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 Rht1Rht1rhl2rht2 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, and Rht2. 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 46:8% 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 Rht1. 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 Rht1,Rht1,rht2rht2.
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