Fungal growth, proteinaceous toxins and virulence of Pyrenophora teres f. teres on barley

Pyrenophora teres f. teres ( Ptt ) causes net form net blotch (NFNB), an important disease of barley, but isolates of Ptt vary in their ability to cause symptoms on susceptible cultivars. Ptt isolates with different virulence were used to compare conidial germination and fungal growth on the barley cultivar ‘Sloop’. Whether proteinaceous toxins from culture filtrates of the six isolates or different fractions and sub-fractions of those filtrates induced different symptoms was also investigated. Greater conidial germination and appressorial formation was observed during infection by more virulent isolates but hyphal length was variable. Even though the six isolates varied in virulence from low to high, the proteinaceous toxins extracted from culture filtrates of all isolates were able to induce necrosis when injected into barley leaves. Ptt isolates therefore appear genetically able to produce proteinaceous toxins and the difference in virulence between isolates may reflect the growth of the fungus and the capacity for toxins to be delivered to the plant tissue. Proteins identified in the biologically active fractions included glycoside hydrolase, cysteine hydrolase, CFEM (common in fungal extracellular membrane) domain-containing protein, lactonase and peptidase. These have been previously suggested to have roles in plant cell wall degradation, fungal growth and/or host-pathogen interactions.