Effect of Leaf Rust on Cereal Forage

Abstract

FEW investigators have examined the effect of leaf rust on yield, chemical composition and nutritive value of cereal forage. This situation is unexpected in view of the large acreage of cereals devoted to sheep and cattle grazing in many countries. However, the reviews of Allen¹ and of Chester² indicate that invasion of a susceptible host by an obligate parasite such as leaf rust is accompanied by physiological disturbances mediated by chemical change. Murphy³ found that leaf rust infection of oats, harvested at the boot stage, reduced the yield of forage, altered the chemical composition and delayed maturity except where water-stress occurred. Murphy's observations may apply only to cereal forage at the boot stage of maturity and not necessarily to the much earlier stage of maturity at which cereal forages are grazed in New Zealand and elsewhere. Yarwood⁴ observed increased invasion of rust-infected tissue by fungi, viruses and insects, and measured improved growth-rate of slugs and rats eating rust-infected bean leaves. However, digestion of monogastric animals differs from that of ruminants in several ways, so that Yarwood's observations have limited application to sheep.