This research sought to generate novel information on the epidemiology and life-cycle of Fusarium langsethiae to aid the development of control strategies to minimize T-2 and HT-2 mycotoxin content in cereals.
A field survey was performed to study the infection and development of F. langsethiae in the growing season of wheat, barley, oats and triticale under commercial production (2009 - 2011). Plants sampled (from tillering to harvest) were divided into roots, leaves, lower stem, upper stem and inflorescence/head sub-samples, depending on the growth stage of the cereal. DNA was extracted and F. langsethiae DNA quantified using real-time PCR. Fusarium mycotoxins HT-2 and T-2 were quantified in harvested samples. The data showed oat to contain the highest levels of both F. langsethiae biomass and HT-2+T-2 mycotoxins in harvested heads of the cereals studied. Head infection, if it occurred, was at head emergence but before flowering, a deviation from other Fusarium species. This information is very important for the design of a control strategy against F. langsethiae infection. Seemingly, symptomless heads had high levels of F. langsethiae DNA and HT-2+T-2, confirming previous suggestions that F. langsethiae is a symptomless pathogen of oats. Four field experiments where winter and spring varieties of wheat, barley and oats were cultivated under identical field and agronomic conditions at two sites again showed oats to have the highest F. langsethiae DNA and HT-2+T-2 concentration among the cereals studied. Interestingly, there was a significantly higher quantity of HT-2+T-2 per unit F. langsethiae DNA for oats compared to wheat and barley.
An in-vitro detached leaf assay, where length of lesions formed on wounded detached leaves were used as a measure of resistance, was used to screen UK varieties under testing for the HGCA Recommended List in 2010 of wheat, barley and oats for resistance against F. langsethiae infection. Results from the experiment showed that none of the cereal varieties screened had total resistance to F. langsethiae infection, however, in oats, varieties with low HT-2+T-2 in heads under field conditions also had shorter lesion lengths in-vitro, suggesting that the detached in-vitro leaf assay could be a good predictor of HT-2+T-2 concentration in harvested grain.
Data from four different artificial inoculation methods (seed assay, stem base infection, boot-inoculation and a spray inoculation) established that, although F. langsethiae is a seed borne pathogen, it was not systemically transmitted from the seed to the other plant parts. The stem base infection study showed that F. langsethiae did not cause any stem base infection even when in close contact with the stem. The spray inoculation resulted in cereal heads having F. langsethiae DNA concentrations and subsequent HT-2+T-2 levels comparable to what has been observed 5 under natural infections in commercial fields, suggesting that the infection route for F. langsethiae may not be that different from the other Fusarium head blight pathogens.
Based on all the experiments carried out in this thesis, a generalised life-cycle was hypothesised for F. langsethiae which deviates from that of the other Fusarium species on small grain cereals due to its early head infection and its inability to cause stem base infection.