# Virulence Spectra of Hungarian Pyrenophora teres f. teres Isolates Collected from Experimental Fields Show Continuous Variation without Specific Isolate × Barley Differential Interactions

## TL;DR

This study examines the virulence of Pyrenophora teres f. teres isolates in Hungary and finds continuous variation in their ability to infect barley, with no specific isolate-differential interactions.

## Contribution

The first report on pathogenic variation of Ptt in Hungary, identifying 28 pathotypes and suggesting improvements to the barley differential set.

## Key findings

- Twenty-eight Ptt pathotypes were identified from 34 isolates collected in Hungary.
- Isolates showed continuous virulence variation without specific isolate × barley differential interactions.
- Some barley differentials showed strong resistance to multiple isolates, useful for breeding NFNB-resistant barley.

## Abstract

Pyrenophora teres f. teres (Ptt), the causal agent of net form net blotch (NFNB) disease, is an important and widespread pathogen of barley. This study aimed to quantify and characterize the virulence of Ptt isolates collected from experimental fields of barley in Hungary. Infection responses across 20 barley differentials were obtained from seedling assays of 34 Ptt isolates collected from three Hungarian breeding stations between 2008 and 2018. Twenty-eight Ptt pathotypes were identified. Correspondence analysis followed by hierarchical clustering on the principal components and host-by-pathogen GGE biplots suggested a continuous range of virulence and an absence of specific isolate × barley differential interactions. The isolates were classified into four isolate groups (IG) using agglomerative hierarchical clustering. One IG could be distinguished from other IGs based on avirulence/virulence on one to five barley differentials. Several barley differentials expressed strong resistance against multiple Ptt isolates and may be useful in the development of NFNB-resistant barley cultivars in Hungary. Our results emphasize that the previously developed international barley differential set needs to be improved and adapted to the Hungarian Ptt population. This is the first report on the pathogenic variations of Ptt in Hungary.