Resistance to Hessian fly conditioned by genes H19 and proposed gene H27 of durum wheat line PI422297

The durum wheat (Triticum turgidum Desf.) line PI422297 has been reported to carry two genes that condition resistance to Hessian fly, Mayetiola destructor (Say) biotype L, gene H19 and an unnamed gene that is closely associated with gene H16. It is useful to identify the effects of genes that confer host resistance in parental source lines for wheat improvement. Our objectives were to determine the effectiveness of H19 to biotype L at several temperatures, and to determine the effectiveness of the second gene of PI422297 that is closely associated with gene H16. In the present study, gene H19 was transferred from PI422297 to susceptible durum wheat line D6647 to separate H19 from other genes and to compare it with the other resistance gene in PI422297. Durum wheat lines homozygous for H19 were developed by identifying segregating backcross F2 families and pedigree selection. In the F5 generation, lines homozygous for H19 were identified from testcrosses involving durum wheat line IN80164 (H16H16). Nearly all seedlings of the homozygous H19 lines were resistant at 19 degrees C, only 42 to 66% were resistant at 23 degrees C, and none were resistant at 26 degrees C. All, 89%, and 15% of PI422297 seedlings were resistant at 19, 23, and 26 degrees C, respectively. All seedlings of line IN80164 (H16H16) were resistant at 19 and 23 degrees C and 84% were resistant at 26 degrees C. Thus, the second gene in PI422297 is not H16, and it is tentatively designated as H27