PROPOSED SYSTEM OF NOMENCLATURE FOR BIOTYPES OF HESSIAN FLY (DIPTERA,CECIDOMYIIDAE) IN NORTH-AMERICA

Twenty genes in wheat, Triticum spp., for resistance to Hessian fly, M ayetiola destructor (Say), have been previously designated H1 to H20. The location on wheat chromosomes of some of the genes is known, but s everal have not yet been assigned to specific chromosomes. Four wheat differential cultivars have been used to identify 16 possible biotypes of Hessian fly; biotypes were designated GP and A-O. If an additional differential host genotype were added, it is apparent that there are not enough letters in the alphabet to designate all of the biotypes. T herefore, a new system of biotype designation is proposed. Three diffe rential cultivars or lines are assigned to a set. Sets are designated A, B, C, and so on. There are eight combinations of resistant and susc eptible reactions within a set. These are coded 1 to 8 for each set. T hree sets are proposed to begin biotype designation. A biotype avirule nt to all differentials in three sets is coded 111. If set C were not used, a zero (untested) replaces the digit. In the above case, the bio type is designated 110. The biotype designation system provides flexib ility for the addition of new sets as new genes are identified and for the deletion of sets no longer deemed useful.