloth for 1 h and the mortality counts were recorded daily until 14 days. Results: Mean survival times based on Kaplan–Meier survival analysis showed no significant differences between all the concentrations in both the fungal isolates: T. harzianum and A. tubingensis. However, the evaluation of both the isolates in terms of virulence resulted in low lethal hours in all the concentrations except for the high concentration of A. tubingensis (LT50 = 44.629 h) at the conidial exposure of 1 × 106 spores/mL. Rapid mortality of the bed bugs was observed from Day 6 to Day 12, ranging from 13% to 90% in all three concentrations of A. tubingensis. With reference to the T. harzianum exposure, the concentration of 1 × 104 spores/mL displayed a gradual increase in the percentage mortality of 90 on Day 14. Conclusions: Approaches to the bed bugs treatment should be explored in-depth using a natural biological agent like fungus especially A. tubingensis to reduce this pest population, in order to replace chemical methods