Effect of fungal pathogens on digestibility and chemical composition of Italian ryegrass (Lolium multiflorum) and tall fescue (Festuca arundinacea)

Slight infection by Drechslera siccans or Rhynchosporium spp. significantly reduced in vitro dry matter digestibility, water-soluble carbohydrate and the total amino acid content of Italian ryegrass (Lolium multiflorum) foliage. The concentration of all 15 amino acids detected was reduced, with arginine reduced significantly more than the others. Total nitrogen was either increased or not changed, and the amino acid composition was not altered. Limited work with Drechslera festucae on tall fescue (Festuca arundinacea) gave similar results. Small samples of healthy and diseased grass leaves at three different physiological stages were used to detect these changes.
Limited leaf spotting by D. siccans caused metabolic changes of the same magnitude as extensive leaf blotching by Rhynchosporium. Impaired photosynthesis and growth of the fungi within the leaf tissues are possible causes of these changes. Decreased digestibility and increased dry matter content of diseased grass foliage could be of great practical importance.