CAUSE OF TALL OFF-TYPES IN A SEMIDWARF SPRING WHEAT

Tall off-types that occur in semidwarf wheat, Triticum aestivum L., cultivars may reduce grower acceptance and present problems in seed certification programs. Tall off-types occur in 'Hi-Line' spring wheat at a frequency of 0.20%. Segregation analysis for height indicates Hi-Line contained the Rh(1)Rht(1)rht(2)rht(2) genotype. Cytological analysis of selfed progeny of the tall off-types showed a high proportion of monosomic chromosome numbers, indicating that aneuploidy may be associated with the tall off-types. Further investigation involved the use of PCR (polymerase chain reaction) with primers designed from clones detecting restriction fragment length polymorphism (RFLP) at loci on homoeologous Group 4, which contained height reducing loci Rht(1) and Rht(2). Three sets of primers were used to screen progeny of tall off-types from Hi-Line. The results of this screening indicate 20% of the offspring were nullisomic for chromosome 4B. Analysis of progeny using morphological and PCR based screening indicate that offspring of tall off-types were 72% monosomic 4B: 8% disomic: 20% nullisomic 4B. Thus, cytological and molecular analysis reveal that Hi Line tall off types result from a monosomic 4B condition, which causes hemizygosity for Rht(1). Due to the random occurrence of monosomic 4B progeny from disomic semidwarf wheat, our results suggest that tall off types may be an inherent and unavoidable feature of semidwarf wheats with the genotype Rht(1)Rht(1)rht(2)rht(2).