INHERITANCE OF RESISTANCE TO NECK-ROT DISEASE INCITED BY BOTRYTIS-ALLII IN BULB ONIONS

The inheritance of resistance to neck rot, incited by Botrytis allii M unn, was studied in four crosses between resistant and susceptible bul b onion (Allium cepa L.) lines, one cross between two resistant lines, and one cross between two susceptible lines. Using tests of excised s cale pieces inoculated with a spore suspension and incubated in plasti c boxes at 20C for 6 days, parents, F-1, F-2, and backcrosses were ass igned disease indices (DI) derived from infection severity scores of i ndividual bulbs. Generation means and frequency distribution of DI ind icated that inheritance was quantitative and mostly additive with a sm all amount of dominance for susceptibility. Estimates of gene effects using a three-parameter model also indicated that additive effects pre dominated, with some dominance and no epistasis. Broad-sense heritabil ity estimates ranged from 42% to 63% in the resistant x susceptible cr osses.