THE RELATIONSHIP BETWEEN POWDERY MILDEW (SPHAEROTHECA-FULIGINEA) RESISTANCE AND LEAF CHLOROSIS SENSITIVITY IN CUCUMBER (CUCUMIS-SATIVUS) STUDIED IN SINGLE SEED DESCENT LINES

The genetic relation between powdery mildew resistance and sensitivity for leaf chlorosis of glasshouse cucumber was investigated. The powde ry mildew resistant, leaf chlorosis sensitive hybrid variety 'Profito' was crossed with the powdery mildew susceptible, non chlorosis sensit ive hybrid variety 'Corona'. Forty four F-6 inbred lines of this cross , produced by single seed descent, were tested for powdery mildew resi stance (PMR) and leaf chlorosis sensitivity (LCS). PMR and LCS were po sitively correlated (r = 0.59). One or more of the PMR genes probably causes LCS as a pleiotropic effect or is closely linked to LCS, but al so other factors, not genetically linked to PMR can cause LCS. Five F- 6 lines combined a significantly higher level of PMR than 'Corona' wit h a significantly lower LCS than 'Profito'. Three of these lines could hardly be distinguished from 'Corona' for the level of LCS.