MODIFIED RECURRENT SELECTION FOR BARLEY YELLOW DWARF VIRUS TOLERANCE IN WINTER-WHEAT

Barley yellow dwarf virus (BYDV) causes an economically important dise ase of small grains. We evaluated tolerance to BYDV in a winter wheat population resulting from modified recurrent selection. Chemical hybri dizing agents (CHAs) were used to facilitate recombination, and select ion was based on tolerant genotypes producing more seeds under disease pressure. Seventeen parents, selected for BYDV tolerance, were mated in a partial diallel, with equal amounts of seed from F1 plants consti tuting the original population. Bulked seed from F1 plants was planted in rows in the field. Female rows were sprayed with a CHA (either RH- 007 or MON 21200) and inoculated with BYDV-PAV-IL. Seed was harvested from female rows. Our objectives were to determine if BYDV tolerance i ncreased over cycles, if plant height and heading date were affected b y the selection scheme, and if environmental effects were greater than genotypic effects for symptom expression. For evaluation, the origina l parents and S1:2 lines from Cycles 2, 3, and 4 were planted in paire d hills (one hill in each pair was inoculated with BYDV) in a randomiz ed complete block design. The experiment was repeated With S2:3 lines. No consistent improvements occurred over cycles in early or late dise ase ratings or yield of inoculated hills. Stunting was reduced from 6. 0% in the parent population to 0.8% in Cycle 3 in the S2:3 lines. In c omparison with Cycle 2, average heading date in Cycle 4 was delayed by about 2 d. The modified recurrent selection scheme used was not effec tive in increasing the level of tolerance to BYDV, perhaps because of the limited genotypic variability among the parents, or the use of ind irect selection for the number of seeds produced under disease pressur e rather than BYDV symptoms.