Authors:S. Imathiu, S. Edwards, R. Ray, and M. Back
Fusarium head blight (FHB) is a disease of small-grain cereals that has a proven negative impact on crop yield, quality and food safety. In this regard, it is one of the most studied diseases of small-grain cereals worldwide. This paper reports the commonly used artificial sources of inoculum and inoculation techniques employed in the study of FHB epidemiology. Spore suspensions and grain spawn are the most popular forms of artificial inoculums. Spray inoculation technique is more commonly used than the point inoculation technique for delivering the inocula to the target sites. Spray inoculation has an advantage over point inoculation in that it can be used to detect both Type I and II resistances to FHB, point inoculation can only detect Type II resistance to FHB. Grain spawn is the commonest soil-surface inoculum used in the study of FHB. Its advantage lies in the fact that it is capable of propagating inoculum over a long period of time compared to other methods. It can also detect the five types of resistances reported (Types I, II, III, IV and V). In order to gain further information regarding the epidemiology of FHB, researchers need to explore other potential sources of artificial inoculum.
Authors:S. M. Imathiu, R. V. Ray, M. Back, M. C. Hare, and S. G. Edwards
Fusarium langsethiae, a toxigenic fungus known to contaminate small-grain cereals with type A trichothecene mycotoxins, HT-2 and T-2 was described as a new species in 2004. HT-2 and T-2 are some of the most potent Fusarium toxins in eukaryotes, capable of inhibiting protein synthesis. The epidemiology of F. langsethiae is not well understood and with the intent of the European Commission to set maximum levels of contamination of cereals with these toxins, importance is currently placed in trying to understand the fungal infection process and its favorable growth conditions. A field study was carried out to investigate the effect of artificially inoculated oats straw, ploughing and minimum tillage with and without incorporated crop debris (straw) on infection and mycotoxin production by F. langsethiae on oats cultivar Gerald. The results indicated that cultural field practices had effects on the infection of oats by F. langsethiae. Fusarium langsethiae DNA was quantified in significantly larger amounts (p<0.05) in minimum tilled with incorporated straw plot samples than in other plot samples. It was also shown that inoculated straw had no significant effect (p>0.05) on oat infection by F. langsethiae as quantified by DNA concentration. HT-2+T-2 quantification and analysis, gave no good evidence that either inoculation or cultural practice had any significant influence on the concentration of mycotoxins in the samples (p>0.05), but samples from minimum tillage with incorporated straw plots resulted in 2.5 times more HT-2+T-2 toxins than samples from ploughed with removed straw. These findings indicate the importance of tillage and crop debris management in the mitigation in an effort to prevent F. langsethiae infection, colonization and possible contamination of oats with HT-2 and T-2 toxins.
Authors:S. M. Imathiu, R. V. Ray, M. Back, M. Hare, and S. G. Edwards
Fusarium langsethiae is a fungus that has recently been implicated in the contamination of small-grain cereal crops such as oats, wheat and barley with high levels of HT-2 and T-2 toxins in many European countries. The epidemiology of this fungus is not well known and may therefore be a bigger problem than currently thought to be. A study was carried out investigating the in vitro growth characteristics of F. langsethiae isolates from contaminated oats and wheat at various temperatures; 15, 20, 25 and 30 °C. Results indicated similar growth trends of oats and wheat isolates of F. langsethiae. Wheat isolates grew significantly (p<0.001) faster than oat isolates although this difference may have been confounded by the age of cultures, with oat isolates collected one year earlier. The estimated optimum growth temperature for all isolates was 24 °C. Isolates were macro-morphologically categorized as having lobed or entire colony margins, and either possessing one of the following colony colours: white, orange or purple. Since the estimated optimum growth temperature of F. langsethiae is typical in temperate summers when small-grain cereals are flowering, it is possible that this species can infect, colonise and possibly contaminate the developing grains with HT-2 and T-2 toxins which are of food safety concern.