ASSOCIATION OF RUMEN FUNGI WITH VARIOUS FORAGE GRASSES

Anaerobic fungi in the rumen can significantly influence the degradation of forage fibre, but little is known about the propensity of the fungi to colonize various grass species. The objective of this study was to evaluate factors which may stimulate in vitro the fungal colonization of forage grasses, including the influence of grass species. Growth of fungi on forage tissues was studied with light, scanning electron and transmission electron microscopy. The inclusion of penicillin (1.25 mg per ml broth, 1600 units per mg) and streptomycin (0.2 mg per ml broth, 650 units per mg) inhibited bacterial growth and usually substantially increased (by about six times) the numbers of sporangia on bermudagrass (Cynodon dactylon L. Pers.) leaf blades. At times, hyphae overgrew plant fragments. Cycloheximide (0.5 mg per ml broth) inhibited the growth of rumen fungi. Rumen fungi colonized rigid fibre particles and showed an ability to attack certain lignified (chlorine-sulphite positive) cell walls in grasses and in sisal (Agave spp.). Sporangial numbers were higher on bermudagrass than on pangolagrass (Digitaria decumbens Stent.), orchardgrass (Dactylis glomerata L.) or Kentucky-31 tall fescue (Festuca arundinacea Schreb.). Elemental sulphur, but not organic sulphur or sodium sulphate, added as a supplement to incubations in vitro (0.1% w/v) tended to increase sporangial numbers on leaves (averaging three times more than in the controls) when the steer providing rumen liquor was on mixed pasture of clover and grass, but did not stimulate sporangia when the steer ate bermudagrass hay. Substantial variation occurred frequently in the number of sporangia developing on leaf blades, and this variation was noticeable even on blades incubated within a single vessel. Anaerobic fungi vary in their colonization of leaf blades of various grasses, but the specific factors responsible for their ability to develop on various substrates require further study.