Parastagonospora nodorum (Phaeosphaeria nodorum) is a fungal pathogen of wheat, barley and ryethat induces yield and quality losses.
Life cycle and appearance of Glume blotch
Phaeosphaeria nodorum or Septoria nodorum survives as perithecia containing ascospores and pycnidia containing conidia on crop residues and winter wheat seedlings. Ascospores germinate at any temperature above freezing when water is available. Conidia require a minimum of 5 °C for germination. Primary infection is mostly by ascospores or conidia on the oldest leaves, but seed transmission is also possible. The germ tubes can infect the leaves of the plants directly or through stomata. The lesions become visible after five to seven days. On the lesions, new pycnidia are formed. The conidia that are produced in these pycnidia emerge in a pink slimy substance. The conidia are released at high relative humidity (RH). The optimum temperature for germination of the conidia is between 20 and 25 °C.
The ascospores are responsible for wind dispersal of the fungus over longer distances, but inside an infected crop the conidia cause secondary infection by splash dispersal. Splashing rain water helps the fungus to reach the upper leaves and ears. Seed infection is enhanced by wet weather conditions during heading.
Phaeosphaeria nodorum or Septoria nodorum causes glume blotch, which presents itself as brown, elongated lesions with a light halo on leaves, stems and glumes. In the centre of the lesions, light-coloured translucent pycnidia (fruiting bodies) with new spores occur. The lesions may merge, turning the whole leaf necrotic.
On glumes, similar brown lesions with pycnidia and perithecia occur. Perithecia are also formed on dead glumes and stems. In case of severe infection , the heads of wheat become black and the kernels become shrivelled and deformed. When germinating seedlings are infected, they shrivel.