Four extra early-heading mutants, named extra early-fl owering1 ( exe1 ), exe2 , exe3 , and exe4 , were identifi ed in diploid einkorn wheat ( Triticum monococcum L.) following heavy-ion beam mutagenesis. Based on their phenotypes in the fi eld, the four exe mutants were classifi ed into two groups: Type I (moderately extra early-heading type; exe1 and exe3 ) and Type II (extremely extra early-heading type; exe2 and exe4 ). Analysis of VERNALIZATION 1 ( VRN1 ), a fl owering promoter gene,

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... that it was more highly expressed at earlier stages of vegetative growth in Type II mutants than in Type I mutants. Our analyses indicate that the difference in earliness between Type I and Type II mutants is associated with differences in the expression level of VRN1 .