Contribution à l'étude de l'activité toxique de l'Helminthosporium teres, parasite de l'orge (Hordeum vulgare)

Abstract

Different isolates of Helminthosporium teres produce in vitro phytotoxic compounds which diffuse in the culture medium. These compounds bring about the wilting of barley and tomato plants with roots removed. A semiquantitative estimation of toxin production, which was based on the inhibition of the growth of tomato seedlings, allowed the isolates to be classified according to their level of toxigenicity.The toxins, of variable thermostability according to strains, are not proteins and are not specific. The action of toxin filtrates on the leaf blade of a susceptible barley cultivar brings about the appearance of necrosis on the whole thickness of the leaf blade. There is a positive correlation between toxin production level of the isolates and necrogenic power of their filtrates.During the leaf-colonization stage, the primary action of the parasite on the surrounding cells seems to affect the plasmalemma which retracts from the cell wall and shows evaginations. In such cells, starch builds up and the size of the plastoglobuli is markedly increased in the chloroplasts. The limiting membrane of these chloroplasts is not affected.