Different symptoms in maize root caused by pyrenochaeta terrestris and the fungal colony properties

Abstract

Rot symptoms that Pyrenochaeta terrestris causes on the root of each internode of maize hybrids belonging to different maturity groups, as well as the impact of growing conditions (substrate, temperature and light) on the properties of the colony and the pycnidial formation of this fungus were studied. The large number of symptoms was obtained by various combinations of tissue colour changes (red, brown, yellow, blue and lighter or shades of these colours), changes in a particular part of the root (root top, part of the epidermis, the entire epidermis, tissue under the epidermis or the whole root) and the form of spots and streaks (shape and size). Pinkish red symptoms prevailed on younger roots, particularly from the 5th to the 7th internode. When P. terrestris was grown on potato dextrose agar (PDA) in the dark at 25 degrees C, the variability of the fungus was expressed in relation to the colour of the aerial (white, pink, grey, yellow and brown) and the substrate mycelium (purple, pink, grey, green and yellowish) and to the pycnidial formation (present or absent). The interrelationship between types of symptoms and properties of P. terrestris colonies was not determined on PDA. The fungus always produced the red purple pigment and mostly pycnidia on carnation leaf agar (CLA) at 25 degrees C and under the alternating 12 h combined light (fluorescent and near ultra violet (NUV) light)/dark conditions. These conditions are suitable for the reliable identification of the fungus.