Brown root rot, corky root rot

Brown root: Tomato rot Pyrenochaeta lycopersici

General

Pyrenochaeta lycopersici is a fungal plant pathogen, infecting tomatoes and aubergine. It causes brown root rot and corky root rot.

Life cycle and appearance of Brown root rot, corky root rot

Pyrenochaeta lycopersici survives in the soil and in buried tomato roots as microsclerotia. The microsclerotia germinate and produce mycelium that in turn infect the roots of tomato and other hosts. Several alternate hosts in outdoor cropping systems are known: pepper, melon, aubergine, squash, spinach and safflower. The disease develops between 8 and 32 °C, but the fungus prefers low temperatures. Therefore, optimal temperatures for disease development lie between 15 and 20 °C. Development reduces at temperatures above 20 °C. The fungus produces pycnidia containing conidiophores with conidia and microsclerotia.

Spread happens through dispersal of soil particles by farm equipment and cultivation practices. However, this fungus is a poor competitor against a balanced microbial population in soil.

Damage symptoms

The first signs of this disease, are poorly looking plants in localized areas of the greenhouse or field. The affected plants may wilt. Also, interveinal chlorosis of leaves and premature defoliation may occur. Looking at the roots, there are three different symptoms. Small feeder roots rot completely. Small roots may show smooth brown lesions. On older roots, the outer layers become swollen and corky and gradually break off. The corky areas often occur as horizontal bands on the roots with lengthwise cracks. No discoloration is present in the xylem tissues which distinguishes it from wilts caused by Verticillium or Fusarium. Progressive disease causes more and more destruction of the root system and subsequent loss of vigour and further wilting.