Systemic stem infection by Fusarium species in barley and wheat

Fusarium head blight, caused by Fusarium species, is an important disease of cereals in western Canada. There are conflicting results in the literature regarding the infection pathway leading to disease development. The present study was undertaken to evaluate the potential for systemic infection in barley (Hordeum vulgare) by artificially inoculating F. graminearum and F. pseudograminearum into the growth medium in pots containing seeds or seedlings of 'AC Lacombe' and 'Chevron' barley. Furthermore, naturally infected barley and wheat (Triticum aestivum) kernels were grown to assess the potential for systemic infection by F. graminearum from seed into the stem. Approximately 50% of naturally infected seeds either failed to emerge, or the seedlings died shortly after emergence. Crown and stem discolouration developed oil the inoculated barley and naturally infected wheat seed. Mycelial growth and sporulation were observed in the crown area using light and electron microscopy. Fusarium graminearum and F. pseudograminearum were identified through isolation. Systemic infection was confirmed by isolation from up to 31% of the wheat culm segments and was past the third node, which exceeded the extent of discolouration of the third internode assessed by Visual examination. Fungal hyphae were mostly located in the parenchyma tissue of the culm, with few observed in the vascular tissue. No head blight symptoms resulting from seed infection were observed. In conclusion, no evidence was found for systemic infection from seed or belowground plant tissues that resulted in head blight of barley or wheat using the current inoculation methods and under the current experimental conditions. In the growth chamber, seed and seedling infection by F. graminearum and F. pseudograminearum and subsequent systemic infection can lead to infection of the lower stem. It is still unclear if similar results occur under field conditions.