Effect of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 to soybean

Screenhouse studies were conducted to investigate the effects of Fusarium oxysporum f. sp. glycines and Sclerotium rolfsii on the pathogenicity of Meloidogyne incognita race 2 on soybean and the influence of the nematode on wilt incidence and growth of soybean. The interaction of each fungus with the nematode resulted in reduced shoot and root growth. Final nematode population was also reduced with concomitant inoculation of nematode and fungus or inoculation of fungus before nematode. While M. incognita suppressed wilt incidence in two nematode-susceptible cultivars of soybean (TGX 1485-2D and TGX 1440-IE), it had limited effect on wilt incidence in the nematode resistant cultivar of soybean (TGX 1448-2E). When F. oxysporum was inoculated with the nematode, the mean number of nematodes that penetrated soybean roots decreased by 75% in TGX 1448-2E, 68% in TGX 1485-1D and 65% in TGX 1440-1E. Similarly when the soil was treated with S. rolfsii, the number decreased by 78% in TGX 1448-2E, 77% in TGX 1485-1D and 68% in TGX 1440-1E. The nematode did not develop beyond second-stage juvenile in TGX-1448-2E.

Bioactivity of Fusarium oxysporum f. sp glycines and Sclerotium rolfsii filtrates on egg hatching, survival and infectivity of juveniles of Meloidogyne incognita race 2

The effects of culture filtrates of Fusarium oxysporum and Sclerotium rolfsii on egg hatching and juvenile survival of Meloidogyne incognita in vitro and impact of these filtrates on infectivity of M. incognita were investigated on soybean seedlings. Five- and 10-day-old filtrates of F. oxysporum caused 65 and 54% egg-hatching inhibition, while that of S. rolfsii caused 61 and 49% inhibition, respectively. Juveniles of M. incognita died within 6 days when incubated in 5-day-old filtrate of F. oxysporum, while the similar filtrate of S. rolfsii caused 100% juvenile mortality on the fifth day. Filtrates reduced root galling, egg population, number of adult females in soybean plants at harvest and also soil population. Culture filtrates could be used as source of biological nematicides.

Characterisation of Australian isolates of Fusarium oxysporum f. sp cubense by DNA fingerprinting analysis

Genetic variation among Australian isolates of the fungus Fusarium oxysporum f. sp. cubense (Foc), which causes Fusarium wilt in banana, was examined using DNA amplification fingerprinting (DAF). Ninety-four isolates which represented Races 1, 2, 3, and 4, and vegetative compatibility groups (VCGs) 0120, 0124, 0125, 0128, 0129, 01211, 01213/16, and 01220 were analysed. The genetic relatedness among isolates within each VCG, and between the 8 different VCGs of Foc present in Australia was determined. The DNA fingerprint patterns were VCG-specific, with each VCG representing a unique genotype. The genetic similarity among isolates within each VCG ranged from 97% to 100%. Among the different VCGs of Foc, 3 major clusters were distinguished which corresponded with race. All Race 1 and 2 isolates (VCGs 0124, 0125, 0128, and 01220) were closely related and clustered together, the Race 3 isolates from Heliconia clustered separately, and all Race 4 isolates (VCGs 0120, 0129, 01211, and 01213/16) clustered together. Fifteen isolates from Alstonville, NSW, were characterised because although they were classified as Race 2 based on their recovery from cooking banana cultivars, they belonged in VCG 0124, which had previously contained only Race 1 isolates. The occurrence of more than one race within a VCG means that vegetative compatibility grouping cannot be used to assign pathotype to pathogenic race as previously thought. It was possible to distinguish the Race 1 and Race 2 isolates within VCG 0124 using DNA fingerprinting, as each race produced a unique DNA fingerprint pattern. Among the Australian isolates, DNA fingerprinting analysis identified 9 different VCGs and genotypes of Foc.

