The effect of leaf rust on the growth and chemical composition of oats and ryecorn

Abstract

Leaf-rust infection of severity 3–4 on the modified Cobb scale reduced the dry-matter yield of Dun oat leafage by 30% and N.I.A.B. ryecorn by 23%. The reduction in root growth of ryecorn was similar to that of the aerial parts.The dry-matter percentage of the green forage was significantly increased in two of the three experiments. Palatability reduction due to leaf rust is suggested from field observations.With Dun oats leaf-rust infection increased the percentage of crude protein (C.P.) by a fifth, of ash by a tenth and decreased that of crude fibre (C.F.) by an eighth, and of nitrogen-free extract (N.F.E.) by a nineteenth. With ryecorn, rust increased the percentage of c.p. by a fourteenth, of ash by a fifth, and decreased that of N.F.E. by a twentieth.The decreased forage yield caused by rust is in accord with the results of experiments of other research workers and with field observation. The effect of rust on proximate constituents was interpreted as an improvement to feed value. This agrees with the results of most reported experiments but conflicts with the field evidence.The hypothesis that leaf rust affects forage composition mainly by reducing the physiological age of cereals is proposed.