Net blotch is the most serious disease pestering barley, the primary Finnish crop measured by cultivated area. Caused by the Pyrenophora teres Drech fungus, the disease decreases crop yield and malting quality. Ways to control the disease include clean seeds, crop rotation, alternating the chemical control agents used, and removing plant residue from fields.

Research Scientist Marjo Serenius from MTT Agrifood Research Finland, who will shortly defend her Doctoral Dissertation on barley net blotch, says that the risk of net blotch may be increased by specialisation to a certain line of production and by the replacement of tillage methods with faster direct drilling methods.

- Factors such as the increased amount of plant residue in the field promote the survival of plant diseases, such as net blotch, from one year to the next, Serenius says.

Pathogens highly variable

The study showed that the pathogen strains were highly variable. The causal agent populations of various fields and locations differed from each other.

- The exclusive use of a single pesticide and the cultivation of resistant varieties may modify the pathogen population to better resist these control methods, says Serenius.

The study focussed on Finnish populations of P. teres, and the strains were collected from all over Finland between 1989 and 2003. The actual field populations were collected from south-western Häme and from Ylistaro. Two Russian field populations and a collection of Australian strains were also included in the study.

Need for versatile plant protection

The pathogen strains collected from Finland and Russia were all of the net type of barley net blotch. Both symptom types, net and blotch, were equally common in Finland as recently as in the 70s. The cause for this change is unknown.

An equal amount of both mating types of the pathogen were found in Finland, although previous studies have doubted the significance and prevalence of sexual reproduction.

Findings of the study about the one symptom becoming more common in Finland, sexual reproduction and the diversification of the populations on several levels emphasize the need for versatile plant production.

- Serenius reminds that the pathogen population is selected more easily if the used protection method is based on a single control mechanism, such as a single-agent pesticide, or disease resistance that is based on a single major gene.

Marjo Serenius was born in Nummela, Vihti. She has worked at MTT since 1998. For the last two years Serenius has been doing research in the United States at the Department of Plant Pathodology of Iowa State University. She is returning to Finland by this summer.

Serenius' Doctoral Dissertation shall be examined at the Faculty of Agriculture and Forestry of the University of Helsinki at building A, auditorium B2, Latokartanonkaari 7, on Friday 2 June at 12 noon. Associate Professor Tobin Peever, Washington State University, USA, shall act as opponent and Professor Jari Valkonen from the University of Helsinki as custodian. The Dissertation falls under the field of plant pathodology, and it shall be published in the Agricultural and Food Science series.