CAUSE OF TALL OFF-TYPES IN A SEMIDWARF SPRING WHEAT

Tall off-types that occur in semidwarf wheat, Triticum aestivum L., cu ltivars may reduce grower acceptance and present problems in seed cert ification programs. Tall off-types occur in 'Hi-Line' spring wheat at a frequency of 0.20%. Segregation analysis for height indicates Hi-Lin e 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 m onosomic chromosome numbers, indicating that aneuploidy may be associa ted with the tall off-types. Further investigation involved the use of PCR (polymerase chain reaction) with primers designed from clones det ecting restriction fragment length polymorphism (RFLP) at loci on homo eologous Group 4, which contained height reducing loci Rht(1) and Rht( 2). Three sets of primers were used to screen progeny of tall off-type s from Hi-Line. The results of this screening indicate 20% of the offs pring were nullisomic for chromosome 4B. Analysis of progeny using mor phological and PCR based screening indicate that offspring of tall off -types were 72% monosomic 4B: 8% disomic: 20% nullisomic 4B. Thus, cyt ological and molecular analysis reveal that Hi Line tall off types res ult from a monosomic 4B condition, which causes hemizygosity for Rht(1 ). Due to the random occurrence of monosomic 4B progeny from disomic s emidwarf wheat, our results suggest that tall off types may be an inhe rent and unavoidable feature of semidwarf wheats with the genotype Rht (1)Rht(1)rht(2)rht(2).