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The interaction between the stem and bulb nematode, Ditylenchus dipsaci, and the causal agent of basal rot of garlic, Fusarium oxysporum f. sp. cepae (Foc), was studied in controlled environment tr...

Fusarium wilt is a damaging disease of oil palm in Ghana. Genetic diversity of Fusarium oxysporum f. sp. elaeidis (Foe) the causal organism of the disease was studied via AFLP technique using fluorescence-based automated system for Foe isolates from Ghana in comparison with other Foe isolates from different geographical locations. AFLP was conducted using thirteen MseI primers with three sets of EcoRI primers to generate individual phylogenetic trees. A concatenated phylogenetic tree was constructed from AFLP data using the three primer pairs. Individual phylogenetic trees for each of the primers could cluster Foe isolates from Ghana distinctively from Foe isolates collected in different geographical locations. Isolates from Ghana could not be clustered under one clade for all the individual phylogenetic trees, and this was further confirmed in the concatenated phylogenetic trees for the three-primer dataset that involved 4438 and 117 random markers of polymorphic bands. The use of AFLP has shown more genetic information about Foe isolates from Ghana compared with other collections from different geographical areas. AFLP markers showed all Foe isolates from Ghana are not monophyletic.

The pathogenicity of four Fusarium oxysporum isolates collected from symptomatic oil palm (Elaeis guineensis Jacq.) from Ghana were tested for the first time to develop a new pathogenicity assay for Fusarium oxysporum f. sp. elaeidis (FOE) infection in oil palm seedlings. All four FOE isolates used for pathogenicity assay were pathogenic to oil palm seedlings within a relatively short time compared to other pathogenicity studies, for which infection/symptoms in oil palm seedlings was time consuming. FOE and “presumed-FOE” (i.e. Fusarium isolates collected from symptomatic oil palm trees whose pathogenicity is not confirmed) were characterised based on partial sequences of a housekeeping gene EF-1α and three Secreted In Xylem genes (SIX8, SIX9 and SIX11). All the phylogenetic trees generated for EF-1α, SIX8, SIX9 and SIX11 showed some variation between FOE, and “presumed-FOE”, but could not cluster isolates based on geographical location. Phylogenetic trees for EF-1α and SIX (SIX9 and SIX11) genes clustered both FOE and “presumed-FOE” from FUSARIUM-ID from GenBank, but SIX8 could not.

Myrtle rust, caused by the pathogen Austropuccinia psidii, affects species of the Myrtaceae, many of which are endemic to Australia and New Zealand. Originating from South America, A. psidii is now present in both countries, necessitating effective chemical control for disease management. Using an artificial inoculation protocol, the efficacy of eight fungicides (tebuconazole/trifloxystrobin, cyproconazole/azoxystrobin, fosetyl aluminum, triforine, triadimenol, oxycarboxin, copper, and tebuconazole) applied as curative or protectant treatments was tested on two native New Zealand species (Lophomyrtus × ralphii and Metrosideros excelsa). The impacts of rate (×2), frequency (single or double), and timing (pre- or postinfection) of fungicide application were investigated. Overall, the most effective fungicides tested across both species were those that included a demethylation inhibitor and strobilurin mix, notably tebuconazole/trifloxystrobin (Scorpio) and cyproconazole/azoxystrobin (Amistar Xtra). These fungicides significantly reduced infection of host plants relative to the water control. Timing of application significantly affected bioefficacy, with applications made 7 days before inoculation or 7 days after inoculation being generally the most effective. The rate of fungicide application was not significant for both host species, with few interaction terms showing overall significance. Key findings from this study will set the foundation for further fungicide bioefficacy research conducted to evaluate formulations and adjuvant mixtures, determine suitable application methods for enhanced retention and coverage, and derive optimum application time for effective protection of native and exotic Myrtaceae species in New Zealand.

Fusarium wilt, caused by Fusarium oxysporum f. sp. spinaciae, is a significant constraint to the summer production of bunching spinach in Ontario, Canada. Trials were conducted to assess soil amendments (limestone) and fumigants (metam sodium, chloropicrin and dazomet) for the suppression of Fusarium oxysporum f. sp. spinaciae. Dolomitic limestone applied at a rate of 10 and 20 t ha−1 reduced the incidence of fusarium wilt by 10 and 47%, respectively, even though there was little change in soil pH (7.4–7.5) or soil calcium concentration (1598 vs 1483 in 20 t lime vs control, respectively. Fusarium wilt severity was lower in the 2013 than in the 2014 growing season. In 2014, the fumigants metam sodium, chloropicrin and dazomet reduced the population of Fusarium spp. propagules in the soil by 84, 93 and 100%, respectively. Chloropicrin provided the best control of the spinach fusarium wilt pathogen compared to the other fumigants but was only assessed one year. Chloropicrin was the only treatment to truly reduced spinach Fusarium wilt by preventing vascular discolouration. Brassica juncea and calcium cyanamide were not effective at suppressing the disease. A high rate of nitrogen, consisting of polymer coated sulphur coated urea, was applied to provide the same rate of nitrogen as the Brassica juncea and calcium cyanamide treatments. Applying nitrogen in this formulation was as effective as metam sodium in reducing the incidence and severity of Fusarium wilt and should be evaluated further to determine the economics and environmental impact of this approach.