POWDERY MILDEW RESISTANCE IN KENTUCKY BLUEGRASS GENOTYPES REGENERATEDFROM EXCISED SEED PIECES

Severity of powdery mildew was assessed on seven cultivars and lines o f Kentucky bluegrass propagated by seed and tissue culture. Tissue cul ture plants were started from embryo axes cultured on Murashige and Sk oog medium containing different concentrations of 2,4-dichlorophenoxya cetic acid (2,4-D) and 6-benzylaminopurine (BAP), and incubated (1 to 4 weeks) or not incubated in the dark prior to transfer to a lighted c ulture room. There were significant differences in disease severity (D S) among seed propagated and tissue culture regenerated plants. DS ran ged from highly susceptible (100% of leaf covered by mildew) (DS = 9) to resistant (DS = 3.0). In some tissue culture regenerants the diseas e severity was significantly affected by the tissue culture process. T en clones expressing resistance were selected, and plants propagated v egetatively. In six clones, disease resistance was sustainable in subs equent vegetatively propagated plants, while resistance was lost in fo ur of the selected clones. Results are discussed with a view to using tissue culture to produce Kentucky bluegrass genotypes with resistance to powedery mildew.