Alien Chromosome Substitution—A Cause of Instability for Leaf Rust Resistance in Oats¹

Abstract

Monosomic alien chromosome substitution was discovered in F 11 to F 13 lines of the oat ( Avena sp.) cross, derived‐tetraploid C.I. 7232 (2n=28) ✕ Avena sativa L. cv. ‘Clarion’ (2n=42). Transmission of 21‐chromosome alien substitution gametophytes through the male and female at differential frequencies of 0.0 and 39.0%, respectively, was responsible for lack of homogeneity for resistance to leaf rust ( Puccinia coronata Cda. f. sp. avenae Fraser & Led.). Cytological examination of alien addition (21″ + 1′A), monosomic alien substitution (20″+1′+1′A), and monosomic susceptible plants revealed that the alien chromosome, which carries the gene(s) for resistance from the diploid progenitor, is submetacentric and the replaced A. sativa chromosome is metacentric.