Effect of loose smut (Ustilago segetum f sp tritici) infection in the enhancement of susceptibility to stem rust (Puccinia graminis f sp tritici) of wheat (Triticum aestivum)

A total of 132 bread wheat (Triticum aestivum L. emend, Fiori & Paol.) line s showing loose-smut [Ustilago segetum (Bull.) Rousel f sp tritici] infecti on, were studied over 2 crop seasons during 1997-99 to compare the intensit y of stem rust (Puccinia graminis f sp tritci) infection between the smutte d and non-smutted tillers in each line. The smutted tillers showed higher l evels of stem-rust infection than their non-smutted counterparts in more th an 94% lines. One-third of the wheat lines studied (45/132) could be rated susceptible (average coefficient of infection > 10.0) to stem rust, when ru st reaction of only the smutted tillers was considered for the computation of average coefficient of infection. Stem-rust infection of the smutted til lers was not considered for determining the field response of a wheat line to stem rust, to avoid over-rating.