A foliar rating system for comparing the resistance of banana cultivars grown as tissue-cultured plantlets in the laboratory to Fusarium wilt

A foliar rating system was developed to assess the progress of Fusarium wilt ( Panama disease) caused by Fusarium oxysporum f. sp. cubense in seven banana cultivars differing in their resistance to race 1 of the pathogen. Plantlets were transplanted into unamended soil naturally infested with the pathogen, soil amended with urea and soil amended with aged chicken manure. A corm invasion score was also developed to assess the accuracy of the foliar symptom score as an indicator of cultivar resistance. On the basis of foliar symptom scores alone, the response of five of the seven cultivars in the chicken manure treatment corresponded to their known field response. However, the response of the other two cultivars, both susceptible to the pathogen in the field, fell into two categories. One had a high foliar symptom score and a correspondingly high corm invasion score, whereas the other had a low foliar symptom score and a high corm invasion score. Breeders need to be aware of the two categories of susceptible response, if inferior breeding material is to be rejected early on in a breeding program.

Effect of organic amendments and solarisation on Fusarium wilt in susceptible banana plantlets, transplanted into naturally infested soil

Despite extensive research since pathogenicity was first established in 1919, no cultural or chemical control strategy has proven effective against Fusarium wilt of bananas. The efficacy of cultural control is attributed to the suppression of pathogen activity. Yet, amending naturally infested soil with aged chicken manure has been shown to enhance disease severity, without any change in the activity of the pathogen Fusarium oxysporum f. sp. cubense (Foc) in the soil. In this study, the effect of amending soil with composted sawdust, and of solarising soil, was compared with the effect of amending soil with chicken manure. Bioassays comparing the activity of Foc in the soil with the extent of invasion of banana pseudostem tissue by Foc were used to investigate why strategies targetting pathogen survival have not proven successful in controlling this disease. The enhancement of Foc invasion of the banana plantlets was reproduced with the addition of chicken manure to the naturally infested soil. However, changes in the activity of Foc in the soil were not associated with changes in the frequency of invasion of the plantlets. Invasion of banana pseudostems in the sawdust and solarisation treatments was not significantly different from invasion in the respective control treatments, despite a reduction in the activity of Foc in the sawdust-amended soil and an enhancement in the solarised soil. Moreover, the increase in Foc activity in the solarised soil recorded during the bioassays occurred despite the effectiveness of solarisation in reducing the survival of Foc in pre-colonised banana root tips buried in the soil. Changes in the frequency of invasion were associated with changes in the availability of mineral nitrogen, particularly ammonium N. These results suggest that the physiological response of banana cultivars to ammonium N may be associated with their susceptibility to Fusarium wilt. Accordingly, cultural strategies for controlling Panama disease will only be effective if they enhance the ability of the host to resist invasion.

Fine mapping of the tomato I-3 gene for fusarium wilt resistance and elimination of a co-segregating resistance gene analogue as a candidate for I-3

The I-3 gene from the wild tomato species Lycopersicon pennellii confers resistance to race 3 of the devastating vascular wilt pathogen Fusarium oxysporum f. sp. lycopersici. As an initial step in a positional cloning strategy for the isolation of I-3, we converted restriction fragment length polymorphism and conserved orthologue set markers, known genes and a resistance gene analogue (RGA) mapping to the I-3 region into PCR-based sequence characterised amplified region (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers. Additional PCR-based markers in the I-3 region were generated using the randomly amplified DNA fingerprinting (RAF) technique. SCAR, CAPS and RAF markers were used for high-resolution mapping around the I-3 locus. The I-3 gene was localised to a 0.3-cM region containing a RAF marker, eO6, and an RGA, RGA332. RGA332 was cloned and found to correspond to a putative pseudogene with at least two loss-of-function mutations. The predicted pseudogene belongs to the Toll interleukin-1 receptor-nucleotide-binding site-leucine-rich-repeat sub-class of plant disease resistance genes. Despite the presence of two RGA332 homologues in L. esculentum, DNA gel blot and PCR analysis suggests that no other homologues are present in lines carrying I-3 that could be alternative candidates for the gene.

Identification and characterization of non-pathogenic Fusarium oxysporum capable of increasing and decreasing Fusarium wilt severity

Fusarium wilt of banana is a potentially devastating disease throughout the world. Options for control of the causal organism, Fusarium oxysporum f.sp. cubense (Foc) are limited. Suppressive soil sites have previously been identified where, despite the presence of Foc, Fusarium wilt does not develop. In order to understand some aspects of this disease suppression, endophytic Fusarium oxysporum isolates were obtained from banana roots. These isolates were genetically characterized and compared with an isolate of Fusarium oxysporum previously identified as being capable of suppressing Fusarium wilt of banana in glasshouse trials. Three additional isolates were selected for glasshouse trials to assess suppression of Fusarium wilt in two different cultivars of banana, Cavendish and Lady Finger. One isolate (BRIP 29089) was identified as a potential biocontrol organism, reducing the disease severity of Fusarium wilt in Lady Finger and Cavendish cultivars. Interestingly, one isolate (BRIP 45952) increased Fusarium wilt disease severity on Cavendish. The implications of an isolate of Fusarium oxysporum, non-pathogenic on banana, increasing disease severity and the potential role of non-pathogenic isolates of Fusarium oxysporum in disease complexes are discussed. (c) 2006 Published by Elsevier Ltd on behalf of The British Mycological Society.

Mapping the I-3 gene for resistance to Fusarium wilt in tomato: application of an I-3 marker in tomato improvement and progress towards the cloning of I-3

Fusarium wilt of tomato, caused by the fungal pathogen, Fusarium oxysporum f. sp. lycopersici (Fol), is an economically damaging disease that results in huge losses in Australia and other countries worldwide. The I-3 gene, which confers resistance to Fol race 3, has been described in wild tomato, Lycopersicon pennellii, accessions LA716 and PI414773. We are pursuing the isolation of I-3 from LA716 by map-based cloning. We have constructed a high-resolution map of the I-3 region and have identified markers closely flanking I-3 as well as markers co-segregating with I-3. In addition, construction of a physical map based on these markers has been initiated. This review describes the context of our research and our progress towards isolating the I-3 gene. It also describes some important practical outcomes of our work, including the development and use of a PCR-based marker for marker-assisted selection for I-3, and the finding that the I-3 gene from LA716 is different to that from PI1414773, which we have now designated I-7. Tomato varieties combining I-3 and I-7 have been developed and are currently being introduced into commercial production to further safeguard tomato crops against Fusarium wilt.

Cyclic peroxides and related norterpenes from a southern Australian marine sponge, Mycale sp.

Investigation of a southern Australian marine sponge, Mycale sp., resulted in isolation of the known norsesterterpenes 1-3 as well as two new isomeric norsesterterpenes, mycaperoxide C methyl ester (4) and mycaperoxide D methyl ester (5), and six new norterpenes (6-11).

Sigmosceptrins A-C: New norditerpenes from a southern Australian marine sponge, Sigmosceptrella sp.

A Sigmosceptrella sp. of sponge collected during trawling operations in the Great Australian Eight, Australia, has yielded a series of new norterpenes. These include a new bisnorditerpene, sigmosceptrin-A (5); two new norditerpenes, sigmosceptrin-B (14) and sigmosceptrin-C (15), isolated as their methyl esters (6) and (7) respectively; and an ethylated artefact, sigmosceptrin-B ethyl ester (8). Complete stereostructures were assigned to the sigmosceptrins by spectroscopic analysis, chemical degradation, derivatization, and by a single-crystal X-ray structural analysis. A biosynthetic pathway is proposed that requires a common biosynthetic precursor to both the sigmosceptrins and norterpene cyclic peroxides.

Pholeohedra overstreeti n.g., n.sp. (Digenea : Haploporidae) from Girella zebra (Kyphosidae) in south Australia

Pholeohedra overstreeti n. g., n. sp. (Digenea: Haploporidae) is described from Girella zebra (Kyphosidae) in South Australia. The new genus is compared with all genera of Haploporidae sensu late (including Atractotrematidae, Megasolenidae and Waretrematidae) and has a unique bell-shaped concavity at its posterior end. The genus otherwise resembles Hapladena in the arrangement of the testis, vitellarium and gut but also resembles Megasolena, Metamegasolena and Vitellibaculum except in having a single testis. This is the first haploporid reported from kyphosid fishes in Australia.

cis-3-hydroxy-N-methyl-L-proline: a new amino acid from a southern Australian marine sponge, Dendrilla sp.

A specimen of the sponge Dendrilla sp. collected during commercial trawling operations in the Great Australian Eight, Australia, analyses for a very high natural abundance of the new amino acid cis-3-hydroxy-N-methyl-L-proline (1). The complete stereostructure for (1) was determined by spectroscopic analysis and chemical derivatization